Voyager Therapeutics (VYGR) 10-K 8 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 Transition Report	false
Document Period End Date	Dec. 31, 2021
Entity File Number	001-37625
Entity Registrant Name	Voyager Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-3003182
Entity Address, Address Line One	75 Sidney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	857
Local Phone Number	259-5340
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	VYGR
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	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Central Index Key	0001640266
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Public Float			$ 102.8
Entity Common Stock, Shares Outstanding		38,114,680
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	Boston, Massachusetts

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 117,433	$ 104,440
Marketable securities	15,106	76,698
Related party collaboration receivable	732	8,012
Prepaid expenses and other current assets	3,427	8,619
Total current assets	136,698	197,769
Property and equipment, net	21,920	25,435
Deposits and other non-current assets	1,779	2,316
Operating lease, right-of-use assets	33,458	36,064
Total assets	193,855	261,584
Current liabilities:
Accounts payable	574	634
Accrued expenses	10,950	14,205
Other current liabilities	5,571	4,198
Deferred revenue, current	33,886	7,729
Total current liabilities	50,981	26,766
Deferred revenue, non-current	8,210	36,088
Other non-current liabilities	39,609	44,410
Total liabilities	98,800	107,264
Commitments and contingencies (see note 9)
Stockholders' equity:
Preferred stock, $0.001 par value: 5,000,000 shares authorized; no shares issued and outstanding at December 31, 2021 and 2020
Common stock, $0.001 par value: 120,000,000 shares authorized; 37,918,395 and 37,368,027 shares issued and outstanding at December 31, 2021 and 2020, respectively	38	37
Additional paid-in capital	442,259	430,324
Accumulated other comprehensive loss	(138)	(134)
Accumulated deficit	(347,104)	(275,907)
Total stockholders' equity	95,055	154,320
Total liabilities and stockholders' equity	$ 193,855	$ 261,584

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Consolidated Balance Sheets
Preferred Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	37,918,395	37,368,027
Common Stock, Shares, Outstanding	37,918,395	37,368,027

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Consolidated Statements of Operations and Comprehensive Income (Loss)
Collaboration revenue	$ 37,415	$ 171,128	$ 104,391
Operating expenses:
Research and development	73,787	108,753	119,735
General and administrative	37,246	34,991	36,335
Total operating expenses	111,033	143,744	156,070
Operating (loss) income	(73,618)	27,384	(51,679)
Other income (expense), net:
Interest (expense) income	(390)	1,659	6,457
Other income	2,811	7,698	1,625
Total other income, net	2,421	9,357	8,082
Net (loss) income	(71,197)	36,741	(43,597)
Other comprehensive (loss) income
Net unrealized (loss) gain on available-for-sale-securities	(4)	(30)	29
Total other comprehensive (loss) income	(4)	(30)	29
Comprehensive (loss) income	$ (71,201)	$ 36,711	$ (43,568)
Net (loss) income per share, basic	$ (1.89)	$ 0.99	$ (1.21)
Net (loss) income per share, diluted	$ (1.89)	$ 0.98	$ (1.21)
Weighted-average common shares outstanding, basic	37,668,947	37,132,447	35,898,266
Weighted-average common shares outstanding, diluted	37,668,947	37,348,514	35,898,266

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 32	$ 315,598	$ (133)	$ (269,051)	$ 46,446
Shares, Outstanding, Beginning Balance at Dec. 31, 2018	32,364,895
Exercises of vested stock options	$ 1	2,713			2,714
Exercises of vested stock options (in shares)	250,276
Issuance of common stock in connection with Neurocrine Collaboration Agreement	$ 4	77,613			77,617
Issuance of common stock in connection with Neurocrine Collaboration Agreement (in shares)	4,179,728
Issuance of common stock under ESPP		663			663
Issuance of common stock under ESPP (in shares)	70,217
Stock based compensation expense		15,640			15,640
Unrealized gain on available-for-sale securities			29		29
Net (loss) income				(43,597)	(43,597)
Stockholders' Equity, Ending Balance at Dec. 31, 2019	$ 37	412,227	(104)	(312,648)	99,512
Shares, Outstanding, Ending Balance at Dec. 31, 2019	36,865,116
Exercises of vested stock options		2,319			2,319
Exercises of vested stock options (in shares)	228,436
Vesting of restricted stock units (in shares)	170,367
Issuance of common stock under ESPP		1,279			1,279
Issuance of common stock under ESPP (in shares)	104,108
Stock based compensation expense		14,499			14,499
Unrealized gain on available-for-sale securities			(30)		(30)
Net (loss) income				36,741	36,741
Stockholders' Equity, Ending Balance at Dec. 31, 2020	$ 37	430,324	(134)	(275,907)	154,320
Shares, Outstanding, Ending Balance at Dec. 31, 2020	37,368,027
Exercises of vested stock options	$ 1	27			$ 28
Exercises of vested stock options (in shares)	3,811				3,811
Vesting of restricted stock units (in shares)	346,551
Issuance of common stock under ESPP		918			$ 918
Issuance of common stock under ESPP (in shares)	200,006
Stock based compensation expense		10,990			10,990
Unrealized gain on available-for-sale securities			(4)		(4)
Net (loss) income				(71,197)	(71,197)
Stockholders' Equity, Ending Balance at Dec. 31, 2021	$ 38	$ 442,259	$ (138)	$ (347,104)	$ 95,055
Shares, Outstanding, Ending Balance at Dec. 31, 2021	37,918,395

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flow from operating activities
Net (loss) income	$ (71,197)	$ 36,741	$ (43,597)
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Stock-based compensation expense	11,324	14,934	15,640
Depreciation	5,165	3,817	2,765
Amortization of premiums and discounts on marketable securities	349	27	(3,584)
In-kind research and development expenses			616
Change in fair value of common stock and warrants to purchase equity securities	(2,460)	(7,698)	(1,612)
Changes in operating assets and liabilities:
Related party collaboration receivable	7,280	10,484	(18,496)
Prepaid expenses and other assets	1,883	(551)	1,675
Operating lease, right-of-use assets	2,606	(7,592)	2,951
Other non-current assets	69	275	(343)
Accounts payable	(60)	(3,436)	2,598
Accrued expenses	(3,335)	(6,480)	11,728
Operating lease liabilities	(3,428)	13,439	(2,506)
Deferred revenue	(1,721)	(150,676)	80,831
Net cash (used in) provided by operating activities	(53,525)	(96,716)	48,666
Cash flow from investing activities
Purchases of property and equipment	(1,609)	(12,097)	(7,718)
Proceeds from sale of equipment			172
Purchases of marketable securities	(15,117)	(70,403)	(494,231)
Proceeds from sales and maturities of marketable securities	82,632	195,495	411,300
Net cash provided by (used in) investing activities	65,906	112,995	(90,477)
Cash flow from financing activities
Proceeds from the issuance of common stock in connection with the Neurocrine Collaboration Agreement, net			77,617
Proceeds from the exercise of stock options	28	2,319	2,714
Proceeds from the purchase of common stock under ESPP	584	844	663
Net cash provided by financing activities	612	3,163	80,994
Net increase in cash and cash equivalents	12,993	19,442	39,183
Cash, cash equivalents, and restricted cash beginning of period	106,219	86,777	47,594
Cash, cash equivalents, and restricted cash end of period	119,212	106,219	86,777
Supplemental disclosure of cash and non-cash activities
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	664	10,818	30,964
Capital expenditures incurred but not yet paid	$ 80	$ 831	$ 434

Nature of business

Nature of business	12 Months Ended
	Dec. 31, 2021
Nature of business
Nature of business	1. Nature of business Voyager Therapeutics, Inc. (the “Company”) is a gene therapy company focused on developing life-changing treatments and next-generation platform technologies. The Company focuses on diseases where the Company believes a single dose adeno-associated virus (“AAV”) gene therapy approach that either increases or decreases the production of a specific protein can either halt or slow disease progression or reduce symptom severity, therefore providing clinically meaningful impact to patients. The Company’s gene therapy platforms enable it to engineer, optimize, manufacture and deliver its AAV-based gene therapies that the Company believes have the potential to safely provide durable efficacy. The Company’s team of experts in the field of AAV gene therapy first identifies and selects diseases with target tissues that have tropism for AAV gene therapy. The Company then engineers and optimizes AAV vectors for delivery of the virus payload to the targeted tissue or cells. The Company is identifying proprietary AAV capsids, the outer viral protein shells that enclose genetic material of a virus payload. The Company’s team has developed a proprietary AAV capsid discovery paltform called TRACER TM in vivo The Company is also applying the TRACER discovery platform towards further capsid variant libraries and selection for tropism and transduction in additional cell and tissue types. The Company’s quality and manufacturing processes employ an established system capable of enabling production of high quality AAV vectors at scale sufficient for clinical trials. In addition to the Company’s TRACER discovery platform, the Company has developed a vectorized antibody platform which the Company believes will overcome many of the challenges of passive immunization. The Company’s business strategy focuses on discovering, developing, manufacturing and commercializing its gene therapy programs. As part of this strategy, the Company has developed core competencies specific to AAV gene therapy development and manufacturing. This business strategy also includes business development activities that may include in-licensing activities or partnering certain programs in specific geographies with collaborators, as the Company has demonstrated through its ongoing collaboration with Neurocrine Biosciences, Inc. (“Neurocrine”) under a collaboration agreement that became effective in January 2019 (the “Neurocrine Collaboration Agreement”), or out-licensing activities including license agreements related to the TRACER capsids such as the Company’s October 2021 licensing agreement with Pfizer Inc. The Company is devoting substantially all of its efforts to product research and development, market development, and raising capital. The Company is subject to risks common to companies in the biotechnology and gene therapy industries, including but not limited to, the need to obtain sufficient capital to continue to fund its operations, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary information and technology, protection against data breaches and other cybersecurity threats, compliance with government regulations, development by competitors of technological innovations, and ability to transition from pilot-scale manufacturing to large-scale production of products. The Company has a history of incurring net operating losses. As of December 31, 2021, the Company had an accumulated deficit of $347.1 million. The Company has not generated any product revenue and has financed its operations primarily through public offerings and private placements of its equity securities and funding from its prior collaborations with Sanofi Genzyme Corporation (“Sanofi Genzyme”) and AbbVie Biotechnology Ltd and AbbVie Ireland Unlimited Company (collectively, “AbbVie”) and its ongoing collaboration with Neurocrine, in October 2021, its licensing agreement with Pfizer Inc., and in March 2022, its licensing agreement with Novartis Pharma, A.G. (“Novartis”). Based upon its current operating plan, the Company expects that its existing cash, cash equivalents, and marketable securities, including the $54 million payment from Novartis, quirements There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate product revenue or revenue from collaborative partners on terms acceptable to the Company, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition.

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 The following is a summary of significant accounting policies followed in the preparation of these financial statements. Basis of presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Voyager Securities Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement 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 that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in 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. The carrying amounts reflected in the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Marketable Securities The Company classifies marketable securities with a remaining maturity of greater than three months when purchased as available-for-sale. Marketable securities with a remaining maturity date greater than one year and marketable equity securities are classified as non-current where the Company has the intent and ability to hold these securities for at least the next 12 months. During 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. All equity securities in CLPT held by us were sold or otherwise disposed of during the first half of 2021. All available for sale debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (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. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company uses a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. No other than temporary losses have been recognized. Cash, cash equivalents, and marketable securities as of December 31, 2021 and 2020 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2021 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 100,305 ​ ​ — ​ ​ — ​ $ 100,305 ​ Marketable securities - U.S. Treasury notes ​ 15,117 ​ ​ — ​ ​ (11) ​ 15,106 ​ Total money market funds and marketable securities ​ $ 115,422 ​ $ — ​ $ (11) ​ $ 115,411 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 103,992 ​ $ — ​ $ — ​ $ 103,992 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 70,348 ​ ​ — ​ ​ 6 ​ 70,342 ​ Equity securities ​ ​ 1,220 ​ ​ 5,136 ​ ​ — ​ ​ 6,356 ​ Total marketable securities ​ $ 71,568 ​ $ 5,136 ​ $ 6 ​ $ 76,698 ​ Total money market funds and marketable securities ​ $ 175,560 ​ $ 5,136 ​ $ 6 ​ $ 180,690 ​ ​ All of the Company’s marketable securities at December 31, 2021 and 2020 have a contractual maturity of one year or less. Restricted Cash As of December 31, 2021 and 2020, the Company maintained restricted cash totaling approximately $1.8 million in each year, respectively, held in the form of money market accounts as collateral for the Company’s facility lease obligations. The balance is included within deposits in other non-current assets in the accompanying consolidated balance sheets. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of cash flows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 2020 2019 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 117,433 ​ $ 104,440 ​ $ 86,042 ​ Restricted cash included in deposits and other noncurrent assets ​ ​ 1,779 ​ ​ 1,779 ​ ​ 735 ​ Total cash, cash equivalents, and restricted cash ​ $ 119,212 ​ $ 106,219 ​ $ 86,777 ​ ​ Property and Equipment Property and equipment consists of laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred; while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. Impairment of Long-Lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2021. Revenue Recognition The Company enters into license and collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers 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 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. 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. The promised goods or services in the Company’s arrangements typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and 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 its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related 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 collaboration revenues in the period of adjustment. To date, the Company has not recognized any consideration related to the achievement of development, regulatory, or commercial milestone revenue resulting from any of the Company’s collaboration or license arrangements. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration or license arrangements. The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. 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 are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Upfront payments and fees are recorded as contract liabilities within deferred revenue on the consolidated balance sheets until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. Research and Development Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, external research, consultant costs, sponsored research, license fees, process development and facilities costs. Facilities costs primarily include the allocation of rent, utilities and depreciation. Leases Under Accounting Standards Codification (ASC) 842 Leases Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease prepaid or deferred lease payments and are reduced by lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are generally accounted for separately. Non-lease components as it pertains to the Company's leased premises generally refer to common area maintenance charges related to the premises. Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations. Stock-Based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus, blended with the historical volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received, adjusted for actual forfeitures of unvested awards as they occur. The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date. Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2021, the Company does not have any significant uncertain tax positions. Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities. Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net income (loss) per share is computed by dividing the net income (loss) by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. For purposes of the diluted net income (loss) per share, unvested restricted common stock and outstanding stock options are considered to be potentially dilutive securities. Unvested restricted common stock and outstanding stock options were excluded from the calculation of diluted net loss per share in the years ended December 31, 2021 and 2019, because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for the years ended December 31, 2021 and 2019. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ Unvested restricted common stock awards ​ 137,255 ​ 156,863 ​ 176,471 ​ Unvested restricted common stock units ​ ​ 806,379 ​ ​ 527,625 ​ ​ 455,404 ​ Outstanding stock options ​ 5,013,193 ​ 5,379,856 ​ 5,317,326 ​ Total ​ 5,956,827 ​ 6,064,344 ​ 5,949,201 ​ ​ Basic net income (loss) and diluted weighted-average shares outstanding are as follows for the years ended December 31, 2021, 2020, and 2019. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (71,197) ​ $ 36,741 ​ $ (43,597) ​ Denominator for basic net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Denominator for diluted net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Common stock options and restricted stock units ​ ​ — ​ ​ 216,068 ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 37,668,947 ​ ​ 37,348,514 ​ ​ 35,898,266 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Concentrations of Credit Risk and Off-Balance Sheet Risk The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign currency hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash and cash equivalents. The Company’s cash is held in accounts at financial institutions that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. Concentration of Suppliers The Company is dependent on third-party manufacturers to supply certain products for research and development activities in its programs. In particular, the Company relies on a sole manufacturer to supply it with specific vectors related to the Company’s research and development programs. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment, which is the business of developing and commercializing gene therapies. Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Recent Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) adoption is permitted in fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company is assessing the impact of ASU 2020-06 on the consolidated financial statements and does not expect it to have a material impact.

Fair value measurements

Fair value measurements	12 Months Ended
	Dec. 31, 2021
Fair value measurements
Fair value measurements	3. Fair value measurements Assets and liabilities measured at fair value on a recurring basis as of December 31, 2021 and 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices ​ Significant ​ ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ Assets Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) December 31, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 100,305 ​ $ 100,305 ​ $ — ​ $ — ​ Marketable securities - U.S. Treasury notes ​ ​ 15,106 ​ ​ 15,106 ​ ​ — ​ ​ — ​ Total ​ $ 115,411 ​ $ 115,411 ​ $ — ​ $ — ​ December 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 103,992 ​ $ 103,992 ​ $ — ​ $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 70,342 ​ ​ 70,342 ​ ​ — ​ ​ — ​ Equity securities ​ ​ 6,356 ​ ​ 6,356 ​ ​ — ​ ​ — ​ Total marketable securities ​ $ 76,698 ​ $ 76,698 ​ $ — ​ $ — ​ Warrants to purchase equity securities ​ ​ 3,816 ​ ​ — ​ ​ 3,816 ​ ​ — ​ Total ​ $ 184,506 ​ $ 180,690 ​ $ 3,816 ​ $ — ​ ​ The Company measures the fair value of money market funds, U.S. Treasuries and equity securities based on quoted prices in active markets for identical securities. The Level 2 equity securities include warrants to purchase equity securities that are valued using the Black-Scholes model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the awards, (iii) the risk-free interest rate, and (iv) expected dividends. All warrants were exercised, and the shares of common stock received following exercise were subsequently sold by the Company during the three months ended June 30, 2021.

Prepaid expenses and other curr

Prepaid expenses and other current assets	12 Months Ended
	Dec. 31, 2021
Prepaid expense and other current assets
Prepaid expenses and other current assets	4. Prepaid expenses and other current assets Prepaid expenses and other current assets consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2021 2020 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Other current assets ​ $ 1,701 ​ $ 1,575 ​ Prepaid insurance ​ 1,360 ​ 1,459 ​ Prepaid research and development contracts 350 ​ ​ 1,674 ​ Accrued interest receivable ​ ​ 16 ​ ​ 95 ​ Warrants to purchase equity securities ​ ​ — ​ ​ 3,816 ​ Total ​ $ 3,427 ​ $ 8,619 ​ ​

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 Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Laboratory equipment ​ $ 19,384 ​ $ 18,093 ​ Leasehold improvements ​ ​ 15,695 ​ ​ 15,469 ​ Furniture and office equipment ​ ​ 2,524 ​ ​ 2,410 ​ Construction in progress ​ — ​ 866 ​ Other ​ ​ 230 ​ 167 ​ Total property and equipment ​ 37,833 ​ 37,005 ​ Less: accumulated depreciation ​ (15,913) ​ (11,570) ​ Property and equipment, net ​ $ 21,920 ​ $ 25,435 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The Company recorded $5.2 million, $3.8 million, and $2.8 million in depreciation expense during the years ended December 31, 2021, 2020, and 2019, respectively.

Accrued expenses

Accrued expenses	12 Months Ended
	Dec. 31, 2021
Accrued expenses
Accrued expenses	6. Accrued expenses Accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Employee compensation costs ​ $ 5,022 ​ $ 5,857 ​ Research and development costs ​ ​ 3,719 ​ ​ 6,624 ​ Accrued goods and services ​ 1,482 ​ 496 ​ Professional services ​ 727 ​ 1,153 ​ Other ​ ​ — ​ ​ 75 ​ Total ​ $ 10,950 ​ $ 14,205 ​ ​

Lease obligation

Lease obligation	12 Months Ended
	Dec. 31, 2021
Lease obligation
Lease obligation	7. Lease obligation Operating Leases As of December 31, 2021, the Company has leases for office and laboratory space at 75 and 64 Sidney Street in Cambridge, Massachusetts through November 30, 2026. In March 2020, the Company entered into an agreement to lease additional laboratory and office space at 75 Hayden Avenue in Lexington, Massachusetts through January 31, 2031. The Company gained control of and occupied the space in November of 2020. In September 2021, the Company entered into an agreement with BioNTech US, Inc. to sublease part of the office and laboratory space leased by the Company at 75 Sidney Street in Cambridge, Massachusetts (the “Sublease Agreement”). The sublease term is for approximately 3.3 years and the Company expects to receive $9.1 million from the sublessee over the term of the sublease. The sublease did not relieve the Company of its original obligation under the lease, and therefore the Company did not adjust the operating lease right-of-use asset as a result of the sublease and accounted for the sublease as a separate lease. Sublease payments received are classified within operating expenses to offset the related operating lease payments. The Company received leasehold improvement incentives from the landlord totaling $5.3 million for the 75 and 64 Sidney Street leases. The Company also received $5.6 million of leasehold improvement incentives for the 75 Hayden Avenue lease. The leasehold improvements have been capitalized as leasehold improvements and the Company recorded the incentives as a component of its right-of-use assets and is amortizing them as a reduction of lease expense over the life of the lease. The Company’s lease agreements require the Company to maintain a cash deposit or irrevocable letter of credit of $1.8 million payable to the landlord as security for the performance of its obligations under the leases. These amounts are recorded as restricted cash and included in deposits and other non-current assets in the accompanying consolidated balance sheets. The following table summarizes the Company’s significant contractual obligations under operating leases as of payment due date by period at December 31, 2021: ​ ​ ​ ​ ​ ​ Total Minimum ​ Lease Payments ​ ​ (in thousands) ​ 2022 ​ 8,849 ​ 2023 ​ 8,958 ​ 2024 ​ ​ 9,227 ​ 2025 ​ ​ 9,644 ​ 2026 ​ ​ 9,307 ​ Thereafter ​ ​ 10,638 ​ Total future minimum lease payments ​ $ 56,623 ​ Less: imputed interest ​ ​ (12,444) ​ Total lease liabilities ​ $ 44,179 ​ Reported as: ​ ​ ​ ​ Other current liabilities ​ $ 5,571 ​ Other non-current liabilities ​ ​ 38,608 ​ Total lease liabilities ​ $ 44,179 ​ ​ Total lease cost for operating leases of approximately $6.8 million, $6.2 million, and $5.7 million was incurred during the years ended December 31, 2021, 2020 and 2019 respectively. As of December 31, 2021, the weighted average remaining lease term was 6 years and the weighted average incremental borrowing rate used to determine the operating lease liabilities was 7.9%. The following table summarizes the operating sublease income generated under the Sublease Agreement for the years ended December 31, 2021 and 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended ​ ​ December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Operating sublease income $ 838 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​

Other liabilities

Other liabilities	12 Months Ended
	Dec. 31, 2021
Other liabilities
Other liabilities	8. Other liabilities As of December 31, 2021 and 2020, other current and non-current liabilities consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Other current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities ​ 5,571 ​ ​ 4,198 ​ Total other current liabilities $ 5,571 ​ $ 4,198 ​ ​ ​ ​ ​ ​ ​ ​ Other non-current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities $ 38,608 ​ $ 43,409 ​ Other ​ 1,001 ​ ​ 1,001 ​ Total other non-current liabilities $ 39,609 ​ $ 44,410 ​ ​ Strategic Restructuring ​ On August 6, 2021, the board of directors of the Company approved a strategic restructuring plan to eliminate a portion of its workforce as part of an initiative to reduce expenses and enhance operations. The strategic restructuring plan was approved in connection with its portfolio reevaluation efforts and its strategic shift to invest additional resources in the Company’s TRACER capsid development efforts. During the year ended December 31, 2021, the Company incurred restructuring costs of approximately $2.6 million, which consists of severance-related costs. These costs are reported within our research and development expenses, general and administrative expenses, and accrued expenses. Approximately $1.5 million of these restructuring costs were paid as of December 31, 2021.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and contingencies
Commitments and contingencies	9. Commitments and contingencies Significant Agreements Neurocrine Collaboration Agreement Summary of Agreement In March 2019, the Company entered into the Neurocrine Collaboration Agreement for the research, development and commercialization of certain of its AAV gene therapy products. Under the Neurocrine Collaboration Agreement, the Company agreed to collaborate on the conduct of four collaboration programs (the “Neurocrine Programs”) which include: (i) the VY-AADC Program, (ii) the FA Program (collectively, the “Legacy Programs”); and (iii) two programs to be determined by the Company and Neurocrine at a later date (the “Discovery Programs”) In June 2019, in conjunction with the termination of the Sanofi Genzyme Collaboration Agreement, the Company gained ex-U.S. rights to the FA Program . The Company’s ex-U.S. rights to the FA Program were subsequently transferred to Neurocrine under the terms of the Neurocrine Collaboration Agreement. To facilitate the transfer of the ex-U.S. rights to the FA Program to Neurocrine, the Company and Neurocrine executed an amendment to the Neurocrine Collaboration Agreement (the “June 2019 Modification”), and Neurocrine paid $5.0 million to the Company . There were no other changes in pricing or scope of the obligations required to be performed under the Neurocrine Collaboration Agreement In February 2021, Neurocrine notified the Company that it had elected to terminate the Neurocrine Collaboration Agreement solely with regards to the VY-AADC Program, effective August 2, 2021 (the “Neurocrine VY-AADC Program Termination Effective Date”). The Neurocrine Collaboration Agreement remains in full force and effect for each other program thereunder. As a result of the termination, subsequent to the Neurocrine VY-AADC Program Termination Effective Date, Neurocrine is no longer be obligated to reimburse the Company for research and development activities related to the VY-AADC Program. Under the terms of the Neurocrine Collaboration Agreement, the Company originally agreed to collaborate with Neurocrine on, and to grant, exclusive, royalty-bearing, non-transferable, sublicensable licenses to certain of its intellectual property rights, for all human and veterinary diagnostic, prophylactic, and therapeutic uses, for the research, development, and commercialization of gene therapy products (the “Collaboration Products”) on a worldwide basis under (i) the VY-AADC Program; (ii) the FA Program; and (iii) each Discovery Program. As a result of the termination of the Neurocrine Collaboration Agreement with regards to the VY-AADC Program, in accordance with the terms of the Neurocrine Collaboration Agreement, the licenses granted by the Company to Neurocrine regarding the VY-AADC Program have expired, and the Company has regained worldwide intellectual property rights regarding the VY-AADC Program, in each case as of the VY-AADC Termination Effective Date. Pursuant to development plans agreed by the parties, which are overseen by a joint steering committee (“JSC”), the Company has operational responsibility, subject to certain exceptions, for the conduct of each Neurocrine Program prior to the occurrence of a specified event for such Neurocrine Program (a “Transition Event”), as described below, and is required to use commercially reasonable efforts to develop the corresponding Collaboration Products. Neurocrine has agreed to be responsible for all costs incurred by the Company in conducting these activities for each Neurocrine Program, in accordance with an agreed budget for each Neurocrine Program. If the Company breaches its development responsibilities or in certain circumstances upon a change in control, Neurocrine has the right but not the obligation to assume the activities under such Neurocrine Program. U pon the occurrence of a Transition Event for each Neurocrine Program, Neurocrine has agreed to assume responsibility for development, manufacturing and commercialization activities for such Neurocrine Program from the Company and to pay milestones and royalties on future net sales as described further below. As a result of Neurocrine’s termination of the Neurocrine Collaboration Agreement with respect to the VY-AADC Program, the Transition Event with respect to the VY-AADC Program is no longer applicable. The Transition Events for the remaining programs are (i) with respect to the FA Program, the Company’s receipt of topline data for the initial Phase 1 clinical trial for an FA Program product candidate; and (ii) with respect to each Discovery Program, the preparation by the Company and the approval by Neurocrine of an investigational new drug (“IND”) application to be filed with the U.S. Food and Drug Administration (the “FDA”) by Neurocrine for the first development candidate in such Discovery Program. For the FA Program, the Company was granted the option (the “FA Co-Co Option”) to co-develop and co-commercialize the FA Program upon the occurrence of a specified event (a “FA Co-Co Trigger Event”). The Company agreed, upon its exercise of the FA Co-Co Option, to enter into a cost- and profit-sharing arrangement with Neurocrine (the “FA Co-Co Agreement”), and (i) jointly develop and commercialize the Collaboration Products for the FA Program (“FA Collaboration Products”), (ii) share in its costs, profits and losses, and (iii) forfeit certain milestones and royalties on net sales in the United States during the effective period of the FA Co-Co Agreement. The FA Co-Co Trigger Event is the receipt of topline data for the initial Phase 1 clinical trial for an FA Program product candidate. Under the Neurocrine Collaboration Agreement, subject to exceptions specified therein, the Company and Neurocrine agreed that profits and losses under the Company’s FA Co-Co Option would be allocated 60% to Neurocrine and 40% to the Company for any FA Collaboration Product. The parties agreed that FA Co-Co Agreement would provide the Company the right to terminate for any reason upon prior written notice to Neurocrine and Neurocrine the right to terminate in certain circumstances upon change of control. The Company’s research and development activities under the Neurocrine Collaboration Agreement are conducted pursuant to plans agreed to by the parties, on a program-by-program basis, and are overseen by the JSC, as detailed in the Neurocrine Collaboration Agreement. Under the Neurocrine Collaboration Agreement, the parties committed to agree on a list of up to eight target genes (the “Targets”) from which Neurocrine had the right to nominate Targets for the two Discovery Programs. The Company and Neurocrine completed the nomination process, the JSC approved two Targets for development under the Discovery Program, and the two Targets are currently under development. The Neurocrine Collaboration Agreement provides for an upfront non-refundable payment of $115.0 million, as well as for aggregate development and regulatory milestone payments from Neurocrine to the Company for Collaboration Products under (i) the VY-AADC Program of up to $170.0 million, which the Company is no longer eligible to receive in light of the partial termination of the Neurocrine Collaboration Agreement; (ii) the FA Program of up to $195.0 million, and (iii) each of the two Discovery Programs of up to $130.0 million per Discovery Program. The Company may be entitled to receive aggregate commercial milestone payments for each Collaboration Product of up to $275.0 million, subject to an aggregate cap on commercial milestone payments across all Neurocrine Programs of $1.1 billion. Furthermore, in connection with the Neurocrine Collaboration Agreement, Neurocrine purchased 4,179,728 shares of the Company’s common stock at a price of $11.9625 per share, for an aggregate purchase price of $50.0 million. Neurocrine also agreed to pay the Company royalties, based on future net sales of the Collaboration Products. Such royalty percentages, for net sales in and outside the United States, as applicable, range (i) for the VY-AADC Program, from the mid-teens to low thirties and the low-teens to low twenties, respectively; (ii) for the FA Program, from the low-teens to high-teens and high-single digits to mid-teens, respectively; and (iii) for each Discovery Program, from the high-single digits to mid-teens and mid-single digits to low-teens, respectively. On a country-by-country and program-by-program basis, royalty payments would commence on the first commercial sale of a Collaboration Product and terminate on the later of (a) the expiration of the last patent covering the Collaboration Product or its method of use in such country, (b) ten years from the first commercial sale of the Collaboration Product in such country and (c) the expiration of regulatory exclusivity in such country, or the Royalty Term. Royalty payments may be reduced by up to 50% in specified circumstances, including expiration of patents rights related to a Collaboration Product, approval of biosimilar products in a given country or required payment of licensing fees to third parties related to the development and commercialization of any Collaboration Product. As a result of Neurocrine’s termination of the Neurocrine Collaboration Agreement with respect to the VY-AADC Program, the Company is no longer entitled to receive royalties related to the VY-AADC Program. Additionally, the licenses granted to Neurocrine shall automatically convert to fully paid-up, non-royalty bearing, perpetual, irrevocable, exclusive licenses on a country-by-country and product-by-product basis upon the expiration of the Royalty Term applicable to such Collaboration Product in such country. Under the terms of the Neurocrine Collaboration Agreement and subject to specified exceptions therein, each party owns the entire right, title and interest in and to all intellectual property rights made solely by its employees or agents in the course of the collaboration. The parties jointly own all rights, title and interest in and to all intellectual property rights made or invented jointly by employees or agents of both parties. During the term of the Neurocrine Collaboration Agreement, neither party nor any of its respective affiliates is permitted to directly or indirectly exploit any AAV-based gene therapy products directed to a Target to which a Collaboration Product is directed, subject to specified exceptions including the parties’ conduct of basic research activities. Unless earlier terminated, the Neurocrine Collaboration Agreement expires on the later of (i) the expiration of the last to expire royalty term with respect to a Collaboration Product in all countries in the relevant territory or (ii) the expiration or termination of any FA Co-Co Agreement. Neurocrine may terminate the Neurocrine Collaboration Agreement in its entirety or on a program-by-program or country-by-country basis by providing at least (a) 180-day advance notice if such notice is provided prior to the first commercial sale of the Collaboration Product to which the termination applies or (b) one-year advance notice if such notice is provided after the first commercial sale of the Collaboration Product to which the termination applies. The Company may terminate the Neurocrine Collaboration Agreement, subject to specified conditions, if Neurocrine challenges the validity or enforceability of certain of the Company’s intellectual property rights. Subject to a cure period, either party may terminate the Neurocrine Collaboration Agreement in the event of a material breach by the other party in whole or in part, subject to specified conditions. Upon termination in certain cases, Neurocrine has agreed to grant to the Company licenses to certain Neurocrine intellectual property, subject to a negotiation between the parties to establish royalty rates for use of such intellectual property. In the event of a breach by the Company with respect to a Neurocrine Program, if such termination were to occur after a Transition Event, then (i) with respect to the FA Program, if an FA Co-Co Agreement is in effect, Neurocrine can terminate the FA Co-Co Agreement for such program and the Company would no longer have co- development and co-commercialization rights with respect to the FA Collaboration Products and (ii) subject to any license agreements, Neurocrine would no longer have any obligations with respect to any Collaboration Products resulting from such program. Termination of VY-AADC Program As described above, as of the Neurocrine VY-AADC Program Termination Effective Date, the license granted by the Company to Neurocrine thereunder regarding the VY-AADC Program expired, the Company regained worldwide intellectual property rights regarding the VY-AADC Program, and the restrictions on the Company to develop, manufacture or commercialize a gene therapy product directed to the Target of the VY-AADC Program terminated, in each case in accordance with the terms of the Neurocrine Collaboration Agreement. As of the Neurocrine VY-AADC Program Termination Effective Date, Neurocrine no longer is obligated to reimburse the Company for research and development activities related to the VY-AADC Program, and the Company is no longer entitled to receive future milestone or royalty payments related to the VY-AADC Program. Accounting Analysis At inception, the Neurocrine Collaboration Agreement included the following performance obligations: (i) research and development services for each Legacy Program combined with a development and commercialization license for each such program and (ii) research and development services for each Discovery Program combined with a development and commercialization license for each program. The research services and license on a program by program basis are not distinct as Neurocrine cannot benefit from such license on its own or from other resources commonly available in the industry, without the corresponding research services due to the unique and specialized expertise of the Company that is not readily available in the marketplace. The Company identified $92.4 million of fixed transaction price consisting of the $115.0 million upfront fee and $5.0 million payment from the June 2019 Modification, offset by a discount of $27.6 million related to the $50.0 million equity investment of 4,179,728 shares when measured at fair value on the date of issuance. The Company is also entitled to reimbursement of costs incurred by the Company prior to the Transition Events associated with each Neurocrine Program. These amounts are determinable based on program plans and budgets, and the Company has a contractual right to the payment of cost incurred under the agreed upon program plans. The Company utilized the most likely amount approach and estimated the expected cost reimbursement to be $431.1 million at inception. The Company concluded that these amounts do not require a constraint and are included in the transaction price at inception. The Company considers this estimate at each reporting date and updates the estimate based on information available. During the fourth quarter of 2021, the Company further revised the estimate of the expected reimbursement to $80 million based on current expectations as a result of decisions made at the Joint Steering Committee meeting in the fourth quarter of 2021, which resulted in significantly less research and development services to be provided by the Company under the Neurocrine Collaboration Agreement. Additional consideration to be paid to the Company upon reaching certain milestones are excluded from the transaction price at inception due to the uncertainty of achieving the development and regulatory milestones. The Company allocated the fixed transaction price to the separate performance obligations based on the relative standalone selling price of each performance obligation or in the case of certain variable consideration to one or more performance obligations. The estimated standalone selling prices for performance obligations, that include a license and research services, were developed using the estimated selling price of the license, using comparable and market data, and an estimate of the overall effort to perform the research services along with a reasonable profit for research services. The Company has concluded that the variable consideration related to the cost reimbursement of each program will be allocated to each respective program as the cost reimbursement relates specifically to the respective program services being performed under the Neurocrine Collaboration Agreement. The reimbursement of research services is considered to be at a market rate and the allocation of the fixed consideration to all of the performance obligations depicts the estimated amounts in which it would expect to receive for these obligations, absent the variable consideration related to the research reimbursement. The total variable consideration allocated to each program related to the expected cost reimbursement was as follows at December 31, 2021: ​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Variable Consideration ​ ​ ​ VY-AADC Program ​ $ 53,863 ​ FA Program ​ ​ 17,277 ​ Discovery Program 1 ​ ​ 5,432 ​ Discovery Program 2 ​ ​ 3,456 ​ Total ​ $ 80,028 ​ ​ Based on the relative standalone selling price allocation, the allocation of the transaction price, exclusive of the variable consideration allocated to the individual performance obligations, to the separate performance obligations was as follows: ​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Fixed Consideration ​ ​ ​ VY-AADC Program ​ $ 49,045 ​ FA Program ​ ​ 20,647 ​ Discovery Program 1 ​ ​ 14,443 ​ Discovery Program 2 ​ ​ 8,247 ​ Total ​ $ 92,382 ​ ​ The Company recognizes the transaction price associated with each performance obligation on a proportional performance basis over the period of service using input-based measurements such as costs incurred to date, to estimate proportion performed, and remeasures its progress towards completion at the end of each reporting period. The Company determined the partial termination of the Neurocrine Collaboration Agreement with respect to the VY-AADC Program represented a modification of the arrangement under ASC 606 and that the remaining fixed transaction price at the Neurocrine VY-AADC Program Termination Effective Date of $42.2 million should be re-allocated to the FA Program and Discovery Program 1 and 2 based on their standalone selling prices. Accordingly, the Company recorded a cumulative adjustment to revenue of approximately $0.9 million on the partially satisfied remaining performance obligations, as the remaining services to be performed under each of the performance obligations are not distinct from the services prior to the modification. The Company determined that reasonable changes to the Company’s estimates of standalone selling prices for the FA Program, Discovery Program 1 and Discovery Program 2 performance obligations did not have a material impact on the re-allocation or the amount of revenue recorded pursuant to the cumulative catch-up adjustment. During the years ended December 31, 2021 and 2020, the Company recognized $37.4 million and $56.7 million of revenue, respectively, associated with its collaboration with Neurocrine related to research and development services performed during the period and the corresponding cost reimbursement receivable. As of December 31, 2021, there was $12.1 million of deferred revenue related to the Neurocrine Collaboration Agreement, which is classified as either current or non-current in the accompanying consolidated balance sheet based on the period the services are expected to be delivered. Additionally, as of December 31, 2021, there was $0.7 million of collaboration receivables related to reimbursable costs expected to be received from Neurocrine for research and development services performed. The following table presents changes in the balances of the Company’s related party collaboration receivables and contract liabilities during the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ Balance at ​ ​ ​ December 31, 2020 ​ Additions ​ Deductions ​ December 31, 2021 ​ ​ ​ ​ ( in thousands) ​ Related party collaboration receivable ​ $ 8,012 ​ $ 7,034 ​ $ (14,314) ​ $ 732 ​ Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue ​ $ 43,689 ​ $ — ​ $ (31,593) ​ $ 12,096 ​ ​ The change in the receivables balance for the year ended December 31, 2021 is primarily driven by amounts owed to the Company for research and development services provided, offset by amounts collected from Neurocrine during the period. The change in contract liabilities relates to amounts recognized as revenue associated with research and development services performed during the year, including the impact of the change in estimate associated with the remaining research and development services to be performed under the Neurocrine Collaboration Agreement that was recorded in the fourth quarter of 2021. Costs incurred relating to the Collaboration Programs consist of internal and external research and development costs, which primarily include: salaries and benefits, lab supplies, preclinical research studies, clinical studies, consulting services, and commercial development. These costs are included in research and development expenses in the Company’s consolidated statements of operations during the year ended December 31, 2021. The Company incurred approximately $0.8 million of costs to obtain the Neurocrine Collaboration Agreement which were payable only upon the close of the deal and therefore considered incremental costs of obtaining a contract with a customer and capitalized. The costs are recorded in prepaid expenses and other non-current assets and are being amortized over the period in which the research services will be provided. Pfizer Option and License Agreement Summary of Agreement On October 1, 2021, the Company entered into an option and license agreement with Pfizer, which is referred to as the Pfizer License Agreement, pursuant to which the Company has granted Pfizer options to receive an exclusive license, or the License Options, to certain TRACER capsids to develop and commercialize certain AAV gene therapy candidates comprised of a capsid and specified Pfizer transgenes, which are referred to as the Pfizer Transgenes. Under the terms of the Pfizer License Agreement, Pfizer intends to evaluate the potential use of the capsids in combination with up to two Pfizer Transgenes to help treat respective central nervous system and cardiovascular diseases. Under the Pfizer License Agreement, the Company has agreed to provide Pfizer with certain quantities of materials encoding specified existing capsids for Pfizer’s evaluation. During the research term, which extends until October 1, 2022, or, in the event Pfizer exercises a License Option, until October 1, 2024, the Company may, at its sole discretion and expense, conduct additional research activities to identify additional proprietary capsids that may be useful for AAV gene therapies for the treatment of central nervous system or cardiovascular diseases. The Company has agreed to disclose to Pfizer, on a rolling basis, the performance characteristics identified during the research term for all such capsid candidates. Following such disclosure, Pfizer has the right, in its sole discretion, to select any capsid candidate for evaluation to determine its interest in exercising a License Option with respect to such capsid candidate. Pfizer may exercise up to two License Options, provided that it may exercise only one License Option for each Pfizer Transgene. The Company has granted Pfizer, effective upon Pfizer’s exercise of a License Option, with respect to a capsid candidate for the Pfizer Transgene identified therein, an exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property, the rights to develop and commercialize the applicable licensed capsid as incorporated into products containing the corresponding Pfizer Transgene, or the Licensed Products. Additionally, upon such License Option exercise, the Company and Pfizer have agreed that the Company shall provide certain additional know-how that has not been previously provided to Pfizer to enable Pfizer to exploit such licensed capsid and the corresponding Pfizer Transgene for use in a Licensed Product. Upon the exercise of a License Option, until October 1, 2024, while the Company is not obligated to conduct additional research activities upon option exercise to identify additional proprietary capsids that may be useful for AAV gene therapies for the treatment of central nervous system or cardiovascular diseases, it has agreed to continue to disclose to Pfizer, on a rolling basis, the performance characteristics identified for all such capsid candidates, if and when available. Pfizer may, during the research term conduct additional evaluation of such capsid candidates and has the right to substitute any other capsid candidate for the capsid it previously elected to license when it exercised the License Option. Under the Pfizer License Agreement, Pfizer is solely responsible for, and has sole decision-making authority with respect to, development and commercialization of the Licensed Products. In the event Pfizer exercises a License Option, Pfizer is required to use commercially reasonable efforts to develop and obtain regulatory approval for at least one Licensed Product for each Pfizer Transgene for which Pfizer has exercised its License Option in (i) the United States and (ii) at least one of the following countries: the United Kingdom, France, Germany, Italy, Spain and Japan, each of which is referred to as a Major Market Country, subject to certain limitations. Pfizer is also required to use commercially reasonable efforts to commercialize each Licensed Product in the United States and at least one Major Market Country where Pfizer or its designated affiliates or sublicensees has received regulatory approval for such Licensed Product, subject to certain limitations. Under the terms of the Pfizer License Agreement, Pfizer paid the Company an upfront payment of $30.0 million. The Company received this upfront payment in October 2021. Pfizer has also agreed to pay the Company, upon each License Option exercise, a fee of $10.0 million. Following each License Option exercise, with respect to a Pfizer Transgene, the Company is also eligible to receive specified development, regulatory, and commercialization milestone payments of up to an aggregate of $115.0 million for the first corresponding Licensed Product to achieve the corresponding milestone. On a Licensed Product-by-Licensed Product basis, the Company is also eligible to receive (a) specified sales milestone payments of up to an aggregate of $175.0 million per Licensed Product and (b) tiered, escalating royalties in the mid- to high-single-digit percentages of annual net sales of each Licensed Product. The royalties are subject to potential reductions in customary circumstances including patent claim expiration, payments for certain third-party licenses, and biosimilar market penetration, subject to specified limits. Under the terms of the Pfizer License Agreement, each the Company and Pfizer owns the entire right, title, and interest in and to all patents or know-how controlled by such party and existing as of or before the effective date of the Pfizer License Agreement, or invented, developed, created, generated or acquired solely by or on behalf of such party after such effective date. Subject to certain specified exceptions, any patents and know-how that are invented or otherwise developed jointly by or on behalf of the parties during the term of the Pfizer License Agreement and in the course of the Company’s and Pfizer’s activities under the Pfizer License Agreement will follow inventorship under U.S. patent law. Subject to certain limitations and exceptions, the Company agreed (i) during the research term, not to conduct any internal program or program on behalf of a third party that is directed to development or commercialization of any capsid candidates, or grant any third party or affiliate any right or license under the Company’s rights in such capsid candidates to exploit any therapeutic product, in combination with any Pfizer Transgene in any indication for therapeutic, diagnostic and prophylactic human and veterinary use; and (ii) after Pfizer’s exercise of a License Option, not to grant any third party or affiliate any right or license under the Company’s patents to exploit any licensed capsid in combination with any Pfizer Transgene. Unless earlier terminated, the Pfizer License Agreement expires on the earlier to occur of (i) the first anniversary of the effective date of the Pfizer License Agreement, if no License Option is exercised, and (ii) the expiration of the last-to-expire royalty term with respect to all Licensed Products in all countries if at least one License Option is exercised. Subject to a cure period, either party may terminate the Pfizer License Agreement, in whole or in part, subject to specified conditions, in the event of the other party’s uncured material breach. Pfizer may also terminate the Pfizer License Agreement, in whole or in part, subject to specified conditions, for the Company’s insolvency, the occurrence of a violation of global trade control laws, or for the Company’s noncompliance with certain anti-bribery or anti-corruption covenants. Pfizer may also terminate the Pfizer License Agreement, in whole or in part, for any or no reason upon ninety days ’ written notice to us. Upon certain terminations for cause by Pfizer, the licenses that the Company has granted to Pfizer under the Pfizer License Agreement shall become irrevocable and perpetual, and all milestone payments and royalties that would have otherwise been payable by Pfizer under such licenses had the Pfizer License Agreement remained in effect would be substantially reduced. Accounting Analysis The Company assessed the promised goods and services under the Pfizer License Agreement, in accordance with ASC 606, and determined that the Pfizer License Agreement contains two performance obligations consisting of two material rights, one for each of the License Options. The Company concluded that each License Option provides a material right as consideration for each option is less than the amount that the Company would otherwise have expected to receive outside the context of the contract. The promises at inception do not include the underlying goods or services that would be delivered upon exercise of the option, but rather represent the value to the customer of having the right to exercise the License Option at the specified exercise fee. Upon the exercise of a License Option, until October 1, 2024, while the Company is not obligated to conduct additional research activities upon option exercise to identify additional proprietary capsids that may be useful for AAV gene therapies for the treatment of central nervous system or cardiovascular diseases, it has agreed to continue to disclose to Pfizer, on a rolling basis, the performance characteristics identified for all such capsid candidates, if and when available. Pfizer may, conduct additional evaluation of such capsid candidates and has the right to substitute any other capsid candidate for the capsid it previously elected to license when it exercised the License Option. The Company received a nonrefundable, upfront payment of $30.0 million as consideration under the Pfizer License Agreement, which represents the transaction price at inception. Additional consideration to be paid to the Company upon exercise of the License Options or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that could only be achieved subsequent to an option exercise. The Company allocated the transaction price to the two material rights based on their relative standalone selling prices. The estimated standalone selling price for each material right was based on an adjusted market assessment approach. The Company concluded that the market would be willing to pay an equal amount for each License Option on a standalone basis. The Company reached this conclusion after considering (i) the downstream economics including option fees, milestones and royalties related to each License Option being identical, and (ii) comparable market data. The Company determined the standalone selling price for t

Common stock

Common stock	12 Months Ended
	Dec. 31, 2021
Common stock.
Common stock	10. Common stock As of December 31, 2021 and 2020, the Company had authorized 120,000,000 shares of common stock, at $0.001 par value per share. General The voting, dividend and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers and preferences of the holders of preferred stock. The common stock has the following characteristics: Voting The holders of shares of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders and written actions in lieu of meetings. Dividends The holders of shares of common stock are entitled to receive dividends, if and when declared by the Board of Directors. No dividends have been declared or paid by the Company since its inception. Liquidation The holders of shares of common stock are entitled to share ratably in the Company’s remaining assets available for distribution to its stockholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon occurrence of a deemed liquidation event. Shares Reserved For Future Issuance ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 Shares reserved for vesting of restricted stock awards under the Founder Agreements 137,255 ​ 156,863 ​ Shares reserved for exercise of outstanding stock options 5,013,193 ​ 5,485,078 Shares reserved for vesting of outstanding restricted stock units 806,379 ​ 638,471 Shares reserved for issuances under the 2015 Stock Option Plan ​ 4,374,539 ​ 2,827,185 ​ Shares reserved for issuances under the 2015 Employee Stock Purchase Plan ​ 1,659,574 ​ 1,484,923 ​ ​ 11,990,940 ​ 10,592,520 ​

Stock-based compensation

Stock-based compensation	12 Months Ended
	Dec. 31, 2021
Stock-based compensation
Stock-based compensation	11. Stock-based compensation 2014 Stock Option and Grant Plan In January 2014, the Company adopted the 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it could grant incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of common stock to employees, officers, directors and consultants of the Company. The terms of stock option agreements, including vesting requirements, were determined by the Board of Directors and were subject to the provisions of the 2014 Plan. Restricted stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Stock options granted to employees generally vest over four years, with 25% vesting on the one year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Stock options granted to non-employee consultants generally vest monthly over a period of one Founder Awards In January 2014, the Company issued 1,188,233 shares of restricted stock to its founders (each, a “Founder”) at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the Founders, 835,292 shares generally vest over one to four years , based on each Founder’s continued service to the Company in varying capacity as a Scientific Advisory Board member, consultant, director, officer or employee, as set forth in each grantee’s individual restricted stock purchase agreement. The remaining 352,941 of the shares issued begin vesting upon the achievement of certain performance objectives as well as continued service to the Company, as set forth in the agreements. These performance conditions are tied to certain milestone events specific to the Company’s corporate goals, including but not limited to preclinical and clinical development milestones related to the Company’s product candidates. Stock-based compensation expense associated with these performance-based awards is recognized when the achievement of the performance condition is considered probable, using management’s best estimates. The performance milestone for one of the three performance-based awards has been met related to this award. In December 2019, the Company modified one of the remaining performance awards, repurchasing 58,823 shares of common stock previously issued to one of the Company’s founders. Additionally, the Company modified the award to vest solely based on time rather than on performance. The Company revalued the award at the modification date and is recognizing expense on a straight-line basis over the three 2015 Stock Option Plan In October 2015, the Company s board of directors and stockholders The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (i) 1,311,812 shares of common stock and (ii) the number of shares under the 2014 Plan that are not needed to fulfill the Company s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company s issued and outstanding shares of common stock on the immediately preceding December 31. Effective January 1, 2016 and every anniversary thereafter an additional 4% of outstanding common stock was added to the Company’s 2015 Stock Option Plan pursuant to its “evergreen” provision, for future issuance. This has accumulated to a total of 9,226,183 shares through January 1, 2022. During the year ended December 31, 2021, the Company granted options to purchase 1,441,729 shares of common stock to employees and directors under the 2015 Stock Option Plan. As of December 31, 2021, there were 4,374,539 shares available for future issuance under the 2015 Stock Option Plan. 2015 Employee Stock Purchase Plan In October 2015, the Company’s board of directors and stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). Under the 2015 ESPP, all full-time employees of the Company are eligible to purchase common stock of the Company twice per year, at the end of each six-month payment period. During each payment period, eligible employees who so elect, may authorize payroll deductions in an amount of 1% to 10% (whole percentages only) of the employee’s base pay for each payroll period. At the end of each payment period, the accumulated deductions are used to purchase shares of common stock from the Company at a discount. A total of 262,362 shares of common stock were initially authorized for issuance under this plan. The 2015 ESPP became effective upon the completion of the IPO. Effective January 1, 2016 and every anniversary thereafter an additional 1% of outstanding common stock was added to the 2015 ESPP, pursuant to its evergreen provision, for future issuance . This has accumulated to a total of 2,306,542 shares through January 1, 2022. The Company issued 200,006 and 104,108 shares of common stock under the 2015 ESPP in the years ended December 31, 2021 and 2020. As of December 31, 2021, there were 1,659,574 shares available for future purchase under the 2015 ESPP. Inducement Awards In the years ended December 31, 2021, 2020, and 2019, the Company issued non-statutory stock options to purchase an aggregate of 76,500, 172,500 and 338,750 shares of the Company’s common stock and restricted stock unit awards for an aggregate of 13,000, 29,000 and 58,125 shares of the Company’s common stock, respectively, in each case outside of the Company’s 2015 Stock Option Plan as an inducement material to certain individuals’ acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). The stock options will vest over a four-year period, with 25% of the shares underlying the option award vesting on the first anniversary of the award and the remaining 75% of the shares underlying the award vesting monthly thereafter over the subsequent 36-month period. The restricted stock units vest over a three-year period, with 33% of the restricted stock units vesting on the first anniversary of the award, 33% of the restricted stock units vesting on the second anniversary, and the remaining restricted stock units vesting on the third anniversary. Stock-based Compensation Expense Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive income (loss) is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2021 2020 2019 ​ ​ (in thousands) General and administrative ​ $ 7,191 ​ $ 8,577 ​ $ 8,257 ​ Research and development ​ 4,133 ​ 6,357 ​ 7,383 ​ Total stock-based compensation expense ​ $ 11,324 ​ $ 14,934 ​ $ 15,640 ​ ​ Stock-based compensation expense by type of award included within the consolidated statements of operations and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ ​ 2021 2020 2019 ​ ​ ​ (in thousands) ​ Stock options ​ $ 7,438 ​ $ 11,387 ​ $ 13,380 ​ Restricted stock awards and units ​ ​ 3,551 ​ ​ 3,110 ​ ​ 1,935 ​ Employee stock purchase plan awards ​ 335 ​ 437 ​ 325 ​ Total stock-based compensation expense ​ $ 11,324 ​ $ 14,934 ​ $ 15,640 ​ ​ In June 2019, the Company entered into a consulting agreement (the “Sah Agreement”) with Dr. Dinah Sah, Ph.D., the Company’s former Chief Scientific Officer, pursuant to which Dr. Sah has agreed to provide consulting and advisory services, including but not limited to scientific guidance in connection with certain of the Company’s collaborations and research and development programs for a three-year period which commenced on June 28, 2019. In accordance with its terms, the Sah Agreement triggered an equity modification resulting in the recognition in 2019 of $2.2 million of stock-based compensation expense related to the non-substantive service period of the Sah Agreement. Restricted Stock Units A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the year ended December 31, 2021 was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Grant Date ​ ​ ​ ​ ​ Fair Value ​ ​ ​ Units Per Unit ​ Unvested restricted stock units as of December 31, 2020 ​ 638,471 ​ $ 12.74 ​ Awarded ​ 1,268,301 ​ $ 5.30 ​ Vested ​ (326,943) ​ $ 12.25 ​ Forfeited ​ (773,450) ​ $ 8.93 ​ Unvested restricted stock units as of December 31, 2021 ​ 806,379 ​ $ 7.26 ​ ​ Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and recognized over the vesting period. In the year ended December 31, 2021, the Company granted 538,301 restricted stock units vesting in equal amounts, annually over three years, and 730,000 restricted stock units vesting in equal amounts, annually over two years. The stock-based compensation expense related to awards granted to employees was $3.3 million, $2.8 million, and $1.9 million for the years ended December 31, 2021, 2020, and 2019, respectively. As of December 31, 2021, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $3.5 million which is expected to be recognized over the remaining weighted average vesting period of 1.4 years Stock Options A summary of the status of, and changes in, stock options was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Remaining Aggregate ​ ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ ​ ​ ​ Exercise ​ Life ​ Value ​ ​ Shares Price (in years) (in thousands) ​ Outstanding at December 31, 2020 5,485,078 ​ $ 14.77 ​ ​ ​ ​ ​ Granted ​ 1,518,229 ​ $ 6.32 ​ ​ ​ ​ ​ ​ Exercised ​ (3,811) ​ $ 7.27 ​ ​ ​ ​ ​ ​ Cancelled or forfeited ​ (1,986,303) ​ $ 13.58 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2021 ​ 5,013,193 ​ $ 12.69 ​ 5.6 ​ $ 1,165 ​ Exercisable at December 31, 2021 3,611,863 ​ $ 14.16 4.5 ​ $ — ​ ​ Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the year ended December 31, 2021 was $4.11. The stock-based compensation expense related to stock option awards granted to employees and directors was $7.3 million, $11.2 million, and $13.3 million for the years ended December 31, 2021, 2020, and 2019, respectively. The fair value of each option was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2021 2020 2019 ​ Risk-free interest rate 0.9 % 1.0 % ​ 2.2 % ​ Expected dividend yield — % — % ​ — % ​ Expected term (in years) 6.0 ​ 6.0 ​ ​ 6.0 ​ ​ Expected volatility 75.0 % 73.7 % ​ 74.7 % ​ ​ As of December 31, 2021, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $7.3 million which is expected to be recognized over the remaining weighted average vesting period of 2.3 years.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2021
401(k) Savings Plan
401(k) Savings Plan	12. 401(k) Savings plan The Company has a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. The Company expensed approximately $1.1 million, $1.1 million, and $1.0 million related to employer contributions made during the years ended December 31, 2021, 2020, and 2019, respectively.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2021
Income taxes
Income taxes	13. Income taxes The Company recognized deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on differences between the financial statement carrying amounts and the tax bases of the assets and liabilities using the enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all the deferred tax assets will not be realized. The Company accounts for uncertain tax positions using a more-likely-than-not threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity, and changes in facts or circumstances related to a tax position. The Company evaluates its tax positions on an annual basis. The benefit for incomes taxes is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2021 ​ 2020 ​ 2019 ​ (in thousands) ​ ​ ​ Current ​ ​ ​ ​ ​ ​ ​ ​ Federal $ — ​ $ — ​ $ — State ​ — ​ ​ — ​ ​ — Total current ​ — ​ ​ — ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ — ​ ​ — ​ ​ — State ​ — ​ ​ — ​ ​ — Total deferred ​ — ​ ​ — ​ ​ — Total tax expense $ — ​ $ — ​ $ — ​ A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate at the Company’s effective tax rate for the years ended December 31, 2021, 2020, and 2019 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2021 ​ 2020 ​ 2019 ​ Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 21.0 % ​ State taxes, net of federal benefit ​ 6.6 % ​ (2.3) % ​ 8.0 % ​ Provision to return ​ 4.9 % ​ — % ​ — % ​ General business credit carryovers ​ 3.2 % ​ (20.6) % ​ 9.4 % ​ Non-deductible expenses ​ (3.8) % ​ 5.0 % ​ (2.2) % ​ Other ​ — % ​ 1.9 % ​ — % ​ Change in valuation allowance ​ (31.9) % ​ (5.0) % ​ (36.2) % ​ Total ​ — % ​ — % ​ — % ​ ​ The Company incurred net operating losses (“NOLs”) through December 31, 2019 and during 2021. During 2020, the Company did not generate federal and state NOL carryforwards. As of December 31, 2021, the Company had federal and state net operating loss carryforwards of $210.8 million and $198.9 million, respectively, with the pre-2018 NOLs beginning to expire in 2033, and the post 2019 portion limited to 80% of taxable income and carried forward indefinitely As of December 31, 2021, the Company had federal and state research and development tax credit carryforwards of $22.6 million and $9.0 million, respectively, which expire beginning in 2033. As of December 31, 2021, the Company had state investment credits of $0.6 million, which expire beginning in 2022. Under the provisions of the Internal Revenue Code, certain substantial changes in the Company’s ownership may result in a limitation on the amount of NOL carryforwards and research and development credit carryforwards that may be utilized annually to offset future taxable income and taxes payable. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of 5% stockholders or public groups in the stock of a corporation by more than 50 percent in the aggregate over a three-year period. During 2016, the Company completed a study through June 30, 2016, to determine whether any ownership change had occurred since the Company’s formation and determined that its transactions had resulted in three ownership changes, as defined by Section 382. Additionally, in the first quarter of the 2020 calendar year, and in the first quarter of the 2021 calendar year, the Company completed additional studies that did not identify additional ownership changes. There could be additional ownership changes in the future that could further limit the amount of NOLs and tax credit carryforwards that the Company can utilize. The significant components of the Company’s deferred tax assets and (liabilities) as of December 31, 2021 and 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 ​ 2020 ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards $ 56,756 ​ $ 41,130 ​ Tax credit carryforwards 30,122 ​ 28,173 ​ Lease liability ​ 12,012 ​ ​ 13,006 ​ Deferred revenue ​ 11,485 ​ ​ 12,176 ​ Stock compensation ​ 7,784 ​ ​ 4,368 ​ Non-deductible accruals and reserves 1,507 ​ 1,288 ​ Intangibles 664 ​ 721 ​ Total deferred tax assets 120,330 ​ 100,862 ​ Less valuation allowance (107,563) ​ (84,866) ​ Net deferred tax assets 12,767 ​ 15,996 ​ Deferred tax liabilities ​ ​ ​ ​ ​ Right of use assets ​ (9,128) ​ (9,852) ​ Depreciation and amortization ​ (3,632) ​ ​ (6,136) ​ Other temporary differences ​ (7) ​ ​ (8) ​ Net deferred taxes $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ As required by ASC 740, management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which principally comprise NOL carryforwards, research and development credit carryforwards, and lease liability. Management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $107.6 million and $84.9 million has been established at December 31, 2021 and 2020, respectively. The change in valuation allowance was $22.7 million for the year ended December 31, 2021. The primary reason for the difference between the income tax expense recorded by the Company and the amount of income tax expense at statutory income tax rates was the change in the valuation allowance. At December 31, 2021 and 2020, the Company had no unrecognized tax benefits. The Company has not as yet conducted a study of its research and development credit carryforwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheets or statements of operations if an adjustment were required. Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statements of operations. As of December 31, 2021 and 2020, the Company has no accrued interest related to uncertain tax positions. Since the Company is in a loss carryforward position, it is generally subject to examination by the U.S. federal, state, and local income tax authorities for all tax years in which a loss carryforward is available.

Related party transactions

Related party transactions	12 Months Ended
	Dec. 31, 2021
Related party transactions
Related party transactions	14. Related-party transactions During the years ended December 31, 2021, 2020, and 2019, the Company received board and scientific advisory services from two of its prior executives, Steven M. Paul, M.D., the Company’s former President and Chief Executive Officer, and Dinah Sah, Ph.D., the Company’s former Chief Scientific Officer. As of December 31, 2020, Dr. Paul’s consulting agreement was complete. The total amount of fees paid to Dr. Paul for services provided during the years ended December 31, 2020 and 2019 was $0.2 million in each year. The total amount of fees paid to Dr. Sah for services provided during the years ended December 31, 2021, December 31, 2020 and December 31, 2019 was $0.2 million, $0.4 million, and $0.4 million, respectively. Amounts due from Neurocrine are reflected as related party collaboration receivables. The Company recorded approximately $0.7 million and $8.0 million in related party collaboration receivables associated with Neurocrine as of December 31, 2021 and 2020, respectively.

Subsequent event

Subsequent event	12 Months Ended
	Dec. 31, 2021
Subsequent event
Subsequent event	15. Subsequent event In March 2022, the Company entered into an option and license agreement (the “Novartis License Agreement”) with Novartis Pharma, AG (“Novartis”). Pursuant to the Novartis License Agreement, the Company granted Novartis options (the “Novartis License Options”) to license novel capsids generated from the Company’s TRACER™ discovery platform (the “Novartis Licensed Capsids”) on a target-exclusive basis to develop and commercialize certain adeno-associated virus gene therapy candidates comprised of a Novartis Licensed Capsid and a specified DNA sequence provided by Novartis (the “Novartis Payload”). Under the terms of the Novartis License Agreement, Novartis intends to evaluate the potential use of the Novartis Licensed Capsids in combination with Novartis Payloads to target three specified genes and, upon the payment of additional fees on a target-by-target basis, up to two other gene targets (the “Additional Novartis Targets”). Under the terms of the Novartis License Agreement, Novartis has agreed to pay the Company an upfront payment of $54 million. Novartis has also agreed to pay the Company a fee of $18 million per Additional Novartis Target it elects to add to the collaboration and, upon each exercise of a Novartis License Option, an option exercise fee of $12.5 million. Following each exercise of a Novartis License Option, the Company is also eligible to receive specified development, regulatory, and commercialization milestone payments of up to an aggregate of $125 million for the first corresponding licensed product under the Novartis License Agreement to achieve the corresponding milestone. On a Novartis licensed product-by-Novartis licensed product basis, the Company is also eligible to receive (a) specified sales milestone payments of up to an aggregate of $175 million per Novartis licensed product and (b) tiered, escalating royalties in the mid- to high-single-digit percentages of annual net sales of each Novartis licensed product. The royalties are subject to potential reductions in customary circumstances including patent claim expiration, payments for certain third-party licenses, and biosimilar market penetration, subject to specified limits.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2021
Summary of significant accounting policies
Basis of Presentation	Basis of presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Voyager Securities Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement 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 that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in 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. The carrying amounts reflected in the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds.
Marketable Securities	Marketable Securities The Company classifies marketable securities with a remaining maturity of greater than three months when purchased as available-for-sale. Marketable securities with a remaining maturity date greater than one year and marketable equity securities are classified as non-current where the Company has the intent and ability to hold these securities for at least the next 12 months. During 2016, the Company invested in a supplier and received common stock and warrants to purchase common stock in that entity. All equity securities in CLPT held by us were sold or otherwise disposed of during the first half of 2021. All available for sale debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (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. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company uses a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. No other than temporary losses have been recognized. Cash, cash equivalents, and marketable securities as of December 31, 2021 and 2020 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2021 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 100,305 ​ ​ — ​ ​ — ​ $ 100,305 ​ Marketable securities - U.S. Treasury notes ​ 15,117 ​ ​ — ​ ​ (11) ​ 15,106 ​ Total money market funds and marketable securities ​ $ 115,422 ​ $ — ​ $ (11) ​ $ 115,411 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 103,992 ​ $ — ​ $ — ​ $ 103,992 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 70,348 ​ ​ — ​ ​ 6 ​ 70,342 ​ Equity securities ​ ​ 1,220 ​ ​ 5,136 ​ ​ — ​ ​ 6,356 ​ Total marketable securities ​ $ 71,568 ​ $ 5,136 ​ $ 6 ​ $ 76,698 ​ Total money market funds and marketable securities ​ $ 175,560 ​ $ 5,136 ​ $ 6 ​ $ 180,690 ​ ​ All of the Company’s marketable securities at December 31, 2021 and 2020 have a contractual maturity of one year or less.
Restricted Cash	Restricted Cash As of December 31, 2021 and 2020, the Company maintained restricted cash totaling approximately $1.8 million in each year, respectively, held in the form of money market accounts as collateral for the Company’s facility lease obligations. The balance is included within deposits in other non-current assets in the accompanying consolidated balance sheets. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of cash flows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 2020 2019 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 117,433 ​ $ 104,440 ​ $ 86,042 ​ Restricted cash included in deposits and other noncurrent assets ​ ​ 1,779 ​ ​ 1,779 ​ ​ 735 ​ Total cash, cash equivalents, and restricted cash ​ $ 119,212 ​ $ 106,219 ​ $ 86,777 ​ ​
Property and Equipment	Property and Equipment Property and equipment consists of laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred; while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2021.
Revenue Recognition	Revenue Recognition The Company enters into license and collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers 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 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. 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. The promised goods or services in the Company’s arrangements typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and 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 its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related 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 collaboration revenues in the period of adjustment. To date, the Company has not recognized any consideration related to the achievement of development, regulatory, or commercial milestone revenue resulting from any of the Company’s collaboration or license arrangements. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration or license arrangements. The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. 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 are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Upfront payments and fees are recorded as contract liabilities within deferred revenue on the consolidated balance sheets until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.
Research and Development	Research and Development Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, external research, consultant costs, sponsored research, license fees, process development and facilities costs. Facilities costs primarily include the allocation of rent, utilities and depreciation.
Leases	Leases Under Accounting Standards Codification (ASC) 842 Leases Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease prepaid or deferred lease payments and are reduced by lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. The Company has lease agreements with lease and non-lease components, which are generally accounted for separately. Non-lease components as it pertains to the Company's leased premises generally refer to common area maintenance charges related to the premises.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations.
Stock-based Compensation Expense	Stock-Based Compensation Expense The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (i) the expected stock price volatility, (ii) the calculation of expected term of the award, (iii) the risk-free interest rate and (iv) expected dividends. Due to a lack of company-specific historical and implied volatility data, the Company bases the estimate of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus, blended with the historical volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received, adjusted for actual forfeitures of unvested awards as they occur. The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2021, the Company does not have any significant uncertain tax positions.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net income (loss) per share is computed by dividing the net income (loss) by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. For purposes of the diluted net income (loss) per share, unvested restricted common stock and outstanding stock options are considered to be potentially dilutive securities. Unvested restricted common stock and outstanding stock options were excluded from the calculation of diluted net loss per share in the years ended December 31, 2021 and 2019, because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for the years ended December 31, 2021 and 2019. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ Unvested restricted common stock awards ​ 137,255 ​ 156,863 ​ 176,471 ​ Unvested restricted common stock units ​ ​ 806,379 ​ ​ 527,625 ​ ​ 455,404 ​ Outstanding stock options ​ 5,013,193 ​ 5,379,856 ​ 5,317,326 ​ Total ​ 5,956,827 ​ 6,064,344 ​ 5,949,201 ​ ​ Basic net income (loss) and diluted weighted-average shares outstanding are as follows for the years ended December 31, 2021, 2020, and 2019. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (71,197) ​ $ 36,741 ​ $ (43,597) ​ Denominator for basic net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Denominator for diluted net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Common stock options and restricted stock units ​ ​ — ​ ​ 216,068 ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 37,668,947 ​ ​ 37,348,514 ​ ​ 35,898,266 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Concentrations of Credit Risk and Off Balance Sheet Risk & Concentration of Suppliers	Concentrations of Credit Risk and Off-Balance Sheet Risk The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign currency hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash and cash equivalents. The Company’s cash is held in accounts at financial institutions that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. Concentration of Suppliers The Company is dependent on third-party manufacturers to supply certain products for research and development activities in its programs. In particular, the Company relies on a sole manufacturer to supply it with specific vectors related to the Company’s research and development programs.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment, which is the business of developing and commercializing gene therapies.
Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Recent Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) adoption is permitted in fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company is assessing the impact of ASU 2020-06 on the consolidated financial statements and does not expect it to have a material impact.

Summary of significant accoun_3

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of significant accounting policies
Schedule of money market funds and marketable securities	Cash, cash equivalents, and marketable securities as of December 31, 2021 and 2020 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2021 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 100,305 ​ ​ — ​ ​ — ​ $ 100,305 ​ Marketable securities - U.S. Treasury notes ​ 15,117 ​ ​ — ​ ​ (11) ​ 15,106 ​ Total money market funds and marketable securities ​ $ 115,422 ​ $ — ​ $ (11) ​ $ 115,411 ​ As of December 31, 2020 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 103,992 ​ $ — ​ $ — ​ $ 103,992 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 70,348 ​ ​ — ​ ​ 6 ​ 70,342 ​ Equity securities ​ ​ 1,220 ​ ​ 5,136 ​ ​ — ​ ​ 6,356 ​ Total marketable securities ​ $ 71,568 ​ $ 5,136 ​ $ 6 ​ $ 76,698 ​ Total money market funds and marketable securities ​ $ 175,560 ​ $ 5,136 ​ $ 6 ​ $ 180,690 ​
Reconciliation of cash, cash equivalents, and restricted cash	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 2020 2019 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 117,433 ​ $ 104,440 ​ $ 86,042 ​ Restricted cash included in deposits and other noncurrent assets ​ ​ 1,779 ​ ​ 1,779 ​ ​ 735 ​ Total cash, cash equivalents, and restricted cash ​ $ 119,212 ​ $ 106,219 ​ $ 86,777 ​
Outstanding potentially dilutive securities excluded in the calculation of diluted net loss per share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ Unvested restricted common stock awards ​ 137,255 ​ 156,863 ​ 176,471 ​ Unvested restricted common stock units ​ ​ 806,379 ​ ​ 527,625 ​ ​ 455,404 ​ Outstanding stock options ​ 5,013,193 ​ 5,379,856 ​ 5,317,326 ​ Total ​ 5,956,827 ​ 6,064,344 ​ 5,949,201 ​ ​
Schedule of weighted average number of shares, basic and diluted	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2021 ​ 2020 ​ 2019 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (71,197) ​ $ 36,741 ​ $ (43,597) ​ Denominator for basic net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Denominator for diluted net (loss) income per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 37,668,947 ​ ​ 37,132,447 ​ ​ 35,898,266 ​ Common stock options and restricted stock units ​ ​ — ​ ​ 216,068 ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 37,668,947 ​ ​ 37,348,514 ​ ​ 35,898,266 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fair value measurements (Tables

Fair value measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair value measurements
Assets and liabilities measured at fair value on a recurring basis	Assets and liabilities measured at fair value on a recurring basis as of December 31, 2021 and 2020 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices ​ Significant ​ ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ Assets Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) December 31, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 100,305 ​ $ 100,305 ​ $ — ​ $ — ​ Marketable securities - U.S. Treasury notes ​ ​ 15,106 ​ ​ 15,106 ​ ​ — ​ ​ — ​ Total ​ $ 115,411 ​ $ 115,411 ​ $ — ​ $ — ​ December 31, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 103,992 ​ $ 103,992 ​ $ — ​ $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 70,342 ​ ​ 70,342 ​ ​ — ​ ​ — ​ Equity securities ​ ​ 6,356 ​ ​ 6,356 ​ ​ — ​ ​ — ​ Total marketable securities ​ $ 76,698 ​ $ 76,698 ​ $ — ​ $ — ​ Warrants to purchase equity securities ​ ​ 3,816 ​ ​ — ​ ​ 3,816 ​ ​ — ​ Total ​ $ 184,506 ​ $ 180,690 ​ $ 3,816 ​ $ — ​

Prepaid expenses and other cu_2

Prepaid expenses and other current assets (Tables)	12 Months Ended
	Dec. 31, 2021
Prepaid expense and other current assets
Schedule of prepaid expense and other current assets	Prepaid expenses and other current assets consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2021 2020 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Other current assets ​ $ 1,701 ​ $ 1,575 ​ Prepaid insurance ​ 1,360 ​ 1,459 ​ Prepaid research and development contracts 350 ​ ​ 1,674 ​ Accrued interest receivable ​ ​ 16 ​ ​ 95 ​ Warrants to purchase equity securities ​ ​ — ​ ​ 3,816 ​ Total ​ $ 3,427 ​ $ 8,619 ​

Property and equipment, net (Ta

Property and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2021
Property and equipment, net
Schedule of property and equipment, net	Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Laboratory equipment ​ $ 19,384 ​ $ 18,093 ​ Leasehold improvements ​ ​ 15,695 ​ ​ 15,469 ​ Furniture and office equipment ​ ​ 2,524 ​ ​ 2,410 ​ Construction in progress ​ — ​ 866 ​ Other ​ ​ 230 ​ 167 ​ Total property and equipment ​ 37,833 ​ 37,005 ​ Less: accumulated depreciation ​ (15,913) ​ (11,570) ​ Property and equipment, net ​ $ 21,920 ​ $ 25,435 ​ ​ ​ ​ ​ ​ ​ ​ ​

Accrued expenses (Tables)

Accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2021
Accrued expenses
Schedule of accrued expenses	Accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Employee compensation costs ​ $ 5,022 ​ $ 5,857 ​ Research and development costs ​ ​ 3,719 ​ ​ 6,624 ​ Accrued goods and services ​ 1,482 ​ 496 ​ Professional services ​ 727 ​ 1,153 ​ Other ​ ​ — ​ ​ 75 ​ Total ​ $ 10,950 ​ $ 14,205 ​

Lease obligation (Tables)

Lease obligation (Tables)	12 Months Ended
	Dec. 31, 2021
Lease obligation
Summary of significant contractual obligations under operating leases	The following table summarizes the Company’s significant contractual obligations under operating leases as of payment due date by period at December 31, 2021: ​ ​ ​ ​ ​ ​ Total Minimum ​ Lease Payments ​ ​ (in thousands) ​ 2022 ​ 8,849 ​ 2023 ​ 8,958 ​ 2024 ​ ​ 9,227 ​ 2025 ​ ​ 9,644 ​ 2026 ​ ​ 9,307 ​ Thereafter ​ ​ 10,638 ​ Total future minimum lease payments ​ $ 56,623 ​ Less: imputed interest ​ ​ (12,444) ​ Total lease liabilities ​ $ 44,179 ​ Reported as: ​ ​ ​ ​ Other current liabilities ​ $ 5,571 ​ Other non-current liabilities ​ ​ 38,608 ​ Total lease liabilities ​ $ 44,179 ​
Summary of operating sublease income	​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended ​ ​ December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Operating sublease income $ 838 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​

Other liabilities (Tables)

Other liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Other liabilities
Summary of other current and non-current liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 ​ ​ (in thousands) ​ Other current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities ​ 5,571 ​ ​ 4,198 ​ Total other current liabilities $ 5,571 ​ $ 4,198 ​ ​ ​ ​ ​ ​ ​ ​ Other non-current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities $ 38,608 ​ $ 43,409 ​ Other ​ 1,001 ​ ​ 1,001 ​ Total other non-current liabilities $ 39,609 ​ $ 44,410 ​

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Schedule of collaboration receivables and contract liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ Balance at ​ ​ ​ December 31, 2020 ​ Additions ​ Deductions ​ December 31, 2021 ​ ​ ​ ​ ( in thousands) ​ Related party collaboration receivable ​ $ 8,012 ​ $ 7,034 ​ $ (14,314) ​ $ 732 ​ Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue ​ $ 43,689 ​ $ — ​ $ (31,593) ​ $ 12,096 ​
AbbVie Tau Collaboration Agreement
Schedule of allocation of transaction price	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Research Services ​ $ 34,482 ​ First Development Option Material Right ​ ​ 34,518 ​ Total ​ $ 69,000 ​
AbbVie Alpha Synuclein Collaboration Agreement
Schedule of allocation of transaction price	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ ASN Research Services ​ $ 23,768 ​ ASN First Development Option Material Right ​ ​ 41,232 ​ Total ​ $ 65,000 ​
Neurocrine Collaboration Agreement
Schedule of allocation of variable consideration	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Variable Consideration ​ ​ ​ VY-AADC Program ​ $ 53,863 ​ FA Program ​ ​ 17,277 ​ Discovery Program 1 ​ ​ 5,432 ​ Discovery Program 2 ​ ​ 3,456 ​ Total ​ $ 80,028 ​
Schedule of allocation of fixed consideration	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Fixed Consideration ​ ​ ​ VY-AADC Program ​ $ 49,045 ​ FA Program ​ ​ 20,647 ​ Discovery Program 1 ​ ​ 14,443 ​ Discovery Program 2 ​ ​ 8,247 ​ Total ​ $ 92,382 ​

Common stock (Tables)

Common stock (Tables)	12 Months Ended
	Dec. 31, 2021
Common stock.
Schedule of shares reserved for future issuance	Shares Reserved For Future Issuance ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 2020 Shares reserved for vesting of restricted stock awards under the Founder Agreements 137,255 ​ 156,863 ​ Shares reserved for exercise of outstanding stock options 5,013,193 ​ 5,485,078 Shares reserved for vesting of outstanding restricted stock units 806,379 ​ 638,471 Shares reserved for issuances under the 2015 Stock Option Plan ​ 4,374,539 ​ 2,827,185 ​ Shares reserved for issuances under the 2015 Employee Stock Purchase Plan ​ 1,659,574 ​ 1,484,923 ​ ​ 11,990,940 ​ 10,592,520

Stock-based compensation (Table

Stock-based compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Stock-based compensation
Compensation cost recognized for all stock-based compensation awards	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2021 2020 2019 ​ ​ (in thousands) General and administrative ​ $ 7,191 ​ $ 8,577 ​ $ 8,257 ​ Research and development ​ 4,133 ​ 6,357 ​ 7,383 ​ Total stock-based compensation expense ​ $ 11,324 ​ $ 14,934 ​ $ 15,640 ​
Summary of stock-based compensation expense by type of award	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ ​ 2021 2020 2019 ​ ​ ​ (in thousands) ​ Stock options ​ $ 7,438 ​ $ 11,387 ​ $ 13,380 ​ Restricted stock awards and units ​ ​ 3,551 ​ ​ 3,110 ​ ​ 1,935 ​ Employee stock purchase plan awards ​ 335 ​ 437 ​ 325 ​ Total stock-based compensation expense ​ $ 11,324 ​ $ 14,934 ​ $ 15,640 ​
Summary of status and changes in unvested restricted stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Grant Date ​ ​ ​ ​ ​ Fair Value ​ ​ ​ Units Per Unit ​ Unvested restricted stock units as of December 31, 2020 ​ 638,471 ​ $ 12.74 ​ Awarded ​ 1,268,301 ​ $ 5.30 ​ Vested ​ (326,943) ​ $ 12.25 ​ Forfeited ​ (773,450) ​ $ 8.93 ​ Unvested restricted stock units as of December 31, 2021 ​ 806,379 ​ $ 7.26 ​
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Remaining Aggregate ​ ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ ​ ​ ​ Exercise ​ Life ​ Value ​ ​ Shares Price (in years) (in thousands) ​ Outstanding at December 31, 2020 5,485,078 ​ $ 14.77 ​ ​ ​ ​ ​ Granted ​ 1,518,229 ​ $ 6.32 ​ ​ ​ ​ ​ ​ Exercised ​ (3,811) ​ $ 7.27 ​ ​ ​ ​ ​ ​ Cancelled or forfeited ​ (1,986,303) ​ $ 13.58 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2021 ​ 5,013,193 ​ $ 12.69 ​ 5.6 ​ $ 1,165 ​ Exercisable at December 31, 2021 3,611,863 ​ $ 14.16 4.5 ​ $ — ​
Summary of weighted-average assumptions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2021 2020 2019 ​ Risk-free interest rate 0.9 % 1.0 % ​ 2.2 % ​ Expected dividend yield — % — % ​ — % ​ Expected term (in years) 6.0 ​ 6.0 ​ ​ 6.0 ​ ​ Expected volatility 75.0 % 73.7 % ​ 74.7 % ​

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income taxes
Schedule of components of income expense (benefit)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2021 ​ 2020 ​ 2019 ​ (in thousands) ​ ​ ​ Current ​ ​ ​ ​ ​ ​ ​ ​ Federal $ — ​ $ — ​ $ — State ​ — ​ ​ — ​ ​ — Total current ​ — ​ ​ — ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ — ​ ​ — ​ ​ — State ​ — ​ ​ — ​ ​ — Total deferred ​ — ​ ​ — ​ ​ — Total tax expense $ — ​ $ — ​ $ —
Schedule of reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the effective income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2021 ​ 2020 ​ 2019 ​ Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 21.0 % ​ State taxes, net of federal benefit ​ 6.6 % ​ (2.3) % ​ 8.0 % ​ Provision to return ​ 4.9 % ​ — % ​ — % ​ General business credit carryovers ​ 3.2 % ​ (20.6) % ​ 9.4 % ​ Non-deductible expenses ​ (3.8) % ​ 5.0 % ​ (2.2) % ​ Other ​ — % ​ 1.9 % ​ — % ​ Change in valuation allowance ​ (31.9) % ​ (5.0) % ​ (36.2) % ​ Total ​ — % ​ — % ​ — % ​
Schedule of principal components of the Company's deferred tax assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 ​ 2020 ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforwards $ 56,756 ​ $ 41,130 ​ Tax credit carryforwards 30,122 ​ 28,173 ​ Lease liability ​ 12,012 ​ ​ 13,006 ​ Deferred revenue ​ 11,485 ​ ​ 12,176 ​ Stock compensation ​ 7,784 ​ ​ 4,368 ​ Non-deductible accruals and reserves 1,507 ​ 1,288 ​ Intangibles 664 ​ 721 ​ Total deferred tax assets 120,330 ​ 100,862 ​ Less valuation allowance (107,563) ​ (84,866) ​ Net deferred tax assets 12,767 ​ 15,996 ​ Deferred tax liabilities ​ ​ ​ ​ ​ Right of use assets ​ (9,128) ​ (9,852) ​ Depreciation and amortization ​ (3,632) ​ ​ (6,136) ​ Other temporary differences ​ (7) ​ ​ (8) ​ Net deferred taxes $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​

Nature of business (Details)

Nature of business (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accumulated deficit	$ (347,104)	$ (275,907)
Novartis Pharma, AG | Novartis License Agreement
Cash, cash equivalents, and marketable debt securities	$ 54,000

Summary of significant accoun_4

Summary of significant accounting policies - Cash, Cash Equivalents, and Marketable Securities - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost Basis [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 117,433	$ 104,440	$ 86,042
Total marketable securities, amortized cost		71,568
Total money market funds and marketable securities	115,422	175,560
Fair Value Disclosure [Abstract]
Total marketable securities		76,698
Total money market funds and marketable securities	115,411	180,690
Unrealized Gain and Loss [Abstract]
Total marketable securities, unrealized gains		5,136
Total money market funds and marketable securities		5,136
Total marketable securities, unrealized losses		6
Total money market funds and marketable securities	11	6
Other than temporary losses	0
Money market funds
Amortized Cost Basis [Abstract]
Cash and Cash Equivalents, at Carrying Value	100,305	103,992
Fair Value Disclosure [Abstract]
Cash and cash equivalents	100,305	103,992
U.S. Treasury notes
Amortized Cost Basis [Abstract]
Marketable securities, amortized cost	15,117	70,348
Fair Value Disclosure [Abstract]
Marketable securities, fair value	15,106	70,342
Unrealized Gain and Loss [Abstract]
Marketable securities, unrealized losses	$ 11	6
Equity securities
Amortized Cost Basis [Abstract]
Marketable equity securities, amortized cost		1,220
Fair Value Disclosure [Abstract]
Marketable equity securities, fair value		6,356
Unrealized Gain and Loss [Abstract]
Equity securities, unrealized gains		$ 5,136
Maximum
Unrealized Gain and Loss [Abstract]
Debt securities, contractual maturity period	1 year	1 year

Summary of significant accoun_5

Summary of significant accounting policies - Restricted Cash - (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of significant accounting policies
Cash and cash equivalents	$ 117,433	$ 104,440	$ 86,042
Restricted cash included in deposits and other noncurrent assets	1,779	1,779	735
Total cash, cash equivalents, and restricted cash	$ 119,212	$ 106,219	$ 86,777	$ 47,594

Summary of significant accoun_6

Summary of significant accounting policies - Stock Based Compensation Expense - (Details)	12 Months Ended
	Dec. 31, 2021
Summary of significant accounting policies
Expected dividend yield	0.00%

Summary of significant accoun_7

Summary of significant accounting policies - Net income (loss) per share - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	5,956,827	6,064,344	5,949,201
Numerator:
Net (loss) income	$ (71,197)	$ 36,741	$ (43,597)
Denominator for basic net (loss) income per share:
Weighted average shares outstanding-basic	37,668,947	37,132,447	35,898,266
Denominator for diluted net (loss) income per share:
Weighted average shares outstanding-basic	37,668,947	37,132,447	35,898,266
Common stock options and restricted stock units		216,068
Weighted average shares outstanding-diluted	37,668,947	37,348,514	35,898,266
Financial instruments with off-balance sheet risk	$ 0
Unvested restricted common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	137,255	156,863	176,471
Unvested restricted common stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	806,379	527,625	455,404
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	5,013,193	5,379,856	5,317,326

Fair value measurements - Asset

Fair value measurements - Assets measured on a recurring basis - (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 117,433	$ 104,440	$ 86,042
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities		76,698
Total assets measured at fair value	115,411	184,506
Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities		76,698
Total assets measured at fair value	115,411	180,690
Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value		3,816
U.S. Treasury notes | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	15,106	70,342
U.S. Treasury notes | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	15,106	70,342
Equity securities | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities		6,356
Equity securities | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities		6,356
Warrants | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities		3,816
Warrants | Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Warrants to purchase equity securities		3,816
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	100,305	103,992
Money market funds | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	100,305	103,992
Money market funds | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 100,305	$ 103,992

Prepaid expenses and other cu_3

Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Prepaid expense and other current assets
Other current assets	$ 1,701	$ 1,575
Prepaid insurance	1,360	1,459
Prepaid research and development contracts	350	1,674
Accrued interest receivable	16	95
Warrants to purchase equity securities		3,816
Total	$ 3,427	$ 8,619

Property and equipment, net (De

Property and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 37,833	$ 37,005
Less: accumulated depreciation	(15,913)	(11,570)
Property and equipment, net	21,920	25,435
Depreciation expense	5,165	3,817	$ 2,765
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	19,384	18,093
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,695	15,469
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,524	2,410
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross		866
Other
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 230	$ 167

Accrued expenses (Details)

Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued expenses
Employee compensation costs	$ 5,022	$ 5,857
Research and development costs	3,719	6,624
Accrued goods and services	1,482	496
Professional services	727	1,153
Other		75
Total	$ 10,950	$ 14,205

Lease obligation (Details)

Lease obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021
Lease expense	$ 6,800	$ 6,200	$ 5,700
Restricted cash included in deposits and other noncurrent assets	$ 1,779	1,779	$ 735
Weighted average remaining lease term	6 years
Weighted average incremental borrowing rate	7.90%
Total minimum lease payments
2022	$ 8,849
2023	8,958
2024	9,227
2025	9,644
2026	9,307
Thereafter	10,638
Total future minimum lease payments	56,623
Less: imputed interest	(12,444)
Total lease liability	44,179
Current lease liabilities	$ 5,571	$ 4,198
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Non-current lease liabilities	$ 38,608	$ 43,409
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
75 and 64 Sidney Street
Leasehold improvements	$ 5,300
75 Sidney Street
Lease term				3 years 3 months 18 days
Financial obligations from sublessee				$ 9,100
75 Hayden Avenue
Entitled leasehold improvements	5,600
Deposits and other non-current assets
Restricted cash included in deposits and other noncurrent assets	$ 1,800

Lease obligation - Operating su

Lease obligation - Operating sublease income (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Lease obligation
Operating sublease income	$ 838

Other liabilities (Details)

Other liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Other current liabilities
Lease liability	$ 5,571	$ 4,198
Total other current liabilities	5,571	4,198
Other non-current liabilities
Lease liability	38,608	43,409
Other	1,001	1,001
Total other non-current liabilities	39,609	$ 44,410
Restructuring costs	2,600
Restructuring costs paid	$ 1,500

Commitments and contingencies -

Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)shares	Mar. 31, 2019USD ($)item$ / sharesshares	Dec. 31, 2021USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Allocation of Transaction Price
Revenue recognized				$ 31,593
Deferred revenue			$ 12,096	12,096	$ 43,689
Related party collaboration receivable			732	732	8,012
Neurocrine Collaboration Agreement
Allocation of Transaction Price
Related party collaboration receivable			700	700	8,000
Neurocrine Collaboration Agreement | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		40.00%
Neurocrine Collaboration Agreement | Neurocrine
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaboration programs | item		4
Number of discovery programs | item		2
Programs added later | item		2
Discovery programs under development | item		2
Number of targets | item		8
Upfront payment	$ 115,000	$ 115,000
Purchase of common stock, shares | shares	4,179,728	4,179,728
Purchase of common stock	$ 5,000	$ 50,000
Price per share | $ / shares		$ 11.9625
Aggregate maximum milestone payments to be received from collaborative partner		$ 170,000
Estimated cost reimbursement	431,100		80,000
Termination period		10 years
Period of advance notice for termination prior to first commercial sale		180 days
Period of advance notice for termination after first commercial sale		1 year
Discount related to equity investment	27,600
Equity investment	50,000
Allocation of Transaction Price
Allocation of variable consideration			80,028	80,028
Allocation of fixed consideration	92,400		92,382	92,382
Revenue recognized				37,400	$ 56,700
Cumulative catch up of revenue recognized				900
Deferred revenue			12,100	12,100
Reimbursement costs expected to be received				700
Costs to obtain collaboration agreement			800	800
Consideration received	$ 5,000
Neurocrine Collaboration Agreement | Neurocrine | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of reduction in royalty payments		50.00%
Neurocrine Collaboration Agreement | Neurocrine | VY-AADC
Allocation of Transaction Price
Allocation of variable consideration			53,863	53,863
Allocation of fixed consideration			49,045	49,045
Neurocrine Collaboration Agreement | Neurocrine | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		60.00%
Allocation of Transaction Price
Allocation of variable consideration			17,277	17,277
Allocation of fixed consideration			20,647	20,647
Neurocrine Collaboration Agreement | Neurocrine | Discovery and FA Programs
Allocation of Transaction Price
Allocation of fixed consideration			42,200	42,200
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration			5,432	5,432
Allocation of fixed consideration			14,443	14,443
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration			3,456	3,456
Allocation of fixed consideration			$ 8,247	$ 8,247
Neurocrine Collaboration Agreement | Neurocrine | Development and regulatory milestones | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		$ 195,000
Neurocrine Collaboration Agreement | Neurocrine | Development and regulatory milestones | Discovery program 1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		130,000
Neurocrine Collaboration Agreement | Neurocrine | Commercial Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		275,000
Aggregate maximum milestone payments to be received from collaborative partner		$ 1,100,000

Commitments and contingencies_2

Commitments and contingencies - Collaboration receivables and contract liabilities - (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Commitments and contingencies
Related party collaboration receivables, beginning balance	$ 8,012
Additions	7,034
Deductions	(14,314)
Related party collaboration receivables, ending balance	732
Deferred revenue, beginning balance	43,689
Deductions	(31,593)
Deferred revenue, ending balance	$ 12,096

Commitments and contingencies_3

Commitments and contingencies - Pfizer Option and License Agreement - (Details)	Oct. 01, 2021USD ($)item	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized		$ 31,593,000
Deferred revenue		12,096,000	$ 43,689,000
Pfizer | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgences | item	2
Number of exercise options | item	1
Number of options exercised | item	0
Number of performance obligations | item	2
Number of material rights | item	2
Upfront payment	$ 30,000,000
Non-refundable upfront payment received	$ 30,000,000
Number of license options | item	1
Allocation of transaction price	$ 15,000,000
Aggregate milestone payments, if exercise rights	$ 10,000,000
Revenue recognized		0
Deferred revenue		$ 30,000,000
Number of days written notice required by reporting entity to terminate agreement	90 days
Pfizer | Development, regulatory and commercialization milestone | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	$ 115,000,000
Pfizer | Sales milestone | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	$ 175,000,000
Minimum | Pfizer | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of countries received regulatory approval | item	1
Number of major market countries received regulatory approval | item	1
Maximum | Pfizer
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of options exercised | item	1

Commitments and contingencies_4

Commitments and contingencies - Significant Agreements - (Details) - Collaborative Arrangement - Sanofi Genzyme $ in Millions	1 Months Ended
	Feb. 28, 2015USD ($)shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received	$ 65
Redeemable Convertible Preferred Stock Series B
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Temporary equity issued (in shares) | shares	10,000,000
Temporary equity issued	$ 30
Maximum potential in-kind services to be provided by collaborative partner	$ 5

Commitments and contingencies_5

Commitments and contingencies - Termination of Agreement (Details) - Termination Agreement - Sanofi Genzyme $ in Millions	Jun. 14, 2019USD ($)item
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of non central nervous system | item	2
Up-front payment made	$ 10
Milestone payment agreed to be paid	$ 10
Period in which milestone payment will be made of filing of investigational new drug	15 days
Percentage of threshold sublicensing income agreed to be paid	50.00%
Unused in-kind services waived	$ 0.4
Threshold number of capsids having exclusive options to evaluate for no consideration | item	4
Threshold additional number of capsids having options to evaluate for low six-figure payment per capsid | item	2
Threshold number of capsids that has right to obtain an exclusive license | item	2
Option exercise fee	$ 1
Development and regulatory milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	15
Sales milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 20

Commitments and contingencies_6

Commitments and contingencies - Accounting Analysis - (Details) $ in Thousands	Jun. 14, 2019USD ($)	Feb. 28, 2018USD ($)item	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Feb. 28, 2015USD ($)
Income Statement Related Disclosures [Abstract]
Revenue recognized			$ 31,593
Deferred revenue			$ 12,096	$ 43,689
Total payable amount	$ 20,000
Sanofi Genzyme | Collaborative Arrangement
Income Statement Related Disclosures [Abstract]
Revenue recognized	28,700				$ 32,600
Deferred revenue	48,700
Non-refundable upfront payment received						$ 65,000
Up-front fee paid on date of termination	10,000
Milestone payable upon achievement	10,000
Sanofi Genzyme | Termination Agreement
Income Statement Related Disclosures [Abstract]
Non-refundable upfront payment received	$ 1,000
AbbVie | AbbVie Tau Collaboration Agreement
Income Statement Related Disclosures [Abstract]
Revenue recognized				46,300
Non-refundable upfront payment received		$ 69,000
Number of development options | item		3
AbbVie | AbbVie Tau Collaboration Agreement | Research Services
Income Statement Related Disclosures [Abstract]
Revenue recognized				$ 4,500	$ 11,300

Commitments and contingencies_7

Commitments and contingencies - AbbVie Tau Collaboration Agreement - (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2018USD ($)item	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		$ 12,096	$ 43,689
Revenue recognized		31,593
AbbVie Tau Collaboration Agreement | AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable upfront payment received	$ 69,000
First Research Compound payment	80,000
Two additional research compounds payment to be received for each	$ 30,000
Number of additional research compounds | item	2
One-time payment upon exercise of license option	$ 75,000
Milestone payments to be received for licensed compound in case Alzheimer disease indication	550,000
Milestone payments to be received for licensed compound in case first indication other than Alzheimer disease	230,000
Milestone payments to be received for licensed compound for subsequent non-Alzheimer disease indication	$ 115,000
Number of development options | item	3
Number of research antibodies | item	1
Revenue recognized			46,300
Allocation of Transaction Price
Allocation of transaction price		69,000
AbbVie Tau Collaboration Agreement | AbbVie | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of development options | item	1
Antibodies to include in Research Period | item	2
The number of Licensed Products | item	1
AbbVie Tau Collaboration Agreement | AbbVie | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of antibodies encoded by virus | item	5
Antibodies to include in Research Period | item	3
AbbVie Tau Collaboration Agreement | AbbVie | Research Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized			$ 4,500	$ 11,300
Allocation of Transaction Price
Allocation of transaction price		34,482
AbbVie Tau Collaboration Agreement | AbbVie | First Development Option Material Right
Allocation of Transaction Price
Allocation of transaction price		$ 34,518

Commitments and contingencies_8

Commitments and contingencies - AbbVie Alpha Synuclein Collaboration Agreement - (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2019USD ($)item	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		$ 12,096	$ 43,689
Revenue recognized		$ 31,593
AbbVie Alpha Synuclein Collaboration Agreement | AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of antibodies encoded by virus | item	1
Number of research antibodies | item	1
Non-refundable upfront payment received	$ 65,000
First Research Compound payment	80,000
Three additional research compounds payment to be received for each	$ 30,000
Number of additional research compounds | item	3
Milestone payments to be received for licensed compound in case Parkinson's disease indication	$ 450,000
Milestone payments to be received for licensed compound in case first indication other than Parkinson's disease	185,000
Milestone payments to be received for licensed compound for subsequent non-Parkinson's disease indication	92,500
Revenue recognized			58,900
Allocation of Transaction Price
Allocation of transaction price	$ 65,000
AbbVie Alpha Synuclein Collaboration Agreement | AbbVie | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Antibodies to include in Research Period | item	1
The number of Licensed Products | item	1
AbbVie Alpha Synuclein Collaboration Agreement | AbbVie | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Antibodies to include in Research Period | item	4
AbbVie Alpha Synuclein Collaboration Agreement | AbbVie | Research Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized			$ 4,800	$ 1,300
Allocation of Transaction Price
Allocation of transaction price	$ 23,768
AbbVie Alpha Synuclein Collaboration Agreement | AbbVie | First Development Option Material Right
Allocation of Transaction Price
Allocation of transaction price	41,232
AbbVie Alpha Synuclein Collaboration Agreement | Commercial Milestone | AbbVie
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Specified commercial milestone payments	$ 500,000

Commitments and contingencies_9

Commitments and contingencies - Other Agreements - (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)multiple	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2016USD ($)
Loss Contingency [Abstract]
Contingency reserves for litigation liabilities		$ 0	$ 0
Non-profit organization agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum funding	$ 4
Funding multiple | multiple	2.6
Milestone payment liability				$ 1
MRIC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of investment					$ 2

Common stock (Details)

Common stock (Details)	12 Months Ended
	Dec. 31, 2021Vote$ / sharesshares	Jan. 01, 2022shares	Dec. 31, 2020$ / sharesshares	Oct. 31, 2015shares
Class of Stock [Line Items]
Common Stock, Shares Authorized	120,000,000		120,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001		$ 0.001
Number of votes entitled for each share of common stock | Vote	1
Dividends declared | $ / shares	$ 0
Dividends paid | $ / shares	$ 0
Shares available for future issuance (in shares)	11,990,940		10,592,520
2015 Stock Option Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	4,374,539	9,226,183		1,311,812
Vesting of restricted stock awards | Founder Awards
Class of Stock [Line Items]
Shares available for future issuance (in shares)	137,255		156,863
Exercise of stock options
Class of Stock [Line Items]
Shares available for future issuance (in shares)	5,013,193		5,485,078
Vesting of restricted stock units
Class of Stock [Line Items]
Shares available for future issuance (in shares)	806,379		638,471
Issuance under share based compensation plans | 2015 Stock Option Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	4,374,539		2,827,185
Issuance under share based compensation plans | 2015 Employee Stock Purchase Plan.
Class of Stock [Line Items]
Shares available for future issuance (in shares)	1,659,574		1,484,923

Stock-based compensation (Detai

Stock-based compensation (Details) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended				72 Months Ended
	Dec. 31, 2019shares	Oct. 31, 2015shares	Jan. 31, 2014$ / sharesshares	Dec. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2016item	Dec. 31, 2021USD ($)$ / sharesshares	Jan. 01, 2022shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)				11,990,940	10,592,520			11,990,940
Stock-based compensation. | $				$ 11,324	$ 14,934	$ 15,640
Stock options granted (in shares)				1,518,229
Exercise price | $ / shares				$ 12.69	$ 14.77			$ 12.69
2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for stock-based compensation plan (in shares)			823,529
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)				1,659,574				1,659,574	2,306,542
Percentage of outstanding common stock								1.00%
New stock options issued				200,006	104,108
Number of shares authorized for stock-based compensation plan (in shares)		262,362
Period to purchase shares				6 months
2015 Employee Stock Purchase Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction		1.00%
2015 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction		10.00%
2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)		1,311,812		4,374,539				4,374,539	9,226,183
Percentage limit of issued and outstanding shares up to which additional shares may be issued		4.00%
Percentage of outstanding common stock								4.00%
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				$ 7,438	$ 11,387	13,380
Stock options | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
Stock options | Inducement Awards | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				25.00%
Stock options | Inducement Awards | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				36 months
Vesting percentage				75.00%
Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				$ 3,551	3,110	$ 1,935
Unrecognized stock-based compensation expense | $				$ 7,300	$ 3,500			$ 7,300
Restricted stock granted, original issued price (in dollars per share) | $ / shares				$ 5.30
Unvested restricted common stock units | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years
Unvested restricted common stock units | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				2 years
Unvested restricted common stock units | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued				13,000	29,000	58,125
Vesting period				3 years
Unvested restricted common stock units | Inducement Awards | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				33.00%
Unvested restricted common stock units | Inducement Awards | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				33.00%
Performance based milestone awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Probable performance milestones | item							1
Performance milestones | item							3
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	58,823					58,823
Vesting period	3 years
Founders restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)			1,188,233
Restricted stock granted, original issued price (in dollars per share) | $ / shares			$ 0.0425
Founders restricted stock | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)			835,292
Founders restricted stock | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)			352,941
Founders restricted stock | Minimum | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Founders restricted stock | Maximum | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Non-statutory stock options | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued				76,500	172,500	338,750
Employees and directors stock options | 2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
Employees and directors stock options | 2014 Stock Option and Grant Plan | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				1 year
Vesting percentage				25.00%
Employees and directors stock options | 2014 Stock Option and Grant Plan | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years
Vesting percentage				75.00%
Employees and directors stock options | 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)				1,441,729
Non-employees stock options | 2014 Stock Option and Grant Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				1 year
Non-employees stock options | 2014 Stock Option and Grant Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
Share-based Payment Arrangement, Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				$ 7,300	$ 11,200	$ 13,300
Share-based Payment Arrangement, Employee | Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				3,300	2,800	1,900
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				4,133	6,357	7,383
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation. | $				$ 7,191	$ 8,577	$ 8,257

Stock-based compensation - Comp

Stock-based compensation - Compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	$ 11,324	$ 14,934	$ 15,640
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	7,438	11,387	13,380
Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	3,551	3,110	1,935
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	335	437	325
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	4,133	6,357	7,383
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.	$ 7,191	$ 8,577	8,257
Dr. Sah
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.			$ 2,200
Consultant duration			3 years

Stock-based compensation - Rest

Stock-based compensation - Restricted Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Restricted stock disclosures
Stock-based compensation.	$ 11,324	$ 14,934	$ 15,640
Unvested restricted common stock units
Shares
Balance, beginning (in shares)	638,471
Granted (in shares)	1,268,301
Vested (in shares)	(326,943)
Forfeited (in shares)	(773,450)
Balance, ending (in shares)	806,379	638,471
Weighted Average Grant Date Fair Value Per Share
Balance, beginning (in dollars per share)	$ 12.74
Granted (in dollars per share)	5.30
Vested (in dollars per share)	12.25
Forfeited (in dollars per share)	8.93
Balance, ending (in dollars per share)	$ 7.26	$ 12.74
Restricted stock disclosures
Stock-based compensation.	$ 3,551	$ 3,110	1,935
Unrecognized stock-based compensation expense	$ 7,300	$ 3,500
Remaining weighted-average remaining vesting period	2 years 3 months 18 days	1 year 4 months 24 days
Share-based Payment Arrangement, Employee
Restricted stock disclosures
Stock-based compensation.	$ 7,300	$ 11,200	13,300
Share-based Payment Arrangement, Employee | Unvested restricted common stock units
Restricted stock disclosures
Stock-based compensation.	$ 3,300	$ 2,800	$ 1,900
Vesting period, tranche one | Unvested restricted common stock units
Shares
Granted (in shares)	538,301
Restricted stock disclosures
Vesting period	3 years
Vesting period, tranche two | Unvested restricted common stock units
Shares
Granted (in shares)	730,000
Restricted stock disclosures
Vesting period	2 years

Stock-based compensation - Stoc

Stock-based compensation - Stock Options - (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares) | shares	5,485,078
Granted (in shares) | shares	1,518,229
Exercised (in shares) | shares	(3,811)
Cancelled or forfeited (in shares) | shares	(1,986,303)
Outstanding, ending balance (in shares) | shares	5,013,193
Exercisable (in shares) | shares	3,611,863
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 14.77
Granted (in dollars per share)	6.32
Exercised (in dollars per share)	7.27
Cancelled or forfeited (in dollars per share)	13.58
Outstanding (in dollars per share)	12.69
Exercisable (in dollars per share)	$ 14.16
Remaining Contractual Life
Outstanding	5 years 7 months 6 days
Exercisable	4 years 6 months
Aggregate Intrinsic Value
Outstanding | $	$ 1,165
Share-based Payment Arrangement, Employee
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 4.11

Stock-based compensation - Unre

Stock-based compensation - Unrecognized expense and weighted-average period (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair value assumptions
Expected dividend yield	0.00%
Employees and directors stock options
Fair value assumptions
Risk-free interest rate	0.90%	1.00%	2.20%
Expected term	6 years	6 years	6 years
Expected volatility	75.00%	73.70%	74.70%
Share-based Payment Arrangement, Employee
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 4.11

401(k) Savings Plan (Details)

401(k) Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
401(k) Savings Plan
Employer contribution expense	$ 1.1	$ 1.1	$ 1

Income taxes - Net operating lo

Income taxes - Net operating loss carryforwards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2016item
Operating Loss Carryforwards [Line Items]
Maximum NOL carryforwards (as a percent)		80.00%
Valuation Allowance	$ 107,563	$ 84,866	$ 84,900
Change in the valuation allowance	$ 22,700
Number of ownership changes | item				3
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax computed at federal statutory tax rate	21.00%	21.00%	21.00%
State taxes, net of federal benefit	6.60%	(2.30%)	8.00%
Provision to return	4.90%
General business credit carryovers	3.20%	(20.60%)	9.40%
Nondeductible expenses	(3.80%)	5.00%	(2.20%)
Other		1.90%
Change in valuation allowance	(31.90%)	(5.00%)	(36.20%)
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 210,800
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		198,900
Investment tax credit		600
Research and development tax credits carryforwards | Federal
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards		22,600
Research and development tax credits carryforwards | State
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards		$ 9,000

Income taxes - Deferred tax ass

Income taxes - Deferred tax assets (liabilities) and unrecognized tax benefits (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income taxes
Unrecognized tax benefits	$ 0	$ 0
Amounts in uncertain tax position	0	0
Accrued interest	0	0
Deferred tax assets:
Net operating loss carryforwards	56,756	41,130
Tax credit carryforwards	30,122	28,173
Lease liability	12,012	13,006
Deferred revenue	11,485	12,176
Stock compensation	7,784	4,368
Non-deductible accruals and reserves	1,507	1,288
Intangibles	664	721
Total deferred tax assets	120,330	100,862
Less valuation allowance	(107,563)	(84,866)	$ (84,900)
Net deferred tax assets	12,767	15,996
Deferred tax liabilities
Right of use assets	(9,128)	(9,852)
Depreciation and amortization	(3,632)	(6,136)
Other temporary differences	$ (7)	$ (8)

Related party transactions (Det

Related party transactions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)item	Dec. 31, 2020USD ($)item	Dec. 31, 2019USD ($)item
Related party transactions
Related party collaboration receivable	$ 732	$ 8,012
Former Executives | Board and scientific advisory services
Related party transactions
Number of individuals providing services | item	2	2	2
Dr. Paul | Board and scientific advisory services
Related party transactions
Total amount of services received		$ 200	$ 200
Dr. Sah | Board and scientific advisory services
Related party transactions
Total amount of services received	$ 200	400	$ 400
Neurocrine Collaboration Agreement
Related party transactions
Related party collaboration receivable	$ 700	$ 8,000

Subsequent event - (Details)

Subsequent event - (Details) $ in Millions	Mar. 01, 2022USD ($)item	Oct. 01, 2021USD ($)item
Pfizer | Option and license agreement
Subsequent events
Upfront payment		$ 30
Number of exercise options | item		1
Aggregate milestone payments, if exercise rights		$ 10
Pfizer | Development, regulatory and commercialization milestone | Option and license agreement
Subsequent events
Aggregate maximum milestone payments to be received from collaborative partner		115
Pfizer | Sales milestone | Option and license agreement
Subsequent events
Aggregate maximum milestone payments to be received from collaborative partner		$ 175
Novartis Pharma, AG | Novartis License Agreement | Subsequent Event.
Subsequent events
Number of transgenes | item	3
Number of additional targets | item	2
Upfront payment	$ 54
Additional fee agreed to pay	18
Aggregate milestone payments, if exercise rights	12.5
Novartis Pharma, AG | Development, regulatory and commercialization milestone | Novartis License Agreement | Subsequent Event.
Subsequent events
Aggregate maximum milestone payments to be received from collaborative partner	125
Novartis Pharma, AG | Sales milestone | Novartis License Agreement | Subsequent Event.
Subsequent events
Aggregate maximum milestone payments to be received from collaborative partner	$ 175