Neon Therapeutics 10-Q1 May 202020 Q1 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Document and Entity Information
Entity Registrant Name	Neon Therapeutics, Inc.
Entity Central Index Key	0001694187
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		28,966,658
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 15,047	$ 29,395
Prepaid expenses and other current assets	1,962	1,848
Total current assets	17,009	31,243
Operating lease, right-of-use assets	7,228	7,542
Property and equipment, net	6,694	7,109
Other long-term assets	471	478
Total assets	31,402	46,372
Current liabilities:
Accounts payable	3,043	1,702
Accrued expenses	6,437	7,464
Operating lease liabilities, current	1,287	1,241
Total current liabilities	10,767	10,407
Operating lease liabilities, net of current portion	6,200	6,542
Other liabilities	4	6
Total liabilities	16,971	16,955
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock, $0.001 par value; 150,000,000 shares authorized as of March 31, 2020 and December 31, 2019; 28,963,858 and 28,729,725 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively	29	29
Additional paid-in capital	284,538	282,926
Accumulated deficit	(270,136)	(253,538)
Total stockholders’ equity	14,431	29,417
Total liabilities and stockholders’ equity	$ 31,402	$ 46,372

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	28,963,858	28,729,725
Common stock, shares outstanding (in shares)	28,963,858	28,729,725

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses:
Research and development	$ 9,446	$ 16,172
General and administrative	7,220	5,408
Total operating expenses	16,666	21,580
Loss from operations	(16,666)	(21,580)
Interest income	68	556
Net loss	$ (16,598)	$ (21,024)
Net loss per share, basic and diluted (in dollars per share)	$ (0.58)	$ (0.76)
Weighted average common shares outstanding, basic and diluted (in shares)	28,535,948	27,651,067
Comprehensive loss:
Net loss	$ (16,598)	$ (21,024)
Other comprehensive income:
Unrealized gains on marketable securities	0	67
Total other comprehensive income	0	67
Comprehensive loss	$ (16,598)	$ (20,957)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at the beginning of the period (in shares) at Dec. 31, 2018		28,314,274
Balance at the beginning of the period at Dec. 31, 2018	$ 101,249	$ 28	$ 275,058	$ (75)	$ (173,762)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	1,729		1,729
Exercise of stock options (in shares)		17,070
Exercise of stock options	45		45
Vesting of restricted common stock	5		5
Unrealized gains on marketable securities	67			67
Net loss	(21,024)				(21,024)
Balance at the end of the period (in shares) at Mar. 31, 2019		28,331,344
Balance at the end of the period at Mar. 31, 2019	$ 82,071	$ 28	276,837	(8)	(194,786)
Balance at the beginning of the period (in shares) at Dec. 31, 2019	28,729,725	28,729,725
Balance at the beginning of the period at Dec. 31, 2019	$ 29,417	$ 29	282,926	0	(253,538)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	1,669		1,669
Vesting of restricted common stock and restricted stock units (in shares)		273,461
Vesting of restricted common stock and restricted stock units	2		2
Repurchase of common stock for employee tax withholdings (in shares)		(39,328)
Repurchase of common stock for employee tax withholdings	(59)		(59)
Unrealized gains on marketable securities	0
Net loss	$ (16,598)				(16,598)
Balance at the end of the period (in shares) at Mar. 31, 2020	28,963,858	28,963,858
Balance at the end of the period at Mar. 31, 2020	$ 14,431	$ 29	$ 284,538	$ 0	$ (270,136)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (16,598)	$ (21,024)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	424	415
Non-cash lease expense	314	287
Net amortization of premiums and discounts on marketable securities	0	(21)
Stock-based compensation expense	1,669	1,729
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(114)	(233)
Other long-term assets	6	(42)
Accounts payable	1,341	0
Accrued expenses and other liabilities	(1,027)	(2,012)
Lease liabilities	(295)	(254)
Net cash used in operating activities	(14,280)	(21,155)
Cash flows from investing activities:
Sales and maturities of marketable securities	0	18,700
Purchases of property and equipment	(9)	(1,026)
Net cash (used in) provided by investing activities	(9)	17,674
Cash flows from financing activities:
Proceeds from exercise of stock options	0	45
Payments for repurchase of common stock for employee tax withholdings	(59)	0
Net cash (used in) provided by financing activities	(59)	45
Net decrease in cash, cash equivalents and restricted cash	(14,348)	(3,436)
Cash, cash equivalents and restricted cash, beginning of period	29,851	53,156
Cash, cash equivalents and restricted cash, end of period	15,503	49,720
Supplemental disclosure of non-cash items:
Purchases of property and equipment included in accounts payable and accrued expenses	$ 0	$ 168

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of the cash, cash equivalents and restricted cash balances
Cash and cash equivalents	$ 15,047	$ 49,264
Restricted cash included in other long-term assets	456	456
Total cash, cash equivalents and restricted cash	$ 15,503	$ 49,720

Nature of the Business

Nature of the Business	3 Months Ended
Nature of the Business	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	Nature of the Business Neon Therapeutics, Inc. (the "Company") is a clinical-stage immuno-oncology company and a leader in the field of neoantigen-targeted therapies, dedicated to transforming the treatment of cancer by directing the immune system towards neoantigens. The Company is leveraging over a decade of insights from its founders to develop neoantigen-targeted therapies that use two distinct approaches: the first approach utilizes fully personal therapies that target neoantigens specific to each individual, and the second approach utilizes shared therapies that target neoantigens that are shared across subsets of patients or tumor types. Both the personal neoantigen approach and the shared neoantigen approach focus on targeting a prioritized set of what the Company believes are the most therapeutically-relevant neoantigens. The Company is subject to risks common to early-stage companies in the biotechnology industry including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the ability to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. Even if the Company's development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Merger Agreement with BioNTech SE On January 15, 2020, the Company entered into an agreement with BioNTech SE, a Societas Europaea organized and existing under the laws of Germany ("BioNTech"), and Endor Lights, Inc., a Delaware corporation and a direct, wholly-owned subsidiary of BioNTech ("Merger Sub" and, together with BioNTech, the "Acquiring Parties"), pursuant to which, subject to the satisfaction or waiver of the conditions therein, Merger Sub will merge with and into the Company, with the Company surviving as a wholly-owned subsidiary of BioNTech (the "Merger Agreement" and such transaction, the "Merger"). The Merger Agreement was unanimously approved by the members of the board of directors of the Company (the "Board") and the Board resolved to recommend approval of the Merger Agreement to the Company’s shareholders. The closing of the Merger is subject to approval of the Company's shareholders and the satisfaction of customary closing conditions. Certain of the Company's stockholders who collectively own approximately 36% of the outstanding shares of the Company's common stock have entered into voting agreements, pursuant to which they have agreed, among other things, and subject to the terms and conditions of the agreements, to vote in favor of the Merger. The special meeting of the Company’s shareholders to consider approval of the Merger is scheduled to be held on May 4, 2020. Subject to the terms of the Merger Agreement, at the effective time of the Merger (the "Effective Time"), each share of the Company’s common stock issued and outstanding immediately prior to the Effective Time shall automatically be canceled and converted into the right to receive 0.063 of an American Depositary Share of BioNTech ("BioNTech ADS"), with each BioNTech ADS representing one ordinary share of BioNTech, without interest but subject to any withholding required under applicable law. The Merger is expected to close during the second quarter of 2020. Liquidity In accordance with Accounting Standards Update ("ASU") No. 2014-15, Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (Subtopic 205-40) , management must evaluate whether there are conditions or events, when considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the financial statements are issued. The Company's financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through March 31, 2020 , the Company has funded its operations primarily with net proceeds of $89.9 million from its initial public offering ("IPO") in June 2018, as well as an aggregate of $161.1 million of net proceeds from sales of the Company’s preferred stock and convertible debt. Since inception, the Company has incurred recurring losses and negative cash flows from operations in each period and on an aggregate basis. As of March 31, 2020 and December 31, 2019 , the Company had an accumulated deficit of $270.1 million and $253.5 million , respectively. The Company expects its operating losses and negative operating cash flows to continue into the foreseeable future as it continues to develop, manufacture and commercialize its products. As of March 31, 2020 , the Company had cash and cash equivalents of $15.0 million . The Company expects that, based on its current operating plan, its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements into the third quarter of 2020. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. The Company expects that it will continue to incur significant expenses in connection with its ongoing business activities. As a result, the Company will need substantial additional funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the pursuit of a strategic transaction, sale of equity, debt financings or other capital sources, including collaborations with other companies. The Company may be unable to raise additional funds or enter into such other agreements or arrangements, including a strategic transaction, when needed on favorable terms, or at all. If the Company is unable to obtain funding on a timely basis, the Company may be required to curtail, delay or discontinue one or more of its research and development programs or may be unable to expand its operations or otherwise capitalize on its business opportunities, as desired, which could materially affect the Company's business, financial condition and results of operations. The Company has determined that its cash runway of less than twelve months, along with its accumulated deficit, history of losses and future expected losses, raises substantial doubt about the Company's ability to continue as a going concern within one year from the issuance date of these condensed consolidated financial statements. While the Company has plans in place to mitigate this risk, which primarily consist of pursuing a strategic transaction and reducing cash expenditures, there is no guarantee that the Company will be successful in these mitigation efforts.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in conformity with the accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Neon Therapeutics, Inc. and its wholly owned subsidiary, Neon Securities Corporation. All intercompany transactions and balances have been eliminated. The Company consolidates entities in which it has a controlling financial interest. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2019 , and notes thereto, which are contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 filed with the Securities and Exchange Commission (the "SEC") on March 2, 2020 (the “Annual Report on Form 10-K”). The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position as of March 31, 2020 , and the results of its operations for the three months ended March 31, 2020 and 2019 , and its cash flows for the three months ended March 31, 2020 and 2019 . The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from the Company's audited financial statements, but does not contain all of the footnote disclosures required by GAAP. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results that may be expected for the full year or any other subsequent interim period. Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2019 , and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the three months ended March 31, 2020 . Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates of accounting reflected in these condensed consolidated financial statements include, but are not limited to, estimates related to accrued expenses, the valuation of common stock prior to the completion of the Company's IPO, stock-based compensation, the present value of lease liabilities and the corresponding right-of-use assets and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results could differ from those estimates or assumptions. Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board ("FASB") issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement ("ASU 2018-13"), which eliminates, adds and modifies certain disclosure requirements for fair value measurements. The Company adopted ASU 2018-13 as of the effective date January 1, 2020. The adoption of the standard did not have a material impact on the Company's condensed consolidated financial statements or disclosures. In August 2018, the FASB issued ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract ("ASU 2018-15") , which provides additional guidance on the accounting for costs of implementation activities performed in a cloud computing arrangement that is a service contract. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The internal-use software guidance requires that certain costs incurred during the application development stage be capitalized and other costs incurred during the preliminary project stage and post-implementation stage be expensed as they are incurred. The accounting for the service element of a hosting arrangement that is a service contract is not affected. The Company adopted ASU 2018-15 as of the effective date of January 1, 2020 on a prospective basis. The adoption of the standard did not have a material impact on the Company's condensed consolidated financial statements. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). This standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The standard also establishes additional disclosure requirements related to credit risks. This guidance was originally effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard for smaller reporting companies was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company will now adopt this standard effective January 1, 2023, and it is currently evaluating the potential impact that ASU 2016-13 may have on the condensed consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which is intended to simplify various aspects related to the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company does not anticipate a material impact to the condensed consolidated financial statements as a result of the adoption of this standard.

Fair Value Measurement

Fair Value Measurement	3 Months Ended
Fair Value Measurement	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements at March 31, 2020 Using: Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 14,749 $ 14,749 $ — $ — $ 14,749 $ 14,749 $ — $ — Fair Value Measurements at December 31, 2019 Using: Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 29,075 $ 29,075 $ — $ — $ 29,075 $ 29,075 $ — $ — There were no changes in valuation techniques or transfers between the fair value measurement levels during the three months ended March 31, 2020 or 2019 . There were no liabilities measured at fair value on a recurring basis as of March 31, 2020 or December 31, 2019 .

Marketable Securities

Marketable Securities	3 Months Ended
Marketable Securities	Mar. 31, 2020
Marketable Securities [Abstract]
Marketable Securities	Marketable Securities The Company did no t hold any marketable securities at March 31, 2020 or December 31, 2019 . There were no sales of available-for-sale securities during the three months ended March 31, 2020 or 2019 . Net unrealized holding gains or losses for the period that have been included in accumulated other comprehensive loss were not material to the Company’s consolidated results of operations.

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
Property and Equipment, Net	Mar. 31, 2020
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): March 31, 2020 December 31, 2019 Software $ 1,180 $ 1,180 Laboratory equipment 9,242 9,234 Computer equipment 102 102 Furniture and fixtures 316 316 Leasehold improvements 680 680 11,520 11,512 Less: Accumulated depreciation and amortization (4,826 ) (4,403 ) $ 6,694 $ 7,109 Depreciation and amortization expense for the three months ended March 31, 2020 and 2019 was $0.4 million and $0.4 million , respectively.

Accrued Expenses

Accrued Expenses	3 Months Ended
Accrued Expenses	Mar. 31, 2020
Accrued Liabilities, Current [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consisted of the following (in thousands): March 31, 2020 December 31, 2019 Accrued compensation costs $ 1,573 $ 2,635 Accrued retention payments 2,517 795 Accrued restructuring costs 128 981 Accrued professional services 594 904 Accrued external research and manufacturing costs 1,095 1,717 Other accrued expenses 530 432 $ 6,437 $ 7,464

Leases

Leases	3 Months Ended
Leases	Mar. 31, 2020
Leases [Abstract]
Leases	Leases On January 21, 2016, the Company entered into an operating lease agreement for office and laboratory space at its current headquarters in Cambridge, Massachusetts. The lease commenced on September 28, 2016 and expires on September 27, 2024. The Company has the right to extend the lease for one additional five -year period at a market rental rate as determined by the landlord and agreed to by the Company. Per the terms of the lease agreement, the Company does not have any residual value guarantees. In connection with the lease agreement, the Company issued a letter of credit to the landlord for $0.5 million . The Company secured the letter of credit for the full amount of the letter with cash on deposit, which is reported as restricted cash, and which is classified within other long-term assets. The Company identified and assessed the following significant assumptions in recognizing the right-of-use asset and corresponding liability related to the lease: • Expected lease term - The expected lease term includes the contractual lease period. The lease agreement contains a renewal option, which was not included in the calculation of the right-of-use asset and lease liabilities as the renewal is not reasonably certain. • Incremental borrowing rate - As the Company’s lease does not provide a readily determinable implicit rate, nor is it available from the lessor, the Company estimated the incremental borrowing rate based on information available at the commencement date in determining the present value of lease payments. The Company used the incremental borrowing rate on January 1, 2019 for operating leases that commenced prior to that date. The Company recognized the right-of-use asset and corresponding lease liability on January 1, 2019 by calculating the present value of lease payments, discounted at 10% , the Company’s estimated incremental borrowing rate, over the 5.7 years expected remaining lease term. The Company also, from time to time, enters into short-term operating lease arrangements for certain laboratory and office equipment. Leases with a term of twelve months or less are not recorded on the balance sheet and the Company recognizes lease expense for these leases on a straight-line basis over the lease term. For lease agreements entered into or reassessed after the adoption of ASU 2016-02, the Company has elected to combine lease and non-lease components for all classes of underlying assets. The components of lease expense and related cash flows were as follows (in thousands): Three Months Ended March 31, 2020 2019 Lease cost Operating lease cost $ 502 $ 502 Variable lease cost 246 243 Short-term lease cost 109 108 Total lease cost $ 857 $ 853 Cash paid for amounts included in the measurement of lease liabilities $ 483 $ 469 Variable lease expense includes common area maintenance, utility charges and management fees, and was $0.2 million for each of the three months ended March 31, 2020 and 2019 . The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows: As of March 31, 2020 Weighted average remaining lease term in years 4.4 Weighted average discount rate 10 % Amortization of the operating lease right-of-use asset for the lease was $0.3 million and $0.3 million for the three months ended March 31, 2020 and 2019 , respectively, and was included in operating expenses. Future lease payments for the Company's operating leases as of March 31, 2020 were as follows (in thousands): Year Ending December 31, 2020 (remaining nine months) $ 1,464 2021 2,006 2022 2,066 2023 2,128 2024 1,632 Total future minimum lease payments $ 9,296 Less: interest (1,809 ) Present value of operating lease liabilities $ 7,487

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Significant Agreements Peptide and Vaccine Manufacturing Agreement In December 2015, the Company entered into a manufacturing agreement, as amended in October 2016, January 2017 and November 2018 (collectively as amended, the "Manufacturing Agreement"), with an independent third party (the "Vendor") whereby the Vendor performed manufacturing, analytical testing and quality assurance services related to the manufacture of drug product and/or peptides for use in the Company's preclinical and clinical activities. The Manufacturing Agreement provided for the development and establishment of two manufacturing suites at the Vendor's facility to be used in the manufacturing process to fill orders of peptides ordered by the Company, and required the Company to reimburse the Vendor for specified manufacturing costs incurred in the manufacture of the peptides, plus a fixed profit margin. The Manufacturing Agreement had a five -year term and was terminable by the Company for convenience with three -months' notice. All amounts incurred under the Manufacturing Agreement were recognized as research and development expense as incurred. In December 2019, the Company provided notice to the Vendor that it was terminating the Manufacturing Agreement for convenience and the Manufacturing Agreement was terminated in March 2020. The Company has paid all amounts due associated with the termination of the Manufacturing Agreement and does not expect to incur any additional future costs to the Vendor. T Cell Manufacturing Agreement In August 2019, the Company entered into a manufacturing agreement (the "NKI Agreement") with the Netherlands Cancer Institute (the "NKI") whereby the NKI performs manufacturing, analytical testing and quality assurance services related to the manufacture of the Company's autologous T cell therapy drug product for use in the Company's preclinical and clinical activities. The NKI Agreement has a three -year term, which can be extended for an additional six months at the Company's sole discretion, and can be terminated by the Company for convenience with three -months' notice. All amounts incurred under the NKI Agreement are recognized as research and development expense as incurred. Other Agreements License Agreement with the Broad Institute, Inc. On November 13, 2015, the Company entered into a license agreement with the Broad Institute, Inc. (the "Broad"), a related party (see Note 12) and, in January and November 2018, the Company entered into amendments to the license agreement (as amended to date, the “Broad Agreement”). Under the Broad Agreement, the Company has been granted an exclusive worldwide license to certain intellectual property rights owned or controlled by the Broad, Dana-Farber Cancer Institute (the "DFCI") and The General Hospital Corporation d/b/a Massachusetts General Hospital ("MGH") to develop and commercialize any diagnostic, prognostic, preventative or therapeutic product for humans, including any neoantigen vaccine product. In particular, at the time of entry into this agreement, the Company was granted both exclusive and non-exclusive licenses to a patent portfolio comprised of twelve patent families, including certain granted patents and pending patent applications in the United States and foreign jurisdictions. Pursuant to the terms of the Broad Agreement, the Company has also been granted (i) a non-exclusive license under each institution's respective interest in certain of its patent rights to exploit the licensed products in the field in the territory during the term of the license and (ii) a non-exclusive license under each institution's licensed know-how, to exploit any diagnostic, prognostic, preventative or therapeutic product in the field in the territory during the term of the license. The Company is also entitled to sub-license the rights granted to it under the Broad Agreement. In connection with the Broad Agreement, the Company has also entered into a non-exclusive software license with the Broad under which it licenses certain object and source codes for several software programs. These licenses and rights are subject to certain limitations and retained rights, including field restrictions. As consideration for the license, the Company paid the Broad a non-refundable license fee of $0.1 million . As additional consideration for the license, the Company must pay the Broad immaterial annual license maintenance fees. Additionally, the Company granted 60,000 shares of restricted common stock to each of the Broad, DFCI and MGH, which were determined to have an aggregate fair value of $0.2 million , and reimbursed the Broad $0.6 million for a portion of its past patent expenses related to the in-licensed patent rights. In June 2018, to align with institutional policies in place between the Broad, DFCI and MGH, DFCI and MGH transferred certain of the shares of restricted common stock that they had previously received to the Broad. Under the Broad Agreement, the Company agreed to reimburse the Broad for future patent expenses related to the patents covered by the license agreement. The Company could be obligated to make up to $12.6 million of developmental milestone payments to the Broad if certain development milestones are achieved over the term of the license agreement. Additionally, under the terms of the license agreement, the Company could be obligated to make up to an aggregate of $97.5 million of payments upon the achievement of specified sales milestones and to pay tiered royalties of low to mid single-digit percentages on net sales of products licensed under the agreement. The Company is required to pay the Broad a low double-digit percentage of any consideration received by the Company from a sublicensee in consideration for a sublicense. No developmental or commercial milestones have been achieved to date. The Company has the right to terminate the agreement for any reason, with or without cause. License Agreement with the Dana-Farber Cancer Institute On August 5, 2016, the Company entered into a license agreement with the DFCI to grant the Company an exclusive, royalty-free license to provide certain licensed know-how. The know-how in this agreement has particular utility in connection with the development of the licensed products referred to in the Broad Agreement. The agreement also grants a non-exclusive, royalty free right to certain clinical data being generated by the DFCI. The Company has the right to terminate the license agreement with the DFCI for any reason, with or without cause. In consideration for the licenses, the Company granted 120,000 shares of common stock to each of the Broad and the DFCI. The shares issued to the Broad were unrestricted and fully vested. The 120,000 shares issued to the DFCI contained contingent repurchase options whereby, if the DFCI failed to achieve three specific milestones over the subsequent three -year period, the Company could repurchase the shares (one-third for each milestone) at the original purchase price, which is at zero cost. The Company accounted for these awards consistent with equity awards with performance-based vesting conditions and, upon it being probable that the Company would not repurchase the award associated with a milestone, the associated expense would be recognized as incremental stock-based compensation expense and reflected within research and development expenses in the condensed consolidated financial statements. Through March 31, 2020 , the repurchase option on all 120,000 of these shares has expired. The Company did no t recognize any incremental stock-based compensation expense related to these awards during the three months ended March 31, 2020 or 2019 . Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters arising out of the relationship between the parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and certain executive officers and other employees that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or employees. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of these indemnification obligations. The Company does not believe that the outcome of any existing claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it had not accrued any liabilities related to its obligations under these agreements in its condensed consolidated financial statements as of March 31, 2020 or December 31, 2019 . Legal Proceedings As of March 31, 2020, the Company was not party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to its legal proceedings.

Preferred Stock and Common Stoc

Preferred Stock and Common Stock	3 Months Ended
Preferred Stock and Common Stock	Mar. 31, 2020
Equity [Abstract]
Preferred Stock and Common Stock	Preferred Stock and Common Stock Preferred Stock The Company's amended and restated certificate of incorporation authorizes the Company to issue up to 10,000,000 shares of undesignated preferred stock, $0.001 par value per share, none of which was issued or outstanding as of March 31, 2020 or December 31, 2019 . Common Stock As of March 31, 2020 and December 31, 2019 , the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 shares of common stock with a par value of $0.001 per share. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Company’s board of directors, if any. No dividends have been declared or paid during the three months ended March 31, 2020 or 2019 . As of March 31, 2020 and December 31, 2019 the Company has reserved for future issuance the following number of shares of common stock: March 31, 2020 December 31, 2019 Shares reserved for exercise of outstanding stock options 3,179,605 3,374,541 Shares reserved for vesting of restricted stock units 1,756,059 1,053,394 Shares reserved for future issuance under the 2018 Stock Option and Grant Plan 395,741 — Shares reserved for future issuance under the 2018 Employee Stock Purchase Plan 777,512 490,215 6,108,917 4,918,150 At-the-market equity offering program In July 2019, the Company filed a registration statement on Form S-3 (File No. 333-232487) with the SEC, which was declared effective on July 8, 2019 (the "Shelf Registration Statement") in relation to the registration of common stock, preferred stock, warrants and/or units of any combination thereof for the purposes of selling, from time to time, its common stock, convertible securities or other equity securities in one or more offerings. Simultaneous with the Shelf Registration Statement, the Company entered into a Controlled Equity Offering SM Sales Agreement (the "Sales Agreement") with Cantor Fitzgerald & Co. ("Cantor") to establish an at-the-market equity offering program ("ATM"). Under the Sales Agreement, Cantor may sell up to $50.0 million of the Company’s common stock by any method permitted by law deemed to be an "at the market" offering as defined in Rule 415 of the Securities Act, subject to the terms of the Sales Agreement. Under the Sales Agreement, the Company is required to pay to Cantor cash commissions of 3.0% of the aggregate gross proceeds of sales of common stock under the Sales Agreement. No shares were sold under the ATM and no proceeds were received by the Company in respect of the ATM during the three months ended March 31, 2020.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
Stock-Based Compensation	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2015 Stock Option and Grant Plan The Company’s 2015 Stock Option and Grant Plan, as amended (the “2015 Plan”), provided for the Company to grant incentive or nonqualified stock options, restricted stock awards, unrestricted stock awards or restricted stock units to employees, directors and consultants of the Company. As of June 26, 2018, the effective date of the 2018 Stock Option and Incentive Plan, and as of March 31, 2020 and December 31, 2019 , no shares remained available for future issuance under the 2015 Plan. 2018 Stock Option and Incentive Plan On June 13, 2018, the Company’s stockholders approved the 2018 Stock Option and Incentive Plan (the “2018 Plan”), which became effective on June 26, 2018. The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards and dividend equivalent rights to the Company’s officers, employees, directors and other key persons (including consultants). The number of shares initially reserved for issuance under the 2018 Plan was 1,215,000 shares, which was cumulatively increased on January 1, 2019 and which will be cumulatively increased each January 1 thereafter by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s compensation committee. Effective January 1, 2019 and 2020, 1,132,570 and 1,149,189 additional shares, respectively, were automatically added to the shares authorized for issuance under the 2018 Plan and these shares were subsequently registered on Registration Statements on Form S-8. As of the effective date of the 2018 Plan, the Company will not grant any further awards under the 2015 Plan. However, the shares of common stock underlying any awards that are forfeited, canceled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) under the 2018 Plan and the 2015 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. The terms of stock options and restricted stock awards, including vesting requirements, are determined by the board of directors or its delegates, subject to the provisions of the 2018 Plan. As of March 31, 2020 , there were 395,741 shares available for future issuance under the 2018 Plan. 2018 Employee Stock Purchase Plan On June 13, 2018, the Company’s stockholders approved the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective on June 26, 2018. A total of 270,000 shares of common stock were reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on January 1, 2019, and each January 1 thereafter through January 1, 2028, by the lesser of (i) 405,000 shares of common stock, (ii) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or (iii) such lesser number of shares determined by the administrator of the Company’s ESPP. Effective January 1, 2019 and 2020, 283,142 and 287,297 additional shares, respectively, were automatically added to the shares authorized for issuance under the ESPP and these shares were subsequently registered on Registration Statements on Form S-8. As of March 31, 2020 , there were 62,927 shares issued under the ESPP and 777,512 shares were reserved and available for issuance under the ESPP. The Company initiated its first offering period under the ESPP on July 1, 2019. Stock-based compensation expense related to the ESPP was insignificant for the three months ended March 31, 2020 . There was no stock-based compensation expense under the ESPP for the three months ended March 31, 2019 . Stock Options The following table summarizes changes in stock option activity during the three months ended March 31, 2020 : Number of Shares Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Outstanding as of December 31, 2019 3,374,541 $ 6.53 7.59 $ — Granted — — Exercised — — Forfeited (194,936 ) 6.94 Outstanding as of March 31, 2020 3,179,605 $ 6.51 7.74 $ 93 Options vested or expected to vest as of March 31, 2020 3,179,605 $ 6.51 7.74 $ 93 Options exercisable as of March 31, 2020 1,617,860 $ 6.46 7.12 $ 9 There were no stock options granted during the three months ended March 31, 2020 . The weighted average grant-date fair value per share of stock options granted during the three months ended March 31, 2019 was $4.82 per share. There were no stock options exercised during the three months ended March 31, 2020 . The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2019 was $0.1 million . Stock Option Valuation There were no stock options granted during the three months ended March 31, 2020 . The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors during the three months ended March 31, 2019 were as follows, presented on a weighted average basis: Three Months Ended Expected volatility 96.65 % Risk-free interest rate 2.45 % Expected dividend yield — % Expected life (in years) 6.06 There were no stock option awards granted to nonemployees during the three months ended March 31, 2020 or 2019 . Restricted Stock Units The Company has granted restricted stock units ("RSUs") to its employees under the 2018 Plan, as part of its equity compensation program. Pursuant to the terms of the applicable award agreements, each RSU represents the right to receive one share of the Company’s common stock and the RSUs generally vest in equal annual installments over three years, provided the employee remains continuously employed with the Company through the vesting period. Upon vesting, shares of the Company's common stock are delivered to the employee, subject to the payment of applicable withholding taxes. The fair value of RSUs is based on the market value of the Company's common stock on the date of grant. Compensation expense is recognized over the applicable service period. The following table summarizes RSU activity for the three months ended March 31, 2020 : Number of Shares Weighted Average Grant- Date Fair Value per Share Unvested as of December 31, 2019 1,053,394 $ 3.27 Granted 1,000,826 $ 1.20 Vested (273,461 ) $ 3.64 Cancelled (24,700 ) $ 4.48 Unvested as of March 31, 2020 1,756,059 $ 2.02 The aggregate fair value of RSUs that vested during the three months ended March 31, 2020 , based upon the fair values of the stock underlying the RSUs on the day of vesting, was $0.5 million . No RSUs vested during the three months ended March 31, 2019 . Restricted Stock Awards Restricted stock awards originally issued under the terms of the 2015 Plan allow the Company, at its discretion, to repurchase unvested shares at the initial purchase price if the employee or nonemployee terminates his or her service relationship with the Company. No restricted stock awards were issued under the 2015 Plan during the three months ended March 31, 2020 or 2019 . The 2018 Plan provides for the grant of restricted stock awards to the Company’s officers, employees, directors and other key persons (including consultants). No restricted stock awards were issued under the 2018 Plan during the three months ended March 31, 2020 or 2019 . The following table summarizes the Company’s restricted common stock activity under the 2015 Plan since December 31, 2019 : Number of Shares Weighted Average Grant- Date Fair Value per Share Unvested restricted common stock as of December 31, 2019 106,038 $ 2.78 Vested (37,413 ) $ 2.86 Unvested restricted common stock as of March 31, 2020 68,625 $ 2.74 The aggregate fair value of restricted common stock awards that vested during the three months ended March 31, 2020 and 2019 , based upon the fair values of the stock underlying the restricted stock awards on the day of vesting, was $0.1 million and $0.4 million , respectively. Restricted Stock Awards Issued Outside of Equity Plans From May 2015 through July 2016, the Company issued 1,510,000 shares of restricted common stock outside of the 2015 Plan to nonemployee founders and collaborators. The shares were issued under the terms of the respective restricted common stock agreements and unvested shares are subject to repurchase by the Company upon the holder’s termination of their relationship with the Company. The unvested shares of restricted common stock are subject to the Company’s right to repurchase at the original purchase price per share. The Company did no t issue any shares of restricted common stock outside of the Company's 2015 Plan or 2018 Plan during the three months ended March 31, 2020 and 2019 . As of March 31, 2020 and December 31, 2019 , 180,000 restricted common stock awards granted to founders and collaborators outside of the Company's 2015 Plan or 2018 Plan were unvested at a weighted average grant-date fair value per share of $1.29 . These shares are to vest upon the achievement of specified performance milestones. No restricted common stock awards issued outside of the Company's 2015 Plan or 2018 Plan vested during the three months ended March 31, 2020 , and there were no other changes to the amount of such unvested restricted stock awards during the three months ended March 31, 2020 . The aggregate fair value of restricted common stock awards issued outside of the 2015 Plan or 2018 Plan that vested during the three months ended March 31, 2019 , based upon the fair values of the stock underlying the restricted stock awards on the day of vesting, was $0.3 million . Stock-Based Compensation Expense The Company recorded stock-based compensation expense related to all stock-based awards and the ESPP in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months 2020 2019 Research and development expenses $ 640 $ 820 General and administrative expenses 1,029 909 $ 1,669 $ 1,729 As of March 31, 2020 , the Company had an aggregate of $7.1 million of unrecognized stock-based compensation expense related to unvested stock option awards, excluding awards with performance-based vesting conditions, which is expected to be recognized over a weighted-average period of approximately 2.04 years . As of March 31, 2020 , the Company also had an aggregate of $0.2 million of unrecognized stock-based compensation expense related to unvested restricted common stock awards, excluding awards with performance-based vesting conditions, which is expected to be recognized over a weighted-average period of approximately 0.44 years . Additionally as of March 31, 2020 , the Company had an aggregate of $3.3 million of unrecognized stock-based compensation expense related to unvested RSUs, which is expected to be recognized over a weighted-average period of approximately 2.14 years .

Net Loss per Share

Net Loss per Share	3 Months Ended
Net Loss per Share	Mar. 31, 2020
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share The Company excluded 248,625 shares of restricted common stock for the three months ended March 31, 2020 and 603,054 shares of restricted common stock for the three months ended March 31, 2019 from the calculation of basic net loss per share because these shares had not vested. The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share attributable to common stockholders whenever the effect of including them would be to reduce the net loss per share. In periods where there is a net loss, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2020 2019 Outstanding stock options 3,179,605 3,564,631 Unvested restricted stock units 1,756,059 484,339 Unvested restricted common stock 248,625 603,054 ESPP shares issuable and outstanding 70,661 — 5,254,950 4,652,024

Related Parties

Related Parties	3 Months Ended
Related Parties	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Parties	Related Parties A member of the Company’s board of directors is a founding director and the current president of the Broad. In November 2015, the Company entered into the Broad Agreement with the Broad (see Note 8) and, as consideration, the Company granted 60,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.1 million . Additionally, the Company must pay the Broad immaterial annual license maintenance fees. At the time the Company entered into the Broad Agreement, the Company reimbursed the Broad $0.6 million for a portion of past patent expenses and, under the terms of the license agreement, the Company is required to reimburse Broad for future patent expenses related to patents covered by the license agreement. The Company could be obligated to make up to $12.6 million of developmental milestone payments to the Broad if certain development milestones are achieved over the term of the license agreement. Additionally, under the terms of the license agreement, the Company could be obligated to make up to an aggregate of $97.5 million of payments upon the achievement of specified sales milestones and to pay tiered royalties of low to mid single-digit percentages on net sales of products licensed under the agreement. The Company is required to pay the Broad a low double-digit percentage of any consideration received by the Company from a sublicensee in consideration for a sublicense. No developmental or commercial milestones have been achieved to date. In August 2016, the Company entered into a license agreement with the DFCI in connection with the development of licensed products referred to in the Broad Agreement. As consideration, the Company granted 120,000 shares of restricted common stock to the Broad, which were determined to have a fair value of $0.2 million . In June 2018, to align with institutional policies in place between the Broad, DFCI and MGH, the DFCI and MGH transferred certain of the shares of restricted common stock that they had previously received to the Broad. The Company recorded expenses related to payments to the Broad of $0.6 million and $0.5 million during the three months ended March 31, 2020 and 2019 , respectively. At March 31, 2020 and December 31, 2019 , the Company had $0.7 million and $0.3 million in accounts payable and accrued expenses due to the Broad, respectively.

Corporate Restructuring

Corporate Restructuring	3 Months Ended
Corporate Restructuring	Mar. 31, 2020
Restructuring and Related Activities [Abstract]
Corporate Restructuring	Corporate Restructuring On November 20, 2019, the Company announced that, as part of a new strategic focus, it was reducing its workforce by approximately 24% of its then current headcount. This corporate restructuring was substantially completed during the fourth quarter of 2019 and, in accordance with ASC 420, Exit or Disposal Activities , the Company recorded approximately $1.3 million of restructuring-related costs including employee severance, benefits and related costs during the three months ended December 31, 2019. These costs are reflected within research and development expenses in the condensed consolidated statement of operations. During the three months ended March 31, 2020, the Company recorded approximately $0.1 million in restructuring expenses, which are reflected within research and development expenses in the condensed consolidated statement of operations. As of March 31, 2020, the components of the outstanding restructuring liabilities included in accrued expenses were as follows (in thousands): Three Months Ended March 31, 2020 Restructuring reserve at December 31, 2019 $ 981 Restructuring expenses incurred during the period 47 Amounts paid during the period (856 ) Adjustments (44 ) Restructuring reserve at March 31, 2020 $ 128

Subsequent Events

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In connection with the Merger, a putative class action lawsuit, Franchi v. Neon Therapeutics, Inc., et al. , 1:20-cv-00482, was filed on April 7, 2020 by purported Company stockholder Adam Franchi against the Company, its directors, BioNTech, and Merger Sub in the U.S. District Court for the District of Delaware. On April 10, 2020, in connection with the Merger, a complaint, Alvarado v. Neon Therapeutics, Inc., et al. , 1:20-cv-02959, was filed as an individual action by purported Company stockholder Francisco J. Dos Ramos Alvarado against the Company and its directors in the U.S. District Court for the Southern District of New York. On April 13, 2020, in connection with the Merger, a complaint, Ezebunwa v. Neon Therapeutics, Inc., et al. , 1:20-cv-03001, was filed as an individual action by purported Company stockholder Esther Ezebunwa against the Company and its directors in the U.S. District Court for the Southern District of New York. On April 15, 2020, in connection with the Merger, a putative class action lawsuit, Marks v. Neon Therapeutics, Inc., et al. , 1:20-cv-03033, was filed by purported Company stockholder John Marks against the Company and its directors in the U.S. District Court for the Southern District of New York. On April 15, 2020, in connection with the Merger, a complaint, Shen v. Neon Therapeutics, Inc. , et al., 1:20-cv-03035, was filed as an individual action by purported Company stockholder David Shen against the Company and its directors in the U.S. District Court for the Southern District of New York. On April 15, 2020, in connection with the Merger, a complaint , Gilbert v. Neon Therapeutics, et al. , 1:20-cv-01816, was filed as an individual action by purported Company stockholder Phillip Gilbert against the Company and its directors in the U.S. District Court for the Eastern District of New York. The Franchi , Alvarado , Ezebunwa , Marks , Shen , and Gilbert cases are collectively referred to as the “Merger Actions.” The Merger Actions generally allege that the definitive proxy statement filed on April 2, 2020 misrepresents and/or omits certain purportedly material information relating to financial projections, analysis performed by Duff & Phelps, LLC (“Duff & Phelps”), and past engagements of Duff & Phelps and Ondra Partners. The Merger Actions assert violations of Section 14(a) of the Exchange Act and Rule 14a-9 promulgated thereunder against the Company and its directors and violations of Section 20(a) of the Exchange Act against the Company’s directors. The Franchi Merger Action also asserts violations of Section 20(a) of the Exchange Act against BioNTech and Merger Sub. The Shen Merger Action also asserts claims for breach of fiduciary duty against the Company’s directors. The Merger Actions seek, among other things: an injunction enjoining consummation of the Merger, costs of the action, including plaintiff’s attorneys’ fees and experts’ fees, declaratory relief and any other relief the court may deem just and proper. The Company believes the Merger Actions to be without merit. It is possible that additional similar cases could be filed in connection with the Merger. An estimate of the possible loss or range of loss resulting from the Merger Actions described above cannot be made at this time.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in conformity with the accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Neon Therapeutics, Inc. and its wholly owned subsidiary, Neon Securities Corporation. All intercompany transactions and balances have been eliminated. The Company consolidates entities in which it has a controlling financial interest. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2019 , and notes thereto, which are contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 filed with the Securities and Exchange Commission (the "SEC") on March 2, 2020 (the “Annual Report on Form 10-K”). The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position as of March 31, 2020 , and the results of its operations for the three months ended March 31, 2020 and 2019 , and its cash flows for the three months ended March 31, 2020 and 2019 . The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from the Company's audited financial statements, but does not contain all of the footnote disclosures required by GAAP. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results that may be expected for the full year or any other subsequent interim period.
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2019 , and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the three months ended March 31, 2020 .
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates of accounting reflected in these condensed consolidated financial statements include, but are not limited to, estimates related to accrued expenses, the valuation of common stock prior to the completion of the Company's IPO, stock-based compensation, the present value of lease liabilities and the corresponding right-of-use assets and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results could differ from those estimates or assumptions.
Recently Adopted and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board ("FASB") issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement ("ASU 2018-13"), which eliminates, adds and modifies certain disclosure requirements for fair value measurements. The Company adopted ASU 2018-13 as of the effective date January 1, 2020. The adoption of the standard did not have a material impact on the Company's condensed consolidated financial statements or disclosures. In August 2018, the FASB issued ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract ("ASU 2018-15") , which provides additional guidance on the accounting for costs of implementation activities performed in a cloud computing arrangement that is a service contract. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The internal-use software guidance requires that certain costs incurred during the application development stage be capitalized and other costs incurred during the preliminary project stage and post-implementation stage be expensed as they are incurred. The accounting for the service element of a hosting arrangement that is a service contract is not affected. The Company adopted ASU 2018-15 as of the effective date of January 1, 2020 on a prospective basis. The adoption of the standard did not have a material impact on the Company's condensed consolidated financial statements. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). This standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The standard also establishes additional disclosure requirements related to credit risks. This guidance was originally effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard for smaller reporting companies was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company will now adopt this standard effective January 1, 2023, and it is currently evaluating the potential impact that ASU 2016-13 may have on the condensed consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"), which is intended to simplify various aspects related to the accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company does not anticipate a material impact to the condensed consolidated financial statements as a result of the adoption of this standard.

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	3 Months Ended
Fair Value Measurement (Tables)	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Schedule Assets Measured at Fair Value on a Recurring Basis	The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements at March 31, 2020 Using: Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 14,749 $ 14,749 $ — $ — $ 14,749 $ 14,749 $ — $ — Fair Value Measurements at December 31, 2019 Using: Total Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 29,075 $ 29,075 $ — $ — $ 29,075 $ 29,075 $ — $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
Property and Equipment, Net (Tables)	Mar. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): March 31, 2020 December 31, 2019 Software $ 1,180 $ 1,180 Laboratory equipment 9,242 9,234 Computer equipment 102 102 Furniture and fixtures 316 316 Leasehold improvements 680 680 11,520 11,512 Less: Accumulated depreciation and amortization (4,826 ) (4,403 ) $ 6,694 $ 7,109

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
Accrued Expenses (Tables)	Mar. 31, 2020
Accrued Liabilities, Current [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): March 31, 2020 December 31, 2019 Accrued compensation costs $ 1,573 $ 2,635 Accrued retention payments 2,517 795 Accrued restructuring costs 128 981 Accrued professional services 594 904 Accrued external research and manufacturing costs 1,095 1,717 Other accrued expenses 530 432 $ 6,437 $ 7,464

Leases (Tables)

Leases (Tables)	3 Months Ended
Leases (Tables)	Mar. 31, 2020
Leases [Abstract]
Schedule of Components of Lease Expense	The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows: As of March 31, 2020 Weighted average remaining lease term in years 4.4 Weighted average discount rate 10 % The components of lease expense and related cash flows were as follows (in thousands): Three Months Ended March 31, 2020 2019 Lease cost Operating lease cost $ 502 $ 502 Variable lease cost 246 243 Short-term lease cost 109 108 Total lease cost $ 857 $ 853 Cash paid for amounts included in the measurement of lease liabilities $ 483 $ 469
Schedule of Future Lease Payments of the Company's Operating Leases	Future lease payments for the Company's operating leases as of March 31, 2020 were as follows (in thousands): Year Ending December 31, 2020 (remaining nine months) $ 1,464 2021 2,006 2022 2,066 2023 2,128 2024 1,632 Total future minimum lease payments $ 9,296 Less: interest (1,809 ) Present value of operating lease liabilities $ 7,487

Preferred Stock and Common St_2

Preferred Stock and Common Stock (Tables)	3 Months Ended
Preferred Stock and Common Stock (Tables)	Mar. 31, 2020
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	As of March 31, 2020 and December 31, 2019 the Company has reserved for future issuance the following number of shares of common stock: March 31, 2020 December 31, 2019 Shares reserved for exercise of outstanding stock options 3,179,605 3,374,541 Shares reserved for vesting of restricted stock units 1,756,059 1,053,394 Shares reserved for future issuance under the 2018 Stock Option and Grant Plan 395,741 — Shares reserved for future issuance under the 2018 Employee Stock Purchase Plan 777,512 490,215 6,108,917 4,918,150

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
Stock-Based Compensation (Tables)	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Stock Option Activity	The following table summarizes changes in stock option activity during the three months ended March 31, 2020 : Number of Shares Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Outstanding as of December 31, 2019 3,374,541 $ 6.53 7.59 $ — Granted — — Exercised — — Forfeited (194,936 ) 6.94 Outstanding as of March 31, 2020 3,179,605 $ 6.51 7.74 $ 93 Options vested or expected to vest as of March 31, 2020 3,179,605 $ 6.51 7.74 $ 93 Options exercisable as of March 31, 2020 1,617,860 $ 6.46 7.12 $ 9
Schedule of Assumptions Used to Determine Fair Value of the Stock Options Granted to employees and directors	The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors during the three months ended March 31, 2019 were as follows, presented on a weighted average basis: Three Months Ended Expected volatility 96.65 % Risk-free interest rate 2.45 % Expected dividend yield — % Expected life (in years) 6.06
Schedule of Stock-based Compensation Expense	The Company recorded stock-based compensation expense related to all stock-based awards and the ESPP in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months 2020 2019 Research and development expenses $ 640 $ 820 General and administrative expenses 1,029 909 $ 1,669 $ 1,729
ESPP \| Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Restricted Stock Unit Activity	The following table summarizes RSU activity for the three months ended March 31, 2020 : Number of Shares Weighted Average Grant- Date Fair Value per Share Unvested as of December 31, 2019 1,053,394 $ 3.27 Granted 1,000,826 $ 1.20 Vested (273,461 ) $ 3.64 Cancelled (24,700 ) $ 4.48 Unvested as of March 31, 2020 1,756,059 $ 2.02
2015 Plan \| Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Restricted Common Stock Activity	The following table summarizes the Company’s restricted common stock activity under the 2015 Plan since December 31, 2019 : Number of Shares Weighted Average Grant- Date Fair Value per Share Unvested restricted common stock as of December 31, 2019 106,038 $ 2.78 Vested (37,413 ) $ 2.86 Unvested restricted common stock as of March 31, 2020 68,625 $ 2.74

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
Net Loss per Share (Tables)	Mar. 31, 2020
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share	The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2020 2019 Outstanding stock options 3,179,605 3,564,631 Unvested restricted stock units 1,756,059 484,339 Unvested restricted common stock 248,625 603,054 ESPP shares issuable and outstanding 70,661 — 5,254,950 4,652,024

Corporate Restructuring (Tables

Corporate Restructuring (Tables)	3 Months Ended
Corporate Restructuring (Tables)	Mar. 31, 2020
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Reserve	As of March 31, 2020, the components of the outstanding restructuring liabilities included in accrued expenses were as follows (in thousands): Three Months Ended March 31, 2020 Restructuring reserve at December 31, 2019 $ 981 Restructuring expenses incurred during the period 47 Amounts paid during the period (856 ) Adjustments (44 ) Restructuring reserve at March 31, 2020 $ 128

Nature of the Business (Details

Nature of the Business (Details) $ in Thousands	Jan. 15, 2020shares	Mar. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Mar. 31, 2019USD ($)
Class of Stock [Line Items]
Proceeds from sale of preferred stock and convertible debt			$ 161,100
Accumulated deficit		$ 270,136	270,136	$ 253,538
Cash and cash equivalents		15,047	$ 15,047	$ 29,395	$ 49,264
IPO
Class of Stock [Line Items]
Proceeds from IPO		$ 89,900
BioNTech SE and Endor Lights, Inc. \| Common Stock
Class of Stock [Line Items]
Percentage of common shares outstanding entering into voting agreement	36.00%
Number of ordinary shares (in shares) \| shares	1
BioNTech SE and Endor Lights, Inc. \| American Depositary Share of Parent
Class of Stock [Line Items]
Share conversion ratio	0.063

Fair Value Measurement (Details

Fair Value Measurement (Details) - Fair value measurement, Recurring - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value Measurement
Asset at fair value	$ 14,749,000	$ 29,075,000
Liabilities at fair value	0	0
Money market funds
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 1
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 1 \| Money market funds
Fair Value Measurement
Asset at fair value	14,749,000	29,075,000
Level 2
Fair Value Measurement
Asset at fair value	0	0
Level 2 \| Money market funds
Fair Value Measurement
Asset at fair value	0	0
Level 3
Fair Value Measurement
Asset at fair value	0	0
Level 3 \| Money market funds
Fair Value Measurement
Asset at fair value	$ 0	$ 0

Marketable Securities (Details)

Marketable Securities (Details) - USD ($)	3 Months Ended
Marketable Securities (Details) - USD ($)	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Marketable Securities [Abstract]
Marketable securities	$ 0		$ 0
Proceeds from sale of available-for-sale securities	$ 0	$ 0

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,520		$ 11,512
Less: Accumulated depreciation and amortization	(4,826)		(4,403)
Property and equipment, net	6,694		7,109
Depreciation and amortization expense	424	$ 415
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,180		1,180
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,242		9,234
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	102		102
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	316		316
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 680		$ 680

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Liabilities, Current [Abstract]
Accrued compensation costs	$ 1,573	$ 2,635
Accrued retention payments	2,517	795
Accrued restructuring costs	128	981
Accrued professional services	594	904
Accrued external research and manufacturing costs	1,095	1,717
Other accrued expenses	530	432
Total accrued expenses	$ 6,437	$ 7,464

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	Sep. 28, 2016USD ($)renewal_option	Mar. 31, 2020USD ($)	Mar. 31, 2019USD ($)	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Weighted average remaining lease term in years		4 years 4 months 24 days
Variable lease expenses		$ 246	$ 243
Amortization of operating lease right-of-use assets		314	287
Office and Laboratory Space
Property, Plant and Equipment [Line Items]
Number lease renewal options \| renewal_option	1
Term of lease contract	5 years
Operating lease discount rate				10.00%
Weighted average remaining lease term in years				5 years 8 months 12 days
Variable lease expenses		200	200
Amortization of operating lease right-of-use assets		$ 300	$ 300
Office and Laboratory Space \| Restricted Cash Noncurrent
Property, Plant and Equipment [Line Items]
Letters of credit issued to the landlord in connection with lease agreement	$ 500

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Leases [Abstract]
Operating lease cost	$ 502	$ 502
Variable lease cost	246	243
Short-term lease cost	109	108
Total lease cost	857	853
Cash paid for amounts included in the measurement of lease liabilities	$ 483	$ 469

Leases - Weighted Average Remai

Leases - Weighted Average Remaining Lease Term and Discount Rate (Details)	Mar. 31, 2020
Leases [Abstract]
Weighted average remaining lease term in years	4 years 4 months 24 days
Weighted average discount rate	10.00%

Leases - Future Operating Lease

Leases - Future Operating Lease Payments (Details) $ in Thousands	Mar. 31, 2020USD ($)
Leases [Abstract]
2020 (remaining nine months)	$ 1,464
2021	2,006
2022	2,066
2023	2,128
2024	1,632
Total future minimum lease payments	9,296
Less: interest	(1,809)
Present value of operating lease liabilities	$ 7,487

Commitments and Contingencies (

Commitments and Contingencies (Details)

Aug. 05, 2016item$ / sharesshares

Nov. 13, 2015USD ($)patentshares

Aug. 31, 2019

Nov. 30, 2018manufacturing_suite

Aug. 31, 2016USD ($)shares

Nov. 30, 2015USD ($)shares

Mar. 31, 2020USD ($)

Mar. 31, 2019USD ($)

Mar. 31, 2018

Mar. 31, 2017

Mar. 31, 2020shares

Mar. 31, 2020USD ($)

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Stock-based compensation expense

$ 1,669,000

$ 1,729,000

License Agreement | Restricted Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Aggregate fair value

$ 200,000

License Agreement | Broad

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Number of patent families | patent

Non-refundable license fee paid

$ 100,000

Shares granted (in shares) | shares

120,000

60,000

Aggregate fair value

$ 200,000

$ 100,000

Reimbursement amount

600,000

License Agreement | Broad | Maximum

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Developmental milestone payments to be paid on achievements

12,600,000

Payments upon achievement of specified sales milestones and tiered royalties on net sales

$ 97,500,000

Developmental and commercial milestones achieved to date under collaborative arrangement

$ 0

License Agreement | Broad | Restricted Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Shares granted (in shares) | shares

120,000

60,000

Shares expired (in shares) | shares

120,000

Stock-based compensation expense

$ 0

License Agreement | DFCI

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Term of agreement

3 years

Number of specific milestones with contingent repurchase option | item

Percentage of shares with contingent repurchase option expired on achievement of specific criteria

0.33

License Agreement | DFCI | Restricted Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Shares granted (in shares) | shares

120,000

60,000

Shares granted with contingent repurchase option (in shares) | shares

120,000

Original purchase price of shares (in dollars per share) | $ / shares

$ 0

License Agreement | MGH | Restricted Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Shares granted (in shares) | shares

60,000

Vendor | Manufacturing Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Number of manufacturing suites | manufacturing_suite

Term of agreement

5 years

Notice period for termination of agreement

3 months

NKI | Manufacturing Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Term of agreement

3 years

Notice period for termination of agreement

3 months

Additional agreement term

6 months

Preferred Stock and Common St_3

Preferred Stock and Common Stock - Narrative (Details)	3 Months Ended
Preferred Stock and Common Stock - Narrative (Details)	Mar. 31, 2020USD ($)Vote / shares$ / sharesshares	Mar. 31, 2019USD ($)	Dec. 31, 2019$ / sharesshares
Equity [Abstract]
Preferred stock, shares authorized (in shares)	10,000,000
Preferred stock par value per share (in dollars per share) \| $ / shares	$ 0.001
Preferred stock, shares issued (in shares)	0		0
Preferred stock, shares outstanding (in shares)	0		0
Common stock, shares authorized (in shares)	150,000,000		150,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.001		$ 0.001
Votes granted per share of common stock \| Vote / shares	1
Dividends declared and paid \| $	$ 0	$ 0

Preferred Stock and Common St_4

Preferred Stock and Common Stock - Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Shares reserved for exercise of outstanding stock options under the 2015 Stock Option and Grant Plan (in shares)	3,179,605	3,374,541
Shares reserved for vesting of restricted stock units (in units)	1,756,059	1,053,394
Shares reserved for future issuance under the 2018 Stock Option and Grant Plan (in shares)	395,741	0
Shares reserved for future issuance under the 2018 Employee Stock Purchase Plan (in shares)	777,512	490,215
Shares reserves for future issuance (in shares)	6,108,917	4,918,150

Preferred Stock and Common St_5

Preferred Stock and Common Stock - At-the-market equity offering program (Details) - Private Placement - USD ($)	1 Months Ended	3 Months Ended
	Jul. 31, 2019	Mar. 31, 2019
Class of Stock [Line Items]
Proceeds from sale of stock		$ 0
Common Stock
Class of Stock [Line Items]
Number of shares sold (in shares)		0
Cantor Fitzgerald & Co.
Class of Stock [Line Items]
Sale of stock, issuance costs percentage	3.00%
Cantor Fitzgerald & Co. \| Common Stock
Class of Stock [Line Items]
Sale of stock, authorized amount (in shares)	$ 50,000,000

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Options Plans (Details) - USD ($)	Jan. 01, 2020	Jan. 01, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jun. 26, 2018	Jun. 13, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserves available future issuance (in shares)			6,108,917		4,918,150
Stock-based compensation expense			$ 1,669,000	$ 1,729,000
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserves available future issuance (in shares)			0		0	0
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserves available future issuance (in shares)			395,741
Total number of shares authorized for issuance (in shares)							1,215,000
Annual increase as a percentage of common stock outstanding (in percent)			4.00%
Number of additional shares authorized (in shares)	1,149,189	1,132,570
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares authorized for issuance (in shares)							270,000
Number of additional shares authorized (in shares)	287,297	283,142
Shares issued (in shares)				62,927
Shares reserved and available for issuance (in shares)					777,512
Stock-based compensation expense			$ 0	$ 0
ESPP \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase as a percentage of common stock outstanding (in percent)			1.00%
Annual increase to common stock (in shares)			405,000

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Outstanding stock options
Number of Shares
Outstanding at beginning of period (in shares)	3,374,541
Granted (in shares)	0
Exercised (in shares)	0
Forfeited (in shares)	(194,936)
Outstanding at end of period (in shares)	3,179,605		3,374,541
Options vested or expected to vest at end of period (in shares)	3,179,605
Options exercisable at end of period (in shares)	1,617,860
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 6.53
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Forfeited (in dollars per share)	6.94
Outstanding at end of period (in dollars per share)	6.51		$ 6.53
Options vested or expected to vest at end of period (in dollars per share)	6.51
Options exercisable at end of period (in dollars per share)	$ 6.46
Weighted Average Contractual Term
Outstanding	7 years 8 months 27 days		7 years 7 months 2 days
Options vested or expected to vest at end of period	7 years 8 months 27 days
Options exercisable at end of period	7 years 1 month 13 days
Aggregate Intrinsic Value
Outstanding	$ 93		$ 0
Options vested or expected to vest at end of period	93
Options exercisable at end of period	$ 9
Weighted average grant-date fair value per share of stock options granted (in dollars per share)		$ 4.82
Aggregate intrinsic value of stock options exercised		$ 100
Non Employee Stock Options
Number of Shares
Granted (in shares)	0	0

Stock-Based Compensation - St_3

Stock-Based Compensation - Stock Options Valuation (Details) - Outstanding stock options	3 Months Ended
	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	96.65%
Risk-free interest rate	2.45%
Expected dividend yield	0.00%
Expected life (in years)	6 years 22 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Units (Details) - 2018 Plan - RSUs - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares to be received per each award (in shares)	1
Vesting period	3 years
Number of Shares
Unvested at beginning of period (in shares)	1,053,394
Granted (in shares)	1,000,826
Vested (in shares)	(273,461)	0
Cancelled (in shares)	(24,700)
Unvested at end of period (in shares)	1,756,059
Weighted Average Grant- Date Fair Value per Share
Unvested at beginning of period (in dollars per share)	$ 3.27
Granted (in dollars per share)	1.20
Vested (in dollars per share)	3.64
Cancelled (in dollars per share)	4.48
Unvested at end of period (in dollars per share)	$ 2.02
Aggregate intrinsic value of restricted common stock awards vested	$ 0.5

Stock-Based Compensation - Re_2

Stock-Based Compensation - Restricted Stock Awards (Details) - Restricted Stock Awards - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0
Number of Shares
Unvested at beginning of period (in shares)	106,038
Vested (in shares)	(37,413)
Unvested at end of period (in shares)	68,625
Weighted Average Grant- Date Fair Value per Share
Unvested at beginning of period (in dollars per share)	$ 2.78
Vested (in dollars per share)	2.86
Unvested at end of period (in dollars per share)	$ 2.74
Aggregate intrinsic value
Aggregate intrinsic value of restricted common stock awards vested	$ 0.1	$ 0.4
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0

Stock-Based Compensation - Re_3

Stock-Based Compensation - Restricted Stock Awards Issued Outside of Equity Plans (Details) - Outside of Equity Plans - Founder and Collaborator Awards - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		15 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jul. 31, 2016	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	0	0	1,510,000
Shares unvested (in shares)	180,000			180,000
Weighted average grant-date fair value of shares unvested (in dollars per share)	$ 1.29			$ 1.29
Shares vested (in shares)		0
Aggregate intrinsic value of restricted common stock awards vested		$ 0.3

Stock-Based Compensation - St_4

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock-based compensation expense
Stock-based compensation expense	$ 1,669	$ 1,729
Outstanding stock options
Stock-based compensation expense
Unrecognized stock-based compensation expense	$ 7,100
Weighted average period for recognition of shared-based compensation not yet recognized	2 years 15 days
Restricted stock, excluding performance-based vesting
Stock-based compensation expense
Unrecognized stock-based compensation expense	$ 200
Weighted average period expected to be recognized	5 months 9 days
RSUs
Stock-based compensation expense
Unrecognized stock-based compensation expense	$ 3,300
Weighted average period expected to be recognized	2 years 1 month 21 days
Research and development expenses
Stock-based compensation expense
Stock-based compensation expense	$ 640	820
General and administrative expenses
Stock-based compensation expense
Stock-based compensation expense	$ 1,029	$ 909

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	3 Months Ended
Net Loss per Share (Details) - shares	Mar. 31, 2020	Mar. 31, 2019
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	5,254,950	4,652,024
Restricted Stock Awards
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	248,625	603,054
Outstanding stock options
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	3,179,605	3,564,631
Unvested restricted stock units
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	1,756,059	484,339
Unvested restricted common stock
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	248,625	603,054
ESPP shares issuable and outstanding
Antidilutive securities excluded from computation of earnings per share
Potential common shares excluded from calculation of diluted net loss per share	70,661	0

Related Parties (Details)

Related Parties (Details) - Broad - License Agreement - USD ($)	Nov. 13, 2015	Aug. 31, 2016	Nov. 30, 2015	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Related Parties
Shares granted (in shares)		120,000	60,000
Aggregate fair value		$ 200,000	$ 100,000
Reimbursement amount	$ 600,000		600,000
Amount of expenses in relation to related party				$ 600,000	$ 500,000
Accounts payable and accrued expenses due to related party				$ 700,000		$ 700,000	$ 700,000	$ 300,000
Maximum
Related Parties
Developmental milestone payments to be paid on achievements	12,600,000		12,600,000
Payments upon achievement of specified sales milestones and tiered royalties on net sales	$ 97,500,000		$ 97,500,000
Developmental and commercial milestones achieved to date under collaborative arrangement						$ 0	$ 0

Corporate Restructuring - Narra

Corporate Restructuring - Narrative (Details) - USD ($) $ in Millions	Nov. 20, 2019	Mar. 31, 2020	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Workforce reduction percentage	24.00%
Restructuring-related costs		$ 0.1	$ 1.3

Corporate Restructuring - Summa

Corporate Restructuring - Summary of Restructuring Reserve (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)
Restructuring Reserve
Restructuring reserve at December 31, 2019	$ 981
Restructuring expenses incurred during the period	47
Amounts paid during the period	(856)
Adjustments	(44)
Restructuring reserve at March 31, 2020	$ 128