HOOKIPA Pharma (HOOK) 10-Q 12 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 05, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	001-38869
Entity Registrant Name	HOOKIPA PHARMA INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-5395687
Entity Address, Address Line One	350 Fifth Avenue, 72nd Floor, Suite 7240
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10118
Country Region	+43
City Area Code	1
Local Phone Number	890 63 60
Title of 12(b) Security	Common Stock
Trading Symbol	HOOK
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Central Index Key	0001760542
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		26,072,989
Class A common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,819,732

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 102,523	$ 142,743
Accounts receivable	4,923	5,542
Receivable research incentives	15,977	15,115
Prepaid expenses and other current assets	20,028	8,104
Total current assets	143,451	171,504
Non-current assets:
Restricted cash	430	434
Property and equipment, net	13,206	6,219
Operating lease right of use assets	5,266	6,452
Finance lease right of use assets	1,045	1,298
Other non-current assets	2,758	1,910
Total non-current assets	22,705	16,313
Total assets	166,156	187,817
Current liabilities
Loans payable, current	2,674
Accounts payable	10,865	8,009
Deferred revenues	3,020	3,750
Operating lease liabilities, current	1,954	1,998
Accrued expenses and other current liabilities	15,363	7,386
Total current liabilities	33,876	21,143
Non-current liabilities
Loans payable, non-current	2,127	4,537
Operating lease liabilities, non-current	2,753	3,819
Deferred revenues, non-current	31	784
Other non-current liabilities	1,435	1,411
Total non-current liabilities	6,346	10,551
Total liabilities	40,222	31,694
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized at June 30, 2021 and December 31, 2020, respectively; Series A convertible preferred stock, 2,978 shares designated, 2,978 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	0	0
Additional paid-in capital	313,673	309,288
Accumulated other comprehensive loss	(6,250)	(6,067)
Accumulated deficit	(181,492)	(147,101)
Total stockholders' equity	125,934	156,123
Total liabilities and stockholders' equity	166,156	187,817
Common stock
Stockholders' equity:
Common stock	3	3
Class A common stock
Stockholders' equity:
Common stock	$ 0	$ 0

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Series A Convertible Preferred Stock
Preferred stock shares Designated	2,978	2,978
Preferred stock, shares issued	2,978	2,978
Preferred stock, shares outstanding	2,978	2,978
Common stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	26,051,846	25,948,712
Common stock, shares outstanding	26,051,846	25,948,712
Class A common stock
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	3,900,000	3,900,000
Common stock, shares issued	3,819,732	3,819,732
Common stock, shares outstanding	3,819,732	3,819,732

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED)
Revenue from collaboration and licensing	$ 5,378	$ 6,685	$ 10,679	$ 10,381
Operating expenses:
Research and development	(19,572)	(11,564)	(39,736)	(23,090)
General and administrative	(5,095)	(4,347)	(9,404)	(8,976)
Total operating expenses	(24,667)	(15,911)	(49,140)	(32,066)
Loss from operations	(19,289)	(9,226)	(38,461)	(21,685)
Other income (expense):
Grant income	2,505	1,595	4,709	3,067
Interest income	7	59	14	371
Interest expense	(218)	(166)	(437)	(393)
Other income and expenses, net	(158)	646	(216)	622
Total other income, net	2,136	2,134	4,070	3,667
Net loss before tax	(17,153)	(7,092)	(34,391)	(18,018)
Income tax expense	0	0	0	0
Net loss	(17,153)	(7,092)	(34,391)	(18,018)
Other comprehensive loss:
Foreign currency translation gain (loss), net of tax	293	(133)	(183)	(226)
Comprehensive loss	$ (16,860)	$ (7,225)	$ (34,574)	$ (18,244)
Net loss per share - basic and diluted	$ (0.52)	$ (0.28)	$ (1.05)	$ (0.70)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (UNAUDITED) - USD ($) $ in Thousands	Convertible Preferred Stock	Common StockCommon stock	Common StockClass A common stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Balance at the beginning of the period at Dec. 31, 2019		$ 3	$ 0	$ 225,568	$ (4,653)	$ (103,019)	$ 117,899
Balance at the beginning of the period (in shares) at Dec. 31, 2019		21,746,392	3,819,732
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options		$ 0		8			8
Issuance of common stock upon exercise of stock options (in shares)		78,598
Foreign currency translation adjustment, net of tax					(93)		(93)
Stock-based compensation expense				2,094			2,094
Net loss						(10,926)	(10,926)
Balance at the end of the period at Mar. 31, 2020		$ 3	$ 0	227,670	(4,746)	(113,945)	108,982
Balance at the end of the period (in shares) at Mar. 31, 2020		21,824,990	3,819,732
Balance at the beginning of the period at Dec. 31, 2019		$ 3	$ 0	225,568	(4,653)	(103,019)	117,899
Balance at the beginning of the period (in shares) at Dec. 31, 2019		21,746,392	3,819,732
Increase (Decrease) in Stockholders' Equity
Foreign currency translation adjustment, net of tax							(226)
Net loss							(18,018)
Balance at the end of the period at Jun. 30, 2020		$ 3	$ 0	229,828	(4,879)	(121,037)	103,915
Balance at the end of the period (in shares) at Jun. 30, 2020		21,834,692	3,819,732
Balance at the beginning of the period at Dec. 31, 2019		$ 3	$ 0	225,568	(4,653)	(103,019)	117,899
Balance at the beginning of the period (in shares) at Dec. 31, 2019		21,746,392	3,819,732
Increase (Decrease) in Stockholders' Equity
Net loss							(44,100)
Balance at the end of the period at Dec. 31, 2020	$ 0	$ 3	$ 0	309,288	(6,067)	(147,101)	156,123
Balance at the end of the period (in shares) at Dec. 31, 2020	2,978	25,948,712	3,819,732
Balance at the beginning of the period at Mar. 31, 2020		$ 3	$ 0	227,670	(4,746)	(113,945)	108,982
Balance at the beginning of the period (in shares) at Mar. 31, 2020		21,824,990	3,819,732
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options		$ 0		7			7
Issuance of common stock upon exercise of stock options (in shares)		9,702
Foreign currency translation adjustment, net of tax					(133)		(133)
Stock-based compensation expense				2,151			2,151
Net loss						(7,092)	(7,092)
Balance at the end of the period at Jun. 30, 2020		$ 3	$ 0	229,828	(4,879)	(121,037)	103,915
Balance at the end of the period (in shares) at Jun. 30, 2020		21,834,692	3,819,732
Balance at the beginning of the period at Dec. 31, 2020	$ 0	$ 3	$ 0	309,288	(6,067)	(147,101)	156,123
Balance at the beginning of the period (in shares) at Dec. 31, 2020	2,978	25,948,712	3,819,732
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options		$ 0		125			125
Issuance of common stock upon exercise of stock options (in shares)		33,806
Vesting of restricted stock		$ 0		0
Vesting of restricted stock (in shares)		12,140
Foreign currency translation adjustment, net of tax					(476)		(476)
Stock-based compensation expense				1,521			1,521
Net loss						(17,238)	(17,238)
Balance at the end of the period at Mar. 31, 2021	$ 0	$ 3	$ 0	310,934	(6,543)	(164,339)	140,055
Balance at the end of the period (in shares) at Mar. 31, 2021	2,978	25,994,658	3,819,732
Balance at the beginning of the period at Dec. 31, 2020	$ 0	$ 3	$ 0	309,288	(6,067)	(147,101)	$ 156,123
Balance at the beginning of the period (in shares) at Dec. 31, 2020	2,978	25,948,712	3,819,732
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options (in shares)							79,487
Foreign currency translation adjustment, net of tax							$ (183)
Net loss							(34,391)
Balance at the end of the period at Jun. 30, 2021	$ 0	$ 3	$ 0	313,673	(6,250)	(181,492)	125,934
Balance at the end of the period (in shares) at Jun. 30, 2021	2,978	26,051,846	3,819,732
Balance at the beginning of the period at Mar. 31, 2021	$ 0	$ 3	$ 0	310,934	(6,543)	(164,339)	140,055
Balance at the beginning of the period (in shares) at Mar. 31, 2021	2,978	25,994,658	3,819,732
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options		$ 0		112			112
Issuance of common stock upon exercise of stock options (in shares)		45,681
Vesting of restricted stock		$ 0		0
Vesting of restricted stock (in shares)		11,507
Foreign currency translation adjustment, net of tax					293		293
Stock-based compensation expense				2,627			2,627
Net loss						(17,153)	(17,153)
Balance at the end of the period at Jun. 30, 2021	$ 0	$ 3	$ 0	$ 313,673	$ (6,250)	$ (181,492)	$ 125,934
Balance at the end of the period (in shares) at Jun. 30, 2021	2,978	26,051,846	3,819,732

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities:
Net loss	$ (34,391)	$ (18,018)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,148	4,245
Depreciation and amortization expense	2,321	1,874
Other non-cash items	33	(29)
Changes in operating assets and liabilities:
Accounts receivable	444	(2,971)
Prepaid expenses and other current assets	(13,680)	(6,531)
Other non-current assets	(923)	127
Accounts payable	457	4,833
Deferred revenues	(1,364)	1,431
Operating lease liabilities	(1,006)	(927)
Accrued expenses and other liabilities	11,008	(1,668)
Other non-current liabilities	(2,176)	(39)
Net cash used in operating activities	(35,129)	(17,673)
Investing activities:
Purchases of property and equipment	(4,954)	(1,241)
Net cash used in investing activities	(4,954)	(1,241)
Financing activities:
Payments related to finance leases	(51)	(65)
Proceeds from issuance of common stock, net of issuance costs	237	15
Payments for deferred offering costs		(128)
Repayments of borrowings	0	(1,256)
Net cash provided by (used in) financing activities	186	(1,434)
Net decrease in cash, cash equivalents and restricted cash	(39,897)	(20,348)
Cash, cash equivalents and restricted cash at beginning of period	143,177	113,575
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(327)	55
Cash, cash equivalents and restricted cash at end of period	102,953	93,282
Supplemental disclosure of cash flow information:
Cash paid for interest	(24)	(47)
Cash paid for income taxes	0	0
Supplemental disclosure of non-cash investing activities:
Property and equipment additions in accounts payable and accrued expenses	$ (3,426)	$ (368)

Nature of the business and orga

Nature of the business and organization	6 Months Ended
	Jun. 30, 2021
Nature of the business and organization
Nature of the business and organization	1. Nature of the business and organization HOOKIPA Pharma Inc. (“HOOKIPA” or the “Company”) is a clinical-stage biopharmaceutical company developing a new class of immunotherapeutics based on its proprietary arenavirus platform that is designed to reprogram the body’s immune system. The Company was incorporated under the name of Hookipa Biotech, Inc. under the laws of the State of Delaware in February 2017 as a fully-owned subsidiary of Hookipa Biotech AG. In June 2018, the Company changed its name from Hookipa Biotech, Inc. to HOOKIPA Pharma Inc. and in order to effectuate the change of the jurisdiction of incorporation, the Company acquired all of the shares of Hookipa Biotech AG, now Hookipa Biotech GmbH. HOOKIPA is headquartered in New York, with European research and preclinical development operations headquartered in Vienna, Austria. In April 2019, the Company closed its initial public offering (“IPO”) and its common stock started trading on the Nasdaq Global Select Market under the ticker symbol “HOOK”. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities and may not ultimately lead to a marketing approval and commercialization of a product. Even if the Company’s drug development efforts are successful, it is uncertain if and when the Company will realize significant revenue from product sales. ​

Summary of significant accounti

Summary of significant accounting policies	6 Months Ended
	Jun. 30, 2021
Summary of significant accounting policies
Summary of significant accounting policies	2. Summary of significant accounting policies Basis of presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying condensed consolidated balance sheet as of June 30, 2021, the condensed consolidated statements of operations, and comprehensive loss for the three and six months ended June 30, 2021 and 2020, the condensed consolidated statement of convertible preferred stock and stockholders’ equity for the three and six months ended June 30, 2021 and 2020 and the condensed consolidated statements of cash flows for the six months ended June 30, 2021 and 2020 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement for interim reporting. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K, filed with the Securities and Exchange Commission Going concern Since inception, the Company’s activities have consisted primarily of performing research and development to advance its technologies. The Company is still in the development phase and has not been marketing its technologies to date. Through June 30, 2021, the Company has funded its operations with proceeds from sales of common stock, sales of convertible preferred stock, sales of redeemable convertible preferred stock, collaboration and licensing agreements, grants and borrowings under various agreements with foreign public funding agencies. Since inception, the Company has incurred recurring losses, including net losses of $34.4 million for the six months ended June 30, 2021 and $44.1 million for the year ended December 31, 2020. As of June 30, 2021, the Company had an accumulated deficit of $181.5 million. The Company expects to continue to generate operating losses in the foreseeable future. As of August 12, 2021, the filing date of this Quarterly Report on Form 10-Q, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses, capital expenditure requirements and debt service payments through at least 12 months from the issuance date of the condensed consolidated financial statements. The Company will seek additional funding in order to reach its development and commercialization objectives. The Company will seek funds through further equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. The accompanying condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and classification of assets or the amounts and classification of liabilities that might be necessary if the Company is unable to continue as a going concern. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue, income and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the recognition of revenue and income, the accrual of research and development expenses, the present value of lease right of use assets and corresponding liabilities, the valuation of common and preferred stock, the valuation of stock-based awards and the valuation of current and non-current loans payable. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international customers and markets. The Company’s accounting estimates and assumptions may change over time in response to COVID-19 and the change could be material in future periods. As of the date of issuance of these unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update estimates, judgments or revise the carrying value of any assets or liabilities. Actual results may differ from those estimates or assumptions. Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of an equity financing, these costs are recorded in stockholders’ equity as a reduction of the additional paid-in capital on a pro-rata basis generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. Concentrations of credit risk and of significant suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and short-term bank deposits held with banks in excess of publicly insured limits. The net proceeds from the Company’s offerings have been deposited in interest-bearing bank accounts with investment grade U.S. financial institutions and have been partially invested in a money market fund as of June 30, 2021. The money market fund, held in U.S. dollar, is primarily invested in U.S. and foreign short-term debt obligations. As of December 31, 2020 and June 30, 2021, the Company’s cash and cash equivalents included smaller amounts of cash balances held in accounts with European banks at the Company’s Austrian subsidiary, partially in euros. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials. As of June 30, 2021 and December 31, 2020, respectively, Gilead Sciences, Inc. accounted for the majority of the accounts receivable balance. For the six months ended June 30, 2021 and June 30, 2020 one customer accounted for the majority of the Company’s revenues. No other customers accounted for more than 10.0% of accounts receivable or net sales. The Company monitors the financial performance of its customers so that it can appropriately respond to changes in their credit worthiness. To date, the Company has not experienced any significant losses with respect to collection of its accounts receivable. Cash equivalents The Company considers all highly liquid investments with maturities of three months or less at the date of purchase to be cash equivalents. As of June 30, 2021 and December 31, 2020, cash equivalents consisted of money market funds. Fair value measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ● Level 1 - Quoted prices in active markets for identical assets or liabilities. ● Level 2 - Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents are carried at fair value, determined according to the fair value hierarchy described above (see Note 4). Property and equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: ​ ​ ​ ​ ​ Estimated useful life Leasehold improvements 2 - 5 years Laboratory equipment 2 - 10 years Furniture and fixtures 2 - 10 years Computer equipment and software 2 - 4 years ​ Costs for capital assets not yet placed into service are capitalized as construction-in-progress and depreciated once placed into service. Expenditures for repairs and maintenance are charged to expense as incurred. Leases The determination whether an arrangement qualifies as a lease is made at contract inception. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the option will be exercised. The Company uses the implicit rate when readily determinable and uses its incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. The incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. The lease payments used to determine operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized as operating lease assets on the consolidated balance sheets. In addition, certain of the Company’s arrangements contain lease and non-lease components. The Company generally separates lease payments from non-lease payments. Operating leases are reflected in operating lease assets, in accrued expenses and other current liabilities and in non-current operating lease liabilities in the consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. The right-of-use asset is tested for impairment in accordance with Accounting Standards Codification (“ASC”) 360. Capitalized Software Development Cost The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as software business applications used in the normal course of business, are capitalized in accordance with ASC 350. These costs are recognized on a straight-line basis in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement, over the term of the arrangement, plus reasonably certain renewals. Revenue recognition from contracts with customers The Company entered into a collaboration and license agreement (the “Gilead Agreement”) with Gilead Sciences, Inc. (“Gilead”) whereby the parties agreed to collaborate with respect to two preclinical research programs to evaluate potential vaccine products for the treatment, cure, diagnosis or prevention of the hepatitis B virus (“HBV”) and the human immunodeficiency virus (“HIV”). The Company’s performance obligations under the terms of this agreement include one combined performance obligation for each research program (HBV and HIV) comprised of the transfer of intellectual property rights (licenses) and providing research and development services. The licenses do not represent distinct performance obligations, because they cannot be used without the research and development services. Payments to the Company under this agreement include a non-refundable up-front payment, payments for research and development activities, payments based upon the achievement of defined milestones, and if certain future conditions are met, payments for manufacturing services, commercial milestones and royalties on product sales. The Company evaluates its collaboration and licensing arrangements pursuant to ASC 606 Revenue from Contracts with Customers. To determine the recognition of revenue from arrangements that fall within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. Under ASC 606, the Company applies significant judgement to evaluate whether the obligations under the collaboration and licensing arrangement, represent separate or one or more combined performance obligations, the allocation of the transaction price to identified performance obligations, and the determination of when milestone payments are probable of being received. Upfront payment The non-refundable upfront-payment received by the Company under the Gilead Agreement is recorded as deferred revenue and allocated between the two research program performance obligations. Such amounts are recognized as revenue over the performance period of the respective services on a percent of completion basis using total estimated research and development labor hours (input method) for each of the obligations. The percent of completion basis using labor hours was considered the best measure of progress in which control of the combined performance obligations transfers to the customer, due to the short time intervals in which research results are shared with the collaboration partner and the nature of the work being performed. Reimbursement for services Under the Gilead Agreement, the Company incurs employee expenses as well as external costs for research and manufacturing activities presented as operating expenses or prepaid expenses. Based on the nature of the Company's responsibilities under the collaboration arrangement, reimbursement of those costs are presented as revenue and not deducted from expenses, as the Company controls the research activities. Amounts of consideration allocated to the performance of research or manufacturing services are recognized over the period in which services are performed. Reimbursements for external costs are recognized as revenues in the period in which the goods or services are received and external costs are recognized. Unpaid reimbursement amounts are presented as Accounts receivable. ​ Research and development milestones The Gilead Agreement includes contingent milestone payments related to specified preclinical and clinical development milestones. These milestone payments represent variable consideration that are not initially recognized within the transaction price as they are fully constrained under the guidance in ASC 606, due to the scientific uncertainties and the required commitment from Gilead. The Company will continue to assess the probability of significant reversals for any amounts that become likely to be realized prior to recognizing the variable consideration associated with these payments within the transaction price. Sales-based milestones and royalty payments The Gilead Agreement also includes certain sales-based milestone and royalty payments upon successful commercialization of a licensed product. In accordance with ASC 606-10-55-65 Sales-Based or Usage-Based Royalties, the Company recognizes revenues from sales-based milestone and royalty payments at the later of (i) the occurrence of the subsequent sale; or (ii) the performance obligation to which some or all of the sales-based milestone or royalty payments has been allocated has been satisfied. The Company anticipates recognizing these milestones and royalty payments if and when subsequent sales are generated from a licensed product by the collaboration partner. Cost to fulfill contracts The Company incurs costs for personnel, supplies and other costs related to its laboratory operations as well as fees from third parties and license expenses in connection with its research and development obligations under the collaboration and licensing agreement. These costs are recognized as research and development expenses over the period in which services are performed. Sublicense fees triggered by the receipt of payments are capitalized as an asset when the obligation to pay the fee arises. The capitalized asset is amortized over the period in which the revenue from the triggering payment is recognized. Recent accounting pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that the Company adopts as of the specified effective date. Recently Issued Accounting Pronouncements In May 2021, the FASB issued ASU 2021-04, which provides a principles-based framework for issuers to account for a modification or exchange of freestanding equity-classified written call options. The new guidance clarifies that to the extent applicable, issuers should first reference other GAAP to account for the effect of a modification. If other GAAP is not applicable, the guidance clarifies whether to account for the modification or exchange as an adjustment to equity, with the related EPS implications, or an expense, and if so, the manner and pattern of recognition. The accounting depends on the substance of the transaction, such as whether the modification or exchange is the result of raising equity, a financing transaction, or some other event. The new guidance is effective for annual periods beginning after December 15, 2021, including interim periods within those fiscal years with early adoption permitted. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In January 2021, the FASB issued ASU 2021-01, which amends the scope of the recent reference rate reform guidance (ASC 848). New optional expedients allow derivative instruments impacted by changes in the interest rate used for margining, discounting, or contract price alignment (i.e., discount transition) to qualify for certain optional relief. The new optional expedients for contract modifications and hedge accounting are expected to benefit companies, including those with certain centrally cleared derivatives affected by a discount rate transition in 2020. The guidance is effective immediately and can be applied retrospectively to any interim period beginning January 1, 2020 or prospectively to any new modifications in any period including or subsequent to the issuance date. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In August 2020, the FASB issued ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40). The ASU provides guidance that simplified the accounting for certain financial instruments with characteristics of liabilities and equity. The new guidance reduced the number of accounting models for convertible debt and convertible preferred stock instruments and made certain disclosure amendments intended to improve the information provided to users. The guidance also amended the derivative guidance for the “own stock” scope exception, which exempts qualifying instruments from being accounted for as derivatives if certain criteria are met. Finally, the standard changed the way certain convertible instruments are treated when calculating earnings per share. This guidance was effective upon issuance and will need to be applied for interim periods within those fiscal years beginning after December 15, 2023, with early adoption permitted. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions to address the impact of reference rate reform where contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate need to be discontinued. This guidance was effective upon issuance and generally can be applied through December 31, 2022. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements.

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	6 Months Ended
	Jun. 30, 2021
Collaboration and Licensing Agreements
Collaboration and Licensing Agreements	3. Collaboration and Licensing Agreements Gilead Collaboration and License Agreement In June 2018, the Company entered into the Gilead Agreement whereby the Company and Gilead agreed to collaborate with respect to two preclinical research programs to evaluate potential vaccine products for the treatment, cure, diagnosis or prevention of HBV and HIV. Under the Gilead Agreement, the Company granted Gilead an exclusive, royalty-bearing license to the Company’s technology platforms. Upon entering into the agreement, the Company received a non-refundable $10.0 million upfront payment from Gilead. Gilead is also obligated to make additional payments to the Company upon the achievement of pre-clinical, development and commercial milestones. The development milestones amount to a total of $280 million. The commercial milestones amount to a total of $100 million. Additionally, Gilead is obligated to pay royalties on net sales for each program. Payments from Gilead generally have a 60 days payment term. The $10.0 million upfront payment received in 2018 and a $4.0 million milestone payment received in 2020 were initially recorded as deferred revenue in the consolidated balance sheet and are recognized as revenue when revenue recognition criteria are met. As of June 30, 2021, $0.7 million of upfront and milestone payments were included as a liability in deferred revenues, current and non-current. Approximately 67% of deferred revenue is expected to be recognized as revenue in the remainder of 2021 and the remaining 33% in 2022. As of June 30, 2021, $2.3 million of cost reimbursements for research and development services were included as a liability in deferred revenues. Reimbursements for external costs are recognized as revenues in the period in which the services are provided and external costs are recognized. In the three months ended June 30, 2021, the Company recognized $0.4 million of the upfront payment received in 2018 and $0.6 million of the $4.0 million milestone payment received in 2020 as revenue. Furthermore, the Company recognized $4.4 million revenue from cost reimbursements for research and development services, of which $0.4 million were initially recorded as deferred revenue in the consolidated balance sheet. For the three months ended June 30, 2020, revenue from reimbursement of research and development expenses was $4.1 million, and the Company recognized $1.0 million of the upfront payment received in 2018 and $0.6 million of the $4.0 million milestone payment received in 2020 as revenue. In addition, the Company fully recognized revenue for a $1.0 million milestone payment for a milestone achieved in the three months ended June 30, 2020. In the six months ended June 30, 2021, the Company recognized $0.5 million of the upfront payment received in 2018 and $1.2 million of the $4.0 million milestone payment received in 2020 as revenue. Furthermore, the Company recognized $9.0 million revenue from cost reimbursements for research and development services, of which $0.7 million were initially recorded as deferred revenue in the consolidated balance sheet. For the six months ended June 30, 2020, revenue from reimbursement of research and development expenses was $6.8 million, and the Company recognized $1.4 million of the upfront payment received in 2018 and $1.2 million of the $4.0 million milestone payment received in 2020 as revenue. In addition, the Company fully recognized revenue for a $1.0 million milestone payment for a milestone achieved in the six months ended June 30, 2020. Sublicense fees payable to certain licensors of technologies upon the receipt of the deferred upfront and milestone payments, were capitalized as a contract asset and will be amortized over the period in which the revenue from the triggering payment is recognized. As of June 30, 2021 and December 31, 2020, the contract asset and the liability relating to the sublicense payment was less than $0.1 million and $0.1 million, respectively. ​

Fair Value of Financial Assets

Fair Value of Financial Assets	6 Months Ended
	Jun. 30, 2021
Fair Value of Financial Assets
Fair Value of Financial Assets	4. Fair Value of Financial Assets The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicating the level of the fair value hierarchy utilized to determine such fair values (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at June 30, 2021 Using ​ Level 1 Level 2 Level 3 ​ Total Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 35,399 $ — $ — ​ $ 35,399 Total ​ $ 35,399 $ — $ — ​ $ 35,399 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at December 31, 2020 Using ​ Level 1 Level 2 Level 3 ​ Total Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 35,397 $ — $ — ​ $ 35,397 Total ​ $ 35,397 $ — $ — ​ $ 35,397 ​ During the six months ended June 30, 2021 1 3 ​

Property and equipment, net

Property and equipment, net	6 Months Ended
	Jun. 30, 2021
Property and equipment, net
Property and equipment, net	5. Property and equipment, net Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 ​ ​ ​ ​ ​ ​ ​ Leasehold improvements ​ $ 3,419 ​ $ 3,322 Construction in progress ​ ​ 6,448 ​ ​ 28 Laboratory equipment ​ 6,691 ​ 5,982 Furniture and fixtures ​ 573 ​ 430 Computer equipment and software ​ 1,909 ​ 1,554 Property and equipment, gross ​ 19,040 ​ 11,316 Less: Accumulated depreciation ​ (5,834) ​ (5,097) Property and equipment, net ​ $ 13,206 ​ $ 6,219 ​ Construction-in-progress as of June 30, 2021 related to investments in connection with the Companies GMP manufacturing facility project. Construction-in-progress as of December 31, 2020 related to implementation costs for a cloud computing arrangement which is a service contract.

Receivable research incentive

Receivable research incentive	6 Months Ended
	Jun. 30, 2021
Receivable research incentive
Receivable research incentive	6. Receivable research incentive The Company participates in a research incentive program provided by the Austrian government under which it is entitled to reimbursement of a percentage of qualifying research and development expenses and capital expenditures incurred in Austria. Submissions for reimbursement under the program are submitted annually. Incentive amounts are generally paid out during the calendar year that follows the year of the expenses but remain subject to subsequent examinations by the responsible authority. As of June 30, 2021, the Company recognized receivables of $16.0 million from the research incentive program, which are reported in research incentive receivables in the Company’s condensed consolidated balance sheet. As of December 31, 2020 the receivables from the research incentive program were $15.1 million. During the three months ended June 30, 2021 and 2020, the Company recorded $2.3 million and $1.4 million, respectively, of income related to the incentive program within the Company’s condensed consolidated statements of operations as grant income. During the six months ended June 30, 2021 and 2020, the Company recorded $4.3 million and $2.7 million, respectively, of income related to the incentive program within the Company’s condensed consolidated statements of operations as grant income. ​

Accrued expenses and other curr

Accrued expenses and other current liabilities	6 Months Ended
	Jun. 30, 2021
Accrued expenses and other current liabilities
Accrued expenses and other current liabilities	7. Accrued expenses and other current liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 Salaries and bonuses ​ 3,756 ​ 4,381 Social security contributions ​ 388 ​ 211 Unearned grant income (current) ​ 934 ​ 878 Accrued external research and development expenses ​ ​ 7,408 ​ ​ 895 Accrued external general and administration expenses ​ ​ 589 ​ ​ 634 Accrued for property and equipment acquisitions ​ ​ 2,104 ​ ​ — Finance lease liabilities ​ ​ 138 ​ ​ 155 Other accruals and liabilities ​ 46 ​ 232 ​ ​ $ 15,363 ​ $ 7,386 ​

Loans payable

Loans payable	6 Months Ended
	Jun. 30, 2021
Loans payable
Loans payable	8. Loans payable As of June 30, 2021 and December 31, 2020, loans payable consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 Loans from FFG ​ $ 6,359 ​ $ 6,564 Unamortized debt discount ​ (1,558) ​ (2,027) Total Loans payable, net ​ $ 4,801 ​ $ 4,537 ​ In connection with the funding agreements with the Austrian Research Promotion Agency, ( Österreichische Forschungsförderungsgesellschaft, The FFG Loans bear interest at rates that are below market rates of interest. The Company accounts for the imputed benefit arising from the difference between an estimated market rate of interest and the rate of interest charged by FFG as grant income from FFG. On the date that FFG loan proceeds are received, the Company recognizes the portion of the loan proceeds allocated to grant funding as a discount to the carrying value of the loan and as unearned income, which is recognized as grant income over the term of the funding agreement. ​ In November 2019, the Company agreed to an earlier repayment schedule for $3.3 million of the outstanding loans with FFG. As a result of the change, the Company reduced the deferred income attributable to the imputed benefit from below market interest by $0.3 million and increased the carrying value of the loans by the same amount. ​ No principal repayment was made in the three and six months ended June 30, 2021. No principal repayment was made in the three months ended June 30, 2020. A principal repayment of $1.3 million was made in the six months ended June 30, 2020. ​ ​ As of June 30, 2021, the aggregate minimum future principal payments due in connection with the FFG Loans are summarized as follows (in thousands): ​ ​ ​ ​ ​ Payments Due by Calendar Year Amount 2021 (remaining 6 months) ​ ​ — 2022 ​ ​ 3,197 2023 ​ ​ 1,906 2024 ​ ​ 1,256 Thereafter ​ ​ — Total ​ $ 6,359 ​

Common stock, Class A common st

Common stock, Class A common stock and convertible preferred stock	6 Months Ended
	Jun. 30, 2021
Common stock, Class A common stock and convertible preferred stock
Common stock, Class A common stock and convertible preferred stock	9. Common stock, Class A common stock and convertible preferred stock In June 2018, the Company became the reporting entity in a transaction between entities under common control. In the accompanying condensed consolidated financial statements and notes, the common stock is retrospectively presented as if the Company had been the reporting entity for all periods during which the previous reporting entity was under common control. The Company’s capital structure consists of common stock, Class A common stock and preferred stock. As of June 30, 2021, the Company was authorized to issue 100,000,000 shares of common stock, 3,900,000 shares of Class A common stock and 10,000,000 shares of preferred stock. The Company has designated 2,978 of the 10,000,000 authorized shares of preferred stock as non-voting Series A convertible preferred stock. As of June 30, 2021, the Company had 26,051,846 shares of common stock, 3,819,732 shares of Class A common stock and 2,978 shares of preferred outstanding issued. On April 23, 2019, the Company closed its IPO of 6,000,000 shares of common stock, at an offering price to the public of $14.00 per share. The Company received net proceeds of $74.6 million, after deducting $9.4 million in underwriting discounts and commissions and offering expenses. Upon the closing of the Company’s IPO, all then outstanding shares of Preferred Stock converted into 14,582,161 shares of common stock and 3,819,732 shares of Class A common stock. On December 11, 2020, the Company closed a public offering of 3,910,000 shares of its common stock, which included the full exercise of the underwriters’ option to purchase additional shares and of 2,978 shares of Series A convertible preferred stock at a public offering price of $11.75 and $11,750.00 per share, respectively, for net proceeds of $75.0 million after deducting underwriting discounts and commissions and offering expenses. ​ Holders of common stock are entitled to one vote for each share held on all matters submitted to a vote of the stockholders. The holders of Class A common stock and Series A convertible preferred stock are not entitled to vote, except as required by law. The holders of common stock and Class A common stock do not have any cumulative voting rights. Each holder of Class A common stock has the right to convert each share of Class A common stock into one share of common stock at such holder's election. Each holder of Series A convertible preferred stock has the right to convert each share of Series A convertible preferred stock into 1,000 shares of common stock at any time at the holder’s option, provided that the holder will be prohibited, subject to certain exceptions, from converting Series A preferred stock into shares of our common stock if, as a result of such conversion, the holder, together with its affiliates, would own more than 9.99% of the total number of shares of our common stock then issued and outstanding. Holders of common stock and Class A common stock are entitled to receive ratably any dividends declared by the board of directors out of funds legally available for that purpose, subject to any preferential dividend rights of any outstanding preferred stock. Holders of Series A preferred stock will be entitled to receive dividends at a rate equal to (on an as-if-converted-to-common stock basis), and in the same form and manner as, dividends actually paid on shares of our common stock. Holders of common stock and Class A common stock have no preemptive rights, conversion rights, or other subscription rights or redemption or sinking fund provisions. In the event of a liquidation, dissolution, or winding up of the Company, holders of our Series A preferred stock will receive a payment equal to $0.001 per share of Series A preferred stock before any proceeds are distributed to the holders of common stock. Then, holders of common stock and Class A common stock will be entitled to share ratably in all assets remaining after payment of all debts and other liabilities. ​

Stock-based compensation

Stock-based compensation	6 Months Ended
	Jun. 30, 2021
Stock-based compensation
Stock-based compensation	10. Stock-based compensation 2018 Stock Option and Grant Plan In connection with a transaction between entities under common control by which the Company became the reporting entity in June 2018, the Board of Directors approved the 2018 Stock Option and Grant Plan, by which options granted by the previous reporting entity under the 2016 Stock Option Plan and outstanding at the time of the effectiveness of the transaction were replaced at similar commercial terms. In the accompanying condensed consolidated financial statements and notes, options issued under previous stock option plans and respective compensation expenses are retrospectively presented as if such options had been issued and outstanding under the 2018 Stock Option and Grant Plan for all periods during which the previous reporting entity was under common control. The exercise price for options granted as a replacement of the 2016 Stock Option Plan is the U.S. dollar equivalent of €0.09, except for 23,286 options granted to an US employee, for which the exercise price is $2.93 following a repricing of these options in December 2018. For any new options, the exercise price shall not be less than 100% of the fair market value of the common stock on the grant date. Options granted under the 2018 Stock Option and Grant Plan generally vest over four years, with 25% of the options vesting upon the first anniversary of the grant date and the remaining 75% of the options vesting in 12 equal quarterly installments following the first anniversary of the grant date, provided the option holder continues to have an employment or service relationship with the Company on each vesting date. The options expire on the 10 th 2019 Stock Option and Incentive Plan On April 1, 2019, the Company’s stockholders approved the 2019 Stock Option and Incentive Plan, which became effective as of the effective date of the registration statement in connection with the Company’s IPO. The plan provides for the grant of shares of restricted stock, long term incentive awards, stock options or other equity-based awards. The maximum number of shares of the Company’s common stock that may be issued under the Company’s 2019 Stock Option and Incentive Plan is 3,630,686 shares which shall be cumulatively increased each year by up to 4% of the then outstanding number of shares. Options granted under the 2019 Stock Option and Incentive Plan generally vest over four years, with 25% of the options vesting upon the first anniversary of the grant date and the remaining 75% of the options vesting in 12 equal quarterly installments following the first anniversary of the grant date, provided the option holder continues to have an employment or service relationship with the Company on each vesting date. Initial options granted to non-executive directors upon their election generally vest over a three-year term with 33% of the options vesting upon the first anniversary of the grant date and the remaining 67% of the options vesting in eight equal quarterly installments following the first anniversary of the grant date. Option re-grants to non-executive directors generally vest on the first anniversary of the grant date. The options expire on the 10 th Stock option valuation The Company estimates the option’s fair value on the date of grant using the Black-Scholes option-pricing model. Black-Scholes utilizes assumptions related to expected term, volatility, the risk-free interest rate, the dividend and employee exercise behavior. Forfeitures are accounted for when they occur. Expected volatilities utilized in the Black-Scholes model are based on historical volatilities of a group of comparable companies. The group of representative companies have characteristics similar to the Company, including the stage of product development and focus of the life science industry. Management believes that this represents the most accurate basis for estimating expected future volatilities under the current conditions. The risk-free interest rate is derived from the yields for U.S. Treasuries with a remaining term approximating the expected life of the options. The expected term represents the period of time that the options granted are expected to be outstanding. ​ The following table summarizes the assumptions used in the Black-Scholes option-pricing model for estimating the fair value of stock options granted during: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three and six months ended June 30, ​ ​ 2021 2020 ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ 1.07 % 0.44 % Expected term (in years) 6.1 6.0 Expected volatility 85.5 % 79.0 % Expected dividends — % — % ​ For the 2021 and 2020 grants, the Company used the simplified method in developing an estimate of the expected term due to a lack of historical exercise data. ​ Stock option activity The following table summarizes the Company’s stock option activity since January 1, 2021 (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ Shares Price Term Value ​ ​ ​ ​ ​ ​ ​ (in years) ​ ​ ​ Outstanding as of December 31, 2020 3,555,945 ​ $ 8.45 7.9 ​ $ 12,839 Granted 859,956 ​ 12.36 ​ ​ ​ Exercised (79,487) ​ 2.97 ​ ​ ​ Forfeited (52,419) ​ 10.42 ​ ​ ​ Outstanding as of June 30, 2021 4,283,995 ​ $ 9.31 7.9 ​ $ 8,344 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options exercisable as of June 30, 2021 1,960,775 ​ $ 7.09 7.0 ​ $ 7,223 Options unvested as of June 30, 2021 2,323,220 ​ $ 11.17 8.7 ​ $ 1,121 ​ The aggregate intrinsic value of stock options was calculated as the difference between the exercise price of the stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The estimated fair value per common stock used for calculating the intrinsic values as of June 30, 2021 and December 31, 2020, was $9.16 and $11.09, respectively. Cash received from option exercise under share-based payment arrangements for the six months ended June 30, 2021 was $237 thousand. Cash received from option exercise under share-based payment arrangements for the six months ended June 30, 2020 was $15 thousand. Restricted Stock Units In 2020, the Company granted restricted stock units with time-based vesting conditions to officers, employees and a consultant to compensate them for a temporary salary or fee reduction in response to the coronavirus pandemic. The restricted stock units are subject to time-based vesting conditions and generally vest in four equal installments between March 2021 and November 2021. The Company measures the fair value of restricted stock units on the date of grant using the grant date market price of the underlying shares. Expenses are recorded using the graded-vesting method. The table below summarizes the Company’s restricted stock unit activity since December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Grant ​ ​ Number of ​ Date Fair ​ Shares Value Outstanding as of December 31, 2020 43,700 ​ $ 11.87 Granted — ​ — Vested (23,647) ​ 11.87 Forfeited — ​ — Outstanding as of June 30, 2021 20,053 ​ $ 11.87 ​ Stock-based compensation Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended June 30, ​ Six months ended June 30, ​ 2021 2020 2021 2020 Research and development expenses ​ $ 1,145 ​ $ 771 ​ $ 1,769 ​ $ 1,448 General and administrative expenses ​ 1,482 ​ 1,380 ​ 2,379 ​ 2,797 ​ ​ $ 2,627 ​ $ 2,151 ​ $ 4,148 ​ $ 4,245 ​

Income taxes

Income taxes	6 Months Ended
	Jun. 30, 2021
Income taxes
Income taxes	11. Income taxes Income tax expense during the three months ended June 30, 2021 and 2020 resulted from minimum tax obligations. During the three months ended June 30, 2021 and 2020, the Company recorded no income tax benefits for the net operating losses incurred, due to its uncertainty of realizing a benefit from those items. The Company’s losses before income taxes were generated in the United States and Austria. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets resulting from its net operating loss carryforwards. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of its deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of June 30, 2021 and December 31, 2020. Management reevaluates the positive and negative evidence at each reporting period. ​ ​

Commitments and contingencies

Commitments and contingencies	6 Months Ended
	Jun. 30, 2021
Commitments and contingencies
Commitments and contingencies	12. Commitments and contingencies Operating and Finance Leases The Company leases real estate, including office and laboratory space and has entered into various other agreements with respect to assets used in conducting its business. The Company is required to maintain a cash balance of $0.4 million to secure letters of credit associated with real estate leases. This amount was classified as non-current restricted cash in the Company’s condensed consolidated balance sheet as of June 30, 2021. As of June 30, 2021 and December 31, 2020, the Company’s operating lease right-of-use assets were $5.3 million and $6.5 million, respectively, which are reported in operating lease right-of-use assets in the Company’s condensed consolidated balance sheets. As of June 30, 2021 and December 31, 2020, the Company’s finance lease right-of-use assets were $1.0 million and $1.3 million, respectively, which are reported in finance lease right-of-use assets in the Company’s condensed consolidated balance sheets. As of June 30, 2021, the Company had outstanding operating lease obligations of $4.8 million, of which $2.0 million is reported in operating lease liabilities, current portion and $2.8 million is reported in operating lease liabilities, non-current portion in the Company’s condensed consolidated balance sheets. As of June 30, 2021, the Company had outstanding finance lease obligations of $0.3 million, of which $0.1 million is reported in accrued expenses and other current liabilities other non-current liabilities accrued expenses and other current liabilities other non-current liabilities The Company subleased certain of its leased real estate that it did not utilize to a third party. The sublease was qualified as an operating lease and was terminated in April 2021. Contract manufacturing arrangements The Company has entered into arrangements with contract manufacturing organizations (“CMOs”) for manufacturing of materials for research and development purposes, including manufacturing of clinical trial materials. These contracts generally provide for non-cancellable obligations or cancellation penalties depending on the time of cancellation. As of June 30, 2021, the Company’s total non-cancellable obligations under contracts with CMOs, excluding embedded lease liabilities, were $11.4 million, of which $9.7 million relate to 2021 (remaining six months) deliverables, $1.6 million relate to 2022, less than $0.1 million relate to 2023, and less than $0.1 million relate to 2024 deliverables. Intellectual property licenses The Company has entered into certain license agreements under which it is obligated to make milestone payments upon the achievement of certain development and regulatory milestones, to pay royalties on net sales of licensed products, and to pay a percentage of the sublicense fees which the Company receives from its sublicensees. In the three and six months ended June 30, 2021, the Company recorded $0.3 million and $0.5 million, respectively, in licensing fees from intellectual property licenses as research and development expenses. These amounts mainly related to the upfront payment and milestone payments received by the Company under the Gilead Agreement. The amounts recognized as expenses have been agreed to by the licensors but calculation of sublicensing fees on future payments may be subject to interpretation and may change until agreed to by the receiving party. Indemnification agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its Board of Directors and senior management that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of June 30, 2021 and December 31, 2020. Legal proceedings At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. While it is not feasible to predict the outcome of these matters with certainty, and some lawsuits, claims or proceedings may be disposed or decided unfavorably, the Company does not expect that any asserted or un-asserted legal claims or proceedings, individually or in the aggregate, will have a material adverse effect on the Company. The Company expenses the costs related to such legal proceedings as incurred. ​

Net loss per share

Net loss per share	6 Months Ended
	Jun. 30, 2021
Net loss per share
Net loss per share	13. Net loss per share The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except for per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended June 30, ​ Six months ended June 30, ​ 2021 2020 2021 2020 Numerator: ​ ​ ​ ​ Net loss ​ $ (17,153) ​ $ (7,092) ​ $ (34,391) ​ $ (18,018) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding, basic and diluted ​ ​ 29,826,269 ​ ​ 25,647,819 ​ ​ 29,807,382 ​ ​ 25,638,913 Weighted-average Series A convertible preferred shares outstanding, basic and diluted, presented as if converted into common stock (1) ​ ​ 2,978,000 ​ ​ — ​ ​ 2,978,000 ​ ​ — Total number of shares used to calculate net loss per share, basic and diluted ​ 32,804,269 ​ 25,647,819 ​ 32,785,382 ​ 25,638,913 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share, basic and diluted ​ $ (0.52) ​ $ (0.28) ​ $ (1.05) ​ $ (0.70) (1) ​ Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share for all periods as the inclusion of all potential common shares (Common Stock and Class A Common Stock) outstanding would have been anti-dilutive. Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Three and six months ended June 30, ​ 2021 2020 Options issued and outstanding 4,283,995 ​ 3,585,971 Unvested restricted stock units ​ 20,053 ​ — Total 4,304,048 3,585,971 ​

Related parties

Related parties	6 Months Ended
	Jun. 30, 2021
Related parties
Related parties	14. Related parties Following the expiry of the consultancy agreement between the Company and its Chief Scientific Officer, Daniel Pinschewer, on March 19, 2020 the Company entered into a new consultancy agreement with Daniel Pinschewer, pursuant to which he serves as Scientific Advisor to the Chief Executive Officer. The Company is party to research and service arrangements with the University of Basel. Daniel Pinschewer, formerly Chief Scientific Officer, and his spouse are employees of the University of Basel and both involved in providing the services under these arrangements. The University of Basel is also entitled to receive de minimis royalties on the net sales of any product that is based on a patent created by Daniel Pinschewer in the course of his consulting services to the Company. Payments to the University of Basel during Daniel Pinschewer’s term as Chief Scientific Officer were reported as related party transactions but payments following the expiry of that role in March 2020 were no longer considered related party transactions. In the three and six months ended June 30, 2021, the Company recorded no related party transactions. In the six months ended June 30, 2020, the Company recorded $0.3 million in research and development expenses for service fees paid to the University of Basel, which represented related party transactions. None of these expenses were recorded in the three months ended June 30, 2020.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	6 Months Ended
	Jun. 30, 2021
Summary of significant accounting policies
Basis of presentation	Basis of presentation The Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying condensed consolidated balance sheet as of June 30, 2021, the condensed consolidated statements of operations, and comprehensive loss for the three and six months ended June 30, 2021 and 2020, the condensed consolidated statement of convertible preferred stock and stockholders’ equity for the three and six months ended June 30, 2021 and 2020 and the condensed consolidated statements of cash flows for the six months ended June 30, 2021 and 2020 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement for interim reporting. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K, filed with the Securities and Exchange Commission
Going concern	Going concern Since inception, the Company’s activities have consisted primarily of performing research and development to advance its technologies. The Company is still in the development phase and has not been marketing its technologies to date. Through June 30, 2021, the Company has funded its operations with proceeds from sales of common stock, sales of convertible preferred stock, sales of redeemable convertible preferred stock, collaboration and licensing agreements, grants and borrowings under various agreements with foreign public funding agencies. Since inception, the Company has incurred recurring losses, including net losses of $34.4 million for the six months ended June 30, 2021 and $44.1 million for the year ended December 31, 2020. As of June 30, 2021, the Company had an accumulated deficit of $181.5 million. The Company expects to continue to generate operating losses in the foreseeable future. As of August 12, 2021, the filing date of this Quarterly Report on Form 10-Q, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses, capital expenditure requirements and debt service payments through at least 12 months from the issuance date of the condensed consolidated financial statements. The Company will seek additional funding in order to reach its development and commercialization objectives. The Company will seek funds through further equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. The accompanying condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. The condensed consolidated financial statements do not reflect any adjustments relating to the recoverability and classification of assets or the amounts and classification of liabilities that might be necessary if the Company is unable to continue as a going concern.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue, income and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the recognition of revenue and income, the accrual of research and development expenses, the present value of lease right of use assets and corresponding liabilities, the valuation of common and preferred stock, the valuation of stock-based awards and the valuation of current and non-current loans payable. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international customers and markets. The Company’s accounting estimates and assumptions may change over time in response to COVID-19 and the change could be material in future periods. As of the date of issuance of these unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update estimates, judgments or revise the carrying value of any assets or liabilities. Actual results may differ from those estimates or assumptions.
Deferred offering costs	Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of an equity financing, these costs are recorded in stockholders’ equity as a reduction of the additional paid-in capital on a pro-rata basis generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss.
Concentrations of credit risk and of significant suppliers	Concentrations of credit risk and of significant suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and short-term bank deposits held with banks in excess of publicly insured limits. The net proceeds from the Company’s offerings have been deposited in interest-bearing bank accounts with investment grade U.S. financial institutions and have been partially invested in a money market fund as of June 30, 2021. The money market fund, held in U.S. dollar, is primarily invested in U.S. and foreign short-term debt obligations. As of December 31, 2020 and June 30, 2021, the Company’s cash and cash equivalents included smaller amounts of cash balances held in accounts with European banks at the Company’s Austrian subsidiary, partially in euros. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials. As of June 30, 2021 and December 31, 2020, respectively, Gilead Sciences, Inc. accounted for the majority of the accounts receivable balance. For the six months ended June 30, 2021 and June 30, 2020 one customer accounted for the majority of the Company’s revenues. No other customers accounted for more than 10.0% of accounts receivable or net sales. The Company monitors the financial performance of its customers so that it can appropriately respond to changes in their credit worthiness. To date, the Company has not experienced any significant losses with respect to collection of its accounts receivable.
Cash equivalents	Cash equivalents The Company considers all highly liquid investments with maturities of three months or less at the date of purchase to be cash equivalents. As of June 30, 2021 and December 31, 2020, cash equivalents consisted of money market funds.
Fair value measurements	Fair value measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: ● Level 1 - Quoted prices in active markets for identical assets or liabilities. ● Level 2 - Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. ● Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents are carried at fair value, determined according to the fair value hierarchy described above (see Note 4).
Property and equipment	Property and equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows: ​ ​ ​ ​ ​ Estimated useful life Leasehold improvements 2 - 5 years Laboratory equipment 2 - 10 years Furniture and fixtures 2 - 10 years Computer equipment and software 2 - 4 years ​ Costs for capital assets not yet placed into service are capitalized as construction-in-progress and depreciated once placed into service. Expenditures for repairs and maintenance are charged to expense as incurred.
Leases	Leases The determination whether an arrangement qualifies as a lease is made at contract inception. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the option will be exercised. The Company uses the implicit rate when readily determinable and uses its incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. The incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. The lease payments used to determine operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized as operating lease assets on the consolidated balance sheets. In addition, certain of the Company’s arrangements contain lease and non-lease components. The Company generally separates lease payments from non-lease payments. Operating leases are reflected in operating lease assets, in accrued expenses and other current liabilities and in non-current operating lease liabilities in the consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. The right-of-use asset is tested for impairment in accordance with Accounting Standards Codification (“ASC”) 360.
Capitalized Software Development Cost	Capitalized Software Development Cost The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as software business applications used in the normal course of business, are capitalized in accordance with ASC 350. These costs are recognized on a straight-line basis in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement, over the term of the arrangement, plus reasonably certain renewals.
Revenue recognition from contracts with customers	Revenue recognition from contracts with customers The Company entered into a collaboration and license agreement (the “Gilead Agreement”) with Gilead Sciences, Inc. (“Gilead”) whereby the parties agreed to collaborate with respect to two preclinical research programs to evaluate potential vaccine products for the treatment, cure, diagnosis or prevention of the hepatitis B virus (“HBV”) and the human immunodeficiency virus (“HIV”). The Company’s performance obligations under the terms of this agreement include one combined performance obligation for each research program (HBV and HIV) comprised of the transfer of intellectual property rights (licenses) and providing research and development services. The licenses do not represent distinct performance obligations, because they cannot be used without the research and development services. Payments to the Company under this agreement include a non-refundable up-front payment, payments for research and development activities, payments based upon the achievement of defined milestones, and if certain future conditions are met, payments for manufacturing services, commercial milestones and royalties on product sales. The Company evaluates its collaboration and licensing arrangements pursuant to ASC 606 Revenue from Contracts with Customers. To determine the recognition of revenue from arrangements that fall within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. Under ASC 606, the Company applies significant judgement to evaluate whether the obligations under the collaboration and licensing arrangement, represent separate or one or more combined performance obligations, the allocation of the transaction price to identified performance obligations, and the determination of when milestone payments are probable of being received. Upfront payment The non-refundable upfront-payment received by the Company under the Gilead Agreement is recorded as deferred revenue and allocated between the two research program performance obligations. Such amounts are recognized as revenue over the performance period of the respective services on a percent of completion basis using total estimated research and development labor hours (input method) for each of the obligations. The percent of completion basis using labor hours was considered the best measure of progress in which control of the combined performance obligations transfers to the customer, due to the short time intervals in which research results are shared with the collaboration partner and the nature of the work being performed. Reimbursement for services Under the Gilead Agreement, the Company incurs employee expenses as well as external costs for research and manufacturing activities presented as operating expenses or prepaid expenses. Based on the nature of the Company's responsibilities under the collaboration arrangement, reimbursement of those costs are presented as revenue and not deducted from expenses, as the Company controls the research activities. Amounts of consideration allocated to the performance of research or manufacturing services are recognized over the period in which services are performed. Reimbursements for external costs are recognized as revenues in the period in which the goods or services are received and external costs are recognized. Unpaid reimbursement amounts are presented as Accounts receivable. ​ Research and development milestones The Gilead Agreement includes contingent milestone payments related to specified preclinical and clinical development milestones. These milestone payments represent variable consideration that are not initially recognized within the transaction price as they are fully constrained under the guidance in ASC 606, due to the scientific uncertainties and the required commitment from Gilead. The Company will continue to assess the probability of significant reversals for any amounts that become likely to be realized prior to recognizing the variable consideration associated with these payments within the transaction price. Sales-based milestones and royalty payments The Gilead Agreement also includes certain sales-based milestone and royalty payments upon successful commercialization of a licensed product. In accordance with ASC 606-10-55-65 Sales-Based or Usage-Based Royalties, the Company recognizes revenues from sales-based milestone and royalty payments at the later of (i) the occurrence of the subsequent sale; or (ii) the performance obligation to which some or all of the sales-based milestone or royalty payments has been allocated has been satisfied. The Company anticipates recognizing these milestones and royalty payments if and when subsequent sales are generated from a licensed product by the collaboration partner. Cost to fulfill contracts The Company incurs costs for personnel, supplies and other costs related to its laboratory operations as well as fees from third parties and license expenses in connection with its research and development obligations under the collaboration and licensing agreement. These costs are recognized as research and development expenses over the period in which services are performed. Sublicense fees triggered by the receipt of payments are capitalized as an asset when the obligation to pay the fee arises. The capitalized asset is amortized over the period in which the revenue from the triggering payment is recognized.
Recent accounting pronouncements	Recent accounting pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that the Company adopts as of the specified effective date. Recently Issued Accounting Pronouncements In May 2021, the FASB issued ASU 2021-04, which provides a principles-based framework for issuers to account for a modification or exchange of freestanding equity-classified written call options. The new guidance clarifies that to the extent applicable, issuers should first reference other GAAP to account for the effect of a modification. If other GAAP is not applicable, the guidance clarifies whether to account for the modification or exchange as an adjustment to equity, with the related EPS implications, or an expense, and if so, the manner and pattern of recognition. The accounting depends on the substance of the transaction, such as whether the modification or exchange is the result of raising equity, a financing transaction, or some other event. The new guidance is effective for annual periods beginning after December 15, 2021, including interim periods within those fiscal years with early adoption permitted. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In January 2021, the FASB issued ASU 2021-01, which amends the scope of the recent reference rate reform guidance (ASC 848). New optional expedients allow derivative instruments impacted by changes in the interest rate used for margining, discounting, or contract price alignment (i.e., discount transition) to qualify for certain optional relief. The new optional expedients for contract modifications and hedge accounting are expected to benefit companies, including those with certain centrally cleared derivatives affected by a discount rate transition in 2020. The guidance is effective immediately and can be applied retrospectively to any interim period beginning January 1, 2020 or prospectively to any new modifications in any period including or subsequent to the issuance date. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In August 2020, the FASB issued ASU 2020-06, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40). The ASU provides guidance that simplified the accounting for certain financial instruments with characteristics of liabilities and equity. The new guidance reduced the number of accounting models for convertible debt and convertible preferred stock instruments and made certain disclosure amendments intended to improve the information provided to users. The guidance also amended the derivative guidance for the “own stock” scope exception, which exempts qualifying instruments from being accounted for as derivatives if certain criteria are met. Finally, the standard changed the way certain convertible instruments are treated when calculating earnings per share. This guidance was effective upon issuance and will need to be applied for interim periods within those fiscal years beginning after December 15, 2023, with early adoption permitted. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions to address the impact of reference rate reform where contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate need to be discontinued. This guidance was effective upon issuance and generally can be applied through December 31, 2022. The Company is currently assessing the impact that this guidance will have on its consolidated financial statements.

Summary of significant accoun_3

Summary of significant accounting policies (Tables)	6 Months Ended
	Jun. 30, 2021
Summary of significant accounting policies
Schedule of estimated useful life of each asset	​ ​ ​ ​ ​ Estimated useful life Leasehold improvements 2 - 5 years Laboratory equipment 2 - 10 years Furniture and fixtures 2 - 10 years Computer equipment and software 2 - 4 years ​

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value of Financial Assets
Schedule of financial assets measured at fair value on a recurring basis	The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicating the level of the fair value hierarchy utilized to determine such fair values (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at June 30, 2021 Using ​ Level 1 Level 2 Level 3 ​ Total Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 35,399 $ — $ — ​ $ 35,399 Total ​ $ 35,399 $ — $ — ​ $ 35,399 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurement at December 31, 2020 Using ​ Level 1 Level 2 Level 3 ​ Total Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 35,397 $ — $ — ​ $ 35,397 Total ​ $ 35,397 $ — $ — ​ $ 35,397

Property and equipment, net (Ta

Property and equipment, net (Tables)	6 Months Ended
	Jun. 30, 2021
Property and equipment, net
Schedule of Property and equipment, net	Property and equipment, net consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 ​ ​ ​ ​ ​ ​ ​ Leasehold improvements ​ $ 3,419 ​ $ 3,322 Construction in progress ​ ​ 6,448 ​ ​ 28 Laboratory equipment ​ 6,691 ​ 5,982 Furniture and fixtures ​ 573 ​ 430 Computer equipment and software ​ 1,909 ​ 1,554 Property and equipment, gross ​ 19,040 ​ 11,316 Less: Accumulated depreciation ​ (5,834) ​ (5,097) Property and equipment, net ​ $ 13,206 ​ $ 6,219

Accrued expenses and other cu_2

Accrued expenses and other current liabilities (Tables)	6 Months Ended
	Jun. 30, 2021
Accrued expenses and other current liabilities
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 Salaries and bonuses ​ 3,756 ​ 4,381 Social security contributions ​ 388 ​ 211 Unearned grant income (current) ​ 934 ​ 878 Accrued external research and development expenses ​ ​ 7,408 ​ ​ 895 Accrued external general and administration expenses ​ ​ 589 ​ ​ 634 Accrued for property and equipment acquisitions ​ ​ 2,104 ​ ​ — Finance lease liabilities ​ ​ 138 ​ ​ 155 Other accruals and liabilities ​ 46 ​ 232 ​ ​ $ 15,363 ​ $ 7,386

Loans payable (Tables)

Loans payable (Tables)	6 Months Ended
	Jun. 30, 2021
Loans payable
Schedule of loans payable	As of June 30, 2021 and December 31, 2020, loans payable consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ 2021 2020 Loans from FFG ​ $ 6,359 ​ $ 6,564 Unamortized debt discount ​ (1,558) ​ (2,027) Total Loans payable, net ​ $ 4,801 ​ $ 4,537
Schedule of aggregate minimum future principal payments due in connection with the FFG Loans	​ ​ ​ ​ Payments Due by Calendar Year Amount 2021 (remaining 6 months) ​ ​ — 2022 ​ ​ 3,197 2023 ​ ​ 1,906 2024 ​ ​ 1,256 Thereafter ​ ​ — Total ​ $ 6,359

Stock-based compensation (Table

Stock-based compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Stock-based compensation
Schedule of assumptions used in the Black-Scholes option-pricing model for estimating the fair value of stock options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three and six months ended June 30, ​ ​ 2021 2020 ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ 1.07 % 0.44 % Expected term (in years) 6.1 6.0 Expected volatility 85.5 % 79.0 % Expected dividends — % — %
Schedule of summary of stock option activity	The following table summarizes the Company’s stock option activity since January 1, 2021 (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ Shares Price Term Value ​ ​ ​ ​ ​ ​ ​ (in years) ​ ​ ​ Outstanding as of December 31, 2020 3,555,945 ​ $ 8.45 7.9 ​ $ 12,839 Granted 859,956 ​ 12.36 ​ ​ ​ Exercised (79,487) ​ 2.97 ​ ​ ​ Forfeited (52,419) ​ 10.42 ​ ​ ​ Outstanding as of June 30, 2021 4,283,995 ​ $ 9.31 7.9 ​ $ 8,344 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options exercisable as of June 30, 2021 1,960,775 ​ $ 7.09 7.0 ​ $ 7,223 Options unvested as of June 30, 2021 2,323,220 ​ $ 11.17 8.7 ​ $ 1,121
Schedule of summary of restricted stock unit activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average Grant ​ ​ Number of ​ Date Fair ​ Shares Value Outstanding as of December 31, 2020 43,700 ​ $ 11.87 Granted — ​ — Vested (23,647) ​ 11.87 Forfeited — ​ — Outstanding as of June 30, 2021 20,053 ​ $ 11.87
Schedule of stock-based compensation expense	Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended June 30, ​ Six months ended June 30, ​ 2021 2020 2021 2020 Research and development expenses ​ $ 1,145 ​ $ 771 ​ $ 1,769 ​ $ 1,448 General and administrative expenses ​ 1,482 ​ 1,380 ​ 2,379 ​ 2,797 ​ ​ $ 2,627 ​ $ 2,151 ​ $ 4,148 ​ $ 4,245

Net loss per share (Tables)

Net loss per share (Tables)	6 Months Ended
	Jun. 30, 2021
Net loss per share
Schedule of basic and diluted net loss per share	The following table sets forth the computation of the basic and diluted net loss per share attributable to common stockholders (in thousands, except for per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended June 30, ​ Six months ended June 30, ​ 2021 2020 2021 2020 Numerator: ​ ​ ​ ​ Net loss ​ $ (17,153) ​ $ (7,092) ​ $ (34,391) ​ $ (18,018) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding, basic and diluted ​ ​ 29,826,269 ​ ​ 25,647,819 ​ ​ 29,807,382 ​ ​ 25,638,913 Weighted-average Series A convertible preferred shares outstanding, basic and diluted, presented as if converted into common stock (1) ​ ​ 2,978,000 ​ ​ — ​ ​ 2,978,000 ​ ​ — Total number of shares used to calculate net loss per share, basic and diluted ​ 32,804,269 ​ 25,647,819 ​ 32,785,382 ​ 25,638,913 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per share, basic and diluted ​ $ (0.52) ​ $ (0.28) ​ $ (1.05) ​ $ (0.70) (1)
Schedule of potentially dilutive securities that were not included in the diluted per share calculations	​ ​ ​ ​ ​ ​ ​ Three and six months ended June 30, ​ 2021 2020 Options issued and outstanding 4,283,995 ​ 3,585,971 Unvested restricted stock units ​ 20,053 ​ — Total 4,304,048 3,585,971

Summary of significant accoun_4

Summary of significant accounting policies - Going concern and Concentrations of credit risk and of significant suppliers (Details) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Jun. 30, 2021USD ($)customer	Jun. 30, 2020USD ($)customer	Dec. 31, 2020USD ($)
Concentration Risk [Line Items]
Net losses	$ 17,153	$ 17,238	$ 7,092	$ 10,926	$ 34,391	$ 18,018	$ 44,100
Accumulated deficit	$ 181,492				$ 181,492		$ 147,101
Customer Concentration Risk | Revenue
Concentration Risk [Line Items]
Number of customers | customer					1	1

Summary of significant accoun_5

Summary of significant accounting policies - Property and equipment (Details)	6 Months Ended
	Jun. 30, 2021
Leasehold improvements | Minimum
Property and equipment
Estimated useful life (in years)	2 years
Leasehold improvements | Maximum
Property and equipment
Estimated useful life (in years)	5 years
Laboratory equipment | Minimum
Property and equipment
Estimated useful life (in years)	2 years
Laboratory equipment | Maximum
Property and equipment
Estimated useful life (in years)	10 years
Furniture and fixtures | Minimum
Property and equipment
Estimated useful life (in years)	2 years
Furniture and fixtures | Maximum
Property and equipment
Estimated useful life (in years)	10 years
Computer equipment and software | Minimum
Property and equipment
Estimated useful life (in years)	2 years
Computer equipment and software | Maximum
Property and equipment
Estimated useful life (in years)	4 years

Summary of significant accoun_6

Summary of significant accounting policies - Revenue recognition from contracts with customers (Details)	6 Months Ended
	Jun. 30, 2021itemProgram
Summary of significant accounting policies
Number of preclinical research programs | Program	2
Number of combined performance obligation for each research program	1
Number of research program performance obligations	2

Collaboration and Licensing A_2

Collaboration and Licensing Agreements (Details) - Gilead Collaboration and License Agreement $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018USD ($)item	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Collaboration and Licensing Agreements
Number of preclinical research programs | item	2
Upfront payment received	$ 10
Payment term (in days)				60 days
Milestone payment received						$ 4
Upfront and milestone payments included in deferred revenues		$ 0.7		$ 0.7
Percentage of upfront payment included in deferred revenue expected to be recognized in 2021		67.00%		67.00%
Percentage of upfront payment included in deferred revenue expected to be recognized in 2022		33.00%		33.00%
Cost reimbursements for research and development services included in deferred revenues		$ 2.3		$ 2.3
Revenue recognized from upfront payment		0.4	$ 1	0.5	$ 1.4
Revenue recognized from milestone payments		0.6	0.6	1.2	1.2
Revenue recognized from cost reimbursements for research and development services		4.4	4.1	9	6.8
Revenue recognized from cost reimbursements for research and development services initially recorded as deferred revenue		0.4		0.7
Revenue recognized from milestone payments for milestones achieved			$ 1		$ 1
Maximum
Collaboration and Licensing Agreements
Contract asset relating to the sublicense payment		0.1		0.1		0.1
Contract liability relating to sublicense payment		$ 0.1		0.1		$ 0.1
Development Milestones
Collaboration and Licensing Agreements
Total milestone amount				280
Commercial Milestones
Collaboration and Licensing Agreements
Total milestone amount				$ 100

Fair Value of Financial Asset_2

Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Fair Value of Financial Assets
Transfers from Level 1 to Level 2	$ 0
Transfers from Level 2 to Level 1	0
Transfers from into Level 3	0
Transfers from out of Level 3	0
Recurring
Fair Value of Financial Assets
Total	35,399	$ 35,397
Recurring | Money market funds
Fair Value of Financial Assets
Cash equivalents	35,399	35,397
Recurring | Level 1
Fair Value of Financial Assets
Total	35,399	35,397
Recurring | Level 1 | Money market funds
Fair Value of Financial Assets
Cash equivalents	$ 35,399	$ 35,397

Property and equipment, net (De

Property and equipment, net (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property and equipment
Property and equipment, gross	$ 19,040	$ 11,316
Less: Accumulated depreciation	(5,834)	(5,097)
Property and equipment, net	13,206	6,219
Leasehold improvements
Property and equipment
Property and equipment, gross	3,419	3,322
Construction in progress
Property and equipment
Property and equipment, gross	6,448	28
Laboratory equipment
Property and equipment
Property and equipment, gross	6,691	5,982
Furniture and fixtures
Property and equipment
Property and equipment, gross	573	430
Computer equipment and software
Property and equipment
Property and equipment, gross	$ 1,909	$ 1,554

Receivable research incentive (

Receivable research incentive (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Receivable research incentive
Receivable research incentive	$ 15,977		$ 15,977		$ 15,115
Income related to the incentive program recorded as grant income	$ 2,300	$ 1,400	$ 4,300	$ 2,700

Accrued expenses and other cu_3

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accrued expenses and other current liabilities
Salaries and bonuses	$ 3,756	$ 4,381
Social security contributions	388	211
Unearned grant income (current)	934	878
Accrued external research and development expenses	7,408	895
Accrued external general and administration expenses	589	634
Accrued for property and equipment acquisitions	2,104
Finance lease liabilities	138	155
Other accruals and liabilities	46	232
Total	$ 15,363	$ 7,386

Loans payable (Details)

Loans payable (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Loans payable
Loans from FFG		$ 6,359		$ 6,359		$ 6,564
Unamortized debt discount		(1,558)		(1,558)		(2,027)
Total Loans payable, net		4,801		4,801		$ 4,537
Scheduled early repayment	$ 3,300
Principal payment		$ 0	$ 0	$ 0	$ 1,256
Adjustment
Loans payable
Deferred income reduced	$ 300
Minimum
Loans payable
Interest rate (as a percent)		0.75%		0.75%
Maximum
Loans payable
Interest rate (as a percent)		1.00%		1.00%

Loans payable - Schedule of agg

Loans payable - Schedule of aggregate minimum future principal payments (Details) $ in Thousands	Jun. 30, 2021USD ($)
Long-term Debt, Fiscal Year Maturity [Abstract]
2022	$ 3,197
2023	1,906
2024	1,256
Total	$ 6,359

Common stock, Class A common _2

Common stock, Class A common stock and convertible preferred stock (Details) $ / shares in Units, $ in Millions	Dec. 11, 2020USD ($)$ / sharesshares	Apr. 23, 2019USD ($)$ / sharesshares	Jun. 30, 2021Vote$ / sharesshares	Dec. 31, 2020$ / sharesshares
Preferred Stock, Shares Authorized			10,000,000	10,000,000
Share Price | $ / shares			$ 9.16	$ 11.09
Net proceeds from public offering | $	$ 75
Common stock
Common Stock, Shares Authorized			100,000,000	100,000,000
Common stock, issued (in shares)			26,051,846	25,948,712
Common stock, outstanding (in shares)			26,051,846	25,948,712
Issuance of common stock	3,910,000
Share Price | $ / shares	$ 11.75
Number of votes | Vote			1
Class A common stock
Common Stock, Shares Authorized			3,900,000	3,900,000
Common stock, issued (in shares)			3,819,732	3,819,732
Common stock, outstanding (in shares)			3,819,732	3,819,732
Number of common stock issued upon conversion of each share			1
Series A Convertible Preferred Stock
Preferred stock shares Designated			2,978	2,978
Preferred Stock, Shares Issued	2,978		2,978	2,978
Preferred Stock, Shares Outstanding			2,978	2,978
Share Price | $ / shares	$ 11,750
Number of common stock issued upon conversion of each share			1,000
Threshold Percentage For Conversion			9.99%
Liquidation preference per share | $ / shares			$ 0.001
IPO | Common stock
Stock issued upon conversion of Preferred Stock (in shares)		14,582,161
IPO | Class A common stock
Stock issued upon conversion of Preferred Stock (in shares)		3,819,732
IPO | Common Stock
Issuance of common stock		6,000,000
Share Price | $ / shares		$ 14
Net proceeds from IPO | $		$ 74.6
Offering costs | $		$ 9.4

Stock-based compensation - 2018

Stock-based compensation - 2018 Stock Option and Grant Plan (Details)	6 Months Ended
	Jun. 30, 2021installment€ / sharesshares	Dec. 31, 2020shares	Dec. 31, 2018$ / shares
Stock-based compensation
Number of shares granted to US employee	859,956
Options outstanding	4,283,995	3,555,945
2018 Stock Option and Grant Plan
Stock-based compensation
Vesting period	4 years
Options outstanding	1,027,793
2018 Stock Option and Grant Plan | Vesting upon first anniversary
Stock-based compensation
Percentage of options vesting	25.00%
2018 Stock Option and Grant Plan | Vesting in equal quarterly installments
Stock-based compensation
Percentage of options vesting	75.00%
Number of quarterly installments for vesting | installment	12
2016 Stock Option Plan
Stock-based compensation
Percentage of share price with fair market value	100.00%
2016 Stock Option Plan | Exercise price 0.09 euros
Stock-based compensation
Exercise price for options granted as a replacement | € / shares	€ 0.09
Number of shares granted to US employee	23,286
2016 Stock Option Plan | Exercise price $2.93
Stock-based compensation
Exercise price for options granted as a replacement | $ / shares			$ 2.93

Stock-based compensation - 2019

Stock-based compensation - 2019 Stock Option and Incentive Plan (Details)	Apr. 01, 2019installmentshares
Stock-based compensation
Number of common stock entitled for each option upon the exercise of the option | shares	1
2019 Stock Option and Incentive Plan
Stock-based compensation
Number stock option authorized | shares	3,630,686
Number of shares outstanding were cumulatively increased	4.00%
Vesting period	4 years
2019 Stock Option and Incentive Plan | Non Executive Directors
Stock-based compensation
Vesting period	3 years
2019 Stock Option and Incentive Plan | Vesting upon first anniversary
Stock-based compensation
Percentage of options vesting	25.00%
2019 Stock Option and Incentive Plan | Vesting upon first anniversary | Non Executive Directors
Stock-based compensation
Percentage of options vesting	33.00%
2019 Stock Option and Incentive Plan | Vesting in equal quarterly installments
Stock-based compensation
Percentage of options vesting	75.00%
Number of quarterly installments for vesting | installment	12
2019 Stock Option and Incentive Plan | Vesting in equal quarterly installments | Non Executive Directors
Stock-based compensation
Percentage of options vesting	67.00%
Number of quarterly installments for vesting | installment	8

Stock-based compensation - Stoc

Stock-based compensation - Stock option valuation (Details)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Assumptions used in the Black-Scholes option-pricing model
Risk-free interest rate	1.07%	0.44%
Expected term (in years)	6 years 1 month 6 days	6 years
Expected volatility	85.50%	79.00%

Stock-based compensation - St_2

Stock-based compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Number of Shares
Beginning balance	3,555,945
Granted	859,956
Exercised	(79,487)
Forfeited	(52,419)
Ending balance	4,283,995		3,555,945
Option exercisable	1,960,775
Option unvested	2,323,220
Weighted Averaged Exercise Price
Beginning balance	$ 8.45
Granted	12.36
Exercised	2.97
Forfeited	10.42
Ending balance	9.31		$ 8.45
Option exercisable	7.09
Option unvested	$ 11.17
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term (in years)	7 years 10 months 24 days		7 years 10 months 24 days
Weighted Average Remaining Contractual Term, option exercisable	7 years
Weighted Average Remaining Contractual Term, option unvested	8 years 8 months 12 days
Aggregate Intrinsic Value, beginning balance	$ 12,839
Aggregate Intrinsic Value, ending balance	8,344		$ 12,839
Aggregate Intrinsic Value, option exercisable	1,121
Aggregate Intrinsic Value, option unvested	$ 7,223
Average price (in dollars per sale)	$ 9.16		$ 11.09
Cash received from option exercise under share-based payment arrangements	$ 237	$ 15

Stock-based compensation - Rest

Stock-based compensation - Restricted Stock Units (Details) - Restricted stock units	6 Months Ended
	Jun. 30, 2021installment$ / sharesshares
Stock-based compensation
Number of equal installments of vesting | installment	4
Number of Shares
Beginning balance | shares	43,700
Vested | shares	(23,647)
Ending balance | shares	20,053
Weighted Average Grant Date Fair Value
Beginning balance | $ / shares	$ 11.87
Vested | $ / shares	11.87
Ending balance | $ / shares	$ 11.87

Stock-based compensation - St_3

Stock-based compensation - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock-based compensation
Stock-based compensation expense	$ 2,627	$ 2,151	$ 4,148	$ 4,245
Research and development expenses
Stock-based compensation
Stock-based compensation expense	1,145	771	1,769	1,448
General and Administrative Expense
Stock-based compensation
Stock-based compensation expense	$ 1,482	$ 1,380	$ 2,379	$ 2,797

Income taxes (Details)

Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Income taxes
Income tax benefits for the net operating losses incurred	$ 0	$ 0

Commitments and contingencies -

Commitments and contingencies - Operating and Finance Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Commitments and contingencies
Cash balance maintained to secure a letter of credit associated with a real estate lease	$ 430	$ 434
Operating lease right-of-use assets	5,266	6,452
Finance lease right-of-use assets	1,045	1,298
Outstanding operating lease obligations	4,800	5,800
Current operating lease liability	1,954	1,998
Non-current operating lease liability	2,753	3,819
Outstanding finance lease obligations	300	500
Current finance lease liability	$ 138	$ 155
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued Expenses and Other Current Liabilities.	Hook:AccruedExpensesAndOtherCurrentLiabilities
Non-current finance lease liability	$ 200	$ 300
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
Weighted average discount rate on operating lease liabilities (as a percent)	2.30%
Weighted average lease term remaining on operating lease liabilities (in years)	2 years 7 months 6 days
Weighted average discount rate on finance lease liabilities (as a percent)	1.70%
Weighted average lease term remaining on finance lease liabilities (in years)	2 years 7 months 6 days

Commitments and contingencies_2

Commitments and contingencies - Others (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021USD ($)	Jun. 30, 2021USD ($)
Lessee, Lease, Description [Line Items]
Non-cancellable obligations	$ 11.4	$ 11.4
2021 deliverables (remaining six months)	9.7	9.7
2022 deliverables	1.6	1.6
Licensing fees from intellectual property licenses	0.3	0.5
Maximum
Lessee, Lease, Description [Line Items]
2023 deliverables	0.1	0.1
2024 deliverables	$ 0.1	$ 0.1

Net loss per share (Details)

Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Numerator:
Net loss	$ (17,153)	$ (17,238)	$ (7,092)	$ (10,926)	$ (34,391)	$ (18,018)	$ (44,100)
Denominator:
Weighted-average common shares outstanding, basic and diluted	29,826,269		25,647,819		29,807,382	25,638,913
Weighted-average Series A convertible preferred shares outstanding, basic and diluted, presented as if converted into common stock	2,978,000				2,978,000
Total number of shares used to calculate net loss per share, basic and diluted	32,804,269		25,647,819		32,785,382	25,638,913
Net loss per share, basic and diluted (in USD per share)	$ (0.52)		$ (0.28)		$ (1.05)	$ (0.70)
Number of common stock issued upon conversion of each share of Preferred Stock	1,000				1,000
Number of common stock issuable upon conversion of Series A convertible preferred stock	2,978,000				2,978,000

Net loss per share - Antidiluti

Net loss per share - Antidilutive securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Anti-dilutive securities
Anti-dilutive shares	4,304,048	3,585,971	4,304,048	3,585,971
Options
Anti-dilutive securities
Anti-dilutive shares	4,283,995	3,585,971	4,283,995	3,585,971
Restricted stock units
Anti-dilutive securities
Anti-dilutive shares	20,053		20,053

Related parties (Details)

Related parties (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
University of Basel | Research and development expenses
Related parties
Service fees paid	$ 0	$ 0.3