Scholar Rock Holding (SRRK) 10-K 7 Mar 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 02, 2022	Jun. 30, 2021
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-38501
Entity Registrant Name	SCHOLAR ROCK HOLDING CORP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-3750435
Entity Address, Address Line One	301 Binney Street, 3rd Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	259-3860
Title of 12(b) Security	Common Stock
Trading Symbol	SRRK
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 531.8
Entity Common Stock, Shares Outstanding		35,297,455
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	Boston, Massachusetts
Entity Central Index Key	0001727196
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 212,835	$ 160,358
Marketable securities	40,159	180,673
Prepaid expenses and other current assets	12,325	3,373
Total current assets	265,319	344,404
Property and equipment, net	9,564	8,121
Operating lease right-of-use asset	25,442	32,261
Restricted cash	2,498	2,498
Other long-term assets	1,622	1,021
Total assets	304,445	388,305
Current liabilities:
Accounts payable	4,434	3,409
Accrued expenses	17,456	14,958
Operating lease liability	7,407	5,366
Short-term debt	1,577
Deferred revenue	33,193	18,816
Other current liabilities	230	15
Total current liabilities	64,297	42,564
Long-term portion of operating lease liability	19,652	27,093
Long-term debt	48,422	24,680
Other long-term liabilities		5
Long-term portion of deferred revenue		33,193
Total liabilities	132,371	127,535
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2021 and December 31, 2020; no shares issued and outstanding at December 31, 2021 and December 31, 2020
Common stock, $0.001 par value; 150,000,000 shares authorized; 35,209,099 and 34,152,470 shares issued and outstanding as of December 31, 2021 and December 31, 2020, respectively	35	34
Additional paid-in capital	548,204	505,069
Accumulated other comprehensive loss	(35)	(2)
Accumulated deficit	(376,130)	(244,331)
Total stockholders' equity	172,074	260,770
Total liabilities and stockholders' equity	$ 304,445	$ 388,305

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	35,209,099	35,152,470
Common stock, shares outstanding	35,209,099	34,152,470

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Revenue	$ 18,816	$ 15,403
Operating expenses:
Research and development	108,468	74,062
General and administrative	40,269	28,219
Total operating expenses	148,737	102,281
Loss from operations	(129,921)	(86,878)
Other income (expense), net	(1,878)	395
Net loss	$ (131,799)	$ (86,483)
Net loss per share, basic (in dollars per share)	$ (3.59)	$ (2.81)
Net loss per share, diluted (in dollars per share)	$ (3.59)	$ (2.81)
Weighted average common shares outstanding, basic (in shares)	36,711,833	30,734,109
Weighted average common shares outstanding, diluted (in shares)	36,711,833	30,734,109
Comprehensive loss:
Net loss	$ (131,799)	$ (86,483)
Other comprehensive loss:
Unrealized loss on marketable securities	(33)	(39)
Total other comprehensive loss	(33)	(39)
Comprehensive loss	$ (131,832)	$ (86,522)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at beginning at Dec. 31, 2019	$ 30	$ 270,682	$ 37	$ (157,848)	$ 112,901
Balance at beginning (in shares) at Dec. 31, 2019	29,792,922
Increase (decrease) in Stockholders' Equity
Unrealized loss on marketable securities			(39)		(39)
Sale of common shares, net of issuance costs	$ 4	215,918			215,922
Sale of common shares, net of issuance costs (in shares)	3,717,948
Exercise of warrants (in shares)	6,961
Restricted shares forfeited during the period (in shares)	(42,010)
Exercise of stock options		7,294			7,294
Exercise of stock options (in shares)	676,649
Equity-based compensation expense		11,175			11,175
Net Loss				(86,483)	(86,483)
Balance at end at Dec. 31, 2020	$ 34	505,069	(2)	(244,331)	260,770
Balance at end (in shares) at Dec. 31, 2020	34,152,470
Increase (decrease) in Stockholders' Equity
Unrealized loss on marketable securities			(33)		(33)
Sale of common shares, net of issuance costs		13,095			13,095
Sale of common shares, net of issuance costs (in shares)	500,000
Exercise of stock options	$ 1	6,891			6,892
Exercise of stock options (in shares)	556,629
Equity-based compensation expense		23,149			23,149
Net Loss				(131,799)	(131,799)
Balance at end at Dec. 31, 2021	$ 35	$ 548,204	$ (35)	$ (376,130)	$ 172,074
Balance at end (in shares) at Dec. 31, 2021	35,209,099

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (131,799)	$ (86,483)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,627	1,491
Amortization of debt discount and debt issuance costs	335	58
Loss on disposal of property and equipment	24	28
Equity-based compensation	23,149	11,175
Amortization/accretion of investment securities	918	(162)
Non-cash operating lease expense	6,397	2,380
Change in operating assets and liabilities:
Accounts receivable		25,000
Prepaid expenses and other current assets	(8,530)	(3,361)
Other assets	(601)	(923)
Accounts payable	1,016	2,101
Accrued expenses	3,663	5,089
Operating lease liabilities	(5,400)	(1,261)
Deferred revenue	(18,816)	(15,403)
Other liabilities	228
Net cash used in operating activities	(126,789)	(60,271)
Cash flows from investing activities:
Purchases of property and equipment	(5,248)	(4,088)
Purchases of marketable securities	(60,437)	(200,110)
Maturities of marketable securities	200,000	140,700
Net cash provided by (used in) investing activities	134,315	(63,498)
Cash flows from financing activities:
Proceeds from debt	24,984	24,622
Proceeds from sale of common shares and pre-funded warrants, net of issuance costs	13,095	215,922
Proceeds from stock option exercises	6,892	7,294
Other	(20)	(19)
Net cash provided by financing activities	44,951	247,819
Net increase in cash, cash equivalents and restricted cash	52,477	124,050
Cash, cash equivalents and restricted cash, beginning of period	162,856	38,806
Cash, cash equivalents and restricted cash, end of period	215,333	162,856
Supplemental disclosure of non-cash items:
Property and equipment purchases in accounts payable and accrued expenses	212	1,368
Operating lease right-of-use asset obtained in exchange for operating lease obligation		31,286
Supplemental cash flow information:
Cash paid for interest	$ 2,082	$ 251

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2021
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Organization Scholar Rock Holding Corporation (the “Company”) is a biopharmaceutical company focused on the discovery and development of innovative medicines for the treatment of serious diseases in which signaling by protein growth factors plays a fundamental role. The Company’s novel understanding of the molecular mechanisms of growth factor activation enabled the development of a proprietary platform for the discovery and development of monoclonal antibodies that locally and selectively target the precursor, or latent, forms of growth factors. The Company’s first product candidate, apitegromab (formerly SRK-015), is a highly selective, fully human, monoclonal antibody, with a unique mechanism of action that results in inhibition of the activation of the growth factor, myostatin, in skeletal muscle. Apitegromab is being developed as a potential first muscle-directed therapy for the treatment of spinal muscular atrophy (“SMA”). The Company is conducting SAPPHIRE, a pivotal Phase 3 clinical trial to evaluate the efficacy and safety of apitegromab in patients with non-ambulatory Type 2 and Type 3 SMA. The Company’s second product candidate, SRK-181, is being developed for the treatment of cancers that are resistant to checkpoint inhibitor (“CPI”) therapies, such as anti-PD-1 or anti-PD-L1 antibody therapies. SRK-181 is a highly selective inhibitor of the activation of latent transforming growth factor beta-1 (“TGFβ1”) that is being investigated in the Company’s DRAGON Phase 1 proof-of-concept clinical trial in patients with locally advanced or metastatic solid tumors that exhibit primary resistance to anti-PD-(L)1 antibodies. The DRAGON trial consists of two parts: Part A (dose escalation of SRK-181 as a single-agent or in combination with an approved anti-PD-(L)1 therapy) and Part B (dose expansion evaluating SRK-181 in combination with an approved anti-PD- (L)1 antibody therapy). Part B encompasses five cohorts, including urothelial carcinoma, cutaneous melanoma, non-small cell lung cancer, clear cell renal cell carcinoma and other solid tumors and commenced in 2021. Additionally, the Company continues to create a pipeline of product candidates to deliver novel therapies to underserved patients suffering from a wide range of serious diseases, including neuromuscular disorders, cancer, and fibrosis. The Company was originally formed in May 2012. Its principal offices are in Cambridge, Massachusetts. Since its inception, the Company’s operations have focused on research and development of monoclonal antibodies that selectively inhibit activation of growth factors for therapeutic effect, as well as establishing the Company’s intellectual property portfolio and performing research and development activities. The Company has primarily financed its operations through various equity financings (Note 8), as well as research and development collaboration agreements and the Company’s debt facility (Note 12). Revenue generation activities have been limited to two collaborations, both containing research services and the issuance of a license. The first agreement, executed in 2013, was with Janssen Biotech, Inc. (“Janssen”), a subsidiary of Johnson & Johnson. The second agreement (the “Gilead Collaboration Agreement”), executed in December 2018, was with Gilead Sciences, Inc. (“Gilead”). No revenues have been recorded from the sale of any commercial product. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, successful discovery and development of its drug candidates, raising additional capital, development by its competitors of new technological innovations, protection of proprietary technology and regulatory approval and market acceptance of the Company’s product candidates. The Company anticipates that it will continue to incur significant operating losses for the next several years as it continues to develop its product candidates. The Company believes that its existing cash, cash equivalents, and marketable securities at December 31, 2021 will be sufficient to allow the Company to fund its current operations through at least a period of one year after the date these financial statements are issued. Basis of Presentation The consolidated financial statements include the accounts of Scholar Rock Holding Corporation and its wholly owned subsidiaries. All intercompany balances have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in accordance with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities and related disclosures of contingent assets and liabilities at the date of the financial statements and the related reporting of revenues and expenses during the reporting period. Management bases its estimates on historical experience and on various assumptions that are believed to be reasonable under the circumstances. Actual results could differ from those estimates. Concentration of Credit Risk and Off-Balance Sheet Risk The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts or other foreign-hedging arrangements. The Company follows an investment policy approved by the Board of Directors. Its primary objectives are the preservation of capital and maintenance of liquidity. The Company invests only in fixed income instruments denominated and payable in U.S. dollars including obligations of the U.S. government and its agencies and money market funds registered according to SEC Rule 2a-7 of the Investment Company Act of 1940. All securities must have a readily ascertainable market value , must be readily marketable and be U.S. dollar denominated. Cash, Cash Equivalents and Restricted Cash The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are stated at cost, which approximates market value. At December 31, 2021 and 2020, cash equivalents include money market funds that invest primarily in U.S. government-backed securities and treasuries. Restricted cash consists of letters of credit in the amount of $2.5 million related to its leased facilities. The following table reconciles cash, cash equivalents and restricted cash per the balance sheet to the statement of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2021 2020 Cash and cash equivalents ​ $ 212,835 ​ $ 160,358 Restricted cash ​ 2,498 ​ 2,498 ​ ​ $ 215,333 ​ $ 162,856 ​ Property and Equipment Property and equipment are recorded at cost. Expenditures for major renewals or betterments that extend the useful lives of property and equipment are capitalized; expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related asset. Property and equipment are depreciated as follows: ​ ​ ​ ​ ​ ​ Estimated Useful Life ​ (in Years) Laboratory equipment 3 – 5 Computer equipment & software ​ 3 Furniture & fixtures 5 Machinery & equipment 3 – 5 Leasehold improvements ​ Shorter of the useful life or remaining lease term ​ Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2021 or 2020. Leases The Company accounts for leases using ASC Topic 842, Leases (“ASC 842”). At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its estimated incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, components of a lease should be split into three categories: lease components (e.g. land, building, etc.), non-lease components (e.g. common area maintenance, consumables, etc.), and non-components (e.g. property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. For operating leases, lease expense relating to fixed payments is recognized on a straight-line basis over the term and lease expense relating to variable payments is expensed as incurred. Fair Value Measurements ASC Topic 820, Fair Value Measurement ("ASC 820"), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3 — Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Segment Information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment operating exclusively in the U.S. Revenue Recognition The Company accounts for revenue using the provisions of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the contract(s) with the customer, (ii) identification of the promised goods or services in the contract and determination of whether the promised goods or services are performance obligations, (iii) measurement of the transaction price, (iv) allocation of the transaction price to the performance obligations, and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company accounts for a contract with a customer that is within the scope of ASC 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations, (ii) each party’s rights regarding the goods or services to be transferred can be identified, (iii) the payment terms for the goods or services to be transferred can be identified, (iv) the arrangement has commercial substance and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods or services that will be transferred to the customer is probable. The Company first evaluates license and/or collaboration arrangements to determine whether the arrangement (or part of the arrangement) represents a collaborative arrangement pursuant to ASC Topic 808, Collaborative Arrangements, , which represent a collaborative relationship and not a customer relationship, For the arrangements or arrangement components that are subject to revenue accounting guidance, in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract; b) the transaction price under step (iii) above; and c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In determining the stand-alone selling price of a license to the Company’s proprietary technology or a material right provided by a customer option, the Company considers market conditions as well as entity-specific factors, including those factors contemplated in negotiating the agreements as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success and the time needed to commercialize a product candidate pursuant to the license. In validating its estimated stand-alone selling prices, the Company evaluates whether changes in the key assumptions used to determine its estimated stand-alone selling prices will have a significant effect on the allocation of arrangement consideration between performance obligations. ​ The Company estimates the transaction price based on the amount of consideration the Company expects to be received for transferring the promised goods or services in the contract. The consideration may include both fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of the potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the transaction price based on which method better predicts the amount of consideration expected to be received. If it is probable that a significant revenue reversal would not occur, the variable consideration is included in the transaction price. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when: (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own and whether the required expertise is readily available. The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the standalone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Estimating costs for research and development programs is subjective as the Company estimates the costs anticipated to successfully complete the research performance obligations. As the research is novel, efforts to be successful may be significantly different than the estimated costs at the beginning of the contract. Certain variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated to each performance obligation are consistent with the amounts the Company would expect to receive for each performance obligation. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation in order to determine whether the combined performance obligation is satisfied over time or at a point in time. The Company determines the appropriate method of measuring progress of combined performance obligations satisfied over time for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The estimated remaining costs is highly subjective, as the research is novel, therefore efforts to be successful may be significantly different than the estimated costs made at the balance sheet date. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. The Company receives payments from customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets. Exclusive Licenses – Research and Development Services – Exclusive Licenses Customer Options – Milestone Payments – be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. If a milestone or other variable consideration relates specifically to the Company’s efforts to satisfy a single performance obligation or to a specific outcome from satisfying the performance obligation, the Company generally allocates the milestone amount entirely to that performance obligation once it is probable that a significant revenue reversal would not occur. Royalties – For a complete discussion of accounting for collaboration revenues, see Note 13, Agreements. ​ Research and Development Expenses and Accruals Research and development expenses are expensed as incurred and consist of costs incurred in performing research and development activities, including compensation related expenses for research and development personnel, preclinical and clinical activities including cost of drug supply, overhead expenses including facilities expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation of equipment. Upfront license payments related to acquired technologies which have not yet reached technological feasibility and have no alternative future use are also included in research and development expense. The Company has entered into various research and development service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzed the progress of the studies, trials or other services performed, including invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued expense balances at the end of each reporting period. Equity-Based Compensation The Company accounts for equity awards, including restricted stock awards, restricted stock units, and common stock options, granted as equity award compensation in accordance with ASC Topic 718, Compensation — Stock Compensation ("ASC 718"). ASC 718 requires all stock-based payments to employees, which includes grants of employee equity awards, to be recognized as expense in the statements of operations based on their grant date fair values. The fair value of each restricted stock award and restricted stock unit is based on the fair value of the Company’s common stock less any purchase price, if applicable. The fair value of each stock option award is estimated using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company’s common stock and certain subjective assumptions, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information was available. The historical volatility is generally calculated based on a period of time commensurate with the expected term assumptions. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on common stock. Compensation expense related to equity awards to employees that are subject to graded vesting is recognized on a straight-line basis, based on the grant date fair value, over the requisite service period of the award, which is generally the vesting term. For awards subject to performance conditions, the Company recognizes equity award compensation expense using an accelerated recognition method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the relative satisfaction of the performance conditions as of the reporting date. The Company classifies equity-based compensation expense in its consolidated statements of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified. The Company accounts for forfeitures when they occur. Comprehensive Loss Comprehensive loss is the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss includes net loss and the change in accumulated other comprehensive income (loss) for the period. Accumulated other comprehensive loss consisted entirely of unrealized gains and losses on available-for-sale marketable securities during the period ending December 31, 2021 and 2020. Net Loss per Share The Company applies the two-class method to compute basic and diluted net loss per share because it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (losses) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income (losses) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the participating securities do not have a contractual obligation to fund the losses of the Company. The Company calculates basic net loss per share by dividing net loss by the weighted average number of common shares outstanding, including pre-funded warrants and excluding restricted common stock. The Company calculates diluted net loss per share by dividing net loss by the weighted average number of common shares outstanding, as applicable, after giving consideration to the dilutive effect of restricted stock awards, restricted stock units, warrants, pre-funded warrants, and stock options that are outstanding during the period. Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes ("ASC 740"), which provides for deferred taxes using an asset and liability approach. Under this method, deferred income tax assets and liabilities are recognized based on future income tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities, and their respective income tax basis. Deferred income tax assets and liabilities are measured using enacted income tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions, as necessary. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is "more likely than not" to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. The Company is open to examination by the Internal Revenue Service for the tax years ended December 31, 2013 to December 31, 2021. Since the Company is in a U.S. loss carryforward position, carryforward tax attributes generated in prior years may still be adjusted upon future examination if they have or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception. Marketable Securities The Company classifies its marketable securities as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current. Marketable securities are maintained by an investment manager and consist of U.S. treasury securities. Marketable securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the underlying marketable security. Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statement of operations and comprehensive loss. During the years ended December 31, 2021 and 2020, no marketable securities were adjusted for other than temporary declines in fair value. The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be "other than temporary," the Company would reduce the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2021
Fair Value of Financial Assets and Liabilities
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables summarize the assets and liabilities measured at fair value on a recurring basis at December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2021 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Money market funds, included in cash and cash equivalents ​ $ 188,493 ​ $ 188,493 ​ $ — ​ $ — Marketable securities: ​ ​ ​ ​ U.S. Treasury obligations ​ ​ 40,159 ​ ​ 40,159 ​ ​ — ​ ​ — Total assets ​ $ 228,652 ​ $ 228,652 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2020 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Money market funds, included in cash and cash equivalents ​ $ 119,841 ​ $ 119,841 ​ $ — ​ $ — U.S. Treasury obligations, included in cash and cash equivalents ​ ​ 9,998 ​ ​ 9,998 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ U.S. Treasury obligations ​ 180,673 ​ 180,673 ​ — ​ — Total assets ​ $ 310,512 ​ $ 310,512 ​ $ — ​ $ — ​ Cash, cash equivalents and marketable securities are Level 1 assets and include investments in money market funds and U.S. government securities that are valued using quoted market prices. Accordingly, money market funds and government funds are categorized as Level 1 as of December 31, 2021 and 2020. There were no transfers of assets between fair value measurement levels during the years ended December 31, 2021 and 2020. The carrying amounts reflected in the balance sheets for prepaid expenses and other current assets, accounts payable, and accrued expenses approximate their fair values at December 31, 2021 and 2020, due to their short-term nature. The Company believes the terms of its debt reflect current market conditions for an instrument with similar terms and maturity, therefore the carrying value of the Company's debt approximates its fair value based on Level 3 of the fair value hierarchy.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2021
Marketable Securities
Marketable Securities	4. Marketable Securities The following table summarizes the Company’s investments as of December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Losses Fair Value Marketable securities available-for-sale: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury obligations ​ $ 40,194 ​ ​ — ​ ​ (35) ​ $ 40,159 Total available-for-sale securities ​ $ 40,194 ​ $ — ​ $ (35) ​ $ 40,159 ​ The following table summarizes the Company’s investments as of December 31, 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Losses Fair Value Marketable securities available-for-sale: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury obligations ​ $ 180,675 ​ $ 7 ​ $ (9) ​ $ 180,673 Total available-for-sale securities ​ $ 180,675 ​ $ 7 ​ $ (9) ​ $ 180,673 ​ The aggregate fair value of marketable securities with unrealized losses was $30.2 million and $45.7 million at December 31, 2021 and 2020, respectively.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2021
Property and Equipment, Net
Property and Equipment, Net	5. Property and Equipment, Net At December 31, 2021 and 2020, property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2021 ​ 2020 Laboratory equipment ​ $ 9,497 ​ $ 5,359 Leasehold improvements ​ 5,160 ​ 1,579 Computer equipment & software ​ ​ 1,080 ​ ​ 461 Furniture & fixtures ​ 995 ​ 224 Machinery & equipment ​ 75 ​ 75 Construction in progress ​ ​ 48 ​ ​ 5,282 ​ ​ 16,855 ​ 12,980 Less: Accumulated depreciation and amortization ​ (7,291) ​ (4,859) ​ ​ $ 9,564 ​ $ 8,121 ​ Depreciation and amortization expense was $2.6 million and $1.5 million for the years ended December 31, 2021 and 2020, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Accrued Expenses	6. Accrued Expenses At December 31, 2021 and 2020, accrued expenses consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, December 31, ​ 2021 ​ 2020 Accrued external research and development expense ​ $ 8,428 ​ $ 5,387 Accrued payroll and related expenses ​ ​ 7,147 ​ ​ 6,663 Accrued professional and consulting expense ​ ​ 1,421 ​ ​ 1,141 Accrued other ​ ​ 436 ​ ​ 476 Accrued payable for property and equipment ​ 24 ​ 1,291 ​ ​ $ 17,456 ​ $ 14,958 ​

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2021
Preferred Stock
Preferred Stock	7. Preferred Stock The Board of Directors or any authorized committee thereof is expressly authorized, to the fullest extent permitted by law, to provide by resolution or resolutions for, out of the unissued shares of Preferred Stock, the issuance of the shares of Preferred Stock in one or more series of such stock, and by filing a certificate of designations pursuant to applicable law of the State of Delaware, to establish or change from time to time the number of shares of each such series, and to fix the designations, powers, including voting powers, full or limited, or no voting powers, preferences and the relative, participating, optional or other special rights of the shares of each series and any qualifications, limitations and restrictions thereof.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
Common Stock.
Common Stock	8. Common Stock The Company has a sales agreement with Jefferies LLC (“Jefferies”) with respect to an at-the-market (“ATM”) offering program under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock having an aggregate offering price of up to $150.0 million, through Jefferies as its sales agent. In an ATM offering, exchange-listed companies incrementally sell newly issued shares into the secondary trading market through a designated broker-dealer at prevailing market prices. On October 28, 2021, 500,000 shares of common stock were sold pursuant to the ATM, resulting in net proceeds of approximately $13.1 million. ​ On October 28, 2020, the Company entered into an underwriting agreement relating to the issuance and sale of an aggregate of 3,717,948 shares of its common stock at $39.00 per share and pre-funded warrants to purchase 2,179,487 shares of its common stock. The price of each pre-funded warrant was $38.9999 , which Total gross proceeds of the transaction were $230.0 million and net proceeds were $215.9 million, after deducting underwriting discounts and commissions and offering expenses. The pre-funded warrants are exercisable at any time, do not expire, and meet the condition for equity classification and were therefore recorded as a component of stockholders’ equity within additional paid-in capital. No pre-funded warrants have been exercised as of December 31, 2021. ​ In June and July 2019, the Company sold 3,450,000 shares of its common stock, including the exercise of the overallotment option, through an underwritten public offering at a price of $15.00 per share. The offering was made pursuant to the Company’s effective shelf registration statement on Form S ‑ 3. The Company received aggregate net proceeds, after underwriting discounts and commissions and other offering expenses, of approximately $48.3 million. ​ Shares Reserved For Future Issuance As of December 31, 2021, the Company had reserved common shares as follows: ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2021 Common shares reserved for exercise of pre-funded warrants ​ 2,179,487 Common shares reserved for future issuance under the 2018 ESPP ​ 1,137,373 Common shares reserved for exercise of outstanding stock options under the 2017 and 2018 Plans ​ 3,743,400 Common shares reserved for future issuance under the 2018 Plan ​ 2,394,091 Common shares reserved for unvested restricted stock units under the 2018 Plan ​ 314,901 ​ ​ 9,769,252 ​

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2021
Equity-Based Compensation
Equity-Based Compensation	9. Equity-Based Compensation Equity Plans As of December 31, 2021, the Company has three active equity plans, the 2018 Stock Option and Incentive Plan (the “2018 Plan”), the 2017 Stock Option and Incentive Plan (the “2017 Plan”), and the 2018 Employee Stock Purchase Plan (the “2018 ESPP”). 2018 Stock Option and Incentive Plan The 2018 Plan was adopted by the Company’s Board of Directors on May 2, 2018, and approved by the Company’s stockholders on May 11, 2018. The 2018 Plan has replaced the 2017 Plan as no additional awards will be granted under that plan following the consummation of the IPO. At December 31, 2021 there were 2,394,091 shares available to grant under the 2018 Plan. The 2018 Plan provides for the grant of equity-based incentive awards, including incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards and restricted stock units to the Company’s officers, employees, directors and other key persons (including consultants). Stock options and restricted stock units granted under the 2018 Plan to employees generally vest over four years. The shares of common stock underlying any awards that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2018 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board of Directors or compensation committee (the “Annual Increase”). These limits are subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization. 2017 Stock Option and Incentive Plan The 2017 Plan provides for the grant of incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards and restricted stock units. Stock options granted under the 2017 Plan to employees generally vest over four years. The shares of common stock underlying any awards that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2017 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. 2018 Employee Stock Purchase Plan On May 2, 2018, the Board of Directors adopted the 2018 ESPP, and it was approved by the stockholders on May 11, 2018. At December 31, 2021 there were 1,137,373 shares available to grant under the 2018 ESPP and no shares had been issued. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 through January 1, 2028, by the lesser of (i) 353,614 shares of common stock, (ii) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or (iii) such lesser number of shares as determined by the 2018 ESPP administrator. The number of shares reserved under the 2018 ESPP is subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization. Total Equity-Based Compensation Expense The Company recorded equity-based compensation expense related to all equity-based awards, which was allocated as follows in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 2020 Research and development expense ​ $ 10,176 ​ $ 3,554 General and administrative expense ​ 12,973 ​ 7,621 ​ ​ $ 23,149 ​ $ 11,175 ​ Equity-based compensation during the year ended December 31, 2020 includes $1.5 million related to the modification of certain equity awards. The following table summarizes the Company’s unrecognized equity-based compensation expense as of December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2021 ​ ​ Unrecognized Expense (in thousands) Weighted Average Remaining Period of Recognition (years) Restricted Stock Units ​ 12,079 ​ 3.3 Stock Options ​ 45,364 ​ 2.4 ​ $ 57,443 ​ ​ ​ Restricted Stock Awards The following table summarizes the Company’s restricted stock award activity for the current year: ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Fair ​ ​ ​ ​ Value per Share ​ Number of Shares at Issuance Restricted stock awards as of December 31, 2020 57,969 ​ $ 5.77 Vested (57,969) ​ $ 5.77 Restricted stock awards as of December 31, 2021 — ​ $ — ​ Restricted Stock Units The following table summarizes the Company’s restricted stock unit activity for the current year: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Grant ​ Number of Units Date Fair Value Restricted stock units as of December 31, 2020 — ​ $ — Granted 392,661 ​ $ 49.48 Forfeited (77,760) ​ $ 57.98 Restricted stock units as of December 31, 2021 314,901 ​ $ 47.38 ​ Stock Options The following table summarizes the Company’s stock option activity for the current year: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ Number of ​ Average ​ Remaining ​ Aggregate ​ Shares Exercise Price Contractual Term Intrinsic Value ​ ​ ​ ​ ​ ​ ​ (in years) ​ (in thousands) Outstanding as of December 31, 2020 3,679,931 ​ $ 14.96 8.01 ​ $ 123,600 Granted 1,462,930 ​ $ 49.23 ​ ​ ​ ​ ​ Exercised ​ (556,629) ​ $ 12.38 ​ ​ ​ ​ ​ Cancelled (842,832) ​ $ 29.12 ​ ​ ​ ​ ​ Outstanding as of December 31, 2021 3,743,400 ​ $ 25.55 ​ 8.06 ​ $ 26,272 Options exercisable as of December 31, 2021 1,544,062 ​ $ 18.42 ​ 7.18 ​ $ 14,851 ​ Using the Black-Scholes option pricing model, the weighted average fair value of options granted during the year ended December 31, 2021 was $36.08. The following weighted average assumptions were used in determining the fair value of options granted in the years ended December 31, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 2020 ​ Risk-free interest rate 0.86 % 0.92 % Expected dividend yield 0.0 % 0.0 % Expected term (years to liquidity) 6.22 ​ 6.21 ​ Expected volatility 87.62 % 82.09 % ​ ​

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes
Income Taxes	10. Income Taxes The Company has not recorded a current or deferred tax provision for the years ended December 31, 2021 and 2020. The effective income tax rate differed from the amount computed by applying the federal statutory rate to the Company’s loss before income taxes as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ For Year Ended ​ ​ December 31, ​ 2021 2020 ​ Tax effected at statutory rate 21.0 % 21.0 % State taxes 6.8 6.8 ​ Stock compensation 0.9 1.6 ​ Non-deductible expenses (1.6) (2.4) ​ Federal research and development credits 6.5 7.9 ​ Other ​ (1.5) ​ (0.5) ​ Change in valuation allowance (32.1) (34.4) ​ ​ — % — % ​ Deferred tax assets (liabilities) consist of the following at December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2021 2020 Deferred tax assets: ​ ​ ​ ​ Net operating loss carryforwards ​ $ 82,403 ​ $ 46,112 Tax credits ​ 25,800 ​ 17,423 Deferred revenue ​ ​ 9,035 ​ ​ 14,194 Operating lease liability ​ ​ 7,365 ​ ​ 9,196 Stock based compensation ​ 4,751 ​ 1,892 Reserve and accruals ​ ​ 2,844 ​ ​ 2,635 Total gross deferred tax assets ​ 132,198 ​ 91,452 Valuation allowance ​ (124,233) ​ (81,980) Total deferred tax assets ​ ​ 7,965 ​ ​ 9,472 Total deferred tax liabilities: ​ ​ ​ ​ ​ ​ Operating lease right-of-use asset ​ ​ (6,925) ​ ​ (8,805) Fixed and intangible assets ​ (1,040) ​ (667) Total deferred tax liabilities ​ ​ (7,965) ​ ​ (9,472) Total net deferred tax assets ​ $ — ​ $ — ​ Total Net Deferred Tax Assets Deferred tax assets are reduced by a valuation allowance if, based on the weight of available positive and negative evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2021 and 2020. The valuation allowance for deferred tax assets increased by $42.3 million and $29.7 million in 2021 and 2020, respectively. This increase mainly relates to the establishment of a valuation allowance against the Company’s net domestic deferred tax assets in connection with net operating losses generated in each year and the additional tax credit carryforwards generated. As of December 31, 2021, the Company had approximately $302.1 million and $300.2 million of Federal and State operating loss carryforwards respectively, which begin to expire in 2032, except for the $251.6 million of the Company’s federal net operating loss carryforwards that do not expire. These loss carryforwards are available to reduce future taxable income, if any. These loss carryforwards are subject to review and possible adjustment by the appropriate taxing authorities. As of December 31, 2021, the Company also had federal and state credit carryovers of $22.5 million and $4.2 million, respectively. The amount of loss and credit carryforwards that may be utilized in any future period may be limited based upon changes in the ownership of the Company’s ultimate parent. Additionally, the deductibility of federal net operating losses generated after December 31, 2017 is limited to 80% of the Company’s taxable income in any future taxable year. The Company follows the provisions of ASC 740-10, “Accounting for Uncertainty in Income Taxes,” which specifies how tax benefits for uncertain tax positions are to be recognized, measured, and recorded in financial statements; requires certain disclosures of uncertain tax matters; specifies how reserves for uncertain tax positions should be classified on the balance sheet; and provides transition and interim period guidance, among other provisions. As of December 31, 2021 and 2020, the Company has not recorded any amounts for uncertain tax positions. The Company’s policy is to recognize interest and penalties accrued on any uncertain tax positions as a component of income tax expense, if any, in its statements of income.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies
Commitments and Contingencies	11. Commitments and Contingencies Operating Leases 620 Memorial Facility Lease In March 2015, the Company entered into a 5-year lease of office and laboratory space for its corporate headquarters (the “Lease”) at 620 Memorial Drive in Cambridge, Massachusetts. The Lease was amended in February 2018, to add an additional space (the “Expansion Space”) at the current location and to extend the Lease term (the “Amended Lease”). The Amended Lease expires in September 2023. Annual rent payments, including the Expansion Space, increase from $1.4 million to $1.7 million over the term of the Amended Lease. Variable lease payments include the Company’s allocated share of costs incurred and expenditures made by the landlord in the operation and management of the building. The Company has the option to extend the term of the Amended Lease for one additional term of 5 years commencing after the Amended Lease expires. ​ On October 5, 2020, the Company entered into a Sublease Agreement (the “Sublease”) with Orna Therapeutics, Inc. (the “Subtenant”) to sublease the space covered by the Amended Lease at 620 Memorial Drive, Cambridge, Massachusetts. The Sublease term commenced on February 1, 2021 and ends on August 31, 2023, unless terminated earlier. The Sublease provides for initial annual base rent of approximately $1.9 million. The Subtenant is obligated to pay for certain costs, taxes and operating expenses, subject to certain exclusions. The Sublease is subordinate to that certain Indenture of Lease, dated March 5, 2015, by and between 620 Memorial Leasehold LLC and Scholar Rock, Inc., as amended. 301 Binney Facility Lease ​ In November 2019, the Company entered into a lease of office and laboratory space at 301 Binney Street in Cambridge, Massachusetts to be used as its new corporate headquarters. The expiration date of the lease is in August 2025 and the Company has the option to extend the term by two years. The base rent is $6.9 million per year, subject to an annual increase of 3.5%, and the Company was subject to a free-rent period through mid-August 2020. Variable lease payments include the Company’s allocated share of costs incurred and expenditures made by the landlord in the operation and management of the building. The lease included incentives of $14.1 million in the form of an allowance for tenant improvements related to the design and build out of the space. In connection with the lease, the Company has secured a letter of credit for $2.3 million which renews automatically each year. The lease commencement date, for accounting purposes, was reached in September 2020. ​ Other information related to the Company’s leases (excluding the Company’s sublease income of $2.3 million for the year ending December 31, 2021) is as follows (in thousands, except lease term and discount rate): ​ ​ ​ ​ ​ ​ For Year Ended ​ December 31, ​ ​ 2021 Lease Cost: ​ ​ ​ Operating lease cost ​ $ 8,642 Variable lease cost ​ ​ 2,256 Total lease cost ​ $ 10,898 ​ ​ ​ ​ ​ ​ For Year Ended ​ ​ December 31, ​ ​ 2021 ​ Other information: ​ ​ ​ Operating cash flows used for operating leases $ 8,880 ​ Weighted average remaining lease term ​ 3.4 ​ Weighted average incremental borrowing rate ​ 7.5 % ​ ​ The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2021 (in thousands): ​ ​ ​ ​ Year Ending December 31, ​ ​ 2022 ​ 9,183 2023 ​ 9,057 2024 ​ ​ 8,051 2025 ​ ​ 4,498 Total lease payments ​ ​ 30,789 Less imputed interest ​ ​ (3,730) Total operating lease liability ​ $ 27,059 Short-term portion of operating lease liability ​ ​ 7,407 Long-term portion of operating lease liability ​ ​ 19,652 ​ The Company recorded approximately $8.6 million and $3.2 million in rent expense (excluding sublease income) for the years ended December 31, 2021 and 2020, respectively. ​ Specifica Antibody Library On December 20, 2019 (the “Effective Date”), the Company entered into a Library Development and Transfer Agreement with Specifica Inc. (“Specifica”), whereby Specifica is responsible for developing and delivering a customized antibody display library (the “Library”) for the Company to use to identify antibodies for further research, development, and commercialization. As of December 31, 2021 the Company has paid $2.0 million of the total $3.7 million in fees expected to be paid through 2023 related to the Library. As the return right has lapsed, all $3.7 million in fees have been recognized as expense to date. ​ Legal Proceedings The Company, from time to time, may be party to litigation arising in the ordinary course of its business. The Company was not subject to any material legal proceedings during the years ended December 31, 2021 and 2020.

Debt

Debt	12 Months Ended
	Dec. 31, 2021
Debt
Debt	12. Debt On October 16, 2020 (the “Closing Date”) the Company entered into a Loan and Security Agreement with Oxford Finance LLC and Silicon Valley Bank (“SVB”) for $50.0 million (the “Loan and Security Agreement”). Tranche 1 of $25.0 million was funded on the Closing Date. The Company had an additional $25.0 million in loan proceeds available through December 31, 2021 if certain criteria were met under Tranche 2. The Loan and Security Agreement will mature on May 1, 2025 and requires interest only payments through November 2022, with principal payments commencing in December 2022. Prepayment is permitted and may include either a 2% or 3% fee (of the principal amount being prepaid), depending on when the prepayment is made. The Company is also required to make a final payment equal to 4% of the original principal amount. The Company shall maintain cash in an SVB account equal to the lesser of 100% of the Company’s consolidated cash or 105% of the dollar amount of the outstanding debt. ​ The following table shows required payments (excluding interest), during the next five years on debt outstanding at December 31, 2021 (in thousands): ​ ​ ​ ​ ​ Year Ending December 31, Total future payments 2022 ​ ​ 1,667 2023 ​ ​ 20,000 2024 ​ 20,000 2025 ​ ​ 10,333 Total payments ​ $ 52,000 ​ The Company incurred costs on behalf of the lender recorded as a debt discount of $0.3 million and incurred debt issuance costs of $0.1 million, both of which are recorded as a deduction from the carrying amount of the debt and are being amortized as interest expense over the term of the loan. The final payment fee will be treated as an additional debt discount and accreted to the debt balance over the term. ​ For the years ended December 31, 2021 and 2020, the Company recorded total interest expense for the debt of $2.1 million and $0.4 million, respectively.

Agreements

Agreements	12 Months Ended
	Dec. 31, 2021
Agreements
Agreements	13. Agreements Collaboration with Gilead On December 19, 2018 (the “Effective Date”), the Company entered into a three-year Master Collaboration Agreement (the “Gilead Collaboration Agreement”) with Gilead to discover and develop specific inhibitors of TGFβ activation focused on the treatment of fibrotic diseases. Under the collaboration, Gilead had exclusive options to license worldwide rights to product candidates that emerge from three of the Company’s TGFβ programs (each a “Gilead Program”). Pursuant to the Gilead Collaboration Agreement, the Company was responsible for antibody discovery and preclinical research through product candidate nomination, after which, upon exercising the option for a Gilead Program, Gilead would be responsible for the program’s preclinical and clinical development and commercialization. Such option could have been exercised by Gilead at any time from the Effective Date through a date that is 90 days following the expiration of the Research Collaboration Term for a given Gilead Program (no later than March 19, 2022), or until termination of the Gilead Program, whichever is earlier (the “Option Exercise Period”). On January 6, 2022, Gilead agreed that its option exercise period for all programs has been terminated. Revenue associated with the research and development and license performance obligations relating to the Gilead Programs is recognized as revenue as the research and development services are provided using an input method, according to the costs incurred on each Gilead Program and the costs expected to be incurred in the future to satisfy the performance obligation. The transfer of control occurred over time. In management’s judgment, this input method was the best measure of progress towards satisfying the performance obligation. The amounts allocated to the three material rights will be recognized either upon exercise or termination of the respective options. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet. A $25.0 million preclinical milestone was achieved in December 2019 for the successful demonstration of efficacy in preclinical in vivo In the year ended December 31, 2021, the Company recognized $18.8 million in revenue in the Company’s consolidated statements of operations and comprehensive loss under the Gilead Collaboration Agreement, all of which was included in deferred revenue at the beginning of the period. The Company has recognized the revenue related to the research and development services based on a cost input method over the research term for each respective Gilead Program, which ended in December 2021. The aggregate amount of the transaction price allocated to the Company’s unsatisfied performance obligations and recorded in deferred revenue at December 31, 2021 is $33.2 million, which is fully attributable to the material rights. As Gilead agreed in January 2022, its option exercise period for all programs has been terminated. The Company will recognize the remaining deferred revenue in the first quarter of 2022.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2021
Net Loss per Share
Net Loss per Share	14. Net Loss per Share The Company calculates basic net loss per share by dividing net loss by the weighted average number of common shares outstanding, excluding restricted common stock. The weighted average number of common shares used in the basic and diluted net loss per share calculation include the pre-funded warrants issued in connection with the Company’s November 2, 2020 follow-on offering as the warrants are exercisable at any time for nominal cash consideration. The Company has generated a net loss in all periods presented, so the basic and diluted net loss per share are the same, as the inclusion of the potentially dilutive securities would be anti-dilutive. Basic and diluted net loss per share is calculated as follows (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ Year Ended Year Ended ​ December 31, 2021 December 31, 2020 Net loss ​ $ (131,799) ​ $ (86,483) Weighted average common shares outstanding, basic and diluted ​ 36,711,833 ​ 30,734,109 Net loss per share, basic and diluted ​ $ (3.59) ​ $ (2.81) ​ The following table sets forth the outstanding common stock equivalents, presented based on amounts outstanding at each period end, that have been excluded from the calculation of diluted net loss per share for the periods indicated because their inclusion would have been anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 Restricted stock awards ​ — ​ 57,969 Restricted stock units ​ 314,901 ​ — Stock options ​ 3,743,400 ​ 3,679,931 ​ ​ 4,058,301 ​ 3,737,900 ​

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2021
Retirement Plan
Retirement Plan	15. Retirement Plan The Company sponsors a 401(k) retirement plan, in which substantially all employees are eligible to participate upon employment. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. Effective, January 1, 2020, the Company adopted a policy to match 50% of the employee contributions to the 401(k) plan up to a maximum of 6% of the participating employee’s eligible earnings, resulting in a maximum company match of 3% of the participating employee’s eligible earnings subject to statutory limitations. The Company recognized $0.7 million and $0.5 million in expense related to the match during the years ended December 31, 2021 and 2020, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities and related disclosures of contingent assets and liabilities at the date of the financial statements and the related reporting of revenues and expenses during the reporting period. Management bases its estimates on historical experience and on various assumptions that are believed to be reasonable under the circumstances. Actual results could differ from those estimates.
Concentration of Credit Risk and Off-Balance Sheet Risk	Concentration of Credit Risk and Off-Balance Sheet Risk The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts or other foreign-hedging arrangements. The Company follows an investment policy approved by the Board of Directors. Its primary objectives are the preservation of capital and maintenance of liquidity. The Company invests only in fixed income instruments denominated and payable in U.S. dollars including obligations of the U.S. government and its agencies and money market funds registered according to SEC Rule 2a-7 of the Investment Company Act of 1940. All securities must have a readily ascertainable market value , must be readily marketable and be U.S. dollar denominated.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are stated at cost, which approximates market value. At December 31, 2021 and 2020, cash equivalents include money market funds that invest primarily in U.S. government-backed securities and treasuries. Restricted cash consists of letters of credit in the amount of $2.5 million related to its leased facilities. The following table reconciles cash, cash equivalents and restricted cash per the balance sheet to the statement of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2021 2020 Cash and cash equivalents ​ $ 212,835 ​ $ 160,358 Restricted cash ​ 2,498 ​ 2,498 ​ ​ $ 215,333 ​ $ 162,856
Property and Equipment	Property and Equipment Property and equipment are recorded at cost. Expenditures for major renewals or betterments that extend the useful lives of property and equipment are capitalized; expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related asset. Property and equipment are depreciated as follows: ​ ​ ​ ​ ​ ​ Estimated Useful Life ​ (in Years) Laboratory equipment 3 – 5 Computer equipment & software ​ 3 Furniture & fixtures 5 Machinery & equipment 3 – 5 Leasehold improvements ​ Shorter of the useful life or remaining lease term
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2021 or 2020.
Leases	Leases The Company accounts for leases using ASC Topic 842, Leases (“ASC 842”). At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its estimated incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, components of a lease should be split into three categories: lease components (e.g. land, building, etc.), non-lease components (e.g. common area maintenance, consumables, etc.), and non-components (e.g. property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. For operating leases, lease expense relating to fixed payments is recognized on a straight-line basis over the term and lease expense relating to variable payments is expensed as incurred.
Fair Value Measurements	Fair Value Measurements ASC Topic 820, Fair Value Measurement ("ASC 820"), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3 — Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.
Segment Information	Segment Information Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment operating exclusively in the U.S.
Revenue Recognition	Revenue Recognition The Company accounts for revenue using the provisions of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the contract(s) with the customer, (ii) identification of the promised goods or services in the contract and determination of whether the promised goods or services are performance obligations, (iii) measurement of the transaction price, (iv) allocation of the transaction price to the performance obligations, and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company accounts for a contract with a customer that is within the scope of ASC 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations, (ii) each party’s rights regarding the goods or services to be transferred can be identified, (iii) the payment terms for the goods or services to be transferred can be identified, (iv) the arrangement has commercial substance and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods or services that will be transferred to the customer is probable. The Company first evaluates license and/or collaboration arrangements to determine whether the arrangement (or part of the arrangement) represents a collaborative arrangement pursuant to ASC Topic 808, Collaborative Arrangements, , which represent a collaborative relationship and not a customer relationship, For the arrangements or arrangement components that are subject to revenue accounting guidance, in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract; b) the transaction price under step (iii) above; and c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In determining the stand-alone selling price of a license to the Company’s proprietary technology or a material right provided by a customer option, the Company considers market conditions as well as entity-specific factors, including those factors contemplated in negotiating the agreements as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success and the time needed to commercialize a product candidate pursuant to the license. In validating its estimated stand-alone selling prices, the Company evaluates whether changes in the key assumptions used to determine its estimated stand-alone selling prices will have a significant effect on the allocation of arrangement consideration between performance obligations. ​ The Company estimates the transaction price based on the amount of consideration the Company expects to be received for transferring the promised goods or services in the contract. The consideration may include both fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of the potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the transaction price based on which method better predicts the amount of consideration expected to be received. If it is probable that a significant revenue reversal would not occur, the variable consideration is included in the transaction price. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when: (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own and whether the required expertise is readily available. The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the standalone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Estimating costs for research and development programs is subjective as the Company estimates the costs anticipated to successfully complete the research performance obligations. As the research is novel, efforts to be successful may be significantly different than the estimated costs at the beginning of the contract. Certain variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated to each performance obligation are consistent with the amounts the Company would expect to receive for each performance obligation. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation in order to determine whether the combined performance obligation is satisfied over time or at a point in time. The Company determines the appropriate method of measuring progress of combined performance obligations satisfied over time for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The estimated remaining costs is highly subjective, as the research is novel, therefore efforts to be successful may be significantly different than the estimated costs made at the balance sheet date. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. The Company receives payments from customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets. Exclusive Licenses – Research and Development Services – Exclusive Licenses Customer Options – Milestone Payments – be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. If a milestone or other variable consideration relates specifically to the Company’s efforts to satisfy a single performance obligation or to a specific outcome from satisfying the performance obligation, the Company generally allocates the milestone amount entirely to that performance obligation once it is probable that a significant revenue reversal would not occur. Royalties – For a complete discussion of accounting for collaboration revenues, see Note 13, Agreements.
Research and Development Expenses and Accruals	Research and Development Expenses and Accruals Research and development expenses are expensed as incurred and consist of costs incurred in performing research and development activities, including compensation related expenses for research and development personnel, preclinical and clinical activities including cost of drug supply, overhead expenses including facilities expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation of equipment. Upfront license payments related to acquired technologies which have not yet reached technological feasibility and have no alternative future use are also included in research and development expense. The Company has entered into various research and development service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzed the progress of the studies, trials or other services performed, including invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued expense balances at the end of each reporting period.
Equity-Based Compensation	Equity-Based Compensation The Company accounts for equity awards, including restricted stock awards, restricted stock units, and common stock options, granted as equity award compensation in accordance with ASC Topic 718, Compensation — Stock Compensation ("ASC 718"). ASC 718 requires all stock-based payments to employees, which includes grants of employee equity awards, to be recognized as expense in the statements of operations based on their grant date fair values. The fair value of each restricted stock award and restricted stock unit is based on the fair value of the Company’s common stock less any purchase price, if applicable. The fair value of each stock option award is estimated using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company’s common stock and certain subjective assumptions, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information was available. The historical volatility is generally calculated based on a period of time commensurate with the expected term assumptions. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on common stock. Compensation expense related to equity awards to employees that are subject to graded vesting is recognized on a straight-line basis, based on the grant date fair value, over the requisite service period of the award, which is generally the vesting term. For awards subject to performance conditions, the Company recognizes equity award compensation expense using an accelerated recognition method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the relative satisfaction of the performance conditions as of the reporting date. The Company classifies equity-based compensation expense in its consolidated statements of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified. The Company accounts for forfeitures when they occur.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss includes net loss and the change in accumulated other comprehensive income (loss) for the period. Accumulated other comprehensive loss consisted entirely of unrealized gains and losses on available-for-sale marketable securities during the period ending December 31, 2021 and 2020.
Net Loss per Share	Net Loss per Share The Company applies the two-class method to compute basic and diluted net loss per share because it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (losses) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income (losses) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the participating securities do not have a contractual obligation to fund the losses of the Company. The Company calculates basic net loss per share by dividing net loss by the weighted average number of common shares outstanding, including pre-funded warrants and excluding restricted common stock. The Company calculates diluted net loss per share by dividing net loss by the weighted average number of common shares outstanding, as applicable, after giving consideration to the dilutive effect of restricted stock awards, restricted stock units, warrants, pre-funded warrants, and stock options that are outstanding during the period.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes ("ASC 740"), which provides for deferred taxes using an asset and liability approach. Under this method, deferred income tax assets and liabilities are recognized based on future income tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities, and their respective income tax basis. Deferred income tax assets and liabilities are measured using enacted income tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions, as necessary. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is "more likely than not" to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities. The Company is open to examination by the Internal Revenue Service for the tax years ended December 31, 2013 to December 31, 2021. Since the Company is in a U.S. loss carryforward position, carryforward tax attributes generated in prior years may still be adjusted upon future examination if they have or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception.
Marketable Securities	Marketable Securities The Company classifies its marketable securities as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current. Marketable securities are maintained by an investment manager and consist of U.S. treasury securities. Marketable securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the underlying marketable security. Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statement of operations and comprehensive loss. During the years ended December 31, 2021 and 2020, no marketable securities were adjusted for other than temporary declines in fair value. The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be "other than temporary," the Company would reduce the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies
Schedule of reconciles of cash, cash equivalents and restricted cash	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2021 2020 Cash and cash equivalents ​ $ 212,835 ​ $ 160,358 Restricted cash ​ 2,498 ​ 2,498 ​ ​ $ 215,333 ​ $ 162,856
Schedule of useful life of property, plant and equipment	​ ​ ​ ​ ​ ​ Estimated Useful Life ​ (in Years) Laboratory equipment 3 – 5 Computer equipment & software ​ 3 Furniture & fixtures 5 Machinery & equipment 3 – 5 Leasehold improvements ​ Shorter of the useful life or remaining lease term

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value of Financial Assets and Liabilities
Schedule of summary of the assets and liabilities measured at fair value on a recurring basis	The following tables summarize the assets and liabilities measured at fair value on a recurring basis at December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2021 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Money market funds, included in cash and cash equivalents ​ $ 188,493 ​ $ 188,493 ​ $ — ​ $ — Marketable securities: ​ ​ ​ ​ U.S. Treasury obligations ​ ​ 40,159 ​ ​ 40,159 ​ ​ — ​ ​ — Total assets ​ $ 228,652 ​ $ 228,652 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at December 31, 2020 ​ Total Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ ​ ​ ​ ​ Money market funds, included in cash and cash equivalents ​ $ 119,841 ​ $ 119,841 ​ $ — ​ $ — U.S. Treasury obligations, included in cash and cash equivalents ​ ​ 9,998 ​ ​ 9,998 ​ ​ — ​ ​ — Marketable securities: ​ ​ ​ ​ U.S. Treasury obligations ​ 180,673 ​ 180,673 ​ — ​ — Total assets ​ $ 310,512 ​ $ 310,512 ​ $ — ​ $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2021
Marketable Securities
Summary of investments	The following table summarizes the Company’s investments as of December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Losses Fair Value Marketable securities available-for-sale: ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury obligations ​ $ 40,194 ​ ​ — ​ ​ (35) ​ $ 40,159 Total available-for-sale securities ​ $ 40,194 ​ $ — ​ $ (35) ​ $ 40,159 ​ The following table summarizes the Company’s investments as of December 31, 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Losses Fair Value Marketable securities available-for-sale: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury obligations ​ $ 180,675 ​ $ 7 ​ $ (9) ​ $ 180,673 Total available-for-sale securities ​ $ 180,675 ​ $ 7 ​ $ (9) ​ $ 180,673

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2021
Property and Equipment, Net
Summary of property and equipment	At December 31, 2021 and 2020, property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ 2021 ​ 2020 Laboratory equipment ​ $ 9,497 ​ $ 5,359 Leasehold improvements ​ 5,160 ​ 1,579 Computer equipment & software ​ ​ 1,080 ​ ​ 461 Furniture & fixtures ​ 995 ​ 224 Machinery & equipment ​ 75 ​ 75 Construction in progress ​ ​ 48 ​ ​ 5,282 ​ ​ 16,855 ​ 12,980 Less: Accumulated depreciation and amortization ​ (7,291) ​ (4,859) ​ ​ $ 9,564 ​ $ 8,121

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2021
Accrued Expenses
Summary of accrued expenses	At December 31, 2021 and 2020, accrued expenses consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, December 31, ​ 2021 ​ 2020 Accrued external research and development expense ​ $ 8,428 ​ $ 5,387 Accrued payroll and related expenses ​ ​ 7,147 ​ ​ 6,663 Accrued professional and consulting expense ​ ​ 1,421 ​ ​ 1,141 Accrued other ​ ​ 436 ​ ​ 476 Accrued payable for property and equipment ​ 24 ​ 1,291 ​ ​ $ 17,456 ​ $ 14,958

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2021
Common Stock.
Schedule of reserved common stock	​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2021 Common shares reserved for exercise of pre-funded warrants ​ 2,179,487 Common shares reserved for future issuance under the 2018 ESPP ​ 1,137,373 Common shares reserved for exercise of outstanding stock options under the 2017 and 2018 Plans ​ 3,743,400 Common shares reserved for future issuance under the 2018 Plan ​ 2,394,091 Common shares reserved for unvested restricted stock units under the 2018 Plan ​ 314,901 ​ ​ 9,769,252

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Equity-Based Compensation
Summary of allocation of equity-based compensation	The Company recorded equity-based compensation expense related to all equity-based awards, which was allocated as follows in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 2020 Research and development expense ​ $ 10,176 ​ $ 3,554 General and administrative expense ​ 12,973 ​ 7,621 ​ ​ $ 23,149 ​ $ 11,175
Summary of unrecognized equity-based compensation expense	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2021 ​ ​ Unrecognized Expense (in thousands) Weighted Average Remaining Period of Recognition (years) Restricted Stock Units ​ 12,079 ​ 3.3 Stock Options ​ 45,364 ​ 2.4 ​ $ 57,443 ​ ​
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ Number of ​ Average ​ Remaining ​ Aggregate ​ Shares Exercise Price Contractual Term Intrinsic Value ​ ​ ​ ​ ​ ​ ​ (in years) ​ (in thousands) Outstanding as of December 31, 2020 3,679,931 ​ $ 14.96 8.01 ​ $ 123,600 Granted 1,462,930 ​ $ 49.23 ​ ​ ​ ​ ​ Exercised ​ (556,629) ​ $ 12.38 ​ ​ ​ ​ ​ Cancelled (842,832) ​ $ 29.12 ​ ​ ​ ​ ​ Outstanding as of December 31, 2021 3,743,400 ​ $ 25.55 ​ 8.06 ​ $ 26,272 Options exercisable as of December 31, 2021 1,544,062 ​ $ 18.42 ​ 7.18 ​ $ 14,851
Schedule of weighted average assumptions in fair value	​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 2020 ​ Risk-free interest rate 0.86 % 0.92 % Expected dividend yield 0.0 % 0.0 % Expected term (years to liquidity) 6.22 ​ 6.21 ​ Expected volatility 87.62 % 82.09 %
Restricted stock awards
Equity-Based Compensation
Summary of stock activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Fair ​ ​ ​ ​ Value per Share ​ Number of Shares at Issuance Restricted stock awards as of December 31, 2020 57,969 ​ $ 5.77 Vested (57,969) ​ $ 5.77 Restricted stock awards as of December 31, 2021 — ​ $ —
Restricted Stock Units
Equity-Based Compensation
Summary of stock activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Grant ​ Number of Units Date Fair Value Restricted stock units as of December 31, 2020 — ​ $ — Granted 392,661 ​ $ 49.48 Forfeited (77,760) ​ $ 57.98 Restricted stock units as of December 31, 2021 314,901 ​ $ 47.38

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Taxes
Schedule of reconciliation of effective income tax rate differed from the amount computed by applying the federal statutory rate	​ ​ ​ ​ ​ ​ ​ ​ ​ For Year Ended ​ ​ December 31, ​ 2021 2020 ​ Tax effected at statutory rate 21.0 % 21.0 % State taxes 6.8 6.8 ​ Stock compensation 0.9 1.6 ​ Non-deductible expenses (1.6) (2.4) ​ Federal research and development credits 6.5 7.9 ​ Other ​ (1.5) ​ (0.5) ​ Change in valuation allowance (32.1) (34.4) ​ ​ — % — %
Summary of deferred tax assets (liabilities)	Deferred tax assets (liabilities) consist of the following at December 31, 2021 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ December 31, ​ 2021 2020 Deferred tax assets: ​ ​ ​ ​ Net operating loss carryforwards ​ $ 82,403 ​ $ 46,112 Tax credits ​ 25,800 ​ 17,423 Deferred revenue ​ ​ 9,035 ​ ​ 14,194 Operating lease liability ​ ​ 7,365 ​ ​ 9,196 Stock based compensation ​ 4,751 ​ 1,892 Reserve and accruals ​ ​ 2,844 ​ ​ 2,635 Total gross deferred tax assets ​ 132,198 ​ 91,452 Valuation allowance ​ (124,233) ​ (81,980) Total deferred tax assets ​ ​ 7,965 ​ ​ 9,472 Total deferred tax liabilities: ​ ​ ​ ​ ​ ​ Operating lease right-of-use asset ​ ​ (6,925) ​ ​ (8,805) Fixed and intangible assets ​ (1,040) ​ (667) Total deferred tax liabilities ​ ​ (7,965) ​ ​ (9,472) Total net deferred tax assets ​ $ — ​ $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies
Summary of lease costs	Other information related to the Company’s leases (excluding the Company’s sublease income of $2.3 million for the year ending December 31, 2021) is as follows (in thousands, except lease term and discount rate): ​ ​ ​ ​ ​ ​ For Year Ended ​ December 31, ​ ​ 2021 Lease Cost: ​ ​ ​ Operating lease cost ​ $ 8,642 Variable lease cost ​ ​ 2,256 Total lease cost ​ $ 10,898 ​ ​ ​ ​ ​ ​ For Year Ended ​ ​ December 31, ​ ​ 2021 ​ Other information: ​ ​ ​ Operating cash flows used for operating leases $ 8,880 ​ Weighted average remaining lease term ​ 3.4 ​ Weighted average incremental borrowing rate ​ 7.5 % ​
Summary of minimum lease payments	The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2021 (in thousands): ​ ​ ​ ​ Year Ending December 31, ​ ​ 2022 ​ 9,183 2023 ​ 9,057 2024 ​ ​ 8,051 2025 ​ ​ 4,498 Total lease payments ​ ​ 30,789 Less imputed interest ​ ​ (3,730) Total operating lease liability ​ $ 27,059 Short-term portion of operating lease liability ​ ​ 7,407 Long-term portion of operating lease liability ​ ​ 19,652 ​

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2021
Debt
Schedule of future principal payments of loan	The following table shows required payments (excluding interest), during the next five years on debt outstanding at December 31, 2021 (in thousands): ​ ​ ​ ​ ​ Year Ending December 31, Total future payments 2022 ​ ​ 1,667 2023 ​ ​ 20,000 2024 ​ 20,000 2025 ​ ​ 10,333 Total payments ​ $ 52,000

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Net Loss per Share
Schedule of basic and diluted net loss per share	Basic and diluted net loss per share is calculated as follows (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ Year Ended Year Ended ​ December 31, 2021 December 31, 2020 Net loss ​ $ (131,799) ​ $ (86,483) Weighted average common shares outstanding, basic and diluted ​ 36,711,833 ​ 30,734,109 Net loss per share, basic and diluted ​ $ (3.59) ​ $ (2.81)
Summary of anti-dilutive securities	​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2021 2020 Restricted stock awards ​ — ​ 57,969 Restricted stock units ​ 314,901 ​ — Stock options ​ 3,743,400 ​ 3,679,931 ​ ​ 4,058,301 ​ 3,737,900

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2021item
Nature of the Business and Basis of Presentation
Number of collaborations	2

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Risk (Details) $ in Billions	Dec. 31, 2021USD ($)
Summary of Significant Accounting Policies
Off-balance sheet risk	$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash and cash equivalents and restricted cash
Cash and cash equivalents	$ 212,835	$ 160,358
Restricted cash	2,498	2,498
Total	215,333	$ 162,856	$ 38,806
Letter of credit	$ 2,500

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
Laboratory equipment | Financing receivable, lower range of payment terms
Property and Equipment, Net
Estimated Useful Life	3 years
Laboratory equipment | Financing receivable, upper range of payment terms
Property and Equipment, Net
Estimated Useful Life	5 years
Computer equipment & software
Property and Equipment, Net
Estimated Useful Life	3 years
Furniture & fixtures
Property and Equipment, Net
Estimated Useful Life	5 years
Machinery & equipment | Financing receivable, lower range of payment terms
Property and Equipment, Net
Estimated Useful Life	3 years
Machinery & equipment | Financing receivable, upper range of payment terms
Property and Equipment, Net
Estimated Useful Life	5 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Misc (Details)	12 Months Ended
	Dec. 31, 2021USD ($)segment	Dec. 31, 2020USD ($)
Number of operating segments | segment	1
Adjustment for other than temporary decline in fair value | $	$ 0	$ 0
Stock Options
Expected dividend yield	0.00%	0.00%

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Marketable securities:
U.S. Treasury obligations	$ 40,159	$ 180,673
Total assets	228,652	310,512
Money market funds
Assets:
Cash and cash equivalents	188,493	119,841
U.S. Treasury obligations
Assets:
Cash and cash equivalents		9,998
Level 1
Marketable securities:
U.S. Treasury obligations	40,159	180,673
Total assets	228,652	310,512
Level 1 | Money market funds
Assets:
Cash and cash equivalents	$ 188,493	119,841
Level 1 | U.S. Treasury obligations
Assets:
Cash and cash equivalents		$ 9,998

Marketable Securities - Summary

Marketable Securities - Summary of Investments (Details) $ in Thousands	Dec. 31, 2021USD ($)security	Dec. 31, 2020USD ($)security
Marketable securities available-for-sale
Amortization Cost	$ 40,194	$ 180,675
Gross Unrealized Gains		7
Gross Unrealized Losses	(35)	(9)
Estimated Fair Value	40,159	180,673
Aggregate fair value of marketable securities with unrealized gains (losses) position for less than a year	$ 30,200	$ 45,700
Number of investments in an unrealized loss position for less than a year | security	3	5
U.S. Treasury obligations
Marketable securities available-for-sale
Amortization Cost	$ 40,194	$ 180,675
Gross Unrealized Gains		7
Gross Unrealized Losses	(35)	(9)
Estimated Fair Value	$ 40,159	$ 180,673

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property and Equipment, Net
Property and equipment, gross	$ 16,855	$ 12,980
Less: Accumulated depreciation and amortization	(7,291)	(4,859)
Total property and equipment, net	9,564	8,121
Depreciation and amortization expense	2,627	1,491
Laboratory equipment
Property and Equipment, Net
Property and equipment, gross	9,497	5,359
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	5,160	1,579
Computer equipment & software
Property and Equipment, Net
Property and equipment, gross	1,080	461
Furniture & fixtures
Property and Equipment, Net
Property and equipment, gross	995	224
Machinery & equipment
Property and Equipment, Net
Property and equipment, gross	75	75
Construction in progress
Property and Equipment, Net
Property and equipment, gross	$ 48	$ 5,282

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Expenses
Accrued external research and development expense	$ 8,428	$ 5,387
Accrued payroll and related expenses	7,147	6,663
Accrued professional and consulting expense	1,421	1,141
Accrued other	436	476
Accrued payable for property and equipment	24	1,291
Accrued expenses	$ 17,456	$ 14,958

Common Stock - (Details)

Common Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 28, 2021	Nov. 02, 2020	Oct. 28, 2020	Jul. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Subsidiary, Sale of Stock [Line Items]
Sale of common shares, net of issuance costs (in shares)			3,717,948	3,450,000
Proceeds from sale of common shares and pre-funded warrants, net of issuance costs		$ 215,900			$ 13,095	$ 215,922	$ 48,300
Purchase price (in dollars per share)			$ 39	$ 15
Warrant to purchase			2,179,487
Pre-funded warrants (in dollars per share)			$ 38.9999
Warrant purchase price (in dollars per share)			$ 0.0001
Proceeds from stock before issuance costs			$ 230,000
Pre funded warrants exercised during period					0
ATM Offering
Subsidiary, Sale of Stock [Line Items]
Aggregate offering price	$ 150,000
Sale of common shares, net of issuance costs (in shares)	500,000
Proceeds from sale of common shares and pre-funded warrants, net of issuance costs	$ 13,100

Common Stock - Reserved (Detail

Common Stock - Reserved (Details)	Dec. 31, 2021shares
Class of Stock [Line Items]
Shares reserved for future issuance	9,769,252
2018 ESPP
Class of Stock [Line Items]
Shares reserved for future issuance	1,137,373
2018 Plan
Class of Stock [Line Items]
Shares reserved for future issuance	2,394,091
Stock Options
Class of Stock [Line Items]
Shares reserved for future issuance	3,743,400
Restricted Stock Units | 2018 Plan
Class of Stock [Line Items]
Shares reserved for future issuance	314,901
Warrant
Class of Stock [Line Items]
Shares reserved for future issuance	2,179,487

Equity-Based Compensation - 201

Equity-Based Compensation - 2017 and 2018 Plan (Details)	May 11, 2018shares	Dec. 31, 2021itemshares	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award
Number of share-based compensation plans | item		3
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Unused shares available to be granted (in shares)		2,394,091
Increase as percentage of outstanding shares	4.00%
Vesting period	4 years
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized under stock-based plans (in shares)	0
Vesting period			4 years

Equity-Based Compensation - 2_2

Equity-Based Compensation - 2018 ESPP (Details) - 2018 ESPP - shares	May 02, 2018	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized under stock-based plans (in shares)	353,614
Increase as percentage of outstanding shares	1.00%
Shares issued		0
Unused shares available to be granted (in shares)		1,137,373

Equity-Based Compensation - Exp

Equity-Based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Equity-based compensation
Equity-based compensation expense	$ 23,149	$ 11,175
Modification of equity awards expense		1,500
Research, development and engineering
Equity-based compensation
Equity-based compensation expense	10,176	3,554
General and administrative expense
Equity-based compensation
Equity-based compensation expense	$ 12,973	$ 7,621

Equity-Based Compensation - Unr

Equity-Based Compensation - Unrecognized Equity-based Compensation Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Equity-based compensation
Unrecognized Expense	$ 57,443
Restricted Stock Units
Equity-based compensation
Unrecognized Expense	$ 12,079
Weighted Average Remaining Period of Recognition	3 years 3 months 18 days
Stock Options
Equity-based compensation
Unrecognized Expense	$ 45,364
Weighted Average Remaining Period of Recognition	2 years 4 months 24 days

Equity-Based Compensation - Res

Equity-Based Compensation - Restricted stock (Details)	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Restricted stock awards
Number of Shares/Units
Outstanding, beginning (in shares) | shares	57,969
Vested (in shares) | shares	(57,969)
Weighted Average Grant Date Fair Value
Outstanding, beginning (in dollars per share) | $ / shares	$ 5.77
Vested (in dollars per share) | $ / shares	$ 5.77
Restricted Stock Units
Number of Shares/Units
Granted (in shares) | shares	392,661
Forfeited (in shares) | shares	(77,760)
Outstanding, end (in shares) | shares	314,901
Weighted Average Grant Date Fair Value
Granted (in dollars per share) | $ / shares	$ 49.48
Forfeited (in dollars per share) | $ / shares	57.98
Outstanding, end (in dollars per share) | $ / shares	$ 47.38

Equity-Based Compensation - Sto

Equity-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Number of Units
Outstanding, beginning (in shares)	3,679,931
Granted (in shares)	1,462,930
Exercised (in shares)	(556,629)
Cancelled (in shares)	(842,832)
Outstanding, end (in shares)	3,743,400	3,679,931
Options exercisable, end (in shares)	1,544,062
Weighted Average Exercise Price
Outstanding, beginning (in dollars per share)	$ 14.96
Granted (in dollars per share)	49.23
Exercised (in dollars per share)	12.38
Cancelled (in dollars per share)	29.12
Outstanding, end (in dollars per share)	25.55	$ 14.96
Options exercisable, end (in dollars per share)	$ 18.42
Stock options
Weighted average remaining contractual term	8 years 21 days	8 years 3 days
Weighted average remaining contractual term, exercisable	7 years 2 months 4 days
Aggregate intrinsic value, beginning	$ 123,600
Aggregate intrinsic value, end	26,272	$ 123,600
Aggregate intrinsic value, exercisable	$ 14,851
Weighted average grant date fair value (in dollars per share)	$ 36.08

Equity-Based Compensation - Wei

Equity-Based Compensation - Weighted Average Assumptions (Details) - Stock Options	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Assumptions used in determining the fair value of options
Risk-free interest rate	0.86%	0.92%
Expected dividend yield	0.00%	0.00%
Expected term (years to liquidity)	6 years 2 months 19 days	6 years 2 months 15 days
Expected volatility	87.62%	82.09%

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Effective income tax rate
Tax effected at statutory rate	21.00%	21.00%
State taxes	6.80%	6.80%
Stock compensation	0.90%	1.60%
Non deductible expenses	(1.60%)	(2.40%)
Federal research and development credits	6.50%	7.90%
Other	(1.50%)	(0.50%)
Change in valuation allowance	(32.10%)	(34.40%)

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 82,403	$ 46,112
Tax credits	25,800	17,423
Deferred revenue	9,035	14,194
Operating lease liability	7,365	9,196
Stock based compensation	4,751	1,892
Reserve and accruals	2,844	2,635
Total gross deferred tax assets	132,198	91,452
Valuation allowance	(124,233)	(81,980)
Total deferred tax assets	7,965	9,472
Operating lease right-of-use asset	(6,925)	(8,805)
Fixed and intangible assets	(1,040)	(667)
Total deferred tax liabilities	$ (7,965)	$ (9,472)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Contingency
Increase in valuation allowance for deferred tax assets	$ 42.3	$ 29.7
Uncertain tax position	0	$ 0
Federal
Income Tax Contingency
Net operating loss carryforwards	302.1
Operating loss carryforwards without expiration date	251.6
Tax credit carryforward amount	22.5
State
Income Tax Contingency
Net operating loss carryforwards	300.2
Tax credit carryforward amount	$ 4.2

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($) $ in Thousands	Oct. 05, 2020	Nov. 30, 2019	Feb. 28, 2018	Dec. 31, 2021	Dec. 31, 2020	Mar. 31, 2015
Leased assets
Rent for facility lease				$ 8,600	$ 3,200
Letter of credit				2,500
Sublease income				2,300
Lease Cost:
Operating lease cost				8,642
Variable lease cost				2,256
Total lease cost				10,898
Operating cash flows used for operating leases				$ 8,880
Weighted average remaining lease term				3 years 4 months 24 days
Weighted average incremental borrowing rate				7.50%
Payment made on commitment				$ 2,000
Payment commitment				3,700
Antibody library expense				$ 3,700
620 Memorial Drive, Cambridge MA
Leased assets
Term of lease						5 years
Option to extend the term			true
Renewal term			5 years
Sublease annual base rent	$ 1,900
620 Memorial Drive, Cambridge MA | Financing receivable, lower range of payment terms
Leased assets
Rent for facility lease			$ 1,400
620 Memorial Drive, Cambridge MA | Financing receivable, upper range of payment terms
Leased assets
Rent for facility lease			$ 1,700
301 Binney St, Cambridge MA
Leased assets
Option to extend the term		true
Renewal term		2 years
Base rent		$ 6,900
Annual upward adjustment (as a percent)		3.50%
Incentive to lease		$ 14,100
Letter of credit		$ 2,300

Commitments and Contingencies -

Commitments and Contingencies - Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Maturity analysis of the annual undiscounted cash flows
2022	$ 9,183
2023	9,057
2024	8,051
2025	4,498
Total lease payments	30,789
Less imputed interest	(3,730)
Total operating lease liabilities	27,059
Short-term portion of operating lease liability	7,407	$ 5,366
Long-term portion of operating lease liability	$ 19,652	$ 27,093

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	Nov. 16, 2021	Oct. 16, 2020	Dec. 31, 2021	Dec. 31, 2020
Debt
Proceeds from credit facility			$ 24,984	$ 24,622
Loan and Security Agreement
Debt
Line of credit maximum		$ 50,000
Proceeds from credit facility		$ 25,000	25,000
Remaining borrowing capacity			$ 25,000
Variable rate (as a percent)	7.85%
Final payment fee (as a percent)	4.00%
Percentage of dollar value of company's consolidated cash	100.00%
Amount of cash required in a lender's account as a percentage of outstanding obligation (as a percent)	105.00%
Loan and Security Agreement | Financing receivable, lower range of payment terms
Debt
Prepayment penalty (as a percent)	2.00%
Loan and Security Agreement | Financing receivable, upper range of payment terms
Debt
Prepayment penalty (as a percent)	3.00%
Loan and Security Agreement | Wall Street Journal prime rate
Debt
Variable rate (as a percent)	4.60%

Debt - Future Payments (Details

Debt - Future Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Debt
2022	$ 1,667
2023	20,000
2024	20,000
2025	10,333
Total payments	52,000
Interest expense	2,100	$ 400
Loan and Security Agreement
Debt
Debt discount	300
Debt issuance costs payment	$ 100

Agreements - Gilead (Details)

Agreements - Gilead (Details) - USD ($) $ in Thousands	Dec. 19, 2018	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020
Agreements
Revenue earned			$ 18,816	$ 15,403
Gilead
Agreements
Revenue proceeds		$ 25,000
Revenue earned			$ 18,800
Master collaboration agreement, term	3 years

Agreements - Gilead obligation

Agreements - Gilead obligation period (Details) $ in Millions	Dec. 31, 2021USD ($)
Material rights | Gilead
Agreements
Transaction price	$ 33.2

Net Loss per Share - Basic and

Net Loss per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Loss per share
Net loss	$ (131,799)	$ (86,483)
Weighted average common shares outstanding, basic (in shares)	36,711,833	30,734,109
Weighted average common shares outstanding, diluted (in shares)	36,711,833	30,734,109
Net loss per share, basic (in dollars per share)	$ (3.59)	$ (2.81)
Net loss per share, diluted (in dollars per share)	$ (3.59)	$ (2.81)

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Anti-dilutive securities
Pre funded warrants exercised during period	0
Anti-dilutive securities excluded from the calculation of net loss per share	4,058,301	3,737,900
Restricted stock awards
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share		57,969
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	314,901
Stock Options
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	3,743,400	3,679,931

Retirement Plan (Details)

Retirement Plan (Details) - USD ($) $ in Millions	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020
Retirement Plan
Matching contribution 401(k)	50.00%
Matching contribution per employee	6.00%
Employer matching contribution	3.00%
Company contributions		$ 0.7	$ 0.5