Autolus Therapeutics (AUTL) 6-K 5 Aug 21 Index to Condensed Consolidated Financial Statements Financial data

Cover

Cover	6 Months Ended
	Jun. 30, 2021
Cover [Abstract]
Entity Registrant Name	Autolus Therapeutics plc
Entity Central Index Key	0001730463
Document Type	6-K
Document Period End Date	Jun. 30, 2021
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash	$ 216,352	$ 153,299
Restricted cash	210	786
Prepaid expenses and other assets, current	52,944	42,899
Total current assets	269,506	196,984
Non-current assets:
Property and equipment, net	34,190	38,046
Right of use assets, net	20,598	51,637
Long-term deposits	1,846	2,625
Prepaid expenses and other assets, non-current	2,760	3,033
Deferred tax asset	1,643	1,754
Intangible assets, net	112	158
Total assets	330,655	294,237
Current liabilities:
Accounts payable	1,119	2,263
Accrued expenses and other liabilities	23,173	27,781
Lease liabilities	3,895	3,590
Total current liabilities	28,187	33,634
Non-current liabilities:
Lease liabilities	18,786	50,571
Total liabilities	46,973	84,205
Shareholders' equity:
Additional paid-in capital	732,290	595,016
Accumulated other comprehensive loss	(3,046)	(5,861)
Accumulated deficit	(445,683)	(379,244)
Total shareholders' equity	283,682	210,032
Total liabilities and shareholders' equity	330,655	294,237
Ordinary shares
Shareholders' equity:
Share value	3	3
Deferred shares
Shareholders' equity:
Share value	0	0
Deferred B Shares
Shareholders' equity:
Share value	118	118
Deferred C Shares
Shareholders' equity:
Share value	$ 0	$ 0

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parentheticals)	Jun. 30, 2021$ / sharesshares	Jun. 30, 2021£ / sharesshares	Dec. 31, 2020$ / sharesshares	Dec. 31, 2020£ / sharesshares
Ordinary shares
Shareholders' equity:
Stock par value (usd/gbp per share) | $ / shares	$ 0.000042		$ 0.000042
Shares authorized	200,000,000	200,000,000	200,000,000	200,000,000
Shares issued	72,742,582	72,742,582	52,346,231	52,346,231
Shares outstanding	72,742,582	72,742,582	52,346,231	52,346,231
Deferred shares
Shareholders' equity:
Stock par value (usd/gbp per share) | £ / shares		£ 0.00001		£ 0.00001
Shares authorized	34,425	34,425	34,425	34,425
Shares issued	34,425	34,425	34,425	34,425
Shares outstanding	34,425	34,425	34,425	34,425
Deferred B Shares
Shareholders' equity:
Stock par value (usd/gbp per share) | £ / shares		£ 0.00099		£ 0.00099
Shares authorized	88,893,548	88,893,548	88,893,548	88,893,548
Shares issued	88,893,548	88,893,548	88,893,548	88,893,548
Shares outstanding	88,893,548	88,893,548	88,893,548	88,893,548
Deferred C Shares
Shareholders' equity:
Stock par value (usd/gbp per share) | £ / shares		£ 0.000008		£ 0.000008
Shares authorized	1	1	1	1
Shares issued	1	1	1	1
Shares outstanding	1	1	1	1

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ (32,131,000)	$ (31,328,000)	$ (62,862,000)	$ (62,615,000)
General and administrative	(7,237,000)	(8,509,000)	(15,975,000)	(16,123,000)
Loss on disposal of leasehold improvements	0	0	(672,000)	0
Total operating expenses, net	(37,723,000)	(39,544,000)	(77,595,000)	(78,107,000)
Other (expense) income:
Interest income (expense)	42,000	(47,000)	85,000	463,000
Other (expense) income	(1,849,000)	525,000	(1,011,000)	5,009,000
Total other (expense) income, net	(1,807,000)	478,000	(926,000)	5,472,000
Net loss before income tax	(39,530,000)	(39,066,000)	(78,521,000)	(72,635,000)
Income tax benefit	6,357,000	7,021,000	12,081,000	10,717,000
Net loss attributable to ordinary shareholders	(33,173,000)	(32,045,000)	(66,440,000)	(61,918,000)
Other comprehensive income (loss):
Foreign currency exchange translation adjustment	1,542,000	(1,819,000)	2,815,000	(19,520,000)
Total comprehensive loss	$ (31,631,000)	$ (33,864,000)	$ (63,625,000)	$ (81,438,000)
Basic net loss per ordinary share (usd per share)	$ (0.47)	$ (0.62)	$ (1)	$ (1.22)
Diluted net loss per ordinary share (usd per share)	$ (0.47)	$ (0.62)	$ (1)	$ (1.22)
Weighted-average basic ordinary shares	70,832,077	52,041,340	66,663,003	50,956,566
Weighted-average diluted ordinary shares	70,832,077	52,041,340	66,663,003	50,956,566
Grant income
Revenues	$ 138,000	$ 293,000	$ 407,000	$ 631,000
License revenue
Revenues	$ 1,507,000	$ 0	$ 1,507,000	$ 0

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Shareholders’ Equity (Unaudited) - USD ($) $ in Thousands	Total	Common shares	Common sharesOrdinary Shares	Common sharesDeferred Shares	Common sharesDeferred B Shares	Common sharesDeferred C Shares	Additional Paid in Capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance at Dec. 31, 2019	$ 254,839		$ 2	$ 0	$ 118	$ 0	$ 500,560	$ (8,691)	$ (237,150)
Beginning balance (in shares) at Dec. 31, 2019			44,983,006	34,425	88,893,548	1
Stockholders' Equity
Issuance of ordinary shares, net of issuance costs	73,953		$ 1				73,952
Issuance of ordinary shares, net of issuance costs			7,250,000
Share-based compensation expense	6,235						6,235
Restricted shares - forfeited			(50)
Exercise of share options	24						24
Exercise of share options			14,976
Unrealized gain (loss) on foreign currency translation	(17,701)							(17,701)
Net loss	(29,873)								(29,873)
Ending balance at Mar. 31, 2020	287,478		$ 3	$ 0	$ 118	$ 0	580,772	(26,392)	(267,023)
Ending balance (in shares) at Mar. 31, 2020			52,247,932	34,425	88,893,548	1
Beginning balance at Dec. 31, 2019	254,839		$ 2	$ 0	$ 118	$ 0	500,560	(8,691)	(237,150)
Beginning balance (in shares) at Dec. 31, 2019			44,983,006	34,425	88,893,548	1
Stockholders' Equity
Unrealized gain (loss) on foreign currency translation	(19,520)
Net loss	(61,918)
Ending balance at Jun. 30, 2020	258,952		$ 3	$ 0	$ 118	$ 0	586,110	(28,211)	(299,068)
Ending balance (in shares) at Jun. 30, 2020			52,250,404	34,425	88,893,548	1
Beginning balance at Mar. 31, 2020	287,478		$ 3	$ 0	$ 118	$ 0	580,772	(26,392)	(267,023)
Beginning balance (in shares) at Mar. 31, 2020			52,247,932	34,425	88,893,548	1
Stockholders' Equity
Share-based compensation expense	5,305						5,305
Restricted shares - forfeited			(1,919)
Exercise of share options	33						33
Exercise of share options			4,391
Unrealized gain (loss) on foreign currency translation	(1,819)							(1,819)
Net loss	(32,045)								(32,045)
Ending balance at Jun. 30, 2020	258,952		$ 3	$ 0	$ 118	$ 0	586,110	(28,211)	(299,068)
Ending balance (in shares) at Jun. 30, 2020			52,250,404	34,425	88,893,548	1
Beginning balance at Dec. 31, 2020	210,032		$ 3	$ 0	$ 118	$ 0	595,016	(5,861)	(379,244)
Beginning balance (in shares) at Dec. 31, 2020			52,346,231	34,425	88,893,548	1
Stockholders' Equity
Issuance of ordinary shares, net of issuance costs	122,198						122,198
Issuance of ordinary shares, net of issuance costs			18,147,078
Reversal of share-based compensation expense	(670)						(670)
Vesting of restricted stock (in shares)		21,500
Exercise of share options			545
Unrealized gain (loss) on foreign currency translation	1,273							1,273
Net loss	(33,266)								(33,266)
Ending balance at Mar. 31, 2021	299,567		$ 3	$ 0	$ 118	$ 0	716,544	(4,588)	(412,510)
Ending balance (in shares) at Mar. 31, 2021			70,515,354	34,425	88,893,548	1
Beginning balance at Dec. 31, 2020	$ 210,032		$ 3	$ 0	$ 118	$ 0	595,016	(5,861)	(379,244)
Beginning balance (in shares) at Dec. 31, 2020			52,346,231	34,425	88,893,548	1
Stockholders' Equity
Exercise of share options	158,307
Unrealized gain (loss) on foreign currency translation	$ 2,815
Net loss	(66,440)
Ending balance at Jun. 30, 2021	283,682		$ 3	$ 0	$ 118	$ 0	732,290	(3,046)	(445,683)
Ending balance (in shares) at Jun. 30, 2021			72,742,582	34,425	88,893,548	1
Beginning balance at Mar. 31, 2021	299,567		$ 3	$ 0	$ 118	$ 0	716,544	(4,588)	(412,510)
Beginning balance (in shares) at Mar. 31, 2021			70,515,354	34,425	88,893,548	1
Stockholders' Equity
Issuance of ordinary shares, net of issuance costs	14,340						14,340
Issuance of ordinary shares, net of issuance costs			2,069,466
Share-based compensation expense	1,280						1,280
Exercise of share options	126						126
Exercise of share options			157,762
Unrealized gain (loss) on foreign currency translation	1,542							1,542
Net loss	(33,173)								(33,173)
Ending balance at Jun. 30, 2021	$ 283,682		$ 3	$ 0	$ 118	$ 0	$ 732,290	$ (3,046)	$ (445,683)
Ending balance (in shares) at Jun. 30, 2021			72,742,582	34,425	88,893,548	1

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (66,440,000)	$ (61,918,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,906,000	2,528,000
Share-based compensation (net of amount capitalized)	610,000	11,627,000
Loss (gain) on termination of operating lease	11,000	(160,000)
Loss on disposal of property and equipment	672,000	0
Deferred income tax	115,000	0
Changes in operating assets and liabilities
Prepaid expenses and other assets, current	(9,534,000)	(677,000)
Prepaid expenses and other assets, non-current	256,000	(2,507,000)
Long-term deposits	811,000	(455,000)
Right of use assets, net	1,954,000	1,560,000
Accounts payable	(1,286,000)	(1,279,000)
Accrued expenses and other liabilities	(4,260,000)	1,209,000
Lease liabilities	(769,000)	(894,000)
Net cash used in operating activities	(73,954,000)	(50,966,000)
Cash flows from investing activities:
Purchases of property and equipment	(3,411,000)	(5,160,000)
Net cash used in investing activities	(3,411,000)	(5,160,000)
Cash flows from financing activities:
Proceeds of issuance of ordinary shares, net of issuance costs	136,878,000	74,013,000
Net cash provided by financing activities	136,878,000	74,013,000
Effect of exchange rate changes on cash and restricted cash	2,964,000	(16,487,000)
Net increase in cash and restricted cash	62,477,000	1,400,000
Cash and restricted cash, beginning of period	154,085,000	211,430,000
Cash and restricted cash, end of period	216,562,000	212,830,000
Supplemental non-cash flow information
Property and equipment purchases included in accounts payable and accrued expenses	1,753,000	5,050,000
Right of use assets obtained in exchange for operating lease liabilities	0	2,347,000
Right of use assets terminated and obtained in exchange for operating lease liabilities, net	28,517,000	2,487,000
Capitalized implementation costs included in accrued expenses	89,000	334,000
Issuance costs included in accounts payable and accrued expenses	228,000	0
Capitalized share-based compensation	0	(87,000)
Reconciliation of cash and restricted cash reported within the condensed consolidated balance sheets:
Cash	216,352,000	212,044,000
Restricted cash	210,000	786,000
Total cash and restricted cash	$ 216,562,000	$ 212,830,000

Nature of the Business

Nature of the Business	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	Nature of the Business Autolus Therapeutics plc (the “Company”) is a biopharmaceutical company developing next-generation programmed T cell therapies for the treatment of cancer. Using its broad suite of proprietary and modular T cell programming technologies, the Company is engineering precisely targeted, controlled and highly active T cell therapies that are designed to better recognize cancer cells, break down their defense mechanisms and attack and kill these cells. The Company believes its programmed T cell therapies have the potential to be best-in-class and offer cancer patients substantial benefits over the existing standard of care, including the potential for cure in some patients. The Company is a public limited company incorporated in England and Wales. On June 22, 2018, the Company completed its initial public offering ("IPO") of American Depositary Shares (“ADSs”). In the IPO, the Company sold an aggregate of 10,147,059 ADSs representing the same number of ordinary shares, including 1,323,529 ADSs pursuant to the underwriters’ option to purchase additional ADSs, at a public offering price of $17.00 per ADS. Net proceeds were $156.5 million, after deducting underwriting discounts and commissions and offering expenses paid by the Company. On April 15, 2019, the Company completed an underwritten public offering of 4,830,000 ADSs representing 4,830,000 ordinary shares, at a public offering price of $24.00 per ADS, which includes an additional 630,000 ADSs issued upon the exercise in full of the underwriters’ option to purchase additional ADSs. Aggregate net proceeds to the Company, after underwriting discounts and offering expenses, were $108.8 million. On January 27, 2020, the Company completed an underwritten public offering of 7,250,000 ADSs representing 7,250,000 ordinary shares, at a public offering price of $11.00 per ADS. Aggregate net proceeds to the Company, after underwriting discounts and offering expenses, were $75.0 million. In January 2021, the Company sold an aggregate of 1,718,506 ADSs under its Open Market Sale Agreement ("Sales Agreement") with Jefferies LLC as sales agent. Aggregate net proceeds to the Company, after commission fees and offering expenses, were $15.3 million. On February 12, 2021, the Company completed an underwritten public offering of 14,285,715 ADSs, which includes the full exercise by the underwriters to purchase an additional 2,142,857 ADSs, at a public offering price of $7.00 per ADS. Aggregate net proceeds to the Company, after underwriting discounts and offering expenses, were $106.9 million. On June 17, 2021 the Company sold an aggregate of 2,069,466 ADSs under its Sales Agreement with Jefferies LLC as sales agent. Aggregate net proceeds to the Company after commission fees and offering expenses, were $14.3 million. 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 and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from its product sales. The Company has funded its operations primarily with proceeds from the sale of its equity securities. The Company has incurred recurring losses since its inception, including net losses of $33.2 million and $32.0 million for the three months ended June 30, 2021 and 2020, and $66.4 million and $61.9 million for the six months ended June 30, 2021 and 2020, respectively. In addition, the Company had an accumulated deficit of $445.7 million and $379.2 million as of June 30, 2021 and December 31, 2020, respectively. The Company expects to continue to generate operating losses for the foreseeable future. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. The Company’s inability to raise additional capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies. There can be no assurances, however, that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. The Company believes the cash on hand at June 30, 2021 of $216.4 million will be sufficient to fund the Company’s operations for at least twelve months from the issuance of these financial statements. Impact of COVID-19 Pandemic In response to the ongoing coronavirus 2019, or COVID-19, pandemic, the Company established a cross-functional task force and have implemented business continuity plans designed to address and mitigate its impact on the Company's employees and business. While the Company has not experienced any significant financial impact to date, the overall disruption caused by the COVID-19 pandemic on global healthcare systems, and the other risks and uncertainties associated with the pandemic, could cause its business, financial condition, results of operations and growth prospects to be materially adversely affected. In March 2020, our global workforce transitioned to working remotely with the exception of research and clinical trial related activities that required laboratory-based activity or manufacturing. We implemented protocols and procedures to ensure the safety of our employees working on site, including requirement to wear personal protective equipment, temperature checks at entry and offered COVID-19 testing for any employee with symptoms or at suspected risk of exposure to virus. In June 2020, we began the implementation of our workplace re-entry plan, based on a phased approach that is principles-based and local in design, with a focus on continuity of patient treatment and working to bring its workforce back on-site safely. We have also implemented policies to control and limit office and lab access in line with government guidelines and for contact tracing if needed. The Company will continue to monitor guidance, particularly as restrictions ease, to ensure best practice approaches are adopted in order that the Company minimizes risk to its employees and business. We continue to track COVID-19 developments in Europe and the United States closely for their potential impact on our clinical trial sites, logistics and supply chain to ensure we can continue to maintain clinical trial conduct and data integrity. As the patients in our clinical trials are severely immune suppressed as a consequence of their underlying disease and the treatment they receive in the trials, we are also monitoring other transmissible infectious diseases, including influenza. The Company is not aware of any specific event or circumstance that has impacted on its operations in a manner which would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities during the six months ended June 30, 2021. However, these estimates may change, as new events occur and additional information is obtained, relating to the COVID-19 pandemic or otherwise. Changes in estimates would be recognized in the consolidated financial statements as soon as they become known.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements include those of the Company and its wholly-owned subsidiaries, Autolus Limited, Autolus Inc. and Autolus GmbH, and have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All intercompany accounts and transactions have been eliminated upon consolidation. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of 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 accrual for research and development expenses, share-based compensation and income taxes. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates. Cash and Cash Equivalents The Company considers cash and cash equivalents in the condensed consolidated financial statements to include cash at banks with a maturity of less than three months, which is subject to an insignificant risk of changes in value. Restricted Cash The Company entered into a credit card arrangement that requires a security deposit of $0.2 million. The restricted cash of $0.6 million previously held for a letter of credit in connection with a lease was released following the termination of the lease, in April 2021, and the $0.6 million reclassified to cash and cash equivalents. The Company includes the remaining restricted cash balance of $0.2 million in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the Company's condensed consolidated statements of cash flows. Fair Value Measurements The carrying amounts reported in the balance sheets for cash and restricted cash, prepaid expenses and other assets, accounts payable and accrued expenses and other liabilities approximate their fair value because of the short-term nature of these instruments. Concentration of Credit Risk Financial instruments that subject the Company to credit risk consist primarily of cash and restricted cash. The Company places cash and restricted cash in established financial institutions. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements. Property and Equipment Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over the estimated useful lives of the respective assets. As of June 30, 2021 and December 31, 2020, the Company’s property and equipment consisted of office equipment, lab equipment, furniture and fixtures, and leasehold improvements. The office equipment has an estimated useful life of three years, lab equipment has an estimated useful life of five The Company did not recognize a disposal loss in the three months ended June 30, 2021 and recognized a disposal loss of $0.7 million in the six months ended June 30, 2021 for leasehold improvements which are no longer being utilized in the facility in White City. The Company did not recognize a disposal loss in the three and six months ended June 30, 2020. The Company evaluates an asset for potential impairment when events or changes in circumstances indicate the carrying value of the asset may not be recoverable. Recoverability is measured by comparing the book value of the asset to the expected future net undiscounted cash flows that the asset is expected to generate. If such asset is considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the asset exceeds the fair value. The Company did not recognize an impairment in the three and six months ended June 30, 2021 and 2020. Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Most leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize on the balance sheet leases with terms of one year or less. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the right-of-use asset may be required for items such as incentives received, initial direct costs, or prepayments. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, components of a lease should be split into three categories: lease components (e.g. land, building, etc.), non-lease components (e.g. common area maintenance, consumables, etc.), and non-components (e.g. property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. The Company accounts for the lease and non-lease components of leases for classes of all underlying assets and allocates all of the contract consideration to the lease component. Intangible Assets Subject to Amortization The Company’s intangible assets are related to acquired software licenses with finite lives and are amortized over their useful lives and reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. If any indicators of impairment are present, the Company tests for recoverability by comparing the carrying amount of the asset to the net undiscounted cash flows expected to be generated from the asset. If those net undiscounted cash flows do not exceed the carrying amount (i.e., the asset is not recoverable), the Company would perform the next step, which is to determine the fair value of the asset and record an impairment loss, if any. The Company evaluates the useful lives for these intangible assets each reporting period to determine whether events and circumstances warrant a revision in their remaining useful lives. The Company did not recognize an impairment loss in the three and six months ended June 30, 2021 and 2020. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and its chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which is the business of developing and commercializing gene therapies; however, the Company operates in three geographic regions: the United Kingdom, the United States, and Germany. Substantially all of the Company’s assets are held in the United Kingdom. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, depreciation expense, third-party license fees, external costs of outside vendors engaged to conduct clinical development activities, clinical trials, costs to manufacture clinical trial materials and certain tax credits associated with research and development activities. The Company recorded the U.K. research and development expenditure credit (“RDEC”) in the amount of $55,000 and $39,000 for the three months ended June 30, 2021 and 2020, respectively, and $87,000 and $67,000 for the six months ended June 30, 2021 and 2020, respectively, as reductions of research and development expenses within the Company’s statement of operations and comprehensive loss. Accrued Research and Development Expenses As part of the process of preparing its condensed consolidated financial statements, the Company is required to estimate accruals for research and development expenses. This process involves reviewing and identifying services which have been performed by third parties on the Company’s behalf and determining the value of these services. In addition, the Company makes estimates of costs incurred to date but not yet invoiced, in relation to external clinical research organizations and clinical site costs. The Company analyzes the progress of clinical trials, including levels of patient enrollment, invoices received and contracted costs, when evaluating the adequacy of the accrued liabilities for research and development. The Company makes judgments and estimates in determining the accrued balance in any accounting period. Share-Based Compensation The Company recognizes compensation expense for equity awards based on the grant date fair value of the award. The Company recognizes share-based compensation expense for awards granted to employees that have a graded vesting schedule based on a service condition only on a straight-line basis over the requisite service period for each separately vesting portion of the award as if the award was, in substance, multiple awards (the “graded-vesting attribution method”), based on the estimated grant date fair value for each separately vesting tranche. For equity awards with a graded vesting schedule and a combination of service and performance conditions, the Company recognizes share-based compensation expense using a graded-vesting attribution method over the requisite service period when the achievement of a performance-based milestone is probable, based on the relative satisfaction of the performance condition as of the reporting date. For share-based awards granted to consultants and non-employees, compensation expense is recognized using the graded-vesting attribution method over the period during which services are rendered by such consultants and non-employees until completed. The measurement date for employee awards is the date of grant, and share-based compensation costs are recognized as expense over the employees’ requisite service period, which is the vesting period, on an accelerated basis. The Company accounts for forfeitures as they occur. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 7 for the Company’s assumptions used in connection with option grants made during the periods covered by these condensed consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. The Company lacks company-specific historical and implied volatility information for our ADSs for expected terms greater than 3 years. Therefore, it uses a combination of the historical volatility of the ADSs and also the expected share volatility based on the historical volatility of publicly traded peer companies and expect to continue to do so until such time as the Company has adequate historical data regarding the volatility of its own traded security price. Expected term . The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Fair value of ordinary shares. The fair market value of the Company’s ADSs underlying the option is equal to the closing price of the ADSs on the Nasdaq Global Select Market on the date the grant is approved by the Board. Foreign Currency Remeasurement and Translation The Company maintains its condensed consolidated financial statements in its functional currency, which is the pound sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are remeasured into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are remeasured into the functional currency at the exchange rates prevailing at the date of the transaction. Exchange gains or losses arising from foreign currency transactions are included in the determination of net loss for the respective periods. The Company recorded a foreign exchange loss of $1.9 million and foreign exchange gain of $0.5 million for the three months ended June 30, 2021 and 2020, respectively. The Company recorded a foreign exchange loss of $3.1 million and foreign exchange gain of $4.8 million for the six months ended June 30, 2021 and 2020, respectively. Foreign exchange gains and losses are included in other income in the statements of operations and comprehensive loss. For financial reporting purposes, the condensed consolidated financial statements of the Company have been translated into U.S. dollars. Assets and liabilities have been translated at the exchange rates at the balance sheet dates, while revenue and expenses are translated at the average exchange rates over the reporting period and shareholders’ equity amounts are translated based on historical exchange rates as of the date of each transaction. Translation adjustments are not included in determining the Company's net loss but are included in foreign exchange adjustment to other comprehensive loss, a component of shareholders’ equity. Patent Costs The Company expenses patent prosecution and related legal costs as they are incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations and comprehensive loss. The Company recorded patent expenses of $0.6 million and $0.6 million for the three months ended June 30, 2021 and 2020, respectively, and $1.1 million and $1.2 million for the six months ended June 30, 2021 and 2020, respectively. Grant Income The Company has received research grants under which it is reimbursed for specific research and development activities. Payments received are recognized as income in the statements of operations and comprehensive loss over the period in which the Company recognizes the related costs. At the time the Company recognizes grant income, it has complied with the conditions attached to it and the receipt of the reimbursement is reasonably assured. The Company has received grants from the U.K. government, which are repayable under certain circumstances, including breach or noncompliance. For grants with refund provisions, the Company reviews the grant to determine the likelihood of repayment. If the likelihood of repayment of the grant is determined to be remote, then the grant is recognized as grant income. The Company has determined that the likelihood of any repayment events included in its current grants is remote. License Revenue The Company accounts for its revenues pursuant to the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC Topic 606”). The Company has no products approved for commercial sale and have not generated any revenue from commercial product sales. The total revenue to date has been generated principally from license agreements. The terms of the agreement which was entered into during the three months ended June 30, 2021, included a non-refundable upfront license fee, options for future commercial licenses, payments based upon achievement of clinical development and regulatory objectives, payments based upon achievement of certain levels of product sales, and royalties on product sales. The Company recorded $1.5 million of license revenue for the three and six months ended June 30, 2021. The Company did not record any license revenue for the three and six months ended June 30, 2020. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. License Fees and Multiple Element Arrangements If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, upfront fees allocated to the license at such time as the license is transferred to the licensee and the licensee is able to use, and benefit from, the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, upfront fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Appropriate methods of measuring progress include output methods and input methods. In determining the appropriate method for measuring progress, the Company considers the nature of service that the Company promises to transfer to the customer. When the Company decides on a method of measurement, the Company will apply that single method of measuring progress for each performance obligation satisfied over time and will apply that method consistently to similar performance obligations and in similar circumstances. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options that are not determined to be material rights are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. We evaluate the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. We allocate the transaction price to material rights based on the relative standalone selling price, which is determined based on any identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. During the three and six months ended June 30, 2021 the company did not recognize any revenue related to customer options. Contingent Research Milestone Payments ASC Topic 606 constrains the amount of variable consideration included in the transaction price in that either all, or a portion, of an amount of variable consideration should be included in the transaction price. The variable consideration amount should be included only to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The assessment of whether variable consideration should be constrained is largely a qualitative one that has two elements: the likelihood of a change in estimate, and the magnitude thereof. Variable consideration is not constrained if the potential reversal of cumulative revenue recognized is not significant, for example. If the consideration in a contract includes a variable amount, the Company will estimate the amount of consideration in exchange for transfer of promised goods or services. The consideration also can vary if the Company’s entitlement to the consideration is contingent on the occurrence or non-occurrence of a future event. The Company considers contingent research milestone payments to fall under the scope of variable consideration, which should be estimated for revenue recognition purposes at the inception of the contract and reassessed ongoing at the end of each reporting period. The Company assesses whether contingent research milestones should be considered variable consideration that should be constrained and thus not part of the transaction price. This includes an assessment of the probability that all or some of the milestone revenue could be reversed when the uncertainty around whether or not the achievement of each milestone is resolved, and the amount of reversal could be significant. GAAP provides factors to consider when assessing whether variable consideration should be constrained. All of the factors should be considered, and no factor is determinate. The Company considers all relevant factors. For three and six months ended June 30, 2021, the Company has not recognized any variable consideration with regards to the development milestones, which are included in the license agreement that was executed in the period. This is due to the fact that those development milestones have not yet been met and the recognition of the related revenue is not yet probable. Royalty Revenue For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Income Taxes The Company accounts for income taxes under the asset and liability method which includes the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the Company’s condensed consolidated financial statements. Under this approach, deferred taxes are recorded for the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision (benefit) for income taxes represents income taxes paid or payable (or a reduction of such amounts) for the current year plus deferred taxes. Deferred taxes result from differences between the condensed consolidated financial statements and tax bases of the Company’s assets and liabilities, and are adjusted for changes in tax rates and tax law when changes are enacted. The effects of future changes in income tax laws or rates are not anticipated. The Company is subject to income taxes in the United Kingdom and the United States. The calculation of the Company’s tax provision involves the application of United Kingdom and United States tax law and requires judgment and estimates. The Company evaluates the realizability of its deferred tax assets at each reporting date, and establishes a valuation allowance when it is more likely than not that all or a portion of its deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income of the same character and in the same jurisdiction. The Company considers all available positive and negative evidence in making this assessment, including, but not limited to, the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies. In circumstances where there is sufficient negative evidence indicating that the Company’s deferred tax assets are not more likely than not realizable, the Company establishes a valuation allowance. The Company uses a two-step approach for recognizing and measuring uncertain tax positions. The first step is to evaluate tax positions taken or expected to be taken in a tax return by assessing whether they are more likely than not sustainable, based solely on their technical merits, upon examination, and including resolution of any related appeals or litigation process. The second step is to measure the associated tax benefit of each position as the largest amount that the Company believes is more likely than not realizable. Differences between the amount of tax benefits taken or expected to be taken in the Company’s income tax returns and the amount of tax benefits recognized in the its condensed consolidated financial statements represent the Company’s unrecognized income tax benefits, which it either records as a liability or reduction of deferred tax assets. Income Tax Credit The Company benefits from the U.K. research and development tax credit regime under both the small and medium sized enterprise, or SME, scheme and by claiming an RDEC in respect of grant funded projects. Under the SME regime, a portion of the Company’s losses can be surrendered for a cash rebate of up to 33.35% of eligible expenditures. SME credits are accounted for within the tax provision in the year in which the expenditures were incurred. RDEC credits are accounted for within other income in the condensed consolidated statements of operations and comprehensive loss. Comprehensive Loss The Company follows the provisions of the Financial Accounting Standards Board (“FASB”) ASC Topic 220, Comprehensive Income , which establishes standards for the reporting and display of comprehensive income and its components. Comprehensive loss is defined to include all changes in equity during a period except those resulting from investments by owners and distributions to owners. The Company recorded a gain of $1.5 million and a loss of $1.8 million related to foreign currency translation adjustments during the three months ended June 30, 2021 and 2020, respectively. The Company recorded a gain of $2.8 million and a loss of $19.5 million related to foreign currency translation adjustments during the six months ended June 30, 2021 and 2020, respectively. Net Loss Per Share Basic and diluted net loss per ordinary share is determined by dividing net loss by the weighted average number of ordinary shares outstanding during the period. For all periods presented, outstanding but unvested restricted shares and share options have been excluded from the calculation, because their effects would be anti-dilutive. Therefore, the weighted average shares outstanding used to calculate both basic and diluted loss per share are the same for all periods presented. The following potentially dilutive securities have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: As of June 30, 2021 2020 Unvested restricted incentive shares and units 1,105,300 663,917 Share options 6,499,436 5,931,211 Total 7,604,736 6,595,128 Recent Accounting Pronouncements Not Yet Adopted Accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company's financial statements upon adoption.

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Current	6 Months Ended
	Jun. 30, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Assets, Current	Prepaid Expenses and Other Assets, Current Prepaid expenses and other assets, current consisted of the following (in thousands): June 30, 2021 December 31, 2020 Research and development claims receivable $ 37,333 $ 24,711 Prepayments 6,491 10,206 VAT receivable 2,588 3,124 Lease receivables from terminations 1,703 1,237 Other asset 237 — Lease deposits receivable 648 — Grant income receivable 140 414 Other receivable 1,811 199 Deferred cost 1,993 3,008 Total prepaid expenses and other current assets $ 52,944 $ 42,899 The increase in research and development claims receivable is due to an increase in the effective tax rate when compared to the same period last year. More information on the movement in the tax position between periods can be found in Note 9.

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): June 30, 2021 December 31, 2020 Lab equipment $ 33,239 $ 23,491 Office equipment 3,224 2,928 Furniture and fixtures 1,355 1,340 Leasehold improvements 12,411 10,629 Assets under construction 2,651 14,321 Less: accumulated depreciation (18,690) (14,663) Total property and equipment, net $ 34,190 $ 38,046

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	6 Months Ended
	Jun. 30, 2021
Payables and Accruals [Abstract]
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses and other liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Compensation and benefits $ 8,833 $ 8,732 Research and development costs 11,373 15,343 UCLB milestone and option — 205 Professional fees 2,289 3,005 Other liabilities 678 496 Total accrued expenses and other liabilities $ 23,173 $ 27,781

Shareholders_ Equity

Shareholders’ Equity	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Shareholders’ Equity	Shareholders’ Equity Ordinary Shares Each holder of ordinary shares is entitled to one vote per ordinary share and to receive dividends when and if such dividends are recommended by the board of directors and declared by the shareholders. As of June 30, 2021, the Company has not declared any dividends. Effective from June 26, 2018, the board of directors has the authority to allot new ordinary shares or to grant rights to subscribe for or to convert any security into ordinary shares in the Company up to a maximum aggregate nominal amount of $8,400. This authority runs for five years and will expire on June 26, 2023. Effective from June 26, 2018, the board also has the authority to allot ordinary shares for cash or to grant rights to subscribe for or to convert any security into ordinary shares in the Company without first offering them to existing shareholders in proportion to their existing holdings up to an aggregate maximum nominal amount of $8,400. This authority runs for five years and will expire on June 26, 2023. As of June 30, 2021 the Company’s issued capital share consisted of 72,742,582 ordinary shares, with a nominal value of $0.000042 per share, (ii) 34,425 deferred shares, with a nominal value of £0.00001 per share, (iii) 88,893,548 B deferred shares, with a nominal value of £0.00099 per share and (iv) 1 C deferred share, with a nominal value of £0.000008. Each issued share has been fully paid. Open Market Sale Agreement On September 18, 2020, the Company entered into an Open Market Sale Agreement ("Sales Agreement") with Jefferies LLC, under which the Company may, at its option, offer and sell ADSs having an aggregate offering price of up to $100 million from time to time through Jefferies, acting as sales agent. Any such sales made through our sales agent can be made by any method that is deemed an “at-the-market offering” as defined in Rule 415 promulgated under the Securities Act, or in other transactions pursuant to an effective shelf registration statement on Form F-3. The Company agreed to pay Jefferies a commission of 3.0% of the gross proceeds of any sales of ADSs sold pursuant to the Sales Agreement. During three months ended June 30, 2021, the Company issued an aggregate of 2,069,466 ADSs under the Sales Agreement for net proceeds, after underwriting discounts and offering expenses of $14.3 million . During the six months ended June 30, 2021, the Company issued an aggregate of 3,787,972 ADSs under the Sales Agreement for net proceeds, after underwriting discounts and offering expenses of $29.6 million

Share-Based Compensation

Share-Based Compensation	6 Months Ended
	Jun. 30, 2021
Share-based Payment Arrangement [Abstract]
Share-Based Compensation	Share-Based CompensationOptions granted under the Company's 2018 Equity Incentive Plan (the "2018 Plan") and 2017 Stock Option Plan (the "2017 Plan"), as well as restricted shares granted as employee incentives, typically vest over a four-year service period with 25% of the award vesting on the first anniversary of the commencement date and the balance vesting monthly over the remaining three years, unless the award contains specific performance vesting provisions. For equity awards issued that have both a performance vesting condition and a services condition, once the performance criteria is achieved, the awards are then subject to a four-year service vesting with 25% of the award vesting on the first anniversary of the performance condition being achieved and the balance vesting monthly over the remaining three years. Options granted in January 2021 contained performance conditions related to specified clinical milestones. Options granted under the 2018 Plan and 2017 Plan generally expire 10 years from the date of grant. For certain senior members of management and directors, the board of directors has approved an alternative vesting schedule. Restricted stock units awarded in December 2019 vest over a 3-year service period with 50% of the award vesting one and a half years, or 18 months, from commencement date and the remaining 50% of the award vesting at the end of the third year. Restricted stock units awarded in January 2021 contained a performance condition related to specified clinical milestones. Share Option Valuation The assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted by the Company during the six months ended June 30, 2021 were as follows: June 30, 2021 Expected option life (years) 5.27 to 6.08 years Risk-free interest rate 0.62% to 1.14% Expected volatility 80.04% to 81.55% Expected dividend yield —% Share Options The table below summarizes activity for the six months ended June 30, 2021: Number of Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding as of December 31, 2020 5,611,429 $ 17.19 7.96 years $ 4,262 Granted 2,034,750 8.45 — — Exercised (158,307) 0.79 — — Canceled or forfeited (988,438) 16.68 — — Outstanding as of June 30, 2021 6,499,434 $ 14.93 8.20 years $ 1,814 Exercisable as of June 30, 2021 2,873,805 17.91 7.40 years $ 1,565 Vested and expected to vest as of June 30, 2021 6,499,436 $ 14.93 8.20 years $ 1,814 The aggregate intrinsic value of share options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ADSs for those share options that had exercise prices lower than the fair value of the Company’s ADSs. The weighted average grant-date fair value of share options granted was $5.83 per share for the six months ended June 30, 2021, of which none were vested at the date of these financials. As of June 30, 2021, the total unrecognized compensation expense related to unvested options was $7.4 million, which the Company expects to recognize over a weighted average vesting period of 2.4 years. During the six months ended June 30, 2021, the Company granted 1,602,500 options with performance conditions related to specified clinical milestones and 107,500 options with performance conditions were forfeited. As of June 30, 2021, the performance conditions were not determined to be probable and no expense was recorded for the six months ended June 30, 2021. Restricted Ordinary Shares A summary of the changes in the Company’s restricted ordinary shares during the six months ended June 30, 2021 is as follows: Number of Weighted average grant date fair value Unvested and outstanding at December 31, 2020 90,383 $ 4.17 Granted — — Vested (80,233) 4.17 Canceled or forfeited — — Unvested and outstanding at June 30, 2021 10,150 $ 4.17 As of June 30, 2021, there was no unrecognized compensation expense. Restricted Stock Units A restricted stock unit (“RSU”) represents the right to receive one of the Company’s ADSs upon vesting of the RSU. The fair value of each RSU is based on the closing price of the Company’s ADSs on the date of grant. The Company historically granted RSUs with service conditions that vest over 3-year service period with 50% of the award vesting one-and-half years from grant date and the remaining 50% of the award vesting at the end of the third year. In January 2021, the Company awarded restricted stock units that contained a performance condition based on a condition related to a specified clinical milestone. In March 2021, the Company awarded restricted stock units with service conditions that vest over a four year period with 25% on the first anniversary of the grant date, and the balance vesting quarterly over the remaining three years. The following is a summary of RSU activity for the 2018 Plan for the six months ended June 30, 2021: Number of Weighted average grant date fair value Unvested and outstanding at December 31, 2020 415,000 $ 12.09 Granted 1,045,650 8.71 Vested (164,500) 12.09 Canceled or forfeited (201,000) 10.85 Unvested and outstanding at June 30, 2021 1,095,150 $ 9.12 As of June 30, 2021, there was $1.4 million of unrecognized compensation expense related to unvested RSUs, which are expected to be recognized over a weighted average vesting period of 2.4 years. During the three months ended June 30, 2021, 143,000 RSUs vested, however, the shares were not issued as of June 30, 2021, and as such are not included in the Company's outstanding shares at June 30, 2021. During the six months ended June 30, 2021, the Company awarded 920,000 RSUs with a performance condition related to a specified clinical milestone and 70,000 RSUs with performance conditions were forfeited. As of June 30, 2021, the performance condition was not determined to be probable and accordingly, no expense was recorded for the six months ended June 30, 2021. Share-based Compensation Expense Share-based compensation expense recorded as research and development expenses, general and administrative expenses, and capitalized to property and equipment is as follows (in thousands): Three Months Ended June 30, Six Months Ended 2021 2020 2021 2020 Research and development $ 860 $ 3,704 $ (794) $ 8,266 General and administrative 420 1,734 1,404 3,361 Capitalized — (133) — (87) Total share-based compensation $ 1,280 $ 5,305 $ 610 $ 11,540 The decrease in share-based compensation expense of $10.9 million in the six months ended June 30, 2021 relates to forfeitures of share-based payment awards as a result of the reduction in workforce that took place during the period.

License Agreements

License Agreements	6 Months Ended
	Jun. 30, 2021
License Agreements [Abstract]
License Agreements	License Agreements UCL Business plc License In September 2014, the Company entered into an exclusive license agreement (the “License”) with UCL Business Ltd. (“UCLB”), the technology transfer company of University College London (“UCL”), to obtain licenses to certain technology rights in the field of cancer therapy and diagnosis. In March 2016, the License was amended to include additional rights. As part of the consideration for the License in September 2014, the Company issued 1,497,643 ordinary shares to UCLB. The Company paid upfront fees of $0.3 million and issued an additional 313,971 ordinary shares to UCLB when the License was amended in March 2016. In March 2018, the License was further amended and restated to include a license to the Company's product candidate, AUTO1, for which UCL is conducting Phase 1 clinical trials of AUTO1 in pediatric and adult ALL patients. The Company paid an upfront fee of £1.5 million for consideration for the amended and restated License and paid the additional £0.35 million in connection with UCLB's transfer of clinical data to the Company in December 2020. No equity was issued as part of the upfront fee consideration. Additionally, the Company may be obligated to make payments to UCLB under the amended and restated License upon the initiation of certain clinical activities in an aggregate amount of £0.18 million, the receipt of specified regulatory approvals in an aggregate amount of £37.5 million, the start of commercialization in an aggregate amount of £18 million, and the achievement of net sales levels in an aggregate amount of £51 million, as well as royalty payments based on possible future sales resulting from the utilization of the licensed technologies. On a per-product basis, these milestone payments range from £1 million to £18.5 million, depending on which T cell programming modules are used in the product achieving the milestone. Upon commercialization of any of the Company’s products that use the in-licensed patent rights, the Company will be obligated to pay UCLB a flat royalty for each licensed product ranging from the low- to mid-single digits, depending on which technologies are deployed in the licensed product, based on worldwide annual net sales of each licensed product, subject to certain reductions, including for the market entry of competing products and for loss of patent coverage of licensed products. The Company may deduct from the royalties payable to UCLB one-half of any payments made to a third party to obtain a license to such third party’s intellectual property that is necessary to exploit any licensed products. Once net sales of a licensed product have reached a certain specified threshold, the Company may exercise an option to buy out UCLB’s rights to the remaining milestone payments, royalty payments, and sublicensing revenue payments for such licensed product, on terms to be negotiated at the time. The License expires on a product-by-product and country-by-country basis upon the expiration of the royalty term with respect to each product in each country. The Company may unilaterally terminate the license agreement for any reason upon advance notice to UCLB. Either party may terminate the License for the uncured material breach by the other party or for the insolvency of the other party. If UCLB terminates the License following the Company’s insolvency or the Company’s material breach of the License, or if the Company terminates the License unilaterally, all rights and licenses granted to the Company will terminate, and all patent rights and know-how transferred to the Company pursuant to the License will revert back to UCLB, unless and to the extent the Company has exercised its option to acquire ownership of the licensed patent rights. In addition, UCLB has the right to negotiate with the Company for the grant of an exclusive license to the Company’s improvements to the T cell programming modules the Company has licensed on terms to be agreed upon at the time. Noile-Immune Biotech Inc. In November 2019, the Company entered into an exclusive license agreement with Noile-Immune Biotech Inc. ("Noile") under which the Company will have the right to develop CAR T cell therapies incorporating Noile’s PRIME (proliferation-inducing and migration-enhancing) technology. The PRIME technology is designed to improve proliferation and trafficking into solid tumors of both engineered CAR T cells as well as the patient’s own T cells. The Company paid an upfront fee and may be obligated to make additional payments to Noile upon the achievement of development milestones and receipt of regulatory approvals product sale milestones, as well as royalty payments based on possible future sales resulting from the utilization of the licensed technology.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes is based upon the estimated annual effective tax rates for the year applied to the current period loss before tax plus the tax effect of any significant unusual items, discrete events or changes in tax law. Fluctuations in the distribution of pre-tax income among the Company’s operating subsidiaries can lead to fluctuations of the effective tax rate in the condensed consolidated financial statements. In the three months ended June 30, 2021 and 2020, the actual effective tax rates were 16.4% and 18.0%, respectively and in the six months ended June 30, 2021 and 2020, the actual effective tax rates were 15.4% and 14.8%, respectively. The changes in the effective tax rate for the three and six months ended June 30, 2021 as compared to the three and six months ended June 30, 2020 were due to fluctuations in the forecast proportion of qualifying research and development expenditure for the year. The actual effective tax rates are lower than the 19% statutory rate of U.K. tax primarily due to the manner in which the UK research and development credit operates. The tax benefit for the three months ended June 30, 2021 decreased to $6.4 million from $7.0 million for three months ended June 30, 2020 due to a decrease in forecasted qualifying research and development expenditures and the decreased effective tax rate. The tax benefit for the six months ended June 30, 2021 increased to $12.1 million from $10.7 million for six months ended June 30, 2020 due to an increase in pre-tax losses and the increased effective tax rate.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies License Agreement The Company has entered into an exclusive license agreement with UCLB which has subsequently been amended and restated (see Note 8). In connection with the UCLB license agreement, the Company is required to make annual license payments and may be required to make payments upon the achievement of specified milestones. The Company has estimated the probability of the Company achieving each potential milestone in accordance with ASC 450, Contingencies . The Company concluded that, as of June 30, 2021, there were no milestones for which the likelihood of achievement was probable. Legal Proceedings From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. Regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors. The Company was not a party to any litigation and did not have contingency reserves established for any liabilities as of June 30, 2021 and December 31, 2020. Leases The Company leases certain office space, laboratory space, and equipment. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. The Company’s corporate headquarters are located in London, United Kingdom. The Company leases space at this location from Imperial (Forest House) Limited under a ten-year lease, the term of which commenced in September 2015. The lease included an option for the Company to lease additional space within a 15-month period, which the Company exercised in October 2016. The exercise of the option resulted in a separate new lease agreement with a concurrent term through September 2025. The landlord exercised its option to give notice in September 2020 to terminate the Forest House lease and pay the Company a break-lease payment fee in September 2021. The Company recorded a $1.3 million gain upon the notice of lease termination in the third quarter of 2020 and has a lease incentive receivable of $1.7 million as of June 30, 2021. In September 2018, the Company signed a binding letter of intent to enter into a lease for manufacturing space in Enfield, United Kingdom. The letter of intent required the Company to enter into a 15-year lease provided that the landlord completed the required leasehold improvements described in the agreement. The Company executed lease agreements for three manufacturing space units, each for 15-year lease terms. The leases commenced in February 2019 with option to terminate the lease in February 2029. In March 2021, the Company surrendered one of the units. Upon the surrender, the Company recognized a $0.1 million gain in other income after recognizing a termination fee of $0.2 million. The Company has no further obligations for the surrendered unit and the right of use asset and lease liability which were recorded for this unit have been written off in the period. The Company is actively seeking to sub-lease or assign the remaining three lease arrangements to third parties with two units under contract negotiation for sub-leases. The Company completed an asset impairment analysis of the right of use asset concluding the undiscounted cash flows exceeded the carrying value as of June 30, 2021. In October 2018, the Company executed an agreement to sublease office space in Rockville, Maryland for a term through October 2021. The Company then terminated the sublease in February 2020 and immediately entered into a five-year lease for the same space with the landlord. As a result of the sublease termination, the Company recognized a $0.2 million gain in other income (expense) in the three months ending March 31, 2020 . T he lease related to this facility is classified as an operating lease. The Company is obligated to pay its proportionate share of building operating expenses and real estate taxes in excess of base year amounts. These costs are considered to be variable lease payments and are not included in the determination of the lease’s right-of-use asset or lease liability. In January 2019, the Company executed a lease agreement to lease additional office and manufacturing space in Rockville, Maryland. The lease agreement required the Company to enter into a lease provided that the landlord completes the required leasehold improvements described in the agreement. The lease commenced in August 2020 for a term through June 2036. In March 2021, the Company announced plans to move the site of its global launch of manufacturing capacity to the United Kingdom from the United States. As a part of this strategy, the Company entered into a termination agreement with the landlord of its Rockville, Maryland property to terminate the lease for office and manufacturing space. As a result, the Company recognized a $2.0 million termination fee gain from the landlord, a $2.3 million gain from the removal of the leased right of use asset and corresponding lease liability, and expensed $2.4 million of leasehold improvements for the six months ended June 30, 2021. The $2.0 million termination fee was received from the landlord in April 2021.

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans In the United Kingdom, the Company makes contributions to private defined benefit pension schemes on behalf of its employees. The Company expensed $0.3 million and $0.3 million in contributions for the three months ended June 30, 2021 and 2020, respectively, and $0.7 million and $0.6 million in contributions for the six months ended June 30, 2021 and 2020, respectively. In the United States, the Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code in October 2018. The plan covers substantially all U.S. employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company matches employee contributions up to four percent of the employee’s annual salary. The Company expensed $0.1 million and $0.1 million for the three months ended June 30, 2021 and 2020, respectively, and $0.2 million and $0.2 million for the six months ended June 30, 2021 and 2020, respectively. The Company pays all administrative fees related to the 401(k) plan.

Subsequent Event

Subsequent Event	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsThe Company evaluated subsequent events through August 5, 2021, the date on which these financial statements were issued. The Company has concluded that no subsequent event has occurred that requires disclosure.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements include those of the Company and its wholly-owned subsidiaries, Autolus Limited, Autolus Inc. and Autolus GmbH, and have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All intercompany accounts and transactions have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of 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 accrual for research and development expenses, share-based compensation and income taxes. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers cash and cash equivalents in the condensed consolidated financial statements to include cash at banks with a maturity of less than three months, which is subject to an insignificant risk of changes in value.
Restricted Cash	The Company includes the remaining restricted cash balance of $0.2 million in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the Company's condensed consolidated statements of cash flows.
Fair Value Measurements	Fair Value Measurements The carrying amounts reported in the balance sheets for cash and restricted cash, prepaid expenses and other assets, accounts payable and accrued expenses and other liabilities approximate their fair value because of the short-term nature of these instruments.
Concentration of Credit Risk	Concentration of Credit RiskFinancial instruments that subject the Company to credit risk consist primarily of cash and restricted cash. The Company places cash and restricted cash in established financial institutions. The Company has no significant off-balance-sheet risk or concentration of credit risk, such as foreign exchange contracts, options contracts, or other foreign hedging arrangements.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over the estimated useful lives of the respective assets. As of June 30, 2021 and December 31, 2020, the Company’s property and equipment consisted of office equipment, lab equipment, furniture and fixtures, and leasehold improvements. The office equipment has an estimated useful life of three years, lab equipment has an estimated useful life of five
Leases	Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Most leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize on the balance sheet leases with terms of one year or less. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the right-of-use asset may be required for items such as incentives received, initial direct costs, or prepayments. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, components of a lease should be split into three categories: lease components (e.g. land, building, etc.), non-lease components (e.g. common area maintenance, consumables, etc.), and non-components (e.g. property taxes, insurance, etc.). Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. The Company accounts for the lease and non-lease components of leases for classes of all underlying assets and allocates all of the contract consideration to the lease component.
Intangible Assets Subject to Amortization	Intangible Assets Subject to Amortization The Company’s intangible assets are related to acquired software licenses with finite lives and are amortized over their useful lives and reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. If any indicators of impairment are present, the Company tests for recoverability by comparing the carrying amount of the asset to the net undiscounted cash flows expected to be generated from the asset. If those net undiscounted cash flows do not exceed the carrying amount (i.e., the asset is not recoverable), the Company would perform the next step, which is to determine the fair value of the asset and record an impairment loss, if any. The Company evaluates the useful lives for these intangible assets each reporting period to determine whether events and circumstances warrant a revision in their remaining useful lives. The Company did not recognize an impairment loss in the three and six months ended June 30, 2021 and 2020.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and its chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which is the business of developing and commercializing gene therapies; however, the Company operates in three geographic regions: the
Research and Development Costs and Accrued Research and Development Expenses	Research and Development CostsResearch and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, share-based compensation and benefits, depreciation expense, third-party license fees, external costs of outside vendors engaged to conduct clinical development activities, clinical trials, costs to manufacture clinical trial materials and certain tax credits associated with research and development activities. Accrued Research and Development Expenses As part of the process of preparing its condensed consolidated financial statements, the Company is required to estimate accruals for research and development expenses. This process involves reviewing and identifying services which have been performed by third parties on the Company’s behalf and determining the value of these services. In addition, the Company makes estimates of costs incurred to date but not yet invoiced, in relation to external clinical research organizations and clinical site costs. The Company analyzes the progress of clinical trials, including levels of patient enrollment, invoices received and contracted costs, when evaluating the adequacy of the accrued liabilities for research and development. The Company makes judgments and estimates in determining the accrued balance in any accounting period.
Share-Based Compensation	Share-Based Compensation The Company recognizes compensation expense for equity awards based on the grant date fair value of the award. The Company recognizes share-based compensation expense for awards granted to employees that have a graded vesting schedule based on a service condition only on a straight-line basis over the requisite service period for each separately vesting portion of the award as if the award was, in substance, multiple awards (the “graded-vesting attribution method”), based on the estimated grant date fair value for each separately vesting tranche. For equity awards with a graded vesting schedule and a combination of service and performance conditions, the Company recognizes share-based compensation expense using a graded-vesting attribution method over the requisite service period when the achievement of a performance-based milestone is probable, based on the relative satisfaction of the performance condition as of the reporting date. For share-based awards granted to consultants and non-employees, compensation expense is recognized using the graded-vesting attribution method over the period during which services are rendered by such consultants and non-employees until completed. The measurement date for employee awards is the date of grant, and share-based compensation costs are recognized as expense over the employees’ requisite service period, which is the vesting period, on an accelerated basis. The Company accounts for forfeitures as they occur. The fair value of each share option grant is estimated on the date of grant using the Black-Scholes option pricing model. See Note 7 for the Company’s assumptions used in connection with option grants made during the periods covered by these condensed consolidated financial statements. Assumptions used in the option pricing model include the following: Expected volatility. The Company lacks company-specific historical and implied volatility information for our ADSs for expected terms greater than 3 years. Therefore, it uses a combination of the historical volatility of the ADSs and also the expected share volatility based on the historical volatility of publicly traded peer companies and expect to continue to do so until such time as the Company has adequate historical data regarding the volatility of its own traded security price. Expected term . The expected term of the Company’s share options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Risk-free interest rate . The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods that are approximately equal to the expected term of the award. Expected dividend. Expected dividend yield of zero is based on the fact that the Company has never paid cash dividends on ordinary shares and does not expect to pay any cash dividends in the foreseeable future. Fair value of ordinary shares. The fair market value of the Company’s ADSs underlying the option is equal to the closing price of the ADSs on the Nasdaq Global Select Market on the date the grant is approved by the Board.
Foreign Currency Remeasurement and Translation	Foreign Currency Remeasurement and Translation The Company maintains its condensed consolidated financial statements in its functional currency, which is the pound sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are remeasured into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are remeasured into the functional currency at the exchange rates prevailing at the date of the transaction. Exchange gains or losses arising from foreign currency transactions are included in the determination of net loss for the respective periods. The Company recorded a foreign exchange loss of $1.9 million and foreign exchange gain of $0.5 million for the three months ended June 30, 2021 and 2020, respectively. The Company recorded a foreign exchange loss of $3.1 million and foreign exchange gain of $4.8 million for the six months ended June 30, 2021 and 2020, respectively. Foreign exchange gains and losses are included in other income in the statements of operations and comprehensive loss. For financial reporting purposes, the condensed consolidated financial statements of the Company have been translated into U.S. dollars. Assets and liabilities have been translated at the exchange rates at the balance sheet dates, while revenue and expenses are translated at the average exchange rates over the reporting period and shareholders’ equity amounts are translated based on historical exchange rates as of the date of each transaction. Translation adjustments are not included in determining the Company's net loss but are included in foreign exchange adjustment to other comprehensive loss, a component of shareholders’ equity.
Patent Costs	Patent CostsThe Company expenses patent prosecution and related legal costs as they are incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations and comprehensive loss.
Grant Income	Grant Income The Company has received research grants under which it is reimbursed for specific research and development activities. Payments received are recognized as income in the statements of operations and comprehensive loss over the period in which the Company recognizes the related costs. At the time the Company recognizes grant income, it has complied with the conditions attached to it and the receipt of the reimbursement is reasonably assured. The Company has received grants from the U.K. government, which are repayable under certain circumstances, including breach or noncompliance. For grants with refund provisions, the Company reviews the grant to determine the likelihood of repayment. If the likelihood of repayment of the grant is determined to be remote, then the grant is recognized as grant income. The Company has determined that the likelihood of any repayment events included in its current grants is remote.
License Revenue	License Revenue The Company accounts for its revenues pursuant to the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC Topic 606”). The Company has no products approved for commercial sale and have not generated any revenue from commercial product sales. The total revenue to date has been generated principally from license agreements. The terms of the agreement which was entered into during the three months ended June 30, 2021, included a non-refundable upfront license fee, options for future commercial licenses, payments based upon achievement of clinical development and regulatory objectives, payments based upon achievement of certain levels of product sales, and royalties on product sales. The Company recorded $1.5 million of license revenue for the three and six months ended June 30, 2021. The Company did not record any license revenue for the three and six months ended June 30, 2020. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. License Fees and Multiple Element Arrangements If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, upfront fees allocated to the license at such time as the license is transferred to the licensee and the licensee is able to use, and benefit from, the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligations to determine whether the combined performance obligations are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, upfront fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Appropriate methods of measuring progress include output methods and input methods. In determining the appropriate method for measuring progress, the Company considers the nature of service that the Company promises to transfer to the customer. When the Company decides on a method of measurement, the Company will apply that single method of measuring progress for each performance obligation satisfied over time and will apply that method consistently to similar performance obligations and in similar circumstances. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options that are not determined to be material rights are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. We evaluate the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. We allocate the transaction price to material rights based on the relative standalone selling price, which is determined based on any identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. During the three and six months ended June 30, 2021 the company did not recognize any revenue related to customer options. Contingent Research Milestone Payments ASC Topic 606 constrains the amount of variable consideration included in the transaction price in that either all, or a portion, of an amount of variable consideration should be included in the transaction price. The variable consideration amount should be included only to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The assessment of whether variable consideration should be constrained is largely a qualitative one that has two elements: the likelihood of a change in estimate, and the magnitude thereof. Variable consideration is not constrained if the potential reversal of cumulative revenue recognized is not significant, for example. If the consideration in a contract includes a variable amount, the Company will estimate the amount of consideration in exchange for transfer of promised goods or services. The consideration also can vary if the Company’s entitlement to the consideration is contingent on the occurrence or non-occurrence of a future event. The Company considers contingent research milestone payments to fall under the scope of variable consideration, which should be estimated for revenue recognition purposes at the inception of the contract and reassessed ongoing at the end of each reporting period. The Company assesses whether contingent research milestones should be considered variable consideration that should be constrained and thus not part of the transaction price. This includes an assessment of the probability that all or some of the milestone revenue could be reversed when the uncertainty around whether or not the achievement of each milestone is resolved, and the amount of reversal could be significant. GAAP provides factors to consider when assessing whether variable consideration should be constrained. All of the factors should be considered, and no factor is determinate. The Company considers all relevant factors. For three and six months ended June 30, 2021, the Company has not recognized any variable consideration with regards to the development milestones, which are included in the license agreement that was executed in the period. This is due to the fact that those development milestones have not yet been met and the recognition of the related revenue is not yet probable. Royalty Revenue
Income Taxes and Income Tax Credit	Income Taxes The Company accounts for income taxes under the asset and liability method which includes the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the Company’s condensed consolidated financial statements. Under this approach, deferred taxes are recorded for the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision (benefit) for income taxes represents income taxes paid or payable (or a reduction of such amounts) for the current year plus deferred taxes. Deferred taxes result from differences between the condensed consolidated financial statements and tax bases of the Company’s assets and liabilities, and are adjusted for changes in tax rates and tax law when changes are enacted. The effects of future changes in income tax laws or rates are not anticipated. The Company is subject to income taxes in the United Kingdom and the United States. The calculation of the Company’s tax provision involves the application of United Kingdom and United States tax law and requires judgment and estimates. The Company evaluates the realizability of its deferred tax assets at each reporting date, and establishes a valuation allowance when it is more likely than not that all or a portion of its deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income of the same character and in the same jurisdiction. The Company considers all available positive and negative evidence in making this assessment, including, but not limited to, the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies. In circumstances where there is sufficient negative evidence indicating that the Company’s deferred tax assets are not more likely than not realizable, the Company establishes a valuation allowance. The Company uses a two-step approach for recognizing and measuring uncertain tax positions. The first step is to evaluate tax positions taken or expected to be taken in a tax return by assessing whether they are more likely than not sustainable, based solely on their technical merits, upon examination, and including resolution of any related appeals or litigation process. The second step is to measure the associated tax benefit of each position as the largest amount that the Company believes is more likely than not realizable. Differences between the amount of tax benefits taken or expected to be taken in the Company’s income tax returns and the amount of tax benefits recognized in the its condensed consolidated financial statements represent the Company’s unrecognized income tax benefits, which it either records as a liability or reduction of deferred tax assets. Income Tax Credit
Comprehensive Loss	Comprehensive Loss The Company follows the provisions of the Financial Accounting Standards Board (“FASB”) ASC Topic 220, Comprehensive Income
Net Loss Per Share	Net Loss Per ShareBasic and diluted net loss per ordinary share is determined by dividing net loss by the weighted average number of ordinary shares outstanding during the period. For all periods presented, outstanding but unvested restricted shares and share options have been excluded from the calculation, because their effects would be anti-dilutive. Therefore, the weighted average shares outstanding used to calculate both basic and diluted loss per share are the same for all periods presented.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted Accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company's financial statements upon adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Schedule of Anti-dilutive Securities	The following potentially dilutive securities have been excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: As of June 30, 2021 2020 Unvested restricted incentive shares and units 1,105,300 663,917 Share options 6,499,436 5,931,211 Total 7,604,736 6,595,128

Prepaid Expenses and Other As_2

Prepaid Expenses and Other Assets, Current (Tables)	6 Months Ended
	Jun. 30, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other assets, current consisted of the following (in thousands): June 30, 2021 December 31, 2020 Research and development claims receivable $ 37,333 $ 24,711 Prepayments 6,491 10,206 VAT receivable 2,588 3,124 Lease receivables from terminations 1,703 1,237 Other asset 237 — Lease deposits receivable 648 — Grant income receivable 140 414 Other receivable 1,811 199 Deferred cost 1,993 3,008 Total prepaid expenses and other current assets $ 52,944 $ 42,899

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): June 30, 2021 December 31, 2020 Lab equipment $ 33,239 $ 23,491 Office equipment 3,224 2,928 Furniture and fixtures 1,355 1,340 Leasehold improvements 12,411 10,629 Assets under construction 2,651 14,321 Less: accumulated depreciation (18,690) (14,663) Total property and equipment, net $ 34,190 $ 38,046

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	6 Months Ended
	Jun. 30, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Compensation and benefits $ 8,833 $ 8,732 Research and development costs 11,373 15,343 UCLB milestone and option — 205 Professional fees 2,289 3,005 Other liabilities 678 496 Total accrued expenses and other liabilities $ 23,173 $ 27,781

Share-Based Compensation (Table

Share-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Stock Options Valuation Assumptions	The assumptions used in the Black-Scholes option pricing model to determine the fair value of the share options granted by the Company during the six months ended June 30, 2021 were as follows: June 30, 2021 Expected option life (years) 5.27 to 6.08 years Risk-free interest rate 0.62% to 1.14% Expected volatility 80.04% to 81.55% Expected dividend yield —%
Stock Option Rollforward	The table below summarizes activity for the six months ended June 30, 2021: Number of Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding as of December 31, 2020 5,611,429 $ 17.19 7.96 years $ 4,262 Granted 2,034,750 8.45 — — Exercised (158,307) 0.79 — — Canceled or forfeited (988,438) 16.68 — — Outstanding as of June 30, 2021 6,499,434 $ 14.93 8.20 years $ 1,814 Exercisable as of June 30, 2021 2,873,805 17.91 7.40 years $ 1,565 Vested and expected to vest as of June 30, 2021 6,499,436 $ 14.93 8.20 years $ 1,814
Schedule of Nonvested Share Activity	A summary of the changes in the Company’s restricted ordinary shares during the six months ended June 30, 2021 is as follows: Number of Weighted average grant date fair value Unvested and outstanding at December 31, 2020 90,383 $ 4.17 Granted — — Vested (80,233) 4.17 Canceled or forfeited — — Unvested and outstanding at June 30, 2021 10,150 $ 4.17 The following is a summary of RSU activity for the 2018 Plan for the six months ended June 30, 2021: Number of Weighted average grant date fair value Unvested and outstanding at December 31, 2020 415,000 $ 12.09 Granted 1,045,650 8.71 Vested (164,500) 12.09 Canceled or forfeited (201,000) 10.85 Unvested and outstanding at June 30, 2021 1,095,150 $ 9.12
Schedule Share Based Compensation Expense	Share-based compensation expense recorded as research and development expenses, general and administrative expenses, and capitalized to property and equipment is as follows (in thousands): Three Months Ended June 30, Six Months Ended 2021 2020 2021 2020 Research and development $ 860 $ 3,704 $ (794) $ 8,266 General and administrative 420 1,734 1,404 3,361 Capitalized — (133) — (87) Total share-based compensation $ 1,280 $ 5,305 $ 610 $ 11,540

Nature of the Business (Details

Nature of the Business (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 17, 2021	Feb. 12, 2021	Jan. 27, 2020	Apr. 15, 2019	Jun. 22, 2018	Jan. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Class of Stock
Number of shares issued in transaction	2,069,466					1,718,506	2,069,466				3,787,972
Proceeds of issuance of ordinary shares, net of issuance costs	$ 14,300					$ 15,300	$ 14,300				$ 29,600
Net loss							(33,173)	$ (33,266)	$ (32,045)	$ (29,873)	(66,440)	$ (61,918)
Accumulated deficit							445,683				445,683		$ 379,244
Cash							$ 216,352		$ 212,044		$ 216,352	$ 212,044	$ 153,299
Underwriters public offering
Class of Stock
Proceeds of issuance of ordinary shares, net of issuance costs			$ 75,000
Ordinary Shares
Class of Stock
Number of shares issued in transaction		14,285,715
Per share price of issuance (usd per share)		$ 7
Ordinary Shares | IPO
Class of Stock
Number of shares issued in transaction					10,147,059
Per share price of issuance (usd per share)					$ 17
Proceeds of issuance of ordinary shares, net of issuance costs					$ 156,500
Ordinary Shares | Options
Class of Stock
Number of shares issued in transaction		2,142,857		630,000	1,323,529
Ordinary Shares | Underwriters public offering
Class of Stock
Number of shares issued in transaction			7,250,000	4,830,000
Per share price of issuance (usd per share)			$ 11	$ 24
Proceeds of issuance of ordinary shares, net of issuance costs		$ 106,900		$ 108,800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Apr. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Restricted Cash
Restricted cash	$ 210		$ 786	$ 786
Reclassification, Other
Restricted Cash
Cash and cash equivalents		$ 600
Security Deposit
Restricted Cash
Restricted cash	$ 200
Letter of Credit | Reclassification, Other
Restricted Cash
Restricted cash		$ 600

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property Plant and Equipment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property, Plant and Equipment
Loss on disposal of leasehold improvements	$ 0	$ 0	$ (672,000)	$ 0
Loss on disposal of property and equipment		0	672,000	0
Impairment of property, plant and equipment	$ 0	$ 0	$ 0	$ 0
Office equipment
Property, Plant and Equipment
Property, plant and equipment			3 years
Lab equipment | Minimum
Property, Plant and Equipment
Property, plant and equipment			5 years
Lab equipment | Maximum
Property, Plant and Equipment
Property, plant and equipment			10 years
Furniture and fixtures
Property, Plant and Equipment
Property, plant and equipment			5 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Intangible Assets Subject to Amortization (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Impairment of property, plant and equipment	$ 0	$ 0	$ 0	$ 0
Impairment of intangible assets (excluding goodwill)	$ 0		$ 0

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Segment Information (Details)	6 Months Ended
	Jun. 30, 2021segmentregion
Accounting Policies [Abstract]
Number of operating segments | segment	1
Number of geographic regions | region	3

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Research and Development (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Research and development tax credits	$ 55	$ 39	$ 87	$ 67

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Foreign Currency Remeasurement and Translation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Foreign currency translation gain (loss)	$ (1.9)	$ 0.5	$ (3.1)	$ 4.8

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Patent Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Patent costs	$ 0.6	$ 0.6	$ 1.1	$ 1.2

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Foreign currency exchange translation adjustment	$ 1,542	$ 1,273	$ (1,819)	$ (17,701)	$ 2,815	$ (19,520)

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Antidilutive Shares (Details) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities
Anti-dilutive shares	7,604,736	6,595,128
Unvested restricted incentive shares and units
Antidilutive Securities
Anti-dilutive shares	1,105,300	663,917
Share options
Antidilutive Securities
Anti-dilutive shares	6,499,436	5,931,211

Summary of Significant Accou_13

Summary of Significant Accounting Policies - License Revenue (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
License revenue
Product Information [Line Items]
Revenues	$ 1,507,000	$ 0	$ 1,507,000	$ 0

Prepaid Expenses and Other As_3

Prepaid Expenses and Other Assets, Current (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Research and development claims receivable	$ 37,333	$ 24,711
Prepayments	6,491	10,206
VAT receivable	2,588	3,124
Lease receivables from terminations	1,703	1,237
Other asset	237	0
Lease deposits receivable	648	0
Grant income receivable	140	414
Other receivable	1,811	199
Deferred cost	1,993	3,008
Total prepaid expenses and other current assets	$ 52,944	$ 42,899

Prepaid Expenses and Other As_4

Prepaid Expenses and Other Assets, Current - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Decrease to prepaid facility and manufacturing	$ 3.7

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment
Less: accumulated depreciation	$ (18,690)	$ (14,663)
Total property and equipment, net	34,190	38,046
Lab equipment
Property, Plant and Equipment
Property and equipment, gross	33,239	23,491
Office equipment
Property, Plant and Equipment
Property and equipment, gross	3,224	2,928
Furniture and fixtures
Property, Plant and Equipment
Property and equipment, gross	1,355	1,340
Leasehold improvements
Property, Plant and Equipment
Property and equipment, gross	12,411	10,629
Assets under construction
Property, Plant and Equipment
Property and equipment, gross	$ 2,651	$ 14,321

Property and Equipment, Net - N

Property and Equipment, Net - Narratives (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 2.2	$ 1.2	$ 4.1	$ 2.5

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities (Details) £ in Thousands, $ in Thousands	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)	Mar. 31, 2018GBP (£)
Payables and Accruals [Abstract]
Compensation and benefits	$ 8,833	$ 8,732
Research and development costs	11,373	15,343
UCLB milestone and option	0	205	£ 350
Professional fees	2,289	3,005
Other liabilities	678	496
Total accrued expenses and other liabilities	$ 23,173	$ 27,781

Accrued Expenses and Other Li_4

Accrued Expenses and Other Liabilities - Narratives (Details) $ in Millions	Jun. 30, 2021USD ($)
Payables and Accruals [Abstract]
Research and development costs, decrease	$ 4

Shareholders_ Equity - Ordinary

Shareholders’ Equity - Ordinary Shares (Details)	Jun. 26, 2018USD ($)	Jun. 30, 2021$ / sharesshares	Jun. 30, 2021£ / sharesshares	Dec. 31, 2020$ / sharesshares	Dec. 31, 2020£ / sharesshares
Class of Stock
Authorized grant, life	5 years
Ordinary shares
Class of Stock
Maximum nominal shares authorized for grant | $	$ 8,400
Shares issued		72,742,582	72,742,582	52,346,231	52,346,231
Stock par value (usd/gbp per share) | $ / shares		$ 0.000042		$ 0.000042
Deferred Shares
Class of Stock
Shares issued		34,425	34,425	34,425	34,425
Stock par value (usd/gbp per share) | £ / shares			£ 0.00001		£ 0.00001
Deferred B Shares
Class of Stock
Shares issued		88,893,548	88,893,548	88,893,548	88,893,548
Stock par value (usd/gbp per share) | £ / shares			£ 0.00099		£ 0.00099
Deferred C Shares
Class of Stock
Shares issued		1	1	1	1
Stock par value (usd/gbp per share) | £ / shares			£ 0.000008		£ 0.000008

Shareholders_ Equity - Open Mar

Shareholders’ Equity - Open Market Sales Agreement (Details) $ in Millions	Jun. 17, 2021USD ($)shares	Jan. 31, 2021USD ($)shares	Jun. 30, 2021USD ($)shares	Jun. 30, 2021USD ($)shares	Sep. 18, 2020USD ($)
Equity [Abstract]
Sale of stock, authorized amount					$ 100
Commission, percentage of gross sales price					0.030
Number of shares issued in transaction | shares	2,069,466	1,718,506	2,069,466	3,787,972
Proceeds of issuance of ordinary shares, net of issuance costs	$ 14.3	$ 15.3	$ 14.3	$ 29.6

Share-Based Compensation - 2018

Share-Based Compensation - 2018 Plan and 2017 Plan (Details)	6 Months Ended
	Jun. 30, 2021
Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	4 years
Stock option vesting right percentage	25.00%
Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	3 years
Performance Based | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Stock option vesting right percentage	25.00%
Performance Based | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	3 years
Share options
Share-based Compensation Arrangement by Share-based Payment Award
Stock option term	10 years
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	3 years
RSUs | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	18 months
Stock option vesting right percentage	50.00%
RSUs | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period	18 months
Stock option vesting right percentage	50.00%

Share-Based Compensation - Opti

Share-Based Compensation - Options Valuation Assumptions (Details) - Share options	6 Months Ended
	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Risk-free interest rate, minimum	0.62%
Risk-free interest rate, maximum	1.14%
Expected volatility, minimum	80.04%
Expected volatility, maximum	81.55%
Expected dividend yield	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected option life (years)	5 years 3 months 7 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected option life (years)	6 years 29 days

Share-Based Compensation - Shar

Share-Based Compensation - Share Options Rollforward (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Number of Options
Beginning balance (in shares) | shares	5,611,429
Granted (in shares) | shares	2,034,750
Exercised (in shares) | shares	(158,307)
Canceled or forfeited (in shares) | shares	(988,438)
Ending balance (in shares) | shares	6,499,434	5,611,429
Exercisable (in shares) | shares	2,873,805
Vested and expected to vest (in shares) | shares	6,499,436
Weighted-Average Exercise Price
Beginning balance weighted average exercise price (usd per share) | $ / shares	$ 17.19
Granted weighted average exercise price (usd per share) | $ / shares	8.45
Exercised weighted average exercise price (usd per share) | $ / shares	0.79
Canceled or forfeited weighted average exercise price (usd per share) | $ / shares	16.68
Ending balance weighted average exercise price (usd per share) | $ / shares	14.93	$ 17.19
Exercisable weighted average exercise price (usd per share) | $ / shares	17.91
Vested and expected to vest weighted average exercise price (usd per share) | $ / shares	$ 14.93
Weighted-Average Remaining Contractual Term (Years)
Weighted average contractual term outstanding	8 years 2 months 12 days	7 years 11 months 15 days
Weighted average contractual term exercisable	7 years 4 months 24 days
Weighted average contractual term vested and expected to vest	8 years 2 months 12 days
Aggregate Intrinsic Value
Options outstanding | $	$ 1,814	$ 4,262
Options exercisable | $	1,565
Options vested and expected to vest | $	$ 1,814

Share-Based Compensation - Sh_2

Share-Based Compensation - Share Options Narratives (Details) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation not yet recognized for unvested shares | $	$ 7.4
Share based compensation not yet recognized for unvested shares vesting period	2 years 4 months 24 days
Share options
Share-based Compensation Arrangement by Share-based Payment Award
Weighted average grant date fair value (usd per share) | $ / shares	$ 5.83
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, shares issued in period	1,602,500
Share-based Payment, Options, Performance Condition
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, options, forfeitures in period	107,500

Share-Based Compensation - Rest

Share-Based Compensation - Restricted Ordinary Shares Rollforward (Details) - Restricted Stock	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Number of restricted shares
Unvested and outstanding beginning balance (in shares) | shares	90,383
Granted (in shares) | shares	0
Vested (in shares) | shares	(80,233)
Canceled of forfeited (in shares) | shares	0
Unvested and outstanding ending balance (in shares) | shares	10,150
Weighted average grant date fair value
Unvested and outstanding beginning balance weighted average grant date fair value (usd per share) | $ / shares	$ 4.17
Granted weighted average grant date fair value (usd per share) | $ / shares	0
Vested weighted average grant date fair value (usd per share) | $ / shares	4.17
Canceled or forfeited weighted average grant date fair value (usd per share) | $ / shares	0
Unvested and outstanding ending balance weighted average grant date fair value (usd per share) | $ / shares	$ 4.17

Share-Based Compensation - Re_2

Share-Based Compensation - Restricted and Ordinary Shares Narratives (Details)	Jun. 30, 2021USD ($)
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation not yet recognized for unvested shares other than options	$ 0

Share-Based Compensation - Re_3

Share-Based Compensation - Restricted Stock Units Narratives (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021USD ($)shares	Jun. 30, 2021USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation not yet recognized for unvested shares vesting period		2 years 4 months 24 days
Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period		3 years
Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period		4 years
Stock option vesting right percentage		25.00%
RSUs
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period		3 years
Share based compensation not yet recognized for unvested shares other than options | $	$ 1.4	$ 1.4
Share based compensation not yet recognized for unvested shares vesting period		2 years 4 months 24 days
Vested (in shares)	143,000	164,500
Share-based compensation arrangement by share-based payment award, shares issued in period	920,000
Canceled of forfeited (in shares)	70,000	201,000
RSUs | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period		18 months
Stock option vesting right percentage		50.00%
RSUs | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award
Stock options vesting period		18 months
Stock option vesting right percentage		50.00%

Share-Based Compensation - Re_4

Share-Based Compensation - Restricted Stock Units (Details) - RSUs - $ / shares	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Restricted Stock Units
Unvested and outstanding beginning balance (in shares)		415,000
Granted (in shares)		1,045,650
Vested (in shares)	(143,000)	(164,500)
Canceled of forfeited (in shares)	(70,000)	(201,000)
Unvested and outstanding ending balance (in shares)	1,095,150	1,095,150
Weighted average grant date fair value
Unvested and outstanding beginning balance weighted average grant date fair value (usd per share)		$ 12.09
Granted weighted average grant date fair value (usd per share)		8.71
Vested weighted average grant date fair value (usd per share)		12.09
Canceled or forfeited weighted average grant date fair value (usd per share)		10.85
Unvested and outstanding ending balance weighted average grant date fair value (usd per share)	$ 9.12	$ 9.12

Share-Based Compensation - Sh_3

Share-Based Compensation - Share Based Compensation Allocation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	$ 1,280	$ 5,305	$ 610	$ 11,540
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	860	3,704	(794)	8,266
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	420	1,734	1,404	3,361
Capitalized
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	$ 0	$ (133)	$ 0	$ (87)

Share-Based Compensation - Sh_4

Share-Based Compensation - Share Based Compensation Allocation Narratives (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Share-based Payment Arrangement [Abstract]
Share-based payment arrangement, expense, decrease	$ 10.9

License Agreements (Details)

License Agreements (Details) £ in Thousands, $ in Thousands	1 Months Ended
	Mar. 31, 2018GBP (£)	Mar. 31, 2016USD ($)shares	Sep. 30, 2014shares	Jun. 30, 2021USD ($)	Jun. 30, 2021GBP (£)	Dec. 31, 2020USD ($)
Schedule Of License Agreements
Shares issued | shares		313,971
Accrued license fees payable	£ 350			$ 0		$ 205
Product Sales | Minimum
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					£ 1,000
Product Sales | Maximum
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					18,500
UCL Business plc
Schedule Of License Agreements
Shares issued | shares			1,497,643
Payment of upfront fees (usd/gbp per share)	£ 1,500	$ 300
UCL Business plc | Clinical Activities
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					180
UCL Business plc | Regulatory Approval
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					37,500
UCL Business plc | Product Sales
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					18,000
UCL Business plc | Net Sales Levels
Schedule Of License Agreements
Conditional payment, regulatory approval (gbp per share)					£ 51,000

Income Taxes (Details)

Income Taxes (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
Income Tax Contingency [Line Items]
Effective rate of income tax	16.40%	18.00%	15.40%	14.80%
U.K. statutory tax rate			19.00%
Income tax benefit	$ 6,357	$ 7,021	$ 12,081	$ 10,717
Deferred tax asset	1,643		1,643		$ 1,754
Subsidiaries
Income Tax Contingency [Line Items]
Deferred tax asset	$ 1,600		$ 1,600

Commitments and Contingencies -

Commitments and Contingencies - Narratives (Details) $ in Thousands	1 Months Ended			3 Months Ended		6 Months Ended
	Apr. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Oct. 31, 2018	Sep. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Sep. 30, 2018unit
Loss Contingencies
Gain on termination of operating lease						$ (11)	$ 160
Lease incentive receivable						1,700
Imperial (Forest House) Limited
Loss Contingencies
Gain on termination of operating lease				$ 1,300
Manufacturing Space in Enfield, United Kingdom
Loss Contingencies
Gain on termination of operating lease		$ 100
Lease termination fee expense		200
Office and Manufacturing Space in Rockville, Maryland
Loss Contingencies
Gain on termination of operating lease	$ 2,000	2,000
Gain on sale of leased Assets, net, operating leases		$ 2,300
Impairment of leasehold						$ 2,400
Building | Imperial (Forest House) Limited
Loss Contingencies
Operating lease contract term						10 years
Building | Manufacturing Space in Enfield, United Kingdom
Loss Contingencies
Operating lease contract term								15 years
Number of units | unit								3
Building | Office Space In Rockville, Maryland
Loss Contingencies
Gain on termination of operating lease					$ 200
Operating lease rent free period			5 years
Additional Space | Imperial (Forest House) Limited
Loss Contingencies
Operating lease contract term						15 months

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Employer contributions to defined benefit pension	$ 0.3	$ 0.3	$ 0.7	$ 0.6
Employer contribution percent			4.00%
Employer contributions	$ 0.1	$ 0.1	$ 0.2	$ 0.2