ALX Oncology (ALXO) 10-K18 Mar 212020 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2020	Mar. 12, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Registrant Name	ALX ONCOLOGY HOLDINGS INC
Entity Central Index Key	0001810182
Entity File Number	001-39386
Entity Tax Identification Number	85-0642577
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	866 Malcolm Road
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Burlingame
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94010
City Area Code	650
Local Phone Number	466-7125
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
ICFR Auditor Attestation Flag	false
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		40,127,198
Entity Public Float	$ 1.5
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ALXO
Security Exchange Name	NASDAQ
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Certain portions of the registrant's definitive proxy statement relating to the Company's 2021 Annual Meeting of Stockholders, to be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 434,219	$ 9,017
Receivables due from related-party		536
Prepaid expenses and other current assets	1,773	256
Total current assets	435,992	9,809
Property and equipment, net	52	860
Other assets	10	7
Total assets	436,054	10,676
Current liabilities:
Accounts payable	4	3,748
Accrued expenses and other current liabilities	6,200	1,236
Total current liabilities	6,204	4,984
Term loan - non-current		5,421
Other non-current liabilities	5	547
Total liabilities	6,209	10,952
Commitments and contingencies (Note 12)
Convertible preferred stock		70,363
Stockholders’ equity (deficit)
Preferred stock, $0.001 par value; 100,000,000 shares authorized, no shares issued or outstanding
Common stock, $0.001 par value; 1,000,000,000 and 1,519,618,271 shares authorized as of December 31, 2020 and 2019, respectively; 39,844,522 and 3,166,946 shares issued and outstanding as of December 31, 2020 and 2019, respectively	40	3
Additional paid-in capital	548,327	2,140
Accumulated deficit	(118,522)	(72,782)
Total stockholders’ equity (deficit)	429,845	(70,639)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 436,054	10,676
Series A Convertible Preferred Stock
Current liabilities:
Convertible preferred stock		60,933
Series B Convertible Preferred Stock
Current liabilities:
Convertible preferred stock		$ 9,430

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Convertible preferred stock, shares authorized		11,567,003
Convertible preferred stock, liquidation preference		$ 83,585
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	1,000,000,000	1,519,618,271
Common stock, shares issued	39,844,522	3,166,946
Common stock, shares outstanding	39,844,522	3,166,946
Series A Convertible Preferred Stock
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	0	9,421,633
Convertible preferred stock, shares issued	0	9,297,081
Convertible preferred stock, shares outstanding	0	9,297,081
Convertible preferred stock, liquidation preference		$ 73,571
Series B Convertible Preferred Stock
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	0	2,145,370
Convertible preferred stock, shares issued	0	1,016,727
Convertible preferred stock, shares outstanding	0	1,016,727
Convertible preferred stock, liquidation preference		$ 10,014

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Related-party revenue	$ 1,182	$ 4,796	$ 2,067
Type of Revenue [Extensible List]	alxo:RelatedPartyMember	alxo:RelatedPartyMember	alxo:RelatedPartyMember
Operating expenses:
Research and development	$ 28,961	$ 16,306	$ 11,270
General and administrative	14,809	3,313	2,601
Cost of services for related-party revenue	1,075	4,360	1,880
Total operating expenses	44,845	23,979	15,751
Loss from operations	(43,663)	(19,183)	(13,684)
Interest expense	(811)	(21)
Other expense, net	(404)	(5)	(2)
Loss on early debt extinguishment	(621)
Loss before income taxes	(45,499)	(19,209)	(13,686)
Income tax provision	(241)	(34)	(45)
Net loss and comprehensive loss	(45,740)	(19,243)	(13,731)
Cumulative dividends allocated to preferred stockholders	(5,202)	(4,028)	(3,671)
Net loss attributable to common stockholders	$ (50,942)	$ (23,271)	$ (17,402)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.76)	$ (7.56)	$ (6.33)
Weighted-average shares of common stock used to compute net loss per share attributable to common stockholders, basic and diluted	18,485,343	3,076,461	2,750,838

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2017	$ (38,415)		$ 3	$ 1,390	$ (39,808)
Temporary equity, shares at Dec. 31, 2017		9,297,081
Temporary equity, balance at Dec. 31, 2017		$ 60,933
Balance, shares at Dec. 31, 2017			3,205,421
Issuance of common stock under equity incentive plans	7			7
Issuance of common stock under equity incentive plans, shares			6,914
Repurchase of common stock, shares			(43,689)
Vesting of early exercised stock options	92			92
Repurchase of unvested early exercised stock options			(6,899)
Stock-based compensation	269			269
Net loss	(13,731)				(13,731)
Balance at Dec. 31, 2018	(51,778)		$ 3	1,758	(53,539)
Temporary equity, shares at Dec. 31, 2018		9,297,081
Temporary equity, balance at Dec. 31, 2018		$ 60,933
Balance, shares at Dec. 31, 2018			3,161,747
Issuance of convertible preferred stock, net of issuance costs		$ 9,430
Issuance of convertible preferred stock, net of issuance costs, shares		1,016,727
Issuance of common stock under equity incentive plans	10			10
Issuance of common stock under equity incentive plans, shares			5,199
Vesting of early exercised stock options	75			75
Stock-based compensation	297			297
Net loss	(19,243)				(19,243)
Balance at Dec. 31, 2019	(70,639)		$ 3	2,140	(72,782)
Temporary equity, shares at Dec. 31, 2019		10,313,808
Temporary equity, balance at Dec. 31, 2019	70,363	$ 70,363
Balance, shares at Dec. 31, 2019			3,166,946
Issuance of convertible preferred stock, net of issuance costs		$ 104,680
Issuance of convertible preferred stock, net of issuance costs, shares		11,055,966
Reclassification of warrants from liability to equity	1,019			1,019
Conversion of convertible preferred stock in to common stock	175,043	$ (175,043)	$ 21	175,022
Conversion of convertible preferred stock into common stock, shares		(21,369,774)	21,369,774
Cumulative dividends			$ 3	(3)
Cumulative dividends, shares			2,564,759
Issuance of common stock in connection with equity offerings, net of underwriter discounts and issuance costs	364,400		$ 13	364,387
Issuance of common stock in connection with equity offerings, net of underwriter discounts and issuance costs, shares			12,512,000
Issuance of common stock upon net exercise of warrants			48,932
Issuance of common stock under equity incentive plans	299			299
Issuance of common stock under equity incentive plans, shares			182,111
Vesting of early exercised stock options	27			27
Stock-based compensation	5,436			5,436
Net loss	(45,740)				(45,740)
Balance at Dec. 31, 2020	$ 429,845		$ 40	$ 548,327	$ (118,522)
Balance, shares at Dec. 31, 2020			39,844,522

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (45,740)	$ (19,243)	$ (13,731)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	202	429	431
Stock-based compensation	5,436	297	269
Amortization of term loan discount and issuance costs	421	11
Changes in fair value of compound derivative liability and warrants	650
Gain on assignment of lease	(126)
Loss on early debt extinguishment	621
Changes in operating assets and liabilities
Receivables due from related-party	536	396	(932)
Prepaid expenses and other current assets	(1,514)	744	897
Other assets	(10)	7
Accounts payable	(3,744)	2,976	(269)
Accrued expenses and other current liabilities	4,983	134	9
Other non-current liabilities	(4)		136
Net cash used in operating activities	(38,289)	(14,249)	(13,190)
Investing activities
Purchase of property and equipment	(31)	(353)	(653)
Proceeds from assets held for sale	641
Net cash provided by (used in) investing activities	610	(353)	(653)
Financing activities
Proceeds from common stock offerings, net	368,256
Payments of offering costs	(3,848)
Proceeds from exercise of common stock under equity incentive plans	299	10	7
Proceeds from issuance of convertible preferred stock, net	104,680	9,430
Cash paid for repurchase of common stock			6
Proceeds from issuance of term loan, net		5,917
Cash paid for early debt extinguishment	6,506
Net cash provided by financing activities	462,881	15,357	1
Net increase (decrease) in cash and cash equivalents	425,202	755	(13,842)
Cash and cash equivalents at beginning of year	9,017	8,262	22,104
Cash and cash equivalents at end of year	434,219	9,017	8,262
Supplemental disclosure
Cash paid for interest	427
Cash paid for taxes	47
Supplemental disclosure of non-cash investing and financing activities
Vesting of early exercised stock options	27	75	92
Acquisition of property and equipment in accounts payable and accrued expenses	7		$ 20
Debt issuance costs in accounts payable		$ 95
Conversion of convertible preferred stock into common stock upon closing of initial public offering	175,043
Accumulated dividend on convertible preferred stock	$ 3

Organization

Organization	12 Months Ended
Organization	Dec. 31, 2020
Accounting Policies [Abstract]
ORGANIZATION	(1) ORGANIZATION Organization ALX Oncology Holdings Inc., or the Company, was formed as a Delaware corporation on April 1, 2020, or Inception. The Company was formed for the purpose of completing the Company’s initial public offering of its common stock and related transactions in order to carry on the business of ALX Oncology Limited. After Inception, ALX Oncology Limited became a wholly-owned subsidiary of the Company as a result of the internal reorganization. As part of the internal reorganization, all of the equity, option and warrant holders of ALX Oncology Limited became equity, option and warrant holders of the Company, holding the same number of corresponding shares, options and/or warrants in the Company as they did in ALX Oncology Limited immediately prior to the internal reorganization. The information included herein is presented as that of ALX Oncology Holdings Inc. unless such information refers to a date prior to April 1, 2020, in which case it will reflect that of ALX Oncology Limited, the predecessor company. The Company is a clinical-stage immuno-oncology company focused on helping patients fight cancer by developing therapies that block the CD47 checkpoint pathway and bridge the innate and adaptive immune system. The Company owns subsidiaries, consisting of ALX Oncology Limited, incorporated in Ireland; ALX Oncology Inc., incorporated in the United States, Alexo International Holdings Ltd, incorporated in Malta; Alexo Therapeutics International, incorporated in the Cayman Islands, which is a wholly-owned subsidiary of Alexo International Holdings Ltd., and Sirpant Therapeutics, incorporated in the Cayman Islands, which is a wholly-owned subsidiary of Alexo Therapeutics International, or collectively, the Subsidiaries. As of December 31, 2020, the Company has devoted substantially all of its efforts to the formation and financing of the Company, as well as product development, and has not realized product revenues from its planned principal operations. The Company has no manufacturing facilities and all manufacturing related activities are contracted out to third-party service providers. Management expects to incur additional losses in the future to conduct product candidate research and development and to conduct pre-commercialization activities and recognizes that the Company will likely raise additional capital to fully implement its business plan. The Company intends to raise such capital through the sale of additional equity, debt financings or strategic alliances with third parties. However, there can be no assurance that the Company will be successful in acquiring additional funding at levels sufficient to fund its operations or on terms acceptable to the Company. If the Company is unsuccessful in its efforts to raise additional financing, the Company could be required to significantly reduce operating expenses and delay, reduce the scope of or eliminate some of its development programs or its future commercialization efforts, out-license intellectual property rights to its product candidates and sell unsecured assets, or a combination of the above, any of which may have a material adverse effect on the Company’s business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all. The Company believes that the existing capital resources will be sufficient to fund the projected operating requirements for at least the next twelve months.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
Significant Accounting Policies	Dec. 31, 2020
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	(2) SIGNIFICANT ACCOUNTING POLICIES Basis of Preparation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP, and the applicable rules and regulations of the U.S. Securities and Exchange Commission, or SEC. Principles of Consolidation All intercompany balances and transactions have been eliminated in consolidation. Reverse Stock Split On July 8, 2020, the Company’s board of directors approved an amendment to the Company’s certificate of incorporation to effect a 1-for-6.5806 reverse split of its common stock and convertible preferred stock. The par values of the common and convertible preferred stock were not adjusted as a result of the reverse stock split. All authorized, issued and outstanding common stock, convertible preferred stock, stock options, warrants, and related per share amounts contained in the consolidated financial statements have been retroactively adjusted to reflect this reverse stock split for all periods presented. The reverse stock split was effected on July 9, 2020. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, management evaluates its estimates, including those related to the estimated useful lives of long-lived assets, clinical trial accruals, fair value of assets and liabilities, Series B convertible preferred stock warrant liability, term loan compound derivative liability, term loan, valuation of the Company’s common stock, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Cash and Cash Equivalents The Company holds its cash and cash equivalents in checking and money market accounts. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value. Concentration of Credit Risk, Credit Losses and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits, and invests in money market funds. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole-source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration, or FDA, and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation of property and equipment is provided using the straight-line method over the estimated useful lives of the assets. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss. Maintenance and repairs are charged to the consolidated statement of operations and comprehensive loss as incurred. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing. Impairment of Long-Lived Assets The Company reviews property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future undiscounted net cash flows which the asset or asset group are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds its fair value. Fair value is determined using various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as considered necessary. The Company has not recorded impairment of any long-lived assets. Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the consolidated financial statements. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Where observable prices or inputs are not available valuation models are applied. These valuation techniques involve some level of management estimation and judgment, the degree of which is dependent on the price transparency for the instruments or market and the instruments’ complexity. The Company’s financial instruments consist of cash and cash equivalents, receivables due from related-party, accounts payable, the term loan compound derivative liability and the Series B convertible preferred stock warrant liability. The term loan compound derivative liability and the Series B convertible preferred stock warrant liability are re-measured at the end of every period and carried at fair value (Note 3). The recorded value of the Company’s receivables due from related-party and accounts payable approximates its current fair value due to the relatively short-term nature of these items. Term Loan The Company accounts for the Loan and Security Agreement, dated as of December 20, 2019, as amended, with Silicon Valley Bank, or SVB, and WestRiver Innovation Lending Fund VIII, LP, or WestRiver, collectively as lenders, and SVB, as administrative agent and collateral agent, as a liability measured at net proceeds less debt discount and is accreted to the face value of the term loan over its expected term using the effective interest method. The Company considers whether there are any embedded features in its debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging Convertible Preferred Stock The Company records convertible preferred stock net of issuance costs on the dates of issuance, which represents the carrying value. In the event of a change of control of the Company, proceeds will be distributed in accordance with the liquidation preferences set forth in its organization documents unless the holders of convertible preferred stock have converted their convertible preferred stock into common stock. Convertible preferred stock is classified outside of stockholders’ equity (deficit) on the accompanying consolidated balance sheets as events triggering the liquidation preferences are not solely within the Company’s control. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. Upon the consummation of the Company’s initial public offering in July 2020, all shares of convertible preferred stock outstanding and accrued cumulative dividends automatically converted into 23,934,533 shares of common stock. Series B Convertible Preferred Stock Warrant Liability The Company has issued freestanding warrants to purchase its Series B convertible preferred stock. Freestanding warrants for the Company’s convertible preferred stock that are classified outside of permanent equity are recorded at fair value, and are subject to re-measurement at the end of every period until the earlier of the exercise of the warrants or the completion of a liquidation event, including the completion of an initial public offering. Upon exercise, the Series B convertible preferred stock warrant liability would be reclassified to additional paid-in capital, with any change in fair value recognized as a component of other expense, net. Following the Company’s initial public offering, the warrants were automatically converted to warrants to purchase shares of common stock (Note 5). The Company revalued the Series B convertible preferred stock warrants as of the completion of the initial public offering and reclassified the outstanding preferred stock warrant liability balance to additional paid-in capital with no further re-measurement required as common stock warrants are considered permanent equity. Revenue Recognition To date, the Company has derived revenue from providing research and development services on a time and materials basis to a related-party. The Company recognizes such revenues over time as services are delivered, and invoices the customer as the work is incurred in arrears. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC Topic 606, Revenue from Contracts with Customers As part of the Company’s consideration as to whether the Company has entered into a contract with a customer, it considers whether it is probable that it will collect the consideration it is entitled to in exchange for the goods and services it transfers to the customer. At contract inception, the Company assesses the goods or services promised within each contract that falls under the scope of Topic 606, determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Cost of Services for Related-Party Revenue The Company incurs costs associated with related-party services including direct labor and associated employee benefits, laboratory supplies, and other expenses. These costs are recorded in cost of services for related-party revenue as a component of total operating expenses in the accompanying consolidated statements of operations and comprehensive loss. Research and Development Costs Research and development costs are expensed as incurred and consist primarily of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to nonemployees and entities that conduct certain research and development activities on behalf of the Company and expenses incurred in connection with license agreements (Note 9). Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed. Clinical and Manufacturing Accruals The Company records accruals for estimated costs of research, preclinical studies and clinical trials, and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services. The Company makes significant judgments and estimates in determining the accrual balance at the end of each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. To assist in its estimates the Company relies upon the receipt of timely and accurate reporting from its clinical and non-clinical studies and other third-party vendors. Through December 31, 2020, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to, the number of patients enrolled, the rate of patient enrollment, and the actual services performed, and related costs may vary from the Company’s estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations. Stock-based Compensation Expense The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all stock-based payments made to employees, directors and non-employees based on estimated grant-date fair values. The Company uses the straight-line method to allocate compensation expense to reporting periods over each optionee’s requisite service period, which is generally the vesting period, and estimates the fair value of stock-based awards using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free rate of return and the estimated fair value of the underlying common stock on the date of grant. Prior to the Company’s initial public offering, the fair value of the common stock underlying the stock-based awards was determined on each grant date by the board of directors, with input from management, considering the most recently available third-party valuation of common shares. The Company accounts for the effect of forfeitures as they occur. Segment Reporting The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. Foreign Currency Transactions The functional currency of the Company’s operation and each of its subsidiaries is U.S. dollars. All assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rate prevailing on the balance sheet date. Expenses are translated at the average exchange rates prevailing during the applicable period. Foreign currency transaction gains and losses are included in the consolidated statement of operations and comprehensive loss and recorded in other expense, net, and were immaterial for the years December 31, 2020, 2019 and 2018. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates in effect for the period in which the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations and comprehensive loss in the period that includes the enactment date. The Company recognizes deferred tax assets to the extent that it believes these assets are more likely than not to be realized. In making such a determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. If the Company determines that it would be able to realize its deferred tax assets in the future in excess of their net recorded amount, it would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. Comprehensive Loss Comprehensive loss is equal to net loss for all periods presented. Net Loss Per Share Attributable to Common Stockholders Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. The Company applies the two-class method to compute basic and diluted net loss per share when it has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires net loss available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all net loss for the period had been distributed. The Company’s convertible preferred stock participate in any dividends declared by the Company and are therefore considered to be participating securities. The participating securities are not required to participate in the losses of the Company, and therefore during periods of loss there is no allocation required under the two-class method. Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which is intended to simplify various aspects related to accounting for income taxes. The pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2021. ASU 2019-12 is effective for the Company beginning January 1, 2022. Early adoption is permitted. The Company is currently in the process of evaluating the effects of the adoption of this guidance on the Company’s financial statements and does not expect it to have a material impact on its consolidated financial statements. New Accounting Pronouncements Recently Adopted In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), which requires entities to measure all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. This replaces the existing incurred loss model and is applicable to the measurement of credit losses on financial assets measured at amortized cost. The Company early adopted this guidance on January 1, 2020. For trade receivables and other instruments, the Company uses a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are recognized as allowances rather than as reductions in the amortized cost of the securities. The adoption of the guidance did not have a material impact on the Consolidated Financial Statements and related disclosures and there was no allowance for losses for the year ended December 31, 2020. In September 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement. The FASB issued final guidance that eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. Under the ASU, entities will no longer be required to disclose the amount of transfers between Level 1 and Level 2 of the fair value hierarchy. Public companies will be required to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2019, with early adoption permitted. The Company adopted this guidance on January 1, 2020. The adoption of ASU 2018-13 did not have a material impact on its consolidated financial statements.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
Fair Value of Financial Instruments	Dec. 31, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	(3) FAIR VALUE OF FINANCIAL INSTRUMENTS The fair value of the Company’s financial assets and liabilities are determined in accordance with the fair value hierarchy established in ASC Topic 820, Fair Value Measurements and Disclosures. ASC Topic 820 defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy of ASC Topic 820 requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets; Level 2—Inputs, other than the quoted prices in active markets, which are observable either directly or indirectly such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life; and Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The Company’s financial instruments consist of cash and cash equivalents, receivables due from related-party, accounts payable, the term loan compound derivative liability and the Series B convertible preferred stock warrant liability. Cash and cash equivalents are reported at their respective fair values on the Company’s consolidated balance sheets. Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant inputs are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Where applicable, these models project future cash flows and discount the future amounts to a present value using market-based observable inputs obtained from various third-party data providers, including but not limited to benchmark yields, reported trades and broker/dealer quotes. Where applicable the market approach utilizes prices and information from market transactions for similar or identical assets. The Company measures its Series B convertible preferred stock warrant liability and term loan compound derivative liability at fair value on a recurring basis and these are classified as Level 3 liabilities. The fair value of the Series B convertible preferred stock warrant liability was determined using an option-pricing model. The Company revalued the Series B convertible preferred stock warrants as of the completion of the initial public offering and reclassified the outstanding preferred stock warrant liability balance to additional paid-in capital with no further re-measurement required as the common stock warrants are considered permanent equity effective with the completion of the initial public offering. The Company calculated the fair value of the term loan compound derivative liability by computing the difference between the fair value of the term loan with the compound derivative using the “with and without” method under the income approach, and the fair value of the term loan without the compound derivative. The valuation methodology and underlying assumptions are discussed further in Note 5. The compound derivative liability was extinguished upon the extinguishment of the host instrument in December 2020 (Note 5). The following table sets forth the Company’s financial assets and liabilities that are measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): As of December 31, 2020 Level 1 Level 2 Level 3 Fair Value Financial assets Cash equivalents Money market funds $ 424,115 $ — $ — $ 424,115 As of December 31, 2019 Level 1 Level 2 Level 3 Fair Value Financial liabilities Non-current liabilities Compound derivative liability $ — $ — $ 51 $ 51 Warrant liability $ — $ — $ 361 $ 361 The following table is a reconciliation of all financial liabilities measured at fair value using Level 3 unobservable inputs (in thousands): Year Ended December 31, 2020 Compound Warrant Derivative Liability Liability Fair value at beginning of year $ 361 $ 51 Additions — — Change in fair value 658 (8 ) Reclassification to equity (1,019 ) — Extinguishment of compound derivative liability upon extinguishment of host instrument — (43 ) Fair value at end of year $ — $ — There were no transfers of assets or liabilities between the fair value measurement levels during the years ended December 31, 2020 and 2019. The carrying values of the Company’s financial instruments, such as accounts payable and accrued expenses and other current liabilities, approximate fair value due to the short-term nature of these items.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
Balance Sheet Components	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
BALANCE SHEET COMPONENTS	(4) BALANCE SHEET COMPONENTS Property and Equipment, Net The following table presents the components of property and equipment, net as of December 31, 2020 and 2019 (in thousands): December 31, December 31, 2020 2019 Computer hardware and software $ 63 $ 146 Machinery and equipment — 1,698 Furniture and fixtures 9 36 Leasehold improvements 5 429 Property and equipment, gross 77 2,309 Less: accumulated depreciation and amortization (25 ) (1,449 ) Property and equipment, net $ 52 $ 860 Depreciation and amortization expense was $0.2 million, $0.4 million and $0.4 million for years ended December 31, 2020, 2019 and 2018, respectively. At June 30, 2020, certain lab equipment and other assets for an aggregated net book value of $0.6 million relating to the asset transfer with Tallac Therapeutics, Inc. (formerly known as Tollnine, Inc., or Tollnine), or Tallac Therapeutics, a related-party (Note 10), met the criteria as assets held for sale. Those assets were reported at the lower of carrying value or fair value less costs to sell. In July 2020, the Company received $0.6 million cash in exchange for the transfer of such assets. Accrued Expenses and Other Current Liabilities The following table presents the components of accrued expenses and other current liabilities as of December 31, 2020 and 2019 (in thousands): December 31, December 31, 2020 2019 Accrued professional fees $ 300 $ 122 Accrued compensation 1,974 924 Accrued clinical and nonclinical study costs 1,473 — Accrued contract manufacturing 2,123 53 Accrued federal income tax 179 1 Other 151 136 Total accrued expenses and other current liabilities $ 6,200 $ 1,236

Term Loan

Term Loan	12 Months Ended
Term Loan	Dec. 31, 2020
Debt Disclosure [Abstract]
TERM LOAN	(5) TERM LOAN The Company’s wholly-owned subsidiaries Alexo Therapeutics International and Sirpant Therapeutics, as borrowers, entered into a Loan and Security Agreement, or the Loan Agreement, dated as of December 20, 2019, with SVB and WestRiver, collectively as lenders, and SVB, as administrative agent and collateral agent. As a result of the internal reorganization, in May 2020 the Company entered into a Joinder and First Amendment to the Loan and Security Agreement, or the Joinder Amendment, and Amended and Restated Warrants to Purchase Stock, or the Amended Warrants. The purpose for entering into the Joinder Amendment was to add the newly established ALX Oncology Holdings Inc. as additional borrower to the Term Loan. Concurrently, the Company modified the Amended Warrants to change the issuer from ALX Oncology Limited to ALX Oncology Holdings Inc. The Company accounted for the First Amendment to the Loan and Security Agreement as a modification. The Loan Agreement provided for term loans in an aggregate principal amount of up to $10.0 million funded in two tranches, subject to the satisfaction of a certain milestone. The first tranche, in the amount of $6.0 million, was funded on the closing date of the Loan Agreement in December 2019. A second tranche of $4.0 million was available on or before March 31, 2020, upon the Company’s achievement of an equity financing resulting in net cash proceeds in an amount of at least $30.0 million to the Company. The Company elected not to draw down on the second tranche, which is no longer available. The loans under the Loan Agreement bore interest at a floating per annum interest rate equal to the greater of 7.0% or 2.0% plus the prime rate as reported in The Wall Street Journal. The Company was required to make interest-only payments for the first 12 months after the closing of the Loan Agreement, followed by consecutive equal monthly payments of principal and interest commencing on January 1, 2021 and continuing through the maturity date of September 1, 2022. The Loan Agreement also provided for a final payment equal to 6.0% multiplied by the aggregate principal amount of the term loans funded, which was due on the maturity date, upon the acceleration of the term loans, or upon prepayment of the term loans. If the Company elected to prepay the term loans, there was also a prepayment fee of between 1.0% and 3.0% of the principal amount being prepaid depending on the timing and circumstances of prepayment. In conjunction with the Loan Agreement, the Company issued warrants to purchase 61,292 Series B convertible preferred stock to SVB and WestRiver with an exercise price of $9.4972 per share. Following the Company’s initial public offering, these warrants were automatically converted to warrants to purchase 61,292 shares of common stock at an exercise price of $9.4972 per share. The estimated fair value of the warrants at the date of issuance was approximately $0.4 million. The Company revalued the Series B convertible preferred stock warrants as of the completion of the initial public offering and reclassified the outstanding preferred stock warrant liability balance of $1.0 million to additional paid-in capital with no further re-measurement required as the common stock warrants are considered permanent equity effective July 16, 2020. The fair value of the common stock warrant was determined using a Black-Scholes option-pricing model with the following assumptions: an expected term of 9.8 years, a volatility of 84.2%, a dividend rate of zero and a risk-free rate of 0.6%. The changes in fair value in warrant liability were recognized as a component of other expense, net in the accompanying consolidated statement of operations and comprehensive loss. On August 17, 2020, SVB and WestRiver delivered the Notice of Exercise for net exercise of 61,292 warrants at an exercise price of $9.4972 per share. Accordingly, the Company issued 48,932 shares of the Company’s common stock (Note 6). The loans under the Loan Agreement were secured by substantially all of the Company’s assets, except the Company’s intellectual property, which is the subject of a negative pledge. The Company determined that certain loan features were embedded derivatives requiring bifurcation and separate accounting. Those embedded derivatives were bundled together as a single, compound embedded derivative and then bifurcated and accounted for separately from the host contract. The Company recorded a term loan compound derivative liability of approximately $51,000 which was marked-to-market until the extinguishment of the host instrument. The Company calculated the fair value of the compound derivative by computing the difference between the fair value of the term loan with the compound derivative using the “with and without” method under the income approach, and the fair value of the term loan without the compound derivative. The Company calculated the fair values using a probability-weighted discounted cash flow analysis. The key valuation assumptions used consist of the discount rate and the probability of the occurrence of a change in control event. The term loan compound derivative liability was re-measured at each financial reporting period with any changes in fair value being recognized as a component of other expense, net in the consolidated statement of operations and comprehensive loss. The compound derivative liability was extinguished upon the extinguishment of the host instrument in December 2020. The fair value of Series B convertible preferred stock warrant liability at issuance, fair value of embedded derivatives, which were bifurcated and other debt issuance costs were treated as debt discounts on the Company’s consolidated balance sheet and together with the final payment were amortized to interest expense throughout the life of the term loan using the effective interest rate method. In December 2020, the Company used approximately $6.5 million of the net proceeds from the Company’s follow-on public offering to repay the outstanding principal amount of $6.0 million and early extinguish the outstanding Term Loan with SVB and WestRiver. As a result, the Company recognized a $0.6 million loss on early debt extinguishment, representing the difference between the reacquisition price of debt and the net carrying amount of the loan as of the date of the payoff.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2020
Equity [Abstract]
STOCKHOLDERS’ EQUITY	(6) STOCKHOLDERS’ EQUITY On July 21, 2020, the Company’s amended and restated certificate of incorporation became effective, authorizing 1,000,000,000 shares of common stock and 100,000,000 shares of undesignated preferred stock. As of December 31, 2020 and 2019, the Company had 39,844,522 and 3,166,946 shares of common stock outstanding, respectively. As of December 31, 2020 and 2019, the Company had zero and 10,313,808 shares of preferred stock outstanding, respectively. Common Stock In July 2020, the Company consummated its initial public offering and issued 9,775,000 shares of common stock for net proceeds of approximately $169.5 million, after deducting underwriting discounts and commissions of $13.0 million and offering-related expenses of $3.2 million. Upon the closing of the initial public offering, all shares of convertible preferred stock outstanding and accrued cumulative dividends were automatically converted into 23,934,533 shares of common stock. In December 2020, the Company consummated its follow-on public offering and issued 2,737,000 shares of common stock for net proceeds of approximately $194.9 million, after deducting underwriting discounts and commissions of $12.5 million and offering-related expenses of $0.7 million. Common stock reserved for future issuance, on an as if converted basis, as of December 31, 2020 and 2019, consists of the following: December 31, December 31, 2020 2019 Convertible preferred stock issued and outstanding — 10,313,808 Stock options issued and outstanding 4,857,308 1,183,745 Stock options authorized for future issuance 2,835,443 566,900 Warrants issued and outstanding — 61,292 Warrants authorized for future issuance — 30,646 Total 7,692,751 12,156,391 Convertible Preferred Stock As of December 31, 2019, the Company’s convertible preferred stock consisted of the following (in thousands, except share amounts): December 31, 2019 Shares Aggregate Authorized Issued And Net Liquidation Shares Outstanding Proceeds (1) Preference Shares designated as: Series A convertible preferred stock 9,421,633 9,297,081 $ 60,933 $ 73,571 Series B convertible preferred stock 2,145,370 1,016,727 9,430 10,014 Total 11,567,003 10,313,808 $ 70,363 $ 83,585 (1) Net proceeds are gross proceeds from the offerings net of issuance costs Series C Convertible Preferred Stock Issuance In February 2020, the Company entered into a Series C Preferred Stock Purchase Agreement, or the Series C Agreement, with certain existing investors, employees and new investors, or collectively, the Series C Investors. Under the terms of the Series C Agreement, the Company authorized the sale and issuance of up to 11,055,981 Series C convertible preferred stock at a purchase price of $9.4972 per share. All authorized Series C convertible preferred stock have been purchased with gross proceeds of $105.0 million. The Series C convertible preferred stock and related accumulated dividends automatically converted into shares of the Company’s common stock upon the consummation of the Company’s initial public offering. Preferred Stock Warrant Liability On July 21, 2020, the warrants to purchase 61,292 Series B convertible preferred stock issued to SVB and WestRiver with an exercise price of $9.4972 per share were automatically converted to warrants to purchase 61,292 shares of common stock at an exercise price of $9.4972 per share. The Company revalued the Series B convertible preferred stock warrants as of the completion of the initial public offering and reclassified the outstanding preferred stock warrant liability balance to additional paid-in capital with no further re-measurement required as the common stock warrants are considered permanent equity. On August 17, 2020, SVB and WestRiver delivered the Notice of Exercise to net exercise 61,292 warrants at an exercise price of $9.4972 per share. Accordingly, the Company issued 48,932 shares of the Company’s common stock. Dividends Prior to the Company’s initial public offering, cumulative dividends of 6.0% per annum of the original issue price for each convertible preferred stock series were payable when and as declared by the Company’s Board of Directors, or Board of Directors, upon the occurrence of a liquidation event or upon a contingent mandatory conversion of the convertible preferred stock in connection with a qualified initial public offering as described below. The Series A original issue price was $6.58, and the Series B and Series C original issue price was $9.4972. The original issue price was subject to adjustment in the event of any share dividend, share split, combination, consolidation or other recapitalization. The dividends accrued from day to day from the issue date of such preferred stock whether or not declared and were cumulative. In addition, the preferred stockholders participated on an as-converted basis in any dividends payable to common stockholders. As of July 20, 2020, there were approximately $18.0 million of accrued cumulative dividends on the Series A, Series B and Series C convertible preferred stock, which became payable upon the consummation of the Company’s initial public offering and automatically converted into 2,564,759 shares of the Company’s common stock.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
Stock-Based Compensation	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
STOCK-BASED COMPENSATION	(7) STOCK-BASED COMPENSATION Equity Incentive Plans 2015 Share Award Scheme During 2015, the Company adopted an equity compensation plan, the 2015 Share Award Scheme, or the 2015 Share Award Scheme, for eligible employees, officers, directors, advisors, and consultants. The 2015 Share Award Scheme provided for the grant of incentive and non-statutory share options. The 2015 Share Award Scheme permitted the Company to grant up to 2,143,117 common stock awards, including incentive share options, non-statutory share options, conditional share awards and restricted share awards. 2020 Equity Incentive Plan On April 1, 2020, the Board of Directors approved a new equity incentive plan, or the 2020 Equity Incentive Plan, that replaced the 2015 Share Award Scheme. The 2020 Equity Incentive Plan is for employees, non-employee directors and consultants covering 4,379,139 shares of the Company’s common stock and authorizes the award of stock options, restricted stock awards, stock appreciation rights and restricted stock units. 2020 Amended and Restated Equity Incentive Plan In July 2020, the Company adopted the Amended and Restated 2020 Equity Incentive Plan, or the 2020 Plan. The 2020 Plan replaced the Company’s 2020 Equity Incentive Plan and a total of 7,874,862 shares were reserved under the 2020 Plan. The terms of the stock option agreements, including vesting requirements, are determined by the Board of Directors, subject to the provisions of the 2020 Plan. The term of the options generally expire, upon the earliest of (i) termination of continuous service for cause (ii) three months after the termination of continuous service for reasons other than cause, death or disability (iii) twelve months after the termination of continuous service due to disability (iv) eighteen months after the employee’s death if the employee died during the period of continuous service (v) expiration date in the grant notice or (vi) the day before the tenth anniversary of the date of grant. The exercise price of the incentive share options must equal at least the fair market value of the share on the date of grant. All awards that are canceled, forfeited or expired are returned to the 2020 Plan and are available for grant in conjunction with the issuance of new awards. Share options granted are exercisable over a maximum term of 10 years from the date of grant and generally vest over an agreed service period, usually four years. Certain share options granted under the 2020 Plan provide option holders the right to elect to exercise unvested options in exchange for common stock. Such unvested common stock is subject to a repurchase right held by the Company at the original issuance price in the event the optionee’s service to the Company is terminated either voluntarily or involuntarily. The right lapses as the underlying repurchase right expires. These repurchase terms are considered to be a forfeiture provision. The cash received from employees for exercise of unvested options is treated as a refundable deposit and is classified as a liability on the consolidated balance sheets. At December 31, 2020 and 2019, there were unvested early exercised options of 63 and 34,024, respectively, and the liability related to these unvested options was approximately $0 and $27,000, respectively. Stock Option Modification In connection with the transfer of employees to Tallac Therapeutics, Dr. Hong Wan, the Company’s former Chief Scientific Officer, and eight of the Company’s employees, or Transferred Employees, terminated their employment with the Company effective as of June 30, 2020 and became employees of Tallac Therapeutics effective as of July 1, 2020. The options to purchase shares of the Company’s common stock that were previously granted to the Transferred Employees will continue to vest and be exercisable subject to the Transferred Employees remaining service providers under the original terms of the award. The Company evaluated the change in status from an employee to a consultant in accordance with ASC 718. While the Company concluded that the change in status did not affect the vesting condition or the classification of the initial awards, the significant reduction in the level of services that the grantees were expected to provide under the original awards as compared to the level of services expected under the Tallac Services Agreement will no longer meet the substantive service condition requirements and therefore the compensation cost for the unvested awards was recognized immediately with no future service requirement. In September 2020, in connection with the resignation of the Company’s former Chief Business Officer and the entry into a consulting agreement with him, the Company evaluated the change in status from an employee to a consultant in accordance with ASC 718. While the Company concluded that the change in status did not affect the vesting condition or the classification of the initial awards, the significant reduction in the level of services that the grantee was expected to provide under the original awards as compared to the level of services expected under the consulting agreement will no longer meet the substantive service condition requirements and therefore the compensation expense for the unvested awards expected to vest during the consultancy was recognized immediately with no future service requirement. The Company recorded $1.7 million in stock-based compensation expenses related to the modifications for the year ended December 31, 2020. Employee Stock Purchase Plan In July 2020, the Board of Directors and stockholders approved the ALX Oncology Holdings Inc. 2020 Employee Stock Purchase Plan, or the ESPP. The ESPP allows eligible employees to have up to 15 percent of their eligible compensation withheld and used to purchase common stock, subject to a maximum of $25,000 worth of stock purchased in a calendar year or no more than 3,000 shares in an offering period, whichever is less. An offering period consists of a six-month purchase period, with a look back feature to our stock price at the commencement of the offering period. Eligible employees can purchase the Company’s common stock at the end of the offering period at 85% of the lower of the closing price of our common stock on The Nasdaq Global Select Market on the first and last day of the offering periods. The initial number of shares of common stock available for issuance under the ESPP, was 400,000. Unless the Board of Directors provides otherwise, beginning on January 1, 2021, the maximum number of shares which shall be made available for sale under the ESPP will automatically increase on the first trading day in January of each calendar year during the term of the ESPP by an amount equal to the least of: • 800,000 shares; • one percent of the outstanding shares of our common stock on the last day of our immediately preceding fiscal year; or • such number of shares as our board of directors may determine no later than the last day of our immediately preceding fiscal year. In January 2021, the Board of Directors approved the first offering period beginning February 1, 2021. As of December 31, 2020, there were no purchases under the ESPP. Stock Option Activity The following table provides a summary of share option activity under the Plan and related information: Outstanding Options Shares Available to Grant Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 566,900 1,183,745 $ 1.37 8.06 $ 638 Authorized 6,124,217 — Granted (3,857,655 ) 3,857,655 $ 10.92 Exercised — (182,111 ) $ 1.65 Canceled/forfeited 1,981 (1,981 ) $ 0.99 Outstanding at December 31, 2020 2,835,443 4,857,308 $ 8.94 8.86 $ 375,270 Exercisable at December 31, 2020 3,776,399 $ 3.85 8.65 $ 310,999 As of December 31, 2020, there was unrecognized share-based compensation expense of $25.0 million, related to unvested share options which the Company expects to recognize over a weighted-average period of 3.2 years. The aggregate intrinsic values represent the total pre-tax intrinsic value, of options outstanding and exercisable calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock as of December 31, 2020 and 2019. The total intrinsic value of options exercised during the years ended December 31, 2020, 2019 and 2018 were $4.4 million, immaterial and immaterial, respectively. Stock-based Compensation Expenses Compensation cost for share options granted is based on the grant-date fair value estimated and is recognized over the vesting period of the applicable option on a straight-line basis. The weighted-average grant-date fair value per share for share options granted during the years ended December 31, 2020, 2019 and 2018 was $7.74, $1.27 and $1.14, respectively. Stock-based compensation expense includes share options granted to employees and nonemployees and has been reported in the Company’s consolidated statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 2,551 $ 105 $ 195 General and administrative 2,885 33 16 Cost of services for related-party revenue — 159 58 $ 5,436 $ 297 $ 269 Stock Option Valuation Assumptions The Company uses the Black-Scholes option pricing model to determine the estimated fair value of stock options at the date of the grant, and stock-based compensation is adjusted for actual forfeitures as they occur. The fair value of each option grant during the years ended December 31, 2020, 2019 and 2018 was estimated with the Year Ended December 31, 2020 2019 2018 Expected term (in years) 5.8 - 6.1 4.4 - 6.0 5.2 - 6.0 Risk-free interest rate 0.3% - 0.8% 1.7% - 2.1% 2.6% - 3.0% Expected dividend rate - - - Expected stock price volatility 78.7% - 89.0% 75.2% - 80.5% 66.5% - 68.7% Expected Term. The expected term of the options represents the average period the share options are expected to remain outstanding. As the Company does not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior, the expected term of options granted is derived from the average midpoint between the weighted average vesting and the contractual term, also known as the simplified method. Risk-Free Interest Rate. The risk-free interest rate is based on the yield of U.S. Treasury notes as of the grant date with terms commensurate with the expected term of the option. Dividend Yield. The expected dividends assumption is based on the Company’s expectation of not paying dividends in the foreseeable future. Volatility. Since the Company does not have sufficient trading history for its common stock, the expected volatility is based on the historical volatilities of the common shares of comparable publicly traded companies. The Company selected companies with comparable characteristics, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the Company’s share-based awards. Fair Value . Historically, for all periods prior to our initial public offering, the fair value of the shares of common stock underlying our stock option was determined by the Company’s board of directors. Because there was no public market for the Company’s common stock, the board of directors determined fair value of the common stock at the time of grant of the options by considering a number of objective and subjective factors including important developments in the Company’s operations, valuations performed by an independent third party, sales of convertible preferred stock, actual operating results and financial performance, the conditions in the biotechnology industry and the economy in general, the stock price performance and volatility of comparable public companies, and the lack of liquidity of the Company’s common stock, among other factors. Since the completion of our initial public offering, the fair value of each share of common stock underlying stock option grants is based on the closing price of our common stock on the Nasdaq Global Select Market as reported on the date of grant.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2020
Income Tax Disclosure [Abstract]
INCOME TAXES	(8) INCOME TAXES The U.S. domestic and international components of pre-tax loss for the years ending December 31, 2020, 2019 and 2018 are as follows (in thousands): Year Ended December 31, 2020 2019 2018 United States $ (9,457 ) $ 813 $ 855 International (36,042 ) (20,022 ) (14,541 ) Loss before income taxes $ (45,499 ) $ (19,209 ) $ (13,686 ) The federal and state provision for income taxes consist of the following (in thousands): Year Ended December 31, 2020 2019 2018 Current provision for income taxes: Federal $ 239 $ 33 $ 44 State 2 1 1 International — — — Total current 241 34 45 Deferred tax provision: Federal — — — State — — — International — — — Total deferred — — — Provision for income taxes $ 241 $ 34 $ 45 Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, and (b) operating losses and tax credit carryforwards. A reconciliation of the U.S. federal statutory income tax rate to the effective tax for the years ended December 31, 2020, 2019 and 2018 are as follows (in thousands): Year Ended December 31, 2020 2019 2018 At federal statutory income tax rate $ (9,555 ) $ (4,034 ) $ (2,874 ) State income taxes (3,098 ) (1,875 ) (332 ) Stock-based compensation (5 ) 60 57 Research & Development credits (512 ) (861 ) (499 ) Change in valuation allowance 5,710 3,733 732 Other 321 75 100 Foreign rate differential 7,380 3,886 2,899 Prior period true ups — (950 ) (38 ) Provision for income taxes $ 241 $ 34 $ 45 Significant components of the Company’s deferred tax assets as of December 31, 2020 and 2019 are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Loss carryforwards $ 7,283 $ 3,259 Research & other credits 2,861 3,260 Other 76 69 Accrued expenses 383 261 Stock options 696 3 Total deferred tax assets 11,299 6,852 Deferred tax liabilities: Fixed assets 11 166 Total deferred tax liabilities 11 166 Valuation allowance (11,288 ) (6,686 ) Net deferred tax assets $ — $ — Realization of deferred tax assets is dependent upon the Company generating future taxable income, the timing and amount of which are uncertain. Accordingly, the deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by approximately $4.6 million and $4.5 million for the years ended December 31, 2020 and 2019, respectively. Net operating losses and tax credit carryforwards as of December 31, 2020 are as follows (in thousands): Amount Expiration Years Net operating losses, federal (Post December 31, 2017) $ 7,919 Do Not Expire Net operating losses, state $ 71,363 2038-2040 Tax credits, federal $ 1,327 2039-2040 Tax credits, state $ 2,893 N/A Net operating losses, foreign $ 5,086 N/A Utilization of the Company’s U.S. net operating loss and credit carryforwards may be subject to substantial annual limitation due to the ownership change limitations provided by the Internal Revenue Code and similar state provisions. Such annual limitation could result in the expiration of the U.S. net operating loss and credit carryforwards before utilization. To date, the Company has not performed an analysis to determine whether there would be a substantial annual limitation due to a change in ownership. Unrecognized Tax Benefits The Company’s policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for taxes in the consolidated statements of operations and comprehensive loss. If the Company is eventually able to recognize its uncertain tax positions, the Company’s effective tax rate would be reduced. The Company currently has a full valuation allowance against its net deferred tax asset which would impact the timing of the effective tax rate benefit should any of these uncertain tax positions be favorably settled in the future. The unrecognized tax benefits as of December 31, 2020, 2019 and 2018 were $0.8 million, $0.7 million and $0.4 million, respectively. Future changes in the unrecognized tax benefits will not impact the effective tax rate due to the Company's full valuation allowance. The Company will file income tax returns in the U.S. federal and California jurisdiction, is not currently under examination, and all years since inception are open to examination. The Company has the following activity relating to unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 2018 Balance at beginning of year $ 692 $ 418 $ 247 Additions/reversals based on tax positions of prior years (64 ) 2 11 Additions based on tax positions related to the current year 240 272 160 Lapses in statutes of limitations (26 ) — — Balance at end of year $ 842 $ 692 $ 418 Although it is reasonably possible that certain unrecognized tax benefits may increase or decrease within the next 12 months due to tax examination changes, settlement activities, expirations of statute of limitations or the impact on recognition and measurement considerations related to the results of published tax cases or other similar activities, the Company does not anticipate any significant changes to unrecognized tax benefits over the next 12 months. During the years ended December 31, 2020, 2019 and 2018, no interest or penalties were required to be recognized relating to unrecognized tax benefits.

License Agreement

License Agreement	12 Months Ended
License Agreement	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
LICENSE AGREEMENT	(9) LICENSE AGREEMENT Exclusive (Equity) Agreement with The Board of Trustees of the Leland Stanford Junior University In March 2015, the Company entered into a license agreement, or the Stanford Agreement, with the Board of Trustees of the Leland Stanford Junior University, or Stanford, under which the Company obtained a worldwide, royalty-bearing, sublicensable license under certain patents relating to the Company’s current product candidates, to develop, manufacture and commercialize products for use in certain licensed fields, the scope of which would include the application of the licensed intellectual property in oncology. The license granted to the Company in the Stanford Agreement includes an exclusive grant, subject to certain pre-existing non-exclusive or exclusive rights that Stanford retained for grant to third parties with respect to certain categories of the licensed patents in certain fields of use and retained rights by Stanford and all other nonprofit institutions to use and practice the licensed patents and technology for internal research and other nonprofit purposes. The license granted to the Company in the Stanford Agreement also includes non-exclusive grants to certain Stanford patents. In consideration for the rights granted to the Company under the Stanford Agreement, the Company paid Stanford a nonrefundable license royalty and reimbursed Stanford for past patent expenses, together totaling less than $0.1 million, and granted Stanford a specified number of shares of common stock of the Company. In addition, the Company is obligated to pay Stanford ongoing patent expenses and an annual license maintenance fee, which are nominal and will be creditable against any royalties payable to Stanford in the applicable year. The Company is required to make milestone payments up to an aggregate of $5.0 million in respect of a specified number of licensed products that successfully satisfy certain clinical and regulatory milestones. No milestone payments have been made through December 31, 2020. The Company also agreed to pay Stanford tiered royalties on a specified percentage of net sales made by the Company, its affiliates and its sublicensees of licensed products at rates ranging within low single-digit percentages, subject to certain reductions and offsets. The license, on a licensed product-by-licensed product and country-by-country basis, shall become royalty-free and fully paid-up upon the later of the date on which the last valid claim included in the exclusively or non-exclusively licensed patents expires and ten years after the first commercial sale of the licensed product in such country. The Company may terminate the Stanford Agreement, on a licensed product-by-licensed product basis, at any time for any reason by providing at least 60 days’ written notice to Stanford. Stanford may terminate the Stanford Agreement, if the Company is in breach of any provision of the Stanford Agreement and fails to remedy such breach within 60 days after written notice of such breach by Stanford. In addition, Stanford has the right to terminate the Stanford Agreement, on a licensed product-by-licensed product basis, if the Company is not diligently developing and commercializing such licensed product under certain conditions or if the Company fails to achieve specified development milestones for such licensed product by certain dates, subject to the Company’s extension rights. Commercial License Agreement with Selexis SA In June 2016, the Company entered into a license agreement with Selexis SA, or Selexis, under which the Company obtained a worldwide, royalty-bearing, sublicensable license under certain patents, know-how and other intellectual property, to use Selexis generated cell lines to manufacture ALX148 and to make, use and sell licensed product containing such compound in all fields of use. The rights granted under this agreement include the rights to grant sublicenses to contractors or other collaboration partners, in each case to develop production processes or manufacture licensed product containing ALX148. In consideration for the rights granted to the Company under the agreement, the Company paid Selexis a nominal one-time fee and will pay Selexis an annual maintenance fee. The Company also agreed to pay Selexis milestone payments up to an aggregate of 1.2 million Swiss Francs in respect of all licensed products developed and/or commercialized under the grant that successfully satisfies certain milestone events. The Company also agreed to pay Selexis a flat royalty of a very low single-digit percentage on net sales made by the Company, its affiliates and sublicensees of products. This royalty obligation, on a product-by-product and country-by-country basis, shall terminate and become fully paid-up upon the passing of ten years after the first commercial sale of the product in such country, or the Company’s exercise of the royalty buyout option exercisable at any time prior to the first commercial sale of a licensed product. The Company may terminate the license agreement at any time for any reason with at least 60 days’ written notice to Selexis. Either party may terminate the license agreement if the other party enters into a bankruptcy event or in the event of a material breach of the agreement (that cannot be cured or remains uncured for 60 days after the date that the defaulting party is provided with written notice of such breach). The Company’s obligations to pay royalties that are accrued or accruable will survive any termination of the agreement, and in certain circumstances the licenses granted under the agreement will terminate unless they have become fully paid up as described in the previous paragraph. Commercial Antibody Agreement with Crystal Bioscience Inc. (Now a Subsidiary of Ligand Pharmaceuticals Incorporated) In March 2017, the Company entered into an agreement with Crystal Bioscience Inc. (now a subsidiary of Ligand Pharmaceuticals Incorporated), or Crystal, under which the Company obtained an assignment of certain patents, covering certain SIRPα antibodies. Under this agreement, the Company also received a worldwide, royalty-bearing non-exclusive license, with the right to grant sublicenses through multiple tiers of sublicenses, under certain of Crystal’s background patents and know-how necessary to commercialize the rights under the assigned patents. In consideration for the rights granted to the Company under the agreement, it agreed to pay Crystal milestone payments up to $11.1 million in respect of all licensed products developed under the assigned patents, that successfully satisfy certain clinical and regulatory milestones, each milestone being paid only once for all products. The Company also agreed to pay Crystal tiered royalties on net sales made by the Company, its affiliates and sublicensees of products at rates ranging within low single-digit percentages, subject to certain potential reductions. This royalty obligation, on a product-by-product and country-by-country basis, shall terminate and become fully paid-up upon the later of the date on which the last valid claim included in the licensed patents expires and ten years after the first commercial sale of the product in such country. The Company agreed to use commercially reasonable efforts to develop and commercialize licensed products, including meeting defined development milestones by certain specified dates. The Company may terminate the agreement at any time for any reason with at least 60 days’ written notice to Crystal. Either party may terminate the agreement if the other party enters into a bankruptcy event or in the event of material breach of the agreement (that remains uncured for 60 days after the date that it is provided with written notice of such breach). The Company’s obligations to pay royalties and milestone payments which accrued pre-termination or accrue post-termination will survive any termination.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
Related-Party Transactions	Dec. 31, 2020
Related Party Transactions [Abstract]
RELATED-PARTY TRANSACTIONS	(10) RELATED-PARTY TRANSACTIONS Related-party revenue In June 2018, the Company entered into a Research and Development Services Agreement, or Tollnine Agreement, with Tollnine, a related-party of the Company, to provide research and development services to Tollnine. The Company’s Chief Executive Officer was also the Chief Executive Officer of Tollnine until April 2020 and two of the Company’s investors are also investors in Tollnine. As such, Tollnine was deemed to be a related-party. The Tollnine Agreement had an initial term of 3 years, to be automatically renewed for additional one-year terms unless terminated by either party. The services were to be provided at a price based on the costs incurred by the Company plus a mark-up equal to 10% of such costs. The Company recognized revenue when Tollnine, as the Company’s customer, obtained control of promised goods or services, in an amount that reflects the consideration which the Company expected to receive in exchange for those goods or services. The Company recognized related-party revenues of $1.2 million, $4.8 million and $2.1 million for the years ended December 31, 2020, 2019 and 2018, respectively, under the Tollnine Agreement. Effective as of July 1, 2020, the Company terminated the Tollnine Agreement and entered into the Tallac Services Agreement with Tallac Therapeutics. Receivables due from related-party As of December 31, 2020 and 2019, the Company had outstanding related-party receivables from Tollnine of zero and $0.5 million, respectively. Tallac Service Agreement The Company entered into a research and development services agreement, or the Tallac Services Agreement, with Tallac Therapeutics effective as of July 1, 2020. The Tallac Services Agreement provides that Tallac Therapeutics will provide certain preclinical research services to the Company for a service fee based on the costs incurred by Tallac Therapeutics plus a mark-up equal to 10.0% of such costs. The Tallac Services Agreement has an initial term of four years and is renewed automatically for additional one year terms thereafter. The Company records the payments for the research and development services as research and development costs within the consolidated statement of operations and comprehensive loss. The Company has recorded $0.6 million as research and development costs for the year ended December 31, 2020. Tallac Collaboration Agreement On March 4, 2021, the Company entered into a Collaboration Agreement with Tallac Therapeutics pursuant to which the Company and Tallac Therapeutics expect to jointly develop, manufacture, and commercialize a novel class of cancer immunotherapeutics. T he key economic components of the collaboration transaction include that both parties

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
Net Loss Per Share Attributable to Common Stockholders	Dec. 31, 2020
Earnings Per Share [Abstract]
NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS	(11) NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (45,740 ) $ (19,243 ) $ (13,731 ) Less: cumulative preferred dividends allocated to preferred stockholders (5,202 ) (4,028 ) (3,671 ) Net loss attributable to common stockholders $ (50,942 ) $ (23,271 ) $ (17,402 ) Denominator: Weighted-average shares of common stock outstanding 18,485,343 3,076,461 2,750,838 Net loss per share attributable to common stockholders, basic and diluted $ (2.76 ) $ (7.56 ) $ (6.33 ) Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods presented as the inclusion of all potential common stock outstanding would have been anti-dilutive. The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the years ended December 31, 2020, 2019 and 2018, because including them would have been anti-dilutive: December 31, 2020 2019 2018 Convertible preferred stock — 10,313,808 9,297,081 Warrants to purchase convertible preferred stock — 61,292 — Common stock subject to repurchase 63 34,024 229,912 Options issued and outstanding 4,857,308 1,183,745 864,819 4,857,371 11,592,869 10,391,812

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	(12) COMMITMENTS AND CONTINGENCIES Guarantees and Indemnifications In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. The Company also has indemnification obligations to its officers and directors for specified events or occurrences, subject to some limits, while they are serving at the Company’s request in such capacities. There have been no claims to date and the Company has director and officer insurance that may enable the Company to recover a portion of any amounts paid for future potential claims. The Company believes the fair value of these indemnification agreements is minimal. Accordingly, the Company has not recorded any liabilities for these agreements as of December 31, 2020. Contingencies From time to time, the Company may be a party to various claims in the normal course of business. Legal fees and other costs associated with such actions will be expensed as incurred. The Company will assess, in conjunction with its legal counsel, the need to record a liability for litigation and contingencies. Reserve estimates will be recorded when and if it is determined that a loss related matter is both probable and reasonably estimable. For the years ended December 31, 2020, 2019 and 2018, the Company had no pending or threatened litigation. Contractual Obligations and Other Commitments The Company has contractual obligations from its operating lease, manufacturing and service contracts and other research and development activities. The following table aggregates the Company’s material expected contractual obligations and commitments as of December 31, 2020 (in thousands): December 31, 2020 Total 2021 2022 - 2023 2024 - 2025 Thereafter Operating lease obligations (1) $ 346 $ 140 $ 206 $ — $ — Manufacturing and service contracts (2) 10,320 6,292 4,028 — — Total $ 10,666 $ 6,432 $ 4,234 $ — $ — (1) Payments due for the office space in Burlingame, California under a single operating sub-lease agreement that expires in 2023. (2) In November 2015, the Company entered into a Master Service Agreement, or the MSA, with KBI Biopharma, Inc. relating to formulation development, process development and cGMP manufacturing of ALX148 for use in clinical trials on a project basis. The MSA had an initial term of three years with successive one-year renewal periods, is cancellable upon notice and is non-exclusive. Statements of work under the MSA commit the Company to certain purchase obligations of approximately $9.9 million. In addition, the Company has commitments with a second drug product manufacturer that commits the Company to certain purchase obligations of approximately $0.4 million. These amounts are based on non-cancellable commitments and forecasts that include estimates of future market demand, quantity discounts and manufacturing efficiencies that may impact timing of purchases. The Company enters into contracts in the normal course of business with various third parties for clinical trials, preclinical research studies and testing, manufacturing and other services and products for operating purposes. These contracts generally provide for termination upon notice. Payments due upon cancellation consist only of payments for services provided or expenses incurred, including non-cancellable obligations of our service providers, up to the date of cancellation. These payments are not included in the table of contractual obligations above. Facilities In 2017, the Company entered into a lease agreement for office space for a period of five years and four months, commencing February 1, 2018 and ending May 31, 2023. In July 2020, the Company (i) assigned to Tallac Therapeutics, a related party (Note 10), the Company’s lease with respect to the premises located at 866 Malcolm Road, Burlingame, California, and (ii) received a sub-lease for premises from Tallac Therapeutics. Minimum rent payments under operating leases are recognized on a straight-line basis over the term of the lease including any periods of free rent. Rent expense was $0.6 million, $0.8 million and $1.0 million for the years ended December 31, 2020, 2019 and 2018, respectively. Sub-lease expenses are recorded within rent expense.

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	(13) SUBSEQUENT EVENTS Tallac Collaboration Agreement On March 4, 2021, the Company entered into a Collaboration Agreement with Tallac Therapeutics pursuant to which the Company and Tallac Therapeutics expect to jointly develop, manufacture, and commercialize a novel class of cancer immunotherapeutics. The collaboration builds on the Company’s expertise in developing therapies that block the CD47 checkpoint pathway and expands its immuno-oncology pipeline. The companies will leverage their respective scientific and technical expertise to advance an anti-SIRPα antibody conjugated to a Toll-like receptor 9, or TLR9, agonist for targeted activation of both the innate and adaptive immune systems. T he key economic components of the collaboration transaction include that both parties

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
Selected Quarterly Financial Data (Unaudited)	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	(14) SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) The following presents certain unaudited quarterly consolidated financial information for the years ended December 31, 2020 and 2019. This information has been prepared on the same basis as the audited consolidated financial statements and includes all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the unaudited quarterly results of operations set forth herein. Net loss per share for all periods presented has been retroactively adjusted to reflect the 1-for-6.5806 reverse stock split effected on July 8, 2020. 2020 (in thousands, except per share data) Q1 Q2 Q3 Q4 Operating expenses $ 5,897 $ 11,314 $ 9,809 $ 17,825 Net loss attributable to common stockholders (7,437 ) (13,972 ) (10,759 ) (18,774 ) Net loss per share attributable to common stockholders, basic and diluted $ (2.37 ) $ (4.41 ) $ (0.36 ) $ (0.50 ) 2019 (in thousands, except per share data) Q1 Q2 Q3 Q4 Operating expenses $ 5,259 $ 5,484 $ 4,290 $ 8,946 Net loss attributable to common stockholders (5,143 ) (5,178 ) (4,115 ) (8,835 ) Net loss per share attributable to common stockholders, basic and diluted $ (1.71 ) $ (1.68 ) $ (1.33 ) $ (2.83 )

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2020
Basis of Presentation	Basis of Preparation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP, and the applicable rules and regulations of the U.S. Securities and Exchange Commission, or SEC.
Principles of Consolidation	Principles of Consolidation All intercompany balances and transactions have been eliminated in consolidation.
Reverse Stock Split	Reverse Stock Split On July 8, 2020, the Company’s board of directors approved an amendment to the Company’s certificate of incorporation to effect a 1-for-6.5806 reverse split of its common stock and convertible preferred stock. The par values of the common and convertible preferred stock were not adjusted as a result of the reverse stock split. All authorized, issued and outstanding common stock, convertible preferred stock, stock options, warrants, and related per share amounts contained in the consolidated financial statements have been retroactively adjusted to reflect this reverse stock split for all periods presented. The reverse stock split was effected on July 9, 2020.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. On an ongoing basis, management evaluates its estimates, including those related to the estimated useful lives of long-lived assets, clinical trial accruals, fair value of assets and liabilities, Series B convertible preferred stock warrant liability, term loan compound derivative liability, term loan, valuation of the Company’s common stock, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company holds its cash and cash equivalents in checking and money market accounts. The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value.
Concentration Of Credit Risk, Credit Losses And Other Risks And Uncertainties	Concentration of Credit Risk, Credit Losses and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits, and invests in money market funds. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and cash equivalents. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals or sole-source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration, or FDA, and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation of property and equipment is provided using the straight-line method over the estimated useful lives of the assets. Upon sale or retirement of assets, the cost and related accumulated depreciation or amortization are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss. Maintenance and repairs are charged to the consolidated statement of operations and comprehensive loss as incurred.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the equity financing.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future undiscounted net cash flows which the asset or asset group are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds its fair value. Fair value is determined using various valuation techniques including discounted cash flow models, quoted market values and third-party independent appraisals, as considered necessary. The Company has not recorded impairment of any long-lived assets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the consolidated financial statements. The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Where observable prices or inputs are not available valuation models are applied. These valuation techniques involve some level of management estimation and judgment, the degree of which is dependent on the price transparency for the instruments or market and the instruments’ complexity. The Company’s financial instruments consist of cash and cash equivalents, receivables due from related-party, accounts payable, the term loan compound derivative liability and the Series B convertible preferred stock warrant liability. The term loan compound derivative liability and the Series B convertible preferred stock warrant liability are re-measured at the end of every period and carried at fair value (Note 3). The recorded value of the Company’s receivables due from related-party and accounts payable approximates its current fair value due to the relatively short-term nature of these items.
Term Loan	Term Loan The Company accounts for the Loan and Security Agreement, dated as of December 20, 2019, as amended, with Silicon Valley Bank, or SVB, and WestRiver Innovation Lending Fund VIII, LP, or WestRiver, collectively as lenders, and SVB, as administrative agent and collateral agent, as a liability measured at net proceeds less debt discount and is accreted to the face value of the term loan over its expected term using the effective interest method. The Company considers whether there are any embedded features in its debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging
Convertible Preferred Stock	Convertible Preferred Stock The Company records convertible preferred stock net of issuance costs on the dates of issuance, which represents the carrying value. In the event of a change of control of the Company, proceeds will be distributed in accordance with the liquidation preferences set forth in its organization documents unless the holders of convertible preferred stock have converted their convertible preferred stock into common stock. Convertible preferred stock is classified outside of stockholders’ equity (deficit) on the accompanying consolidated balance sheets as events triggering the liquidation preferences are not solely within the Company’s control. The Company has elected not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. Upon the consummation of the Company’s initial public offering in July 2020, all shares of convertible preferred stock outstanding and accrued cumulative dividends automatically converted into 23,934,533 shares of common stock.
Revenue Recognition	Revenue Recognition To date, the Company has derived revenue from providing research and development services on a time and materials basis to a related-party. The Company recognizes such revenues over time as services are delivered, and invoices the customer as the work is incurred in arrears. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC Topic 606, Revenue from Contracts with Customers As part of the Company’s consideration as to whether the Company has entered into a contract with a customer, it considers whether it is probable that it will collect the consideration it is entitled to in exchange for the goods and services it transfers to the customer. At contract inception, the Company assesses the goods or services promised within each contract that falls under the scope of Topic 606, determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.
Cost of Services for Related-Party Revenue	Cost of Services for Related-Party Revenue The Company incurs costs associated with related-party services including direct labor and associated employee benefits, laboratory supplies, and other expenses. These costs are recorded in cost of services for related-party revenue as a component of total operating expenses in the accompanying consolidated statements of operations and comprehensive loss.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred and consist primarily of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to nonemployees and entities that conduct certain research and development activities on behalf of the Company and expenses incurred in connection with license agreements (Note 9). Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed.
Clinical and Manufacturing Accruals	Clinical and Manufacturing Accruals The Company records accruals for estimated costs of research, preclinical studies and clinical trials, and manufacturing development, which are a significant component of research and development expenses. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers, including contract research organizations, or CROs, and contract manufacturing organizations, or CMOs. The Company’s contracts with CROs generally include pass-through fees such as regulatory expenses, investigator fees, travel costs and other miscellaneous costs, including shipping and printing fees. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided to the Company under such contracts. The Company accrues the costs incurred under agreements with these third parties based on estimates of actual work completed in accordance with the respective agreements. The Company determines the estimated costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the services and the agreed-upon fees to be paid for such services. The Company makes significant judgments and estimates in determining the accrual balance at the end of each reporting period. As actual costs become known, the Company adjusts its accruals. Although the Company does not expect its estimates to be materially different from amounts actually incurred, the Company’s understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in the Company reporting amounts that are too high or too low in any particular period. To assist in its estimates the Company relies upon the receipt of timely and accurate reporting from its clinical and non-clinical studies and other third-party vendors. Through December 31, 2020, there have been no material differences from the Company’s accrued estimated expenses to the actual clinical trial expenses. However, variations in the assumptions used to estimate accruals, including, but not limited to, the number of patients enrolled, the rate of patient enrollment, and the actual services performed, and related costs may vary from the Company’s estimates, resulting in adjustments to clinical trial expense in future periods. Changes in these estimates that result in material changes to the Company’s accruals could materially affect its financial position and results of operations.
Stock-based Compensation Expense	Stock-based Compensation Expense The Company accounts for stock-based compensation by measuring and recognizing compensation expense for all stock-based payments made to employees, directors and non-employees based on estimated grant-date fair values. The Company uses the straight-line method to allocate compensation expense to reporting periods over each optionee’s requisite service period, which is generally the vesting period, and estimates the fair value of stock-based awards using the Black-Scholes option-pricing model. The Black-Scholes model requires the input of subjective assumptions, including expected volatility, expected dividend yield, expected term, risk-free rate of return and the estimated fair value of the underlying common stock on the date of grant. Prior to the Company’s initial public offering, the fair value of the common stock underlying the stock-based awards was determined on each grant date by the board of directors, with input from management, considering the most recently available third-party valuation of common shares. The Company accounts for the effect of forfeitures as they occur.
Segment Reporting	Segment Reporting The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of the Company’s operation and each of its subsidiaries is U.S. dollars. All assets and liabilities denominated in a foreign currency are translated into U.S. dollars at the exchange rate prevailing on the balance sheet date. Expenses are translated at the average exchange rates prevailing during the applicable period. Foreign currency transaction gains and losses are included in the consolidated statement of operations and comprehensive loss and recorded in other expense, net, and were immaterial for the years December 31, 2020, 2019 and 2018.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates in effect for the period in which the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations and comprehensive loss in the period that includes the enactment date. The Company recognizes deferred tax assets to the extent that it believes these assets are more likely than not to be realized. In making such a determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies and results of recent operations. If the Company determines that it would be able to realize its deferred tax assets in the future in excess of their net recorded amount, it would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss for all periods presented.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. The Company applies the two-class method to compute basic and diluted net loss per share when it has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires net loss available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all net loss for the period had been distributed. The Company’s convertible preferred stock participate in any dividends declared by the Company and are therefore considered to be participating securities. The participating securities are not required to participate in the losses of the Company, and therefore during periods of loss there is no allocation required under the two-class method.
Recently Issued Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which is intended to simplify various aspects related to accounting for income taxes. The pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2021. ASU 2019-12 is effective for the Company beginning January 1, 2022. Early adoption is permitted. The Company is currently in the process of evaluating the effects of the adoption of this guidance on the Company’s financial statements and does not expect it to have a material impact on its consolidated financial statements.
New Accounting Pronouncements Recently Adopted	New Accounting Pronouncements Recently Adopted In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), which requires entities to measure all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. This replaces the existing incurred loss model and is applicable to the measurement of credit losses on financial assets measured at amortized cost. The Company early adopted this guidance on January 1, 2020. For trade receivables and other instruments, the Company uses a new forward-looking expected loss model that generally results in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses, the losses are recognized as allowances rather than as reductions in the amortized cost of the securities. The adoption of the guidance did not have a material impact on the Consolidated Financial Statements and related disclosures and there was no allowance for losses for the year ended December 31, 2020. In September 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement. The FASB issued final guidance that eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. Under the ASU, entities will no longer be required to disclose the amount of transfers between Level 1 and Level 2 of the fair value hierarchy. Public companies will be required to disclose changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU 2018-13 is effective for public business entities for annual reporting periods, and interim periods within those annual periods, beginning after December 15, 2019, with early adoption permitted. The Company adopted this guidance on January 1, 2020. The adoption of ASU 2018-13 did not have a material impact on its consolidated financial statements.
Series B Preferred Stock
Convertible Preferred Stock Warrant Liability	Series B Convertible Preferred Stock Warrant Liability The Company has issued freestanding warrants to purchase its Series B convertible preferred stock. Freestanding warrants for the Company’s convertible preferred stock that are classified outside of permanent equity are recorded at fair value, and are subject to re-measurement at the end of every period until the earlier of the exercise of the warrants or the completion of a liquidation event, including the completion of an initial public offering. Upon exercise, the Series B convertible preferred stock warrant liability would be reclassified to additional paid-in capital, with any change in fair value recognized as a component of other expense, net. Following the Company’s initial public offering, the warrants were automatically converted to warrants to purchase shares of common stock (Note 5). The Company revalued the Series B convertible preferred stock warrants as of the completion of the initial public offering and reclassified the outstanding preferred stock warrant liability balance to additional paid-in capital with no further re-measurement required as common stock warrants are considered permanent equity.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
Fair Value of Financial Instruments (Tables)	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table sets forth the Company’s financial assets and liabilities that are measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): As of December 31, 2020 Level 1 Level 2 Level 3 Fair Value Financial assets Cash equivalents Money market funds $ 424,115 $ — $ — $ 424,115 As of December 31, 2019 Level 1 Level 2 Level 3 Fair Value Financial liabilities Non-current liabilities Compound derivative liability $ — $ — $ 51 $ 51 Warrant liability $ — $ — $ 361 $ 361
Reconciliation of Financial Liabilities Measured at Fair Value Using Level 3 Unobservable Inputs	The following table is a reconciliation of all financial liabilities measured at fair value using Level 3 unobservable inputs (in thousands): Year Ended December 31, 2020 Compound Warrant Derivative Liability Liability Fair value at beginning of year $ 361 $ 51 Additions — — Change in fair value 658 (8 ) Reclassification to equity (1,019 ) — Extinguishment of compound derivative liability upon extinguishment of host instrument — (43 ) Fair value at end of year $ — $ —

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
Balance Sheet Components (Tables)	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Schedule of Components of Property and Equipment	The following table presents the components of property and equipment, net as of December 31, 2020 and 2019 (in thousands): December 31, December 31, 2020 2019 Computer hardware and software $ 63 $ 146 Machinery and equipment — 1,698 Furniture and fixtures 9 36 Leasehold improvements 5 429 Property and equipment, gross 77 2,309 Less: accumulated depreciation and amortization (25 ) (1,449 ) Property and equipment, net $ 52 $ 860
Components of Accrued Expenses and Other Current Liabilities	The following table presents the components of accrued expenses and other current liabilities as of December 31, 2020 and 2019 (in thousands): December 31, December 31, 2020 2019 Accrued professional fees $ 300 $ 122 Accrued compensation 1,974 924 Accrued clinical and nonclinical study costs 1,473 — Accrued contract manufacturing 2,123 53 Accrued federal income tax 179 1 Other 151 136 Total accrued expenses and other current liabilities $ 6,200 $ 1,236

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
Stockholders' Equity (Tables)	Dec. 31, 2020
Equity [Abstract]
Common Stock Reserved for Future Issuance on Converted Basis	Common stock reserved for future issuance, on an as if converted basis, as of December 31, 2020 and 2019, consists of the following: December 31, December 31, 2020 2019 Convertible preferred stock issued and outstanding — 10,313,808 Stock options issued and outstanding 4,857,308 1,183,745 Stock options authorized for future issuance 2,835,443 566,900 Warrants issued and outstanding — 61,292 Warrants authorized for future issuance — 30,646 Total 7,692,751 12,156,391
Summary of Convertible Preferred Stock	As of December 31, 2019, the Company’s convertible preferred stock consisted of the following (in thousands, except share amounts): December 31, 2019 Shares Aggregate Authorized Issued And Net Liquidation Shares Outstanding Proceeds (1) Preference Shares designated as: Series A convertible preferred stock 9,421,633 9,297,081 $ 60,933 $ 73,571 Series B convertible preferred stock 2,145,370 1,016,727 9,430 10,014 Total 11,567,003 10,313,808 $ 70,363 $ 83,585 (1) Net proceeds are gross proceeds from the offerings net of issuance costs

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
Stock-Based Compensation (Tables)	Dec. 31, 2020
Summary of Share Option Activity	The following table provides a summary of share option activity under the Plan and related information: Outstanding Options Shares Available to Grant Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 566,900 1,183,745 $ 1.37 8.06 $ 638 Authorized 6,124,217 — Granted (3,857,655 ) 3,857,655 $ 10.92 Exercised — (182,111 ) $ 1.65 Canceled/forfeited 1,981 (1,981 ) $ 0.99 Outstanding at December 31, 2020 2,835,443 4,857,308 $ 8.94 8.86 $ 375,270 Exercisable at December 31, 2020 3,776,399 $ 3.85 8.65 $ 310,999
Schedule of Fair Value of Each Option Grant Using Black-Scholes Option-Pricing Model	The fair value of each option grant during the years ended December 31, 2020, 2019 and 2018 was estimated with the Year Ended December 31, 2020 2019 2018 Expected term (in years) 5.8 - 6.1 4.4 - 6.0 5.2 - 6.0 Risk-free interest rate 0.3% - 0.8% 1.7% - 2.1% 2.6% - 3.0% Expected dividend rate - - - Expected stock price volatility 78.7% - 89.0% 75.2% - 80.5% 66.5% - 68.7%
Share Options Granted To Employees And Nonemployees
Share-Based Compensation Expense Includes Share Options Granted to Employees and Nonemployees	Stock-based compensation expense includes share options granted to employees and nonemployees and has been reported in the Company’s consolidated statements of operations and comprehensive loss as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 2,551 $ 105 $ 195 General and administrative 2,885 33 16 Cost of services for related-party revenue — 159 58 $ 5,436 $ 297 $ 269

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule Components of Loss Before Income Taxes	The U.S. domestic and international components of pre-tax loss for the years ending December 31, 2020, 2019 and 2018 are as follows (in thousands): Year Ended December 31, 2020 2019 2018 United States $ (9,457 ) $ 813 $ 855 International (36,042 ) (20,022 ) (14,541 ) Loss before income taxes $ (45,499 ) $ (19,209 ) $ (13,686 )
Schedule of Income Tax Provision (Benefit)	The federal and state provision for income taxes consist of the following (in thousands): Year Ended December 31, 2020 2019 2018 Current provision for income taxes: Federal $ 239 $ 33 $ 44 State 2 1 1 International — — — Total current 241 34 45 Deferred tax provision: Federal — — — State — — — International — — — Total deferred — — — Provision for income taxes $ 241 $ 34 $ 45
Schedule of Statutory and Effective Income Tax Rate Reconciliation	A reconciliation of the U.S. federal statutory income tax rate to the effective tax for the years ended December 31, 2020, 2019 and 2018 are as follows (in thousands): Year Ended December 31, 2020 2019 2018 At federal statutory income tax rate $ (9,555 ) $ (4,034 ) $ (2,874 ) State income taxes (3,098 ) (1,875 ) (332 ) Stock-based compensation (5 ) 60 57 Research & Development credits (512 ) (861 ) (499 ) Change in valuation allowance 5,710 3,733 732 Other 321 75 100 Foreign rate differential 7,380 3,886 2,899 Prior period true ups — (950 ) (38 ) Provision for income taxes $ 241 $ 34 $ 45
Schedule of Components of Deferred Tax Assets	Significant components of the Company’s deferred tax assets as of December 31, 2020 and 2019 are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Loss carryforwards $ 7,283 $ 3,259 Research & other credits 2,861 3,260 Other 76 69 Accrued expenses 383 261 Stock options 696 3 Total deferred tax assets 11,299 6,852 Deferred tax liabilities: Fixed assets 11 166 Total deferred tax liabilities 11 166 Valuation allowance (11,288 ) (6,686 ) Net deferred tax assets $ — $ —
Summary of Net Operating Loss and Tax Credit Carryforwards	Net operating losses and tax credit carryforwards as of December 31, 2020 are as follows (in thousands): Amount Expiration Years Net operating losses, federal (Post December 31, 2017) $ 7,919 Do Not Expire Net operating losses, state $ 71,363 2038-2040 Tax credits, federal $ 1,327 2039-2040 Tax credits, state $ 2,893 N/A Net operating losses, foreign $ 5,086 N/A
Schedule of Unrecognized Tax Benefits	The Company has the following activity relating to unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 2018 Balance at beginning of year $ 692 $ 418 $ 247 Additions/reversals based on tax positions of prior years (64 ) 2 11 Additions based on tax positions related to the current year 240 272 160 Lapses in statutes of limitations (26 ) — — Balance at end of year $ 842 $ 692 $ 418

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (45,740 ) $ (19,243 ) $ (13,731 ) Less: cumulative preferred dividends allocated to preferred stockholders (5,202 ) (4,028 ) (3,671 ) Net loss attributable to common stockholders $ (50,942 ) $ (23,271 ) $ (17,402 ) Denominator: Weighted-average shares of common stock outstanding 18,485,343 3,076,461 2,750,838 Net loss per share attributable to common stockholders, basic and diluted $ (2.76 ) $ (7.56 ) $ (6.33 )
Summary of Outstanding Potentially Dilutive Securities Were Excluded from Computation of Diluted Net Loss Per Share	The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the years ended December 31, 2020, 2019 and 2018, because including them would have been anti-dilutive: December 31, 2020 2019 2018 Convertible preferred stock — 10,313,808 9,297,081 Warrants to purchase convertible preferred stock — 61,292 — Common stock subject to repurchase 63 34,024 229,912 Options issued and outstanding 4,857,308 1,183,745 864,819 4,857,371 11,592,869 10,391,812

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Summary of Company's Commitments and Contractual Obligations	The Company has contractual obligations from its operating lease, manufacturing and service contracts and other research and development activities. The following table aggregates the Company’s material expected contractual obligations and commitments as of December 31, 2020 (in thousands): December 31, 2020 Total 2021 2022 - 2023 2024 - 2025 Thereafter Operating lease obligations (1) $ 346 $ 140 $ 206 $ — $ — Manufacturing and service contracts (2) 10,320 6,292 4,028 — — Total $ 10,666 $ 6,432 $ 4,234 $ — $ — (1) Payments due for the office space in Burlingame, California under a single operating sub-lease agreement that expires in 2023. (2) In November 2015, the Company entered into a Master Service Agreement, or the MSA, with KBI Biopharma, Inc. relating to formulation development, process development and cGMP manufacturing of ALX148 for use in clinical trials on a project basis. The MSA had an initial term of three years with successive one-year renewal periods, is cancellable upon notice and is non-exclusive. Statements of work under the MSA commit the Company to certain purchase obligations of approximately $9.9 million. In addition, the Company has commitments with a second drug product manufacturer that commits the Company to certain purchase obligations of approximately $0.4 million. These amounts are based on non-cancellable commitments and forecasts that include estimates of future market demand, quantity discounts and manufacturing efficiencies that may impact timing of purchases.

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
Selected Quarterly Financial Data (Unaudited) (Tables)	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Certain Unaudited Quarterly Consolidated Financial Information	The following presents certain unaudited quarterly consolidated financial information for the years ended December 31, 2020 and 2019. This information has been prepared on the same basis as the audited consolidated financial statements and includes all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the unaudited quarterly results of operations set forth herein. Net loss per share for all periods presented has been retroactively adjusted to reflect the 1-for-6.5806 reverse stock split effected on July 8, 2020. 2020 (in thousands, except per share data) Q1 Q2 Q3 Q4 Operating expenses $ 5,897 $ 11,314 $ 9,809 $ 17,825 Net loss attributable to common stockholders (7,437 ) (13,972 ) (10,759 ) (18,774 ) Net loss per share attributable to common stockholders, basic and diluted $ (2.37 ) $ (4.41 ) $ (0.36 ) $ (0.50 ) 2019 (in thousands, except per share data) Q1 Q2 Q3 Q4 Operating expenses $ 5,259 $ 5,484 $ 4,290 $ 8,946 Net loss attributable to common stockholders (5,143 ) (5,178 ) (4,115 ) (8,835 ) Net loss per share attributable to common stockholders, basic and diluted $ (1.71 ) $ (1.68 ) $ (1.33 ) $ (2.83 )

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Details)	Jul. 08, 2020	Dec. 31, 2020USD ($)Segment	Jul. 31, 2020shares	Jul. 21, 2020shares
Significant Accounting Policies [Line Items]
Reverse stock split, description		On July 8, 2020, the Company’s board of directors approved an amendment to the Company’s certificate of incorporation to effect a 1-for-6.5806 reverse split of its common stock and convertible preferred stock.
Reverse stock split, conversion ratio	0.151961827
Impairment charges \| $		$ 0
Number of operating segment \| Segment		1
ASU 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
ASU 2018-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
Initial Public Offering \| Common Stock
Significant Accounting Policies [Line Items]
Convertible shares converted in to common stock \| shares			23,934,533	23,934,533

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value on Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial liabilities
Compound derivative liability		$ 51
Warrant liability		361
Money Market Funds
Financial assets
Cash equivalents	$ 424,115
Level 1 \| Money Market Funds
Financial assets
Cash equivalents	$ 424,115
Level 3
Financial liabilities
Compound derivative liability		51
Warrant liability		$ 361

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Reconciliation of Financial Liabilities Measured at Fair Value Using Level 3 Unobservable Inputs (Details) - Level 3 $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Warrant Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value at beginning of year	$ 361
Change in fair value	658
Reclassification to equity	(1,019)
Compound Derivative Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value at beginning of year	51
Change in fair value	(8)
Extinguishment of compound derivative liability upon extinguishment of host instrument	$ (43)

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0	$ 0
Fair value assets transferred from level 2 to level 1	0	0
Fair value liabilities transferred from level 1 to level 2	0	0
Fair value liabilities transferred from level 2 to level 1	0	0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	$ 0	$ 0

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Components of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 77	$ 2,309
Less: accumulated depreciation and amortization	(25)	(1,449)
Property and equipment, net	52	860
Computer Hardware And Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	63	146
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross		1,698
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	9	36
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 5	$ 429

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020
Schedule Of Balance Sheet Components [Line Items]
Depreciation and amortization expense		$ 200	$ 400	$ 400
Property and equipment		$ 52	$ 860
Lab Equipment and Other Assets
Schedule Of Balance Sheet Components [Line Items]
Property and equipment					$ 600
Proceeds from transfer of assets for cash	$ 600

Balance Sheet Components - Comp

Balance Sheet Components - Components of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Accrued professional fees	$ 300	$ 122
Accrued compensation	1,974	924
Accrued clinical and nonclinical study costs	1,473
Accrued contract manufacturing	2,123	53
Accrued federal income tax	179	1
Other	151	136
Total accrued expenses and other current liabilities	$ 6,200	$ 1,236

Term Loan - Additional Informat

Term Loan - Additional Information (Details)	Aug. 17, 2020$ / sharesshares	Dec. 20, 2019USD ($)$ / sharesshares	Dec. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)shares	Jul. 21, 2020$ / sharesshares	Jul. 16, 2020USD ($)	Dec. 31, 2019USD ($)
Debt Instrument [Line Items]
Warrants issued to purchase \| shares	61,292
Warrant exercise price per share \| $ / shares	$ 9.4972
Loss on early debt extinguishment					$ 621,000
Compound Derivative Liability
Debt Instrument [Line Items]
Fair value of compound derivative liability		$ 51,000
Common Stock
Debt Instrument [Line Items]
Warrants to purchase common stock \| shares						61,292
Common stock exercise price per share \| $ / shares						$ 9.4972
Stock issued upon warrants exercise \| shares					21,369,774
Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase \| shares						61,292
Warrant exercise price per share \| $ / shares						$ 9.4972
Loan Agreement
Debt Instrument [Line Items]
Debt instrument, description of variable rate basis					The loans under the Loan Agreement bore interest at a floating per annum interest rate equal to the greater of 7.0% or 2.0% plus the prime rate as reported in The Wall Street Journal.
Term loan, annual floating interest rate		7.00%
Term loan interest-only payments, term					Interest-only payments for the first 12 months after the closing of the Loan Agreement
Frequency of periodic payment					monthly
Term loan principal and interest payment commencement date		Jan. 1, 2021
Term loan maturity date		Sep. 1, 2022
Percentage of principal amount as final payment		6.00%
Net proceeds from follow-on public offering			$ 6,500,000
Repayments of outstanding principal amount			6,000,000
Loss on early debt extinguishment			$ 600,000
Loan Agreement \| Common Stock
Debt Instrument [Line Items]
Warrants to purchase common stock \| shares		61,292
Common stock exercise price per share \| $ / shares		$ 9.4972
Stock issued upon warrants exercise \| shares	48,932
Loan Agreement \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase \| shares	61,292	61,292
Warrant exercise price per share \| $ / shares	$ 9.4972	$ 9.4972
Estimated fair value of warrants		$ 400,000
Outstanding preferred stock warrant liability converted into common stock							$ 1,000,000
Loan Agreement \| Volatility \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants and rights outstanding, measurement input							0.842
Loan Agreement \| Risk-free Rate \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants and rights outstanding, measurement input							0.006
Loan Agreement \| Dividend Rate \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants and rights outstanding, measurement input							0
Loan Agreement \| Prime Rate
Debt Instrument [Line Items]
Term loan, interest rate above prime rate		2.00%
Loan Agreement \| Maximum
Debt Instrument [Line Items]
Term loan, principal amount		$ 10,000,000
Prepayment fee percentage		3.00%
Loan Agreement \| Maximum \| Time to Liquidity \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants and rights outstanding, measurement input term							9 years 9 months 18 days
Loan Agreement \| Minimum
Debt Instrument [Line Items]
Proceeds from equity financing				$ 30,000,000
Prepayment fee percentage		1.00%
Loan Agreement \| Minimum \| Time to Liquidity \| Series B Convertible Preferred Stock
Debt Instrument [Line Items]
Warrants and rights outstanding, measurement input term			2 years		2 years
First Tranche \| Loan Agreement
Debt Instrument [Line Items]
Term loan, principal amount								$ 6,000,000
Second Tranche \| Loan Agreement
Debt Instrument [Line Items]
Term loan, principal amount				$ 4,000,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 21, 2020	Jul. 20, 2020	Dec. 31, 2020	Feb. 29, 2020	Dec. 31, 2020	Aug. 17, 2020	Jul. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Common stock, shares authorized	1,000,000,000		1,000,000,000		1,000,000,000			1,519,618,271
Convertible preferred stock, shares authorized								11,567,003
Common stock, shares outstanding			39,844,522		39,844,522			3,166,946
Underwriting discounts and commissions paid					$ 3,848
Warrants issued to purchase						61,292
Warrant exercise price per share						$ 9.4972
Common stock, shares issued			39,844,522		39,844,522	48,932		3,166,946
Common Stock
Class Of Stock [Line Items]
Issuance of common stock in connection with equity offerings, net of underwriter discounts and issuance costs, shares					12,512,000
Warrants to purchase common stock	61,292
Common stock exercise price per share	$ 9.4972
Initial Public Offering \| Common Stock
Class Of Stock [Line Items]
Issuance of common stock in connection with equity offerings, net of underwriter discounts and issuance costs, shares	9,775,000
Net proceeds from initial public offering	$ 169,500
Underwriting discounts and commissions paid	13,000
Payment for offering related expense	$ 3,200
Convertible shares converted in to common stock	23,934,533						23,934,533
Follow-on Public Offering \| Common Stock
Class Of Stock [Line Items]
Issuance of common stock in connection with equity offerings, net of underwriter discounts and issuance costs, shares			2,737,000
Net proceeds from initial public offering			$ 194,900
Underwriting discounts and commissions paid			12,500
Payment for offering related expense			$ 700
Undesignated Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized	100,000,000
Convertible preferred stock, shares outstanding			0		0			10,313,808
Series C Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				11,055,981
Stock price per share				$ 9.4972
Proceeds from issuance of preferred stock				$ 105,000
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized			0		0			2,145,370
Convertible preferred stock, shares outstanding			0		0			1,016,727
Warrants issued to purchase	61,292
Warrant exercise price per share	$ 9.4972
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares outstanding								10,313,808	9,297,081	9,297,081
Preferred stock, cumulative dividends percentage					6.00%
Accrued cumulative dividends on the Series A, Series B and Series C convertible preferred stock		$ 18,000
Cumulative preferred stock dividend convertible shares issued upon conversion		2,564,759
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized			0		0			9,421,633
Convertible preferred stock, shares outstanding			0		0			9,297,081
Shares original issue price			$ 6.58		$ 6.58
Series B and C Convertible Preferred Stock
Class Of Stock [Line Items]
Shares original issue price			$ 9.4972		$ 9.4972

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock Reserved for Future Issuance on Converted Basis (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock reserved for future issuance	7,692,751	12,156,391
Convertible Preferred Stock Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuance		10,313,808
Stock Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuance	4,857,308	1,183,745
Stock Options Authorized for Future Issuance
Class Of Stock [Line Items]
Common stock reserved for future issuance	2,835,443	566,900
Warrants Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuance		61,292
Warrants Authorized for Future Issuance
Class Of Stock [Line Items]
Common stock reserved for future issuance		30,646

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Authorized Shares		11,567,003
Shares Issued And Outstanding		10,313,808
Net Proceeds		$ 70,363
Aggregate Liquidation Preference		$ 83,585
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Authorized Shares	0	9,421,633
Shares Issued And Outstanding		9,297,081
Net Proceeds		$ 60,933
Aggregate Liquidation Preference		$ 73,571
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Authorized Shares	0	2,145,370
Shares Issued And Outstanding		1,016,727
Net Proceeds		$ 9,430
Aggregate Liquidation Preference		$ 10,014

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015	Jan. 01, 2021	Apr. 01, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		7,692,751	12,156,391
Unvested early exercised options		63	34,024
Liability related to these unvested options		$ 0	$ 27,000
Unrecognized share-based compensation expense		$ 25,000,000
Unrecognized share-based compensation expense, weighted-average period		3 years 2 months 12 days
Total intrinsic value of options exercised		$ 4,400,000
Weighted-average grant-date fair value per share		$ 7.74	$ 1.27	$ 1.14
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share option granted during the period		0
Common stock reserved for future issuance	400,000
Percentage of eligible compensation withheld	15.00%
Share-based compensation, authorized amount	$ 25,000
Share-based compensation, number of shares authorized	3,000
Share-based Compensation, lower of closing price, percentage	85.00%
Stock Option Modification
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expenses		$ 1,700,000
Maximum \| ESPP \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance						800,000
2015 Share Award Scheme \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share option granted during the period					2,143,117
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share option							4,379,139
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	7,874,862
Share options, maximum term		10 years
Share options, service period		4 years

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Available to Grant Balance	566,900
Shares Available to Grant, Authorized	6,124,217
Shares Available to Grant, Granted	(3,857,655)
Shares Available to Grant, Canceled/forfeited	1,981
Shares Available to Grant Balance	2,835,443	566,900
Number of Options, Balance	1,183,745
Number of Options, Granted	3,857,655
Number of Options, Exercised	(182,111)
Number of Options, Canceled/forfeited	(1,981)
Number of Options, Balance	4,857,308	1,183,745
Number of Options, Exercisable at December 31, 2020	3,776,399
Weighted Average Exercise Price, Balance	$ 1.37
Weighted Average Exercise Price, Granted	10.92
Weighted Average Exercise Price, Exercised	1.65
Weighted Average Exercise Price, Canceled/forfeited	0.99
Weighted Average Exercise Price, Balance	8.94	$ 1.37
Weighted Average Exercise Price, Exercisable at December 31, 2020	$ 3.85
Weighted Average Remaining Contractual Life (Years), Outstanding Options	8 years 10 months 9 days	8 years 21 days
Weighted Average Remaining Contractual Life (Years), Outstanding Options Exercisable	8 years 7 months 24 days
Outstanding Options Aggregate Intrinsic Value, Balance	$ 375,270	$ 638
Outstanding Options Aggregate Intrinsic Value, Exercisable	$ 310,999

Stock-Based Compensation - Shar

Stock-Based Compensation - Share-Based Compensation Expense Includes Share Options Granted to Employees and Nonemployees (Details) - Share Options Granted To Employees And Nonemployees - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 5,436	$ 297	$ 269
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	2,551	105	195
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,885	33	16
Cost of Services for Related-party Revenue
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense		$ 159	$ 58

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Fair Value of Each Option Grant Using Black-Scholes Option-Pricing Model (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.30%	1.70%	2.60%
Risk-free interest rate, maximum	0.80%	2.10%	3.00%
Expected dividend rate	0.00%	0.00%	0.00%
Expected stock price volatility, minimum	78.70%	75.20%	66.50%
Expected stock price volatility, maximum	89.00%	80.50%	68.70%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 9 months 18 days	4 years 4 months 24 days	5 years 2 months 12 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years	6 years

Income Taxes - Domestic and Int

Income Taxes - Domestic and International Components of Pre-Tax Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States	$ (9,457)	$ 813	$ 855
International	(36,042)	(20,022)	(14,541)
Loss before income taxes	$ (45,499)	$ (19,209)	$ (13,686)

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current provision for income taxes:
Federal	$ 239	$ 33	$ 44
State	2	1	1
Total current	241	34	45
Deferred tax provision:
Provision for income taxes	$ 241	$ 34	$ 45

Income Taxes - Schedule of Stat

Income Taxes - Schedule of Statutory and Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
At federal statutory income tax rate	$ (9,555)	$ (4,034)	$ (2,874)
State income taxes	(3,098)	(1,875)	(332)
Stock-based compensation	(5)	60	57
Research & Development credits	(512)	(861)	(499)
Change in valuation allowance	5,710	3,733	732
Other	321	75	100
Foreign rate differential	7,380	3,886	2,899
Prior period true ups		(950)	(38)
Provision for income taxes	$ 241	$ 34	$ 45

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Loss carryforwards	$ 7,283	$ 3,259
Research & other credits	2,861	3,260
Other	76	69
Accrued expenses	383	261
Stock options	696	3
Total deferred tax assets	11,299	6,852
Deferred tax liabilities:
Fixed assets	11	166
Total deferred tax liabilities	11	166
Valuation allowance	(11,288)	(6,686)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
Income Taxes - Additional Information (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Deferred tax assets, increase in valuation allowance	$ 4,600,000	$ 4,500,000
Unrecognized tax benefits	842,000	692,000	$ 418,000	$ 247,000
Recognized interest and penalties expense (benefit) related to unrecognized tax benefits	$ 0	$ 0	$ 0

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Operating Losses and Tax Credit Carryforwards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Federal
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 7,919
Tax credits	$ 1,327
Federal \| Minimum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Tax credits, Expiration Years	2039
Federal \| Maximum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Tax credits, Expiration Years	2040
State
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 71,363
Tax credits	$ 2,893
State \| Minimum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses, Expiration Years	2038
State \| Maximum
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses, Expiration Years	2040
Foreign
Net Operating Loss And Tax Credit Carryforwards [Line Items]
Net operating losses	$ 5,086

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 692	$ 418	$ 247
Additions/reversals based on tax positions of prior years	(64)	2	11
Additions based on tax positions related to the current year	240	272	160
Lapses in statutes of limitations	(26)
Balance at end of year	$ 842	$ 692	$ 418

License Agreement - Additional

License Agreement - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Exclusive Equity Agreement \| Stanford Junior University
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Nonrefundable license royalty and patent expenses	$ 0.1
Clinical and regulatory milestones payments	$ 5
Agreement expiry description	licensed patents expires and ten years after the first commercial sale of the licensed product in such country
Termination of agreement written notice period	60 days
Notice period to remedy the breach of agreement	60 days
Commercial License Agreement \| Selexis SA
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Clinical and regulatory milestones payments	$ 1.2
Agreement expiry description	shall terminate and become fully paid-up upon the passing of ten years after the first commercial sale of the product in such country, or the Company’s exercise of the royalty buyout option exercisable at any time prior to the first commercial sale of a licensed product
Termination of agreement written notice period	60 days
Notice period to remedy the breach of agreement	60 days
Commercial Antibody Agreement \| Crystal Bioscience Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Clinical and regulatory milestones payments	$ 11.1
Agreement expiry description	licensed patents expires and ten years after the first commercial sale of the product in such country
Termination of agreement written notice period	60 days
Notice period to remedy the breach of agreement	60 days

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Details) $ in Thousands	Jul. 01, 2020USD ($)	Jun. 30, 2018	Dec. 31, 2020USD ($)Investor	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Related Party Transaction [Line Items]
Related-party revenue			$ 1,182	$ 4,796	$ 2,067
Research and development costs			28,961	16,306	11,270
Tollnine
Related Party Transaction [Line Items]
Outstanding related-party receivables			$ 0	500
Research and Development Services Agreement \| Tollnine
Related Party Transaction [Line Items]
Number of company's investors who are investors in related party as well \| Investor			2
Related-party revenue			$ 1,200	$ 4,800	$ 2,100
Initial term of agreement with related party		3 years
Agreement automatically renewal additional term unless terminated		1 year
Markup cost in percentage		10.00%
Research and Development Services Agreement \| Tallac Therapeutics
Related Party Transaction [Line Items]
Initial term of agreement with related party	4 years
Agreement automatically renewal additional term unless terminated	1 year
Markup cost in percentage	10.00%
Research and development costs	$ 600

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss									$ (45,740)	$ (19,243)	$ (13,731)
Less: cumulative preferred dividends allocated to preferred stockholders									(5,202)	(4,028)	(3,671)
Net loss attributable to common stockholders	$ (18,774)	$ (10,759)	$ (13,972)	$ (7,437)	$ (8,835)	$ (4,115)	$ (5,178)	$ (5,143)	$ (50,942)	$ (23,271)	$ (17,402)
Denominator:
Weighted-average shares of common stock outstanding									18,485,343	3,076,461	2,750,838
Net loss per share attributable to common stockholders, basic and diluted									$ (2.76)	$ (7.56)	$ (6.33)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Summary of Outstanding Potentially Dilutive Securities Were Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,857,371	11,592,869	10,391,812
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		10,313,808	9,297,081
Warrants to Purchase Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		61,292
Common Stock Subject to Repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	63	34,024	229,912
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,857,308	1,183,745	864,819

Commitments and Contingencies -

Commitments and Contingencies - Summary of Company's Commitments and Contractual Obligations (Details) $ in Thousands	Dec. 31, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
Manufacturing and service contracts, Total	$ 10,320
Manufacturing and service contracts, 2021	6,292
Manufacturing and service contracts, 2022 - 2023	4,028
Contractual Obligation, Total	10,666
Contractual Obligation, 2021	6,432
Contractual Obligation, 2022 - 2023	4,234
Operating lease obligations, Total	346
Operating lease obligations, 2021	140
Operating lease obligations, 2022 - 2023	$ 206

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Company's Commitments and Contractual Obligations (Parenthetical) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2020
Commitments And Contingencies [Line Items]
Purchase obligations		$ 10,320
Master Service Agreement
Commitments And Contingencies [Line Items]
Initial term of agreement	3 years
Renewal periods of agreement	1 year
Purchase obligations	$ 9,900
Office and Laboratory Space \| Burlingame, California
Commitments And Contingencies [Line Items]
Operating sub-lease expiration year		2023
Second Drug Product Manufacturer \| Master Service Agreement
Commitments And Contingencies [Line Items]
Purchase obligations	$ 400

Commitments and Contingencies_3

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies [Line Items]
Rent expense	$ 0.6	$ 0.8	$ 1
Office Space
Commitments And Contingencies [Line Items]
Lessee, operating lease, term of contract				5 years 4 months
Lessee, operating lease commencing end date				May 31, 2023

SELECTED QUARTERLY FINANCIAL _3

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) - Additional Information (Details)	Jul. 08, 2020
Quarterly Financial Information Disclosure [Abstract]
Reverse stock split, conversion ratio	0.151961827

SELECTED QUARTERLY FINANCIAL _4

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) - Schedule of Certain Unaudited Quarterly Consolidated Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 17,825	$ 9,809	$ 11,314	$ 5,897	$ 8,946	$ 4,290	$ 5,484	$ 5,259	$ 44,845	$ 23,979	$ 15,751
Net loss attributable to common stockholders	$ (18,774)	$ (10,759)	$ (13,972)	$ (7,437)	$ (8,835)	$ (4,115)	$ (5,178)	$ (5,143)	$ (50,942)	$ (23,271)	$ (17,402)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.50)	$ (0.36)	$ (4.41)	$ (2.37)	$ (2.83)	$ (1.33)	$ (1.68)	$ (1.71)	$ (2.76)	$ (7.56)	$ (6.33)