Document Entity Information Statement	3 Months Ended
Document Entity Information Statement	Dec. 31, 2018 shares
Document Information [Abstract]
Entity Registrant Name	Autolus Therapeutics plc
Entity Central Index Key	0001730463
Document Type	20-F
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	40,145,617

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Current assets:
Cash	$ 217,450,000	$ 246,984,000	$ 137,070,000
Restricted cash	105,000	105,000	0
Prepaid expenses and other current assets	15,411,000	12,189,000	5,412,000
Total current assets	232,966,000	259,278,000	142,482,000
Non-current assets:
Property and equipment, net	19,968,000	13,528,000	6,180,000
Long-term deposits	1,276,000	0	0
Intangible assets, net	0	399,000	0
Total assets	254,210,000	273,205,000	148,662,000
Current liabilities:
Accounts payable	2,022,000	3,036,000	1,946,000
Accrued expenses and other liabilities	19,054,000	14,103,000	3,087,000
Total current liabilities	21,076,000	17,139,000	5,033,000
Non-current liabilities:
Long-term lease incentive obligation	207,000	221,000	265,000
Other long-term payables	285,000	380,000	763,000
Total liabilities	21,568,000	17,740,000	6,061,000
Shareholders' equity:
Additional paid-in capital	361,311,000	357,918,000	194,351,000
Accumulated other comprehensive loss	(15,488,000)	(9,920,000)	(3,849,000)
Accumulated deficit	(113,301,000)	(92,653,000)	(47,902,000)
Total shareholders' equity	232,642,000	255,465,000	142,601,000
Total liabilities and shareholders' equity	254,210,000	273,205,000	148,662,000
Ordinary shares
Shareholders' equity:
Shares value	2,000	2,000	1,000
Deferred Shares
Shareholders' equity:
Shares value	0	0	0
Deferred B shares
Shareholders' equity:
Shares value	118,000	118,000	0
Deferred C shares
Shareholders' equity:
Shares value	$ 0	$ 0	$ 0

Consolidated Balance Sheets (Parentheticals)	Dec. 31, 2018 £ / shares shares	Dec. 31, 2018 $ / shares shares	Sep. 30, 2018 £ / shares shares	Sep. 30, 2018 $ / shares shares	Sep. 30, 2017 $ / shares shares
Ordinary shares
Shareholders' equity:
Common stock, par value (usd/gbp per share) \| $ / shares		$ 0.000042		$ 0.000042	$ 0.000042
Common stock, shares authorized (shares)	200,000,000	200,000,000	200,000,000	200,000,000	37,426,509
Common stock, shares, issued (shares)	40,145,617	40,145,617	40,146,182	40,146,182	29,962,741
Common stock, shares outstanding (shares)	40,145,617	40,145,617	40,146,182	40,146,182	29,962,741
Deferred Shares
Shareholders' equity:
Common stock, par value (usd/gbp per share) \| £ / shares	£ 0.00001		£ 0.00001
Common stock, shares authorized (shares)	34,425	34,425	34,425	34,425	0
Common stock, shares, issued (shares)	34,425	34,425	34,425	34,425	0
Common stock, shares outstanding (shares)	34,425	34,425	34,425	34,425	0
Deferred B shares
Shareholders' equity:
Common stock, par value (usd/gbp per share) \| £ / shares	£ 0.00099		£ 0.00099
Common stock, shares authorized (shares)	88,893,548	88,893,548	88,893,548	88,893,548	0
Common stock, shares, issued (shares)	88,893,548	88,893,548	88,893,548	88,893,548	0
Common stock, shares outstanding (shares)	88,893,548	88,893,548	88,893,548	88,893,548	0
Deferred C shares
Shareholders' equity:
Common stock, par value (usd/gbp per share) \| £ / shares	£ 0.000001		£ 0.000001
Common stock, shares authorized (shares)	1	1	1	1	0
Common stock, shares, issued (shares)	1	1	1	1	0
Common stock, shares outstanding (shares)	1	1	1	1	0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Grant income	$ 296	$ 1,407	$ 1,693	$ 1,212
Operating expenses:
Research and development	(17,713)	(36,150)	(16,012)	(10,436)
General and administrative	(7,593)	(22,790)	(9,099)	(5,152)
Total operating expenses, net	(25,010)	(57,533)	(23,418)	(14,376)
Other income (expense):
Interest income	660	1,532	84	75
Other income (expense)	1,097	3,970	(46)	(26)
Total other income, net	1,757	5,502	38	49
Net loss before income tax	(23,253)	(52,031)	(23,380)	(14,327)
Income tax benefit	2,605	7,280	3,653	1,777
Net loss attributable to ordinary shareholders	(20,648)	(44,751)	(19,727)	(12,550)
Other comprehensive (loss) income:
Foreign currency exchange translation adjustment	(5,568)	(6,071)	802	(2,942)
Total comprehensive loss	$ (26,216)	$ (50,822)	$ (18,925)	$ (15,492)
Basic and diluted net loss per ordinary share (usd per share)	$ (0.52)	$ (1.42)	$ (1.43)	$ (1.26)
Weighted-average basic and diluted ordinary shares (shares)	39,366,634	31,557,034	13,783,222	9,933,399

Consolidated Statements of Shareholders’ Equity - USD ($) $ in Thousands	Total	Ordinary shares	Deferred Shares	Deferred B shares	Deferred C Shares	Common shares Ordinary shares	Common shares Deferred Shares	Common shares Deferred B shares	Common shares Deferred C Shares	Additional Paid in Capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance at Sep. 30, 2015	$ 10,501					$ 0	$ 0	$ 0	$ 0	$ 27,835	$ (1,709)	$ (15,625)
Beginning balance (shares) at Sep. 30, 2015						6,713,663	0	0	0
Increase (Decrease) in Stockholders' Equity
Issuance, net of issuance cost	33,421									33,421
Issuance, net of issuance cost (shares)						7,207,881
Share-based compensation expense	2,257									2,257
Unrealized loss on foreign currency translation	(2,942)										(2,942)
Net loss	(12,550)											(12,550)
Ending, balance at Sep. 30, 2016	30,687					$ 0	$ 0	$ 0	$ 0	63,513	(4,651)	(28,175)
Ending balance (shares) at Sep. 30, 2016						13,921,544	0	0	0
Increase (Decrease) in Stockholders' Equity
Issuance, net of issuance cost	127,686					$ 1				127,685
Issuance, net of issuance cost (shares)						16,041,198
Share-based compensation expense	3,153									3,153
Unrealized loss on foreign currency translation	802										802
Net loss	(19,727)											(19,727)
Ending, balance at Sep. 30, 2017	$ 142,601					$ 1	$ 0	$ 0	$ 0	194,351	(3,849)	(47,902)
Ending balance (shares) at Sep. 30, 2017	29,962,742					29,962,742	0	0	0
Increase (Decrease) in Stockholders' Equity
Net loss	$ (7,524)
Ending, balance at Dec. 31, 2017	137,515
Beginning balance at Sep. 30, 2017	$ 142,601					$ 1	$ 0	$ 0	$ 0	194,351	(3,849)	(47,902)
Beginning balance (shares) at Sep. 30, 2017	29,962,742					29,962,742	0	0	0
Increase (Decrease) in Stockholders' Equity
Issuance, net of issuance cost	$ 156,803					$ 1		$ 118	$ 0	156,802
Issuance, net of issuance cost (shares)						10,183,440	34,425	88,893,548	1
Share-based compensation expense	6,765									6,765
Unrealized loss on foreign currency translation	(6,071)										(6,071)
Net loss	(44,751)											(44,751)
Ending, balance at Sep. 30, 2018	$ 255,465					$ 2	$ 0	$ 118	$ 0	357,918	(9,920)	(92,653)
Ending balance (shares) at Sep. 30, 2018	129,074,156	40,146,182	34,425	88,893,548	1	40,146,182	34,425	88,893,548	1
Increase (Decrease) in Stockholders' Equity
Share-based compensation expense	$ 3,393									3,393
Restricted shares - forfeited (shares)						(565)
Unrealized loss on foreign currency translation	(5,568)										(5,568)
Net loss	(20,648)											(20,648)
Ending, balance at Dec. 31, 2018	$ 232,642					$ 2	$ 0	$ 118	$ 0	$ 361,311	$ (15,488)	$ (113,301)
Ending balance (shares) at Dec. 31, 2018	129,073,591	40,145,617	34,425	88,893,548	1	40,145,617	34,425	88,893,548	1

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statement of Cash Flows - USD ($)	3 Months Ended		12 Months Ended
Consolidated Statement of Cash Flows - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (20,648,000)	$ (7,524,000)	$ (44,751,000)	$ (19,727,000)	$ (12,550,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	645,000		1,709,000	1,009,000	478,000
Loss on disposal of fixed and intangible assets	394,000		8,000	0	0
Non-cash share-based compensation	3,393,000		6,765,000	3,153,000	2,257,000
Non-cash consideration for licenses	0		0	0	1,199,000
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(3,521,000)		(7,132,000)	(2,317,000)	(2,048,000)
Long-term deposits	(1,285,000)		0	0	0
Accounts payable	(723,000)		838,000	434,000	507,000
Accrued expenses and other liabilities	1,960,000		11,026,000	1,088,000	308,000
Net cash used in operating activities	(19,785,000)	(8,797,000)	(31,537,000)	(16,360,000)	(9,849,000)
Cash flows from investing activities:
Purchases of property and equipment	(4,422,000)		(9,119,000)	(2,876,000)	(1,855,000)
Purchase of intangible assets	0		(412,000)	0	0
Net cash used in investing activities	(4,422,000)	(764,000)	(9,531,000)	(2,876,000)	(1,855,000)
Cash flows from financing activities:
Proceeds of issuance of ordinary shares, net of issuance costs	0		156,920,000	127,686,000	32,222,000
Net cash provided by financing activities	0	433,000	156,920,000	127,686,000	32,222,000
Effect of exchange rate changes on cash and restricted cash	(5,327,000)		(5,833,000)	561,000	(2,662,000)
Net (decrease) / increase in cash and restricted cash	(29,534,000)		110,019,000	109,011,000	17,856,000
Cash and restricted cash, beginning of period	247,089,000	137,070,000	137,070,000	28,059,000	10,203,000
Cash and restricted cash, end of period	217,555,000		247,089,000	137,070,000	28,059,000
Supplemental Cash Flow Information
Property and equipment purchases included in accounts payable and accrued expenses	3,343,000		328,000	0	0
Reconciliation of cash and restricted cash reported within the consolidated balance sheets:
Cash		128,984,000
Total cash and restricted cash	$ 247,089,000	$ 137,070,000	$ 137,070,000	$ 28,059,000	$ 10,203,000

Nature of the Business	3 Months Ended
Nature of the Business	Dec. 31, 2018
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 approximately $156.5 million, after deducting underwriting discounts and commissions and offering expenses paid by the Company. Autolus Therapeutics plc is a continuation of Autolus Limited and its subsidiaries. In connection with the IPO, the Company completed a corporate reorganization, which has been accounted for as a combination of entities under common control. The corporate reorganization has been given retrospective effect in these financial statements and such financial statements represent the financial statements of Autolus Therapeutics plc. In connection with the corporate reorganization, outstanding restricted share awards and option grants of Autolus Limited were exchanged for share awards and option grants of Autolus Therapeutics plc with identical restrictions. 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 $20.6 million for the three months ended December 31, 2018 and $44.8 million, $19.7 million and $12.6 million for the years ended September 30, 2018, 2017 and 2016, respectively. In addition, the Company had an accumulated deficit of $113.3 million, $92.7 million and $47.9 million as of December 31, 2018, September 30, 2018 and 2017, respectively. The Company expects to continue to generate operating losses for the foreseeable future. The future viability of the Company beyond that point 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 December 31, 2018 of $217.5 million will be sufficient to fund the Company’s operations into calendar year 2021.

Summary of Significant Accounting Policies

3 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements include those of the Company, Autolus Limited, and its U.S. subsidiary, Autolus Inc., 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. Certain amounts in the Company’s consolidated balance sheet and consolidated cash flows as of and for the year ended September 30, 2018 have been reclassified to conform with the current period presentation.

Use of Estimates

The preparation of 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 consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the fair value of ordinary shares, the valuation of tranche obligations, 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 all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents.

Restricted Cash

The Company has entered into a credit card arrangement that requires a security deposit of $0.1 million. The Company includes the restricted cash balance in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the consolidated statements of cash flows.

Fair Value Measurements

The carrying amounts reported in the balance sheets for 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 cash equivalents. The Company places cash and cash equivalents 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 December 31, 2018 and September 30, 2018 and 2017, 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 and the lab equipment and furniture and fixtures have an estimated useful life of five years. Leasehold improvements are depreciated over the shorter of the lease term or the estimated useful life of the asset. Assets under construction primarily consist of costs incurred with leasehold improvements, and, once placed into service, will be depreciated over the shorter of the lease term or the estimated useful life of the asset. Upon retirement or sale, the cost of assets disposed of, and the related accumulated depreciation, are removed from the accounts and any resulting gain or loss is included in the statement of operations and other comprehensive loss. Repairs and maintenance expenditures, which are not considered improvements and do not extend the useful life of property and equipment, are expensed as incurred.

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 any impairment losses from its inception through September 30, 2017. The Company recognized asset disposals of less than $10,000 for the year ended September 30, 2018. The Company has not recognized any impairment losses in the three months ended December 31, 2018.

Intangible Assets Subject to Amortization

The Company’s intangible assets with finite lives 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 were present, the Company would test 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 recognized an impairment expense of $0.4 million for the three months ended December 31, 2018 related to software the Company elected to discontinue.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which is the business of developing and commercializing gene therapies; however, the Company operates in two geographic regions: the United Kingdom and the United States. Substantially all of the Company’s assets are held in the United Kingdom.

Deferred Rent and Lease Incentives

Rent expense and lease incentives from operating leases are recognized on a straight-line basis over the lease term. The Company has operating leases that include rent escalation payment terms and a rent free period. Deferred rent represents the difference between actual operating lease payments and straight-line rent expense over the term of the lease.

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 $37,000, $0.2 million and $0.2 million for the three months ended December 31, 2018 and years ended September 30, 2018 and 2017, 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 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 CROs 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. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s ordinary shares. The Company accounts for forfeitures as they occur. Forfeitures to date have been infrequent and immaterial.

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 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 its ADSs. Therefore, the Company estimates the expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share 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. Options granted after the Company’s IPO are issued at the fair market value of the Company’s ADS at the date the grant is approved by the Board.

Prior to the IPO, the Company calculated the fair value of its ordinary shares in accordance with the guidelines in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. The Company’s valuations of ordinary shares were prepared using a market approach, based on precedent transactions in the shares, to estimate the Company’s total equity value using the option-pricing method (“OPM”), which used a combination of market approaches and an income approach to estimate the Company’s enterprise value.

The OPM derives an equity value such that the value indicated is consistent with the investment price, and it provides an allocation of this equity value to each class of the Company’s securities. The OPM treats the various classes of shares as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, each class of shares has value only if the funds available for distribution to shareholders exceed the value of the share liquidation preferences of the class or classes of shares with senior preferences at the time of the liquidity event. Key inputs and assumptions used in the OPM calculation include the following:

Expected volatility. The Company applied re-levered equity volatility based on the historical unlevered and re-levered equity volatility of publicly traded peer companies.

Expected term. The expected term of the option or the estimated time until a liquidation event.

Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve for the period commensurate with the expected of the exit event.

When considering the fair value of options granted in the period prior to the IPO, management considered probability-weighted scenarios based on the relative likelihoods of completing the IPO and remaining a privately-held company. In the IPO scenarios, the fair value was calculated by dividing the total estimated equity value by the number of fully diluted ordinary shares outstanding, and then discounting the implied per-share value at a rate intended to approximate the Company's cost of equity between share option grant date and the expected IPO date. The stay-private scenario utilized an OPM "Backsolve" calculation to estimate our equity value implied by the purchase price of the series A preference shares in September 2017. In March and May 2018, the Company issued share option grants to employees that applied a 50% and 80% probability weighting of an IPO, respectively, to the fair value of the underlying ordinary share utilized in the Black-Scholes option pricing model.

Foreign Currency Translation

The Company maintains its financial statements in its functional currency, which is the pounds sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are translated into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are translated 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 income (loss) for the respective periods. The Company recorded foreign exchange gain of $1.1 million for the three months ended December 31, 2018 and a foreign exchange gain of $4.0 million and a foreign exchange loss of $25,000 for the years ended September 30, 2018 and 2017, respectively, which are included in other income in the statements of operations and comprehensive loss.

For financial reporting purposes, the 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 net income (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 $0.2 million, $1.0 million and $0.5 million for the three months ended December 31, 2018 and years ended September 30, 2018 and 2017, 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.

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 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 for income taxes represents income taxes paid or payable for the current year plus deferred taxes. Deferred taxes result from differences between the 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 tax law and requires judgement 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 or 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 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. Such credits are accounted for within the tax provision in the year in which the expenditures were incurred.

Comprehensive Loss

The Company follows the provisions of the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“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 loss of $5.6 million, a loss of $6.1 million, a gain of $0.8 million, and a loss of $2.9 million related to foreign currency translation during the three months ended December 31, 2018 and years ended September 30, 2018, 2017 and 2016, 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, the preferred shares and 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:



	Three Months Ended December 31,	Year Ended September 30,
	2018	2018	2017	2016
Unvested restricted incentive shares	708,834	815,632	1,358,317	1,266,619
Incentive share options	3,711,274	2,065,481	570,309	—
Total	4,420,108	2,881,113	1,928,626	1,266,619

Ordinary Share Conversion

On the date of the IPO, the Company converted its outstanding preferred and ordinary shares as discussed in Note 6. All share and per share information has been retroactively adjusted to reflect the share conversion.

Emerging Growth Company Status

The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act (“JOBS Act”) and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company may take advantage of these exemptions until the Company is no longer an emerging growth company. Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.

These exemptions provided by the JOBS Act will apply up until the last day of the fiscal year following the fifth anniversary of the IPO or such earlier time that the Company no longer meets the requirements of being an emerging growth company. The Company would cease to be an emerging growth company if it has more than $1.07 billion in annual revenue, has more than $700 million in market value of its securities held by non-affiliates (and it has been a public company for at least 12 months, and has filed one annual report on Form 20-F), or it issues more than $1 billion of non-convertible debt securities over a three-year period.

JOBS Act

On April 5, 2012, the Jumpstart Our Business Startups Act, or the JOBS Act, was enacted. The JOBS Act provides that, among other things, an emerging growth company can take advantage of an extended transition period for complying with new or revised accounting standards. As an emerging growth company, the Company has irrevocably elected not to take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards and, as a result, the Company will comply with new or revised accounting standards on the relevant dates on which adoption of such standards is required for non-emerging growth public companies.

In addition, the Company also currently relies on the other exemptions and reduced reporting requirements provided by the JOBS Act. Subject to certain conditions set forth in the JOBS Act, the Company is entitled to continue to rely on certain exemptions as an “emerging growth company.” As an emerging growth company, the Company is not required to, among other things, (i) provide an auditor’s attestation report on the Company’s system of internal controls over financial reporting pursuant to Section 404(b), (ii) provide all of the compensation disclosure that may be required of non-emerging growth public companies under the Dodd-Frank Wall Street Reform and Consumer Protection Act, (iii) comply with any requirement that may be adopted by the Public Company Accounting Oversight Board regarding mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and the financial statements (auditor discussion and analysis), and (iv) disclose certain executive compensation-related items such as the correlation between executive compensation and performance and comparisons of the chief executive officer’s compensation to median employee compensation. These exemptions will apply for a period of five years following the completion of the IPO or until the Company no longer meets the requirements of being an emerging growth company, whichever is earlier.

Recently issued accounting pronouncements not yet adopted

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which requires a lessee to recognize assets and liabilities on the balance sheet for most leases and changes many key definitions, including the definition of a lease. The new standard includes a short-term lease exception for leases with a term of 12 months or less, as part of which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance.

ASU 2016-02 will be effective beginning January 1, 2019 requiring the use of a modified retrospective transition approach applied at the beginning of the earliest comparative period presented in the financial statements. In July 2018, the FASB issued ASU 2018-11, Leases, Targeting Improvements, (“ASU 2018-11”), which contains certain amendments to ASU 2016-02 intended to provide relief in implementing the new standard. ASU 2018-11 provides registrants with an option to not restate comparative periods presented in the financial statements. The Company intends to elect this new transition approach using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods will be presented in accordance with the previous guidance in ASC 840, Leases.

The Company is currently evaluating the potential impact ASU 2016-02 may have on its financial position, results of operations, and related footnotes. The Company expects it will make an accounting policy election to keep leases with an initial term of 12 months or less off of its balance sheet. To date, the Company has identified all of its leases which consist of the London, United Kingdom corporate office and manufacturing leases and the Gaithersburg, Maryland office and manufacturing facility leases, and the Company anticipates that adoption of ASU 2016-2 will result in the recognition of additional assets and lease liabilities.

In July 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718) (“ASU 2018-07”): Improvements to Nonemployee Share-Based Payment Accounting. ASU 2018-07 aligns the guidance on share-based payments to nonemployees with that for share-based payments to employees. Entities will recognize a cumulative-effect adjustment to retained earnings for equity-classified nonemployee awards for which a measurement date has not been established. The guidance is effective in annual periods beginning after December 31, 2018, and interim periods within those years. The Company is currently evaluating the impact that the adoption of ASU 2018-07 will have on its consolidated financial statements.

Shareholders’ Equity

3 Months Ended

Dec. 31, 2018

Equity [Abstract]

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 December 31, 2018, the Company has not declared any dividends.

As of December 31, 2018, the Company’s authorized capital shares consisted of 200 million ordinary shares with a nominal value of $0.000042 per share.

Initial Public Offering and Impact of Corporate Reorganization

On June 18, 2018, Autolus Therapeutics Limited re-registered as a public limited company and its name was changed from Autolus Therapeutics Limited to Autolus Therapeutics plc (see Note 1).

On June 26, 2018, the Company closed its IPO. In the IPO, the Company sold an aggregate of 10,147,059 ADSs representing the same number of ordinary shares at a public offering price of $17.00 per ADS, which included the full exercise by the underwriters of their option to purchase additional ADSs. Net proceeds were approximately $156.5 million, after deducting underwriting discounts, and commissions and offering expenses paid by the Company of $16.0 million. Upon the closing of the IPO, each separate class of ordinary shares of Autolus Therapeutics plc was converted into a single class of ordinary shares of Autolus Therapeutics plc as described further below.

Prior to the Company’s June 2018 reorganization and IPO, the Company had issued series A preferred shares, ordinary B shares, and ordinary C shares to fund its operations and upon the Company completing its IPO of ADSs, the different classes of shares were converted into a single class of ordinary shares on a 3.185-for-1 basis and created various classes of deferred shares.

The following deferred share classes were created:

Deferred Shares - The 34,425 deferred shares, aggregate nominal value less than $1.00, existed in Autolus Limited and were re-created in Autolus Therapeutics plc as part of the share exchange to place Autolus Therapeutics as the ultimate parent entity. The Company was required to replicate the shares to ensure the existing share has the correct nominal value to ensure stamp duty mirroring relief is available on the subsequent share for share exchange. These deferred shares have no voting rights.

Deferred B Shares - The deferred B shares were the product of the reorganization of the series A preferred shares and ordinary B shares into ordinary shares. The nominal residual value was utilized by management as the required £50,000 of share capital to re-register Autolus Therapeutics Limited as Autolus Therapeutics plc. The resulting 88,893,548 deferred shares, aggregate nominal value of $118,000, is presented as a separate class of equity on the balance sheet and statement of shareholder’s equity. These deferred B shares have no voting rights.

Deferred C Share - The deferred C share, nominal value less than $1.00, was created when the shares in Autolus Therapeutics plc were redenominated from GBP to USD as part of the capital reduction to deal with rounding issues that would otherwise have unbalanced the company’s nominal share capital. This deferred C share has no voting rights.

The table below reflects the number of preferred shares, ordinary shares, and deferred shares issued and outstanding at December 31, 2018 and September 30, 2018 and 2017, and also reflects the conversion of preferred and ordinary shares on 3.185-for-1 basis in the current and previous years and the creation of deferred shares.



	December 31,	September 30,
	2018	2018	2017
Series A preferred shares	—	—	24,490,705
Class B ordinary shares	—	—	3,375,196
Class C ordinary shares	—	—	2,096,841
Ordinary Shares	40,145,617	40,146,182	—
Deferred shares	34,425	34,425	—
Deferred B shares	88,893,548	88,893,548	—
Deferred C shares	1	1	—
Total ordinary and deferred shares	129,073,591	129,074,156	29,962,742

Share Based Compensation

3 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share Based Compensation

In February 2017, the Company’s board of directors adopted the 2017 Share Option Plan, or the 2017 Plan. The 2017 Plan was set to expire on February 21, 2027. The 2017 Plan provided for the grant of potentially tax-favored Enterprise Management Incentives, or EMI, options to the Company's U.K. employees and for the grant of options to its U.S. employees.

In June 2018, as part of the Company's reorganization and IPO, the Company’s board of directors and shareholders approved the 2018 Equity Incentive Plan, or the 2018 Plan. The initial maximum number of ordinary shares that may be issued under the 2018 Plan was 3,281,622. This number consists of 3,025,548 new ordinary shares and 256,074 ordinary shares that would have otherwise remained available for future grants under the 2017 Plan. The number of ordinary shares reserved for issuance under the 2018 Plan will automatically increase on October 1st of each year, for a period of not more than ten years, commencing on October 1, 2018 and ending on (and including) October 1, 2027, by an amount equal to the lesser of (i) 4% of the total number of ordinary shares outstanding on September 30th of the same calendar year or (ii) such fewer number of ordinary shares as the board of directors may designate prior to the applicable October 1st date. Shares issued under the 2018 Plan may be authorized but unissued shares, shares purchased on the open market, treasury shares or ADSs. No more than 14,000,000 shares may be issued under the 2018 Plan upon the exercise of incentive share options.

Options granted under the 2018 Plan and 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 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.

Share Option Valuation

The assumptions (see Note 2) used in the Black-Scholes option pricing model to determine the fair value of the share options granted to employees and directors during the three months ended December 31, 2018 and the years ended September 30, 2018 and 2017 were as follows:



	December 31,	September 30,
	2018	2018	2017
Expected option life (years)	6 years	6 years	6 years
Risk-free interest rate	2.70% to 3.09%	2.61% to 3.00%	1.91% to 2.05%
Expected volatility	69.52% to 71.26%	68.15% to 72.99%	68.61% to 68.93%
Expected dividend yield	0.00%	0.00%	0.00%

Share Options

The table below reflects summarizes share option activity for the three months ended December 31, 2018.



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of September 30, 2018	2,065,481		$	9.87	9.35	$	43,146
Granted	1,651,740		$	31.23	—	—
Exercised	—		—		—	—
Canceled or forfeited	(5,947	)	$	5.71	—	—
Outstanding as of December 31, 2018	3,711,274		$	19.25	9.47	$	51,464
Exercisable as of December 31, 2018	206,085		$	0.50	8.48	$	6,664
Vested and expected to vest as of December 31, 2018	3,711,274		$	19.25	9.47	$	51,464

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 $20.04, $8.55 and $4.04 for the three months ended December 31, 2018 and the years ended September 30, 2018 and 2017, respectively, none of which were vested.

The Company recorded share-based compensation expense related to share options to certain consultants, who are not employees, of $50,000 and $0.1 million for the three months ended December 31, 2018 and the year ended September 30, 2018, respectively. There were no share options granted to consultants during the year ended September 30, 2017.

Restricted Ordinary Shares

The assumptions (see Note 2) used in the OPM to determine the fair value of the ordinary shares for the following dates were as follows:



	March 2, 2016		April 26, 2017		September 25, 2017		March 31, 2018		May 31, 2018
Expected term	2.8 years		1.2 years		0.8 years		1.8 years		1.8 years
Risk-free interest rate	1.0	%	1.0	%	1.3	%	2.1	%	2.1	%
Expected volatility	73.2	%	76.6	%	71.0	%	71	%	71	%
Expected dividend yield	0.0	%	0.0	%	0.0	%	0.0	%	0.0	%

A summary of the changes in the Company’s restricted ordinary shares during the three months ended December 31, 2018 is as follows.



	Number of restricted shares		Weighted average grant date fair value
Unvested and outstanding at September 30, 2018	815,632		$	4.17
Granted	—		—
Vested	(106,233	)	3.97
Canceled or forfeited	(565	)	2.99
Unvested and outstanding at December 31, 2018	708,834		$	4.10

During the year ended September 30, 2017, the Company granted an aggregate of 439 restricted ordinary shares with vesting based on service conditions only and 641,711 restricted ordinary shares that included both performance and service conditions in order to vest. During the years ended September 30, 2018 and 2017, 159,490 and 24,896 restricted ordinary shares were vested related to performance-based awards. The remainder of the restricted C ordinary shares and all forfeited restricted C ordinary shares related to awards with only service-based vesting conditions. There were no restricted shares granted during the year ended September 30, 2018 or three months ended December 31, 2018.

The 2017 performance-based restricted shares were scheduled to begin vesting upon the Company’s achievement of specified clinical development milestones. The Company achieved the milestones related to the 2017 performance-based restricted shares during the year ended September 30, 2017 and recorded share-based compensation expense of $1.0 million and $0.8 million related to the vesting of those incentive share awards for the years ended September 30, 2018 and 2017, respectively.

As of December 31, 2018, there was unrecognized compensation of $1.1 million, which will be recognized over the remaining vesting term of the awards.

The Company recorded share-based compensation expense related to awards to certain consultants, who are not employees, of $0.1 million, $1.0 million and $0.2 million for the three months ended December 31, 2018 and years ended September 30, 2018 and 2017, respectively.

Share-based Compensation Expense

The Company recorded share-based compensation expense of $3.4 million, $6.8 million and $3.2 million during the three months ended December 31, 2018 and years ended September 30, 2018 and 2017, respectively, related to both restricted shares and share options based awards. As of December 31, 2018, there was $42.0 million of unrecognized compensation cost related to outstanding but unvested restricted shares and share options, which amounts are expected to be recognized over weighted-average period of 3.8 years.

Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):



	Three months ended December 31,		Year ended September 30,
	2018		2018		2017		2016
Research and development	$	1,906	$	3,116	$	1,145	$	916
General and administrative	1,487		3,649		2,008		1,341
Total share-based compensation	$	3,393	$	6,765	$	3,153	$	2,257

In February 2017, the Company modified the terms of all outstanding share options and restricted share awards to adjust the vesting of the awards in the event of an exit event or IPO. As modified, the options and share awards do not convert to deferred shares and will continue vesting as a result of the June 2018 IPO. The incremental share-based compensation expense due to the modification was nominal.

License Agreements	3 Months Ended
License Agreements	Dec. 31, 2018
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 plc (“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 in March 2018 to include a license to AUTO1, for which UCL is conducting Phase 1 clinical trials in pediatric and adult ALL patients. The Company paid an upfront fee of £1.5 million for consideration for the Amended and Restated License Agreement and is obligated to pay an additional £0.5 million in connection with UCLB's transfer of clinical data to the Company. No equity was issued as part of the upfront fee consideration. The License required the Company to make annual license payments of £30,000 through September 30, 2018. The Company is no longer required to make any further annual license payments to UCLB. Additionally, the Company may be obligated to make payments to UCLB under the Amended and Restated License Agreement upon the receipt of specified regulatory approvals in an aggregate amount of £35.5 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 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.

Income Taxes

3 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

The Company recorded an income tax benefit of $2.6 million, $7.3 million and $3.7 million for the three months ended December 31, 2018 and the years ended September 30, 2018 and 2017, respectively.

Certain amounts previously reported in Income Taxes for the year ended September 30, 2018 have been restated to reflect the correction of an immaterial error as disclosed in the Company's Annual Report on Form 20-F for the year ended September 30, 2018. The error related to the calculation of deferred tax asset and related valuation allowance. The Company believes the effect of the error is not material to its consolidated financial statements.

A reconciliation of income tax expense (benefit) at the statutory corporate income tax rate to the income tax expense (benefit) at the Company’s effective income tax rates is as follows (in thousands):



	Three months ended			Year ended
	December 31,			September 30,
	2018			2018			2017			2016
Net loss before taxes	$	(23,253	)	$	(52,031	)	$	(23,380	)	$	(14,327	)
U.K. statutory tax rate	19.0		%	19.0		%	19.5		%	20.0		%
Income tax benefit at U.K. statutory tax rate	(4,423		)	(9,886		)	(4,559		)	(2,865		)
Tax incentives / credits	(3,234		)	(7,296		)	(3,702		)	(1,837		)
Non-deductible expenses	127			1,553			609			694
Adjustments in respect of prior years	265			(13		)	13			57
Operating losses	3,605			7,317			3,754			2,168
Tax on property, plant, equipment and intangibles	140			233			113			—
Other, net	915			812			119			6
Total income tax benefit	$	(2,605	)	$	(7,280	)	$	(3,653	)	$	(1,777	)
Effective rate of income tax	11.2		%	14.0		%	15.6		%	12.4		%

The effective tax rate for the three months ended December 31, 2018 was 11.2% and for the years ended September 30, 2018, 2017, and 2016 is was 14.0%, 15.6% and 12.4%, respectively. This is lower than the main rate of U.K. tax primarily due to administration of the U.K. research and development tax credit, which is included within the tax incentive/credits line in the table above.

Deferred tax assets and liabilities consisted of the following at December 31, 2018 and September 30, 2018 and 2017 (in thousands):



	December 31,			September 30,
	2018			2018			2017
Deferred tax assets:
Other differences	$	2,870		$	1,785		$	11
Tax losses	7,851			6,515			3,878
Fixed assets	621			1,740			1,098
Total deferred tax assets	11,342			10,040			4,987
Valuation allowances	(11,342		)	(10,040		)	(4,987		)
Net deferred tax asset (liability)	$	—		$	—		$	—

Deferred tax assets resulted from loss carryforwards, fixed assets and retirement benefits, with total deferred tax assets increasing by $1.3 million in the three months December 31, 2018. The Company has recorded a full valuation allowance against the net deferred tax asset as the recoverability due to future taxable profits is unknown. As a result, the net deferred tax remains the same, due to a corresponding increase in valuation allowance.

At December 31, 2018, the Company had U.K. trading losses carry forward of $46.2 million. These losses are carry forwards indefinitely under local law, but are subject to numerous utilization criteria and restrictions.

As required by the authoritative guidance on accounting for income taxes, the Company evaluates the realizability of deferred tax assets at each reporting date. Accounting for income taxes guidance requires that a valuation allowance be established when it is more likely than not that all or a portion of the deferred tax assets will not be realized. In circumstances where this is sufficient negative evidence indicating that the deferred tax assets are not more likely than not realizable, the Company establishes a valuation allowance. The Company recorded valuation allowances in the amounts of $11.3 million at December 31, 2018 and $10.0 million and $5.0 million at September 30, 2018 and 2017, respectively.

Commitments and Contingencies

3 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

License Agreement

The Company has entered into an exclusive license agreement, as amended, with UCLB (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 December 31, 2018 there was a $0.6 million million milestone that was considered probable related to the receipt of clinical data for its AUTO1 program, and accordingly the Company accrued a liability of $0.6 million as of December 31, 2018. As of December 31, 2018, there were no other 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 December 31, 2018 and September 30, 2018 and 2017.

Leases

The Company’s corporate headquarters are located in London, United Kingdom. As of December 31, 2018 and September 30, 2018 and 2017, the Company leased 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 with a concurrent term through August 2025. The Company and the landlord has the option to early terminate both leases in September 2020.

Prior to the lease commencement date of both leases, the Company, in conjunction with the landlord, made improvements to the leased space. The total cost of these improvements was funded by the landlord, a portion of the cost will be reimbursed by the Company over the term of the leases. The total cost of the improvements was capitalized as leasehold improvements on the Company’s balance sheet, with an offset to long-term lease incentive obligation for the portion funded by the landlord and other long-term payables for the portion to be repaid to the landlord. As of September 30, 2018 and 2017, the Company capitalized $0.1 million, and $2.1 million, respectively, as leasehold improvements. No similar costs were capitalized as of December 31, 2018. The lease related to this facility is classified as an operating lease.

In September 2017, the Company executed an arrangement to lease a manufacturing suite at the Cell and Gene Therapy Catapult manufacturing center for a term through May 2021, at which time the Company has the option to renew or terminate the lease. The lease related to this facility is classified as an operating lease. The lease has an six-month rent-free period. The rent-free period is included in the deferred rent. In December 2018, the Company executed an additional lease arrangement for additional manufacturing space for a term through January 2023, at which time the Company has the option to renew or terminate the lease. The lease related to this facility is classified as an operating lease. There is no rent free period.

In June 2018, the Company signed a binding letter of intent to enter into a lease for office and laboratory space in White City, London. The letter of intent requires the Company to enter into a ten-year lease provided that the landlord completes the required leasehold improvements described in the agreement. The expected lease commencement date is in February 2019. The lease will include an option to lease additional space. As of December 31, 2018 and September 30, 2018, the Company capitalized $6.6 million and $2.5 million, respectively, as leasehold improvements. The Company did not include future minimum payments in the lease payment schedule, as the lease agreement was not complete as of December 31, 2018.

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 requires the Company to enter into a 15-year lease provided that the landlord completes the required leasehold improvements described in the agreement. The Company executed the lease agreement in February 2019 and the lease commencement date is expected to be February 2019. The Company has incurred no leasehold improvements to capitalize as of December 31, 2018 and September 30, 2018. The Company did not include future minimum payments in the lease payment schedule as the lease agreement was not entered into as of December 31, 2018.

In October 2018, the Company executed an agreement to sublease office space in Rockville, Maryland for a term through October 2021. The lease related to this facility is classified as an operating lease. The lease has a four-month rent-free period. The rent-free period is included in the deferred rent.

In January 2019, the Company executed a lease agreement to lease additional office and manufacturing space in Rockville, Maryland. The Company expects the lease to commence in June 2020 for a term through June 2035. The Company did not include future minimum payments in the lease payment schedule as the lease agreement was not complete as of December 31, 2018.

The following table summarizes the future minimum lease payments due under operating leases as of December 31, 2018 (in thousands):



Year ending December 31,
2019	$	2,244
2020	2,332
2021	1,934
2022	1,324
2023	1,196
Thereafter	1,121
Total	$	10,151

The Company recognizes rent expense on a straight-line basis over the respective lease period and has recorded deferred rent for rent expense incurred but not yet paid.

The Company recorded rent expense totaling $0.5 million, $0.9 million, and $0.6 million for the three months ended December 31, 2018 and years ended September 30, 2018 and 2017, respectively.

Related Party Transactions	3 Months Ended
Related Party Transactions	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Syncona LLP The Company previously had an agreement with Syncona LLP, an investor in the Company, pursuant to which the Company was charged for services including director compensation fees. The agreement terminated effective as of the Company's IPO. For the three months ended December 31, 2018, the Company paid nominal fees to Syncona. The Company recorded expenses totaling $60,000 $56,000, and $0.2 million for the years ended September 30, 2018, 2017, and 2016, respectively, which are included in general and administrative expenses. As of September 30, 2018 and 2017 there was $13,000 and $3,000 included in accrued expenses on the Company’s balance sheets related to the arrangement with Syncona LLP, respectively. There were no accrued expenses on the Company’s balance sheet at December 31, 2018. University College London and Related Entities The Company, under various agreements, received research and development, office and consulting services from the University College London (“UCL”) and its subsidiaries. UCL is a shareholder of the Company through UCLB. As of September 30, 2018, UCL is no longer a principal shareholder of the Company and, as a result, the Company no longer considers UCL a related party for reporting purposes. For the years ended September 30, 2018, the Company recorded research and development expenses from arrangements with UCL totaling $0.7 million and $2.4 million, respectively, of which $40,000 and $1.5 million represented license fees for the years ended September 30, 2017 and 2016, respectively. As of September 30, 2017, there was $0.2 million included in accrued expenses and accounts payable on the Company’s balance sheet related to the arrangement with UCL. Arix Bioscience The Company previously had an agreement with Arix Bioscience Holdings Limited ("Arix"), an investor of the Company, pursuant to which the Company was charged for director compensation fees. The agreement terminated effective as of the Company's IPO. There were no expenses for the three months ended December 31, 2018. The Company recorded expenses totaling $18,000, $20,000, and $11,000 for the years ended September 30, 2018, 2017, and 2016, respectively. As of December 31, 2018 and September 30, 2018, there were no outstanding balances. As of September 30, 2017, there was $2,000 included in accrued expenses on the Company’s balance sheet. Kapil Dhingra, M.D., The Company entered into a consulting agreement with Dr. Kapil Dhingra, a member of its board of directors, in November 2014, pursuant to which he has agreed to provide up to nine days of healthcare consulting services to the Company. Dr. Dhingra receives an annual fee of £10,000 under the terms of the agreement. Subject to mutual agreement between the Company and Dr. Dhingra, he may provide services to the Company beyond the nine days, in which case the Company has agreed to pay Dr. Dhingra an additional fee of £1,111 per day. As of December 31, 2018 and September 30, 2018 and 2017, there was $3,000, $46,000, and $32,000 included in accrued expenses on the Company’s balance sheet.

Selected Financial Data for the Three Months Ended December 31, 2017

3 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Financial Data for the Three Months Ended December 31, 2017

The following tables present condensed comparative information for the three months ended December 31, 2017:



	Three Months Ended December 31,
	2017
	(unaudited)
Results of Operations
Grant income	$	231
Operating expenses:
Research and development	(5,564		)
General and administrative	(3,084		)
Total operating expenses, net	(8,417		)
Other income (expense):
Interest income	181
Other income (expense)	(685		)
Total other income (expense), net	(504		)
Net loss before income tax	(8,921		)
Income tax benefit	1,397
Net loss attributable to ordinary shareholders	$	(7,524	)

Cash Flows
Net cash used in operating activities	$	(8,797	)
Net cash used in investing activities	(764		)
Net cash provided by financing activities	433
Effect of exchange rate changes on cash	1,042
Net decrease in cash	$	(8,086	)

Balance Sheet Data
Cash	$	128,984
Working capital (1)	131,576
Net assets	137,515
Total assets	142,715
Ordinary shares	1
Additional paid-in-capital	195,644
Total shareholders' equity	137,515
(1) The Company defines working capital as current assets less current liabilities.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include those of the Company, Autolus Limited, and its U.S. subsidiary, Autolus Inc., 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. Certain amounts in the Company’s consolidated balance sheet and consolidated cash flows as of and for the year ended September 30, 2018 have been reclassified to conform with the current period presentation.
Use of Estimates	Use of Estimates The preparation of 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 consolidated financial statements and the reported amounts of income and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the fair value of ordinary shares, the valuation of tranche obligations, 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 all highly liquid investments that have maturities of three months or less when acquired to be cash equivalents.
Restricted Cash	The Company includes the restricted cash balance in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the consolidated statements of cash flows.
Fair Value Measurements	Fair Value Measurements The carrying amounts reported in the balance sheets for 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 Risk Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents. The Company places cash and cash equivalents 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 December 31, 2018 and September 30, 2018 and 2017, 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 and the lab equipment and furniture and fixtures have an estimated useful life of five years. Leasehold improvements are depreciated over the shorter of the lease term or the estimated useful life of the asset. Assets under construction primarily consist of costs incurred with leasehold improvements, and, once placed into service, will be depreciated over the shorter of the lease term or the estimated useful life of the asset. Upon retirement or sale, the cost of assets disposed of, and the related accumulated depreciation, are removed from the accounts and any resulting gain or loss is included in the statement of operations and other comprehensive loss. Repairs and maintenance expenditures, which are not considered improvements and do not extend the useful life of property and equipment, are expensed as incurred. 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 any impairment losses from its inception through September 30, 2017.
Intangible Assets Subject to Amortization	Intangible Assets Subject to Amortization The Company’s intangible assets with finite lives 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 were present, the Company would test 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.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage its business as a single operating segment, which is the business of developing and commercializing gene therapies; however, the Company operates in two geographic regions:
Deferred Rent and Lease Incentive	Deferred Rent and Lease Incentives Rent expense and lease incentives from operating leases are recognized on a straight-line basis over the lease term. The Company has operating leases that include rent escalation payment terms and a rent free period. Deferred rent represents the difference between actual operating lease payments and straight-line rent expense over the term of the lease.
Research and Development Costs	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. Accrued Research and Development Expenses As part of the process of preparing 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 CROs 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. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s ordinary shares. The Company accounts for forfeitures as they occur. Forfeitures to date have been infrequent and immaterial. 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 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 its ADSs. Therefore, the Company estimates the expected share volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share 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. Options granted after the Company’s IPO are issued at the fair market value of the Company’s ADS at the date the grant is approved by the Board. Prior to the IPO, the Company calculated the fair value of its ordinary shares in accordance with the guidelines in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. The Company’s valuations of ordinary shares were prepared using a market approach, based on precedent transactions in the shares, to estimate the Company’s total equity value using the option-pricing method (“OPM”), which used a combination of market approaches and an income approach to estimate the Company’s enterprise value. The OPM derives an equity value such that the value indicated is consistent with the investment price, and it provides an allocation of this equity value to each class of the Company’s securities. The OPM treats the various classes of shares as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, each class of shares has value only if the funds available for distribution to shareholders exceed the value of the share liquidation preferences of the class or classes of shares with senior preferences at the time of the liquidity event. Key inputs and assumptions used in the OPM calculation include the following: Expected volatility. The Company applied re-levered equity volatility based on the historical unlevered and re-levered equity volatility of publicly traded peer companies. 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. Expected term. The expected term of the option or the estimated time until a liquidation event. Risk-free interest rate. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve for the period commensurate with the expected of the exit event.
Foreign Currency Translation	Foreign Currency Translation The Company maintains its financial statements in its functional currency, which is the pounds sterling. Monetary assets and liabilities denominated in currencies other than the functional currency are translated into the functional currency at rates of exchange prevailing at the balance sheet dates. Non-monetary assets and liabilities denominated in foreign currencies are translated 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 income (loss) for the respective periods. The Company recorded foreign exchange gain of $1.1 million for the three months ended December 31, 2018 and a foreign exchange gain of $4.0 million and a foreign exchange loss of $25,000 for the years ended September 30, 2018 and 2017, respectively, which are included in other income in the statements of operations and comprehensive loss. For financial reporting purposes, the 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 net income (loss) but are included in foreign exchange adjustment to other comprehensive loss, a component of shareholders’ equity.
Patent Costs	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.
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.
Income Taxes	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 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 for income taxes represents income taxes paid or payable for the current year plus deferred taxes. Deferred taxes result from differences between the 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 tax law and requires judgement 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 or 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 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. Such credits are accounted for within the tax provision in the year in which the expenditures were incurred.
Comprehensive Loss	Comprehensive Loss The Company follows the provisions of the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“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.
Net Loss per Share	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, the preferred shares and 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	Recently issued accounting pronouncements not yet adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which requires a lessee to recognize assets and liabilities on the balance sheet for most leases and changes many key definitions, including the definition of a lease. The new standard includes a short-term lease exception for leases with a term of 12 months or less, as part of which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. ASU 2016-02 will be effective beginning January 1, 2019 requiring the use of a modified retrospective transition approach applied at the beginning of the earliest comparative period presented in the financial statements. In July 2018, the FASB issued ASU 2018-11, Leases, Targeting Improvements, (“ASU 2018-11”), which contains certain amendments to ASU 2016-02 intended to provide relief in implementing the new standard. ASU 2018-11 provides registrants with an option to not restate comparative periods presented in the financial statements. The Company intends to elect this new transition approach using a cumulative-effect adjustment on the effective date of the standard, for which comparative periods will be presented in accordance with the previous guidance in ASC 840, Leases. The Company is currently evaluating the potential impact ASU 2016-02 may have on its financial position, results of operations, and related footnotes. The Company expects it will make an accounting policy election to keep leases with an initial term of 12 months or less off of its balance sheet. To date, the Company has identified all of its leases which consist of the London, United Kingdom corporate office and manufacturing leases and the Gaithersburg, Maryland office and manufacturing facility leases, and the Company anticipates that adoption of ASU 2016-2 will result in the recognition of additional assets and lease liabilities. In July 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718) (“ASU 2018-07”): Improvements to Nonemployee Share-Based Payment Accounting. ASU 2018-07 aligns the guidance on share-based payments to nonemployees with that for share-based payments to employees. Entities will recognize a cumulative-effect adjustment to retained earnings for equity-classified nonemployee awards for which a measurement date has not been established. The guidance is effective in annual periods beginning after December 31, 2018, and interim periods within those years. The Company is currently evaluating the impact that the adoption of ASU 2018-07 will have on its consolidated financial statements.

Shareholders’ Equity (Tables)

3 Months Ended

Dec. 31, 2018

Equity [Abstract]

Schedule of Shares Outstanding



	December 31,	September 30,
	2018	2018	2017
Series A preferred shares	—	—	24,490,705
Class B ordinary shares	—	—	3,375,196
Class C ordinary shares	—	—	2,096,841
Ordinary Shares	40,145,617	40,146,182	—
Deferred shares	34,425	34,425	—
Deferred B shares	88,893,548	88,893,548	—
Deferred C shares	1	1	—
Total ordinary and deferred shares	129,073,591	129,074,156	29,962,742

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21484-112644

Reference 14: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Share Based Compensation (Tables)

3 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Stock Options Valuation Assumptions



	December 31,	September 30,
	2018	2018	2017
Expected option life (years)	6 years	6 years	6 years
Risk-free interest rate	2.70% to 3.09%	2.61% to 3.00%	1.91% to 2.05%
Expected volatility	69.52% to 71.26%	68.15% to 72.99%	68.61% to 68.93%
Expected dividend yield	0.00%	0.00%	0.00%

Stock Option Rollforward

The table below reflects summarizes share option activity for the three months ended December 31, 2018.



	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of September 30, 2018	2,065,481		$	9.87	9.35	$	43,146
Granted	1,651,740		$	31.23	—	—
Exercised	—		—		—	—
Canceled or forfeited	(5,947	)	$	5.71	—	—
Outstanding as of December 31, 2018	3,711,274		$	19.25	9.47	$	51,464
Exercisable as of December 31, 2018	206,085		$	0.50	8.48	$	6,664
Vested and expected to vest as of December 31, 2018	3,711,274		$	19.25	9.47	$	51,464

Schedule of Nonvested Share Activity

A summary of the changes in the Company’s restricted ordinary shares during the three months ended December 31, 2018 is as follows.



	Number of restricted shares		Weighted average grant date fair value
Unvested and outstanding at September 30, 2018	815,632		$	4.17
Granted	—		—
Vested	(106,233	)	3.97
Canceled or forfeited	(565	)	2.99
Unvested and outstanding at December 31, 2018	708,834		$	4.10

Schedule of Restricted Stock Valuation Assumptions

The assumptions (see Note 2) used in the OPM to determine the fair value of the ordinary shares for the following dates were as follows:



	March 2, 2016		April 26, 2017		September 25, 2017		March 31, 2018		May 31, 2018
Expected term	2.8 years		1.2 years		0.8 years		1.8 years		1.8 years
Risk-free interest rate	1.0	%	1.0	%	1.3	%	2.1	%	2.1	%
Expected volatility	73.2	%	76.6	%	71.0	%	71	%	71	%
Expected dividend yield	0.0	%	0.0	%	0.0	%	0.0	%	0.0	%

Schedule of Allocated Share Based Compensation

Share-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):



	Three months ended December 31,		Year ended September 30,
	2018		2018		2017		2016
Research and development	$	1,906	$	3,116	$	1,145	$	916
General and administrative	1,487		3,649		2,008		1,341
Total share-based compensation	$	3,393	$	6,765	$	3,153	$	2,257

Income Taxes (Tables)

3 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Income Tax Expense (Benefit)



	Three months ended			Year ended
	December 31,			September 30,
	2018			2018			2017			2016
Net loss before taxes	$	(23,253	)	$	(52,031	)	$	(23,380	)	$	(14,327	)
U.K. statutory tax rate	19.0		%	19.0		%	19.5		%	20.0		%
Income tax benefit at U.K. statutory tax rate	(4,423		)	(9,886		)	(4,559		)	(2,865		)
Tax incentives / credits	(3,234		)	(7,296		)	(3,702		)	(1,837		)
Non-deductible expenses	127			1,553			609			694
Adjustments in respect of prior years	265			(13		)	13			57
Operating losses	3,605			7,317			3,754			2,168
Tax on property, plant, equipment and intangibles	140			233			113			—
Other, net	915			812			119			6
Total income tax benefit	$	(2,605	)	$	(7,280	)	$	(3,653	)	$	(1,777	)
Effective rate of income tax	11.2		%	14.0		%	15.6		%	12.4		%

Schedule of Deferred Tax Assets and Liabilities

Deferred tax assets and liabilities consisted of the following at December 31, 2018 and September 30, 2018 and 2017 (in thousands):



	December 31,			September 30,
	2018			2018			2017
Deferred tax assets:
Other differences	$	2,870		$	1,785		$	11
Tax losses	7,851			6,515			3,878
Fixed assets	621			1,740			1,098
Total deferred tax assets	11,342			10,040			4,987
Valuation allowances	(11,342		)	(10,040		)	(4,987		)
Net deferred tax asset (liability)	$	—		$	—		$	—

Selected Financial Data for the Three Months Ended December 31, 2017 (Tables)

3 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Condensed Comparative Information For The Three Months Ended December 31, 2017

The following tables present condensed comparative information for the three months ended December 31, 2017:



	Three Months Ended December 31,
	2017
	(unaudited)
Results of Operations
Grant income	$	231
Operating expenses:
Research and development	(5,564		)
General and administrative	(3,084		)
Total operating expenses, net	(8,417		)
Other income (expense):
Interest income	181
Other income (expense)	(685		)
Total other income (expense), net	(504		)
Net loss before income tax	(8,921		)
Income tax benefit	1,397
Net loss attributable to ordinary shareholders	$	(7,524	)

Cash Flows
Net cash used in operating activities	$	(8,797	)
Net cash used in investing activities	(764		)
Net cash provided by financing activities	433
Effect of exchange rate changes on cash	1,042
Net decrease in cash	$	(8,086	)

Balance Sheet Data
Cash	$	128,984
Working capital (1)	131,576
Net assets	137,515
Total assets	142,715
Ordinary shares	1
Additional paid-in-capital	195,644
Total shareholders' equity	137,515
(1) The Company defines working capital as current assets less current liabilities.

Nature of the Business (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		12 Months Ended
	Jun. 26, 2018	Jun. 22, 2018	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Class of Stock
Net loss			$ 20,648	$ 7,524	$ 44,751	$ 19,727	$ 12,550
Accumulated deficit			113,301		92,653	47,902
Cash			$ 217,450	$ 128,984	$ 246,984	$ 137,070	$ 28,059
Ordinary shares \| IPO
Class of Stock
Number of shares issued in transaction (shares)	10,147,059
Per share price of issuance (usd per share)	$ 17.00
Proceeds of issuance of ordinary shares, net of issuance costs		$ 156,500
Ordinary shares \| Options
Class of Stock
Number of shares issued in transaction (shares)	1,323,529

Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($)	3 Months Ended	12 Months Ended	39 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment
Fixed asset impairment	$ 0	$ 10,000	$ 0
Office equipment
Property, Plant and Equipment
Property, plant and equipment useful life	3 years
Lab equipment
Property, Plant and Equipment
Property, plant and equipment useful life	5 years
Furniture and fixtures
Property, Plant and Equipment
Property, plant and equipment useful life	5 years

Summary of Significant Accounting Policies - Schedule of Anti-dilutive Shares (Details) - shares	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares (shares)	4,420,108	2,881,113	1,928,626	1,266,619
Unvested restricted incentive shares
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares (shares)	708,834	815,632	1,358,317	1,266,619
Incentive share options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares (shares)	3,711,274	2,065,481	570,309	0

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Research and development claims receivable	$ 10,272	$ 7,191	$ 4,069
Prepayments	2,069	2,208	681
VAT receivable	1,973	1,274	248
Other assets	0	717	0
Grant income receivable	661	678	279
Other receivable	436	121	135
Total prepaid expenses and other current assets	$ 15,411	$ 12,189	$ 5,412

Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment
Less: accumulated depreciation	$ (3,708)	$ (3,138)	$ (1,528)
Total property and equipment, net	19,968	13,528	6,180
Lab equipment
Property, Plant and Equipment
Property and equipment, gross	10,771	10,473	4,141
Office equipment
Property, Plant and Equipment
Property and equipment, gross	1,610	1,019	950
Furniture and fixtures
Property, Plant and Equipment
Property and equipment, gross	599	594	517
Leasehold improvements
Property, Plant and Equipment
Property and equipment, gross	2,076	2,124	2,100
Assets under construction
Property, Plant and Equipment
Property and equipment, gross	$ 8,620	$ 2,456	$ 0

Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017
Payables and Accruals [Abstract]
Compensation and benefits	$ 3,296	$ 2,500		$ 1,662
Research and development costs	9,362	6,659		339
UCLB milestone	638	653	$ 500	0
Professional fees	4,130	3,099		300
Deferred rent	561	569		197
Other liabilities	1,067	623		589
Total accrued expenses and other liabilities	19,054	14,103		3,087
Taxes payable	600
Current portion of long term debt and leases	$ 400	$ 400		$ 400

Shareholders’ Equity - Ordinary Shares (Details) - Ordinary shares - $ / shares	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Class of Stock
Common stock, shares authorized (shares)	200,000,000	200,000,000	37,426,509
Common stock, par value (usd per share)	$ 0.000042	$ 0.000042	$ 0.000042

Shareholders’ Equity - Initial Public Offering and Impact of Corporate Reorganization (Details)			3 Months Ended	12 Months Ended
	Jun. 26, 2018 USD ($) $ / shares shares	Jun. 22, 2018 USD ($) shares	Dec. 31, 2018 USD ($) shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($)	Jun. 22, 2018 GBP (£) shares	Dec. 31, 2017 USD ($)
Class of Stock
Proceeds of issuance of ordinary shares, net of issuance costs			$ 0	$ 156,920,000	$ 127,686,000	$ 32,222,000
Payment of stock issuance cost	$ 16,000,000
Equity conversion ratio		3.185
Shares outstanding (shares) \| shares			129,073,591	129,074,156	29,962,742
Shares value								$ 1,000
Ordinary shares
Class of Stock
Shares outstanding (shares) \| shares			40,145,617	40,146,182
Shares value			$ 2,000	$ 2,000	$ 1,000
Ordinary shares \| IPO
Class of Stock
Number of shares issued in transaction (shares) \| shares	10,147,059
Per share price of issuance (usd per share) \| $ / shares	$ 17.00
Proceeds of issuance of ordinary shares, net of issuance costs	$ 156,500,000
Deferred Shares
Class of Stock
Shares outstanding (shares) \| shares		34,425	34,425	34,425			34,425
Shares value		$ 1.00	$ 0	$ 0	0
Deferred B shares
Class of Stock
Shares outstanding (shares) \| shares		88,893,548	88,893,548	88,893,548			88,893,548
Shares value		$ 118,000	$ 118,000	$ 118,000	0
Share capital registration threshold \| £							£ 50,000
Deferred C shares
Class of Stock
Shares outstanding (shares) \| shares			1	1
Shares value		$ 1.00	$ 0	$ 0	$ 0

Shareholders’ Equity (Details) - shares	Dec. 31, 2018	Sep. 30, 2018	Jun. 22, 2018	Sep. 30, 2017
Class of Stock
Total ordinary and Deferred shares (shares)	129,073,591	129,074,156		29,962,742
Series A preferred shares
Class of Stock
Total ordinary and Deferred shares (shares)				24,490,705
Class B ordinary shares
Class of Stock
Total ordinary and Deferred shares (shares)				3,375,196
Class C ordinary shares
Class of Stock
Total ordinary and Deferred shares (shares)				2,096,841
Ordinary shares
Class of Stock
Total ordinary and Deferred shares (shares)	40,145,617	40,146,182
Deferred Shares
Class of Stock
Total ordinary and Deferred shares (shares)	34,425	34,425	34,425
Deferred B shares
Class of Stock
Total ordinary and Deferred shares (shares)	88,893,548	88,893,548	88,893,548
Deferred C Shares
Class of Stock
Total ordinary and Deferred shares (shares)	1	1

Share Based Compensation - 2018 Equity Incentive Plan (Narratives) (Details)	3 Months Ended
	Dec. 31, 2018 shares
Stock options
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation term (years)	10 years
Vesting Group One
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period (years)	4 years
Award vesting percentage	25.00%
Vesting Group One \| Performance Based
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period (years)	4 years
Award vesting percentage	25.00%
Vesting Group Two
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period (years)	3 years
Vesting Group Two \| Performance Based
Share-based Compensation Arrangement by Share-based Payment Award
Vesting period (years)	3 years
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for distribution (shares)	14,000,000
Increase in reserved shares term	10 years
Periodical increase in authorized shares (percentage)	4.00%
2018 Equity Incentive Plan \| Ordinary shares
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for distribution (shares)	3,281,622
2018 Equity Incentive Plan - New \| Ordinary shares
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for distribution (shares)	3,025,548
2018 Equity Incentive Plan - Shares Available Under 2017 Plan \| Ordinary shares
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for distribution (shares)	256,074

Share Based Compensation - Options Valuation Assumptions (Details) - Stock options	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected term (in years)	6 years	6 years	6 years
Risk-free interest rate minimum (percentage)	2.70%	2.61%	1.91%
Risk-free interest rate maximum (percentage)	3.09%	3.00%	2.05%
Expected volatility minimum (percentage)	69.52%	68.15%	68.61%
Expected volatility maximum (percentage)	71.26%	72.99%	68.93%
Expected dividend yield (percentage)	0.00%	0.00%	0.00%

Share Based Compensation - Share Options Rollforward (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding
Beginning balance (shares)	2,065,481
Granted (shares)	1,651,740
Exercised (shares)	0
Canceled or forfeited (shares)	(5,947)
Ending balance (shares)	3,711,274	2,065,481
Shares Exercisable (shares)	206,085
Vested and expected to vest (shares)	3,711,274
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Beginning balance (weighted average exercise price) (usd per share)	$ 9.87
Granted (weighted average exercise price) (usd per share)	31.23
Exercised (weighted average exercise price) (usd per share)	0.00
Canceled or forfeited (weighted average exercise price) (usd per share)	5.71
Ending balance (weighted average exercise price) (usd per share)	19.25	$ 9.87
Exercisable (weighted average exercise price) (usd per share)	0.50
Vested or expected to vest (weighted average exercise price) (usd per share)	$ 19.25
Options outstanding (weighted- average remaining contractual term years)	9 years 5 months 19 days	9 years 4 months 6 days
Options exercisable (weighted- average remaining contractual term years)	8 years 5 months 22 days
Vested and expected to vest (weighted- average remaining contractual term years)	9 years 5 months 19 days
Options outstanding (aggregate intrinsic value)	$ 51,464
Options exercisable (aggregate intrinsic value)	6,664
Options vested and expected to vest (aggregate intrinsic value)	$ 51,464	$ 43,146,000

Share Based Compensation - Share Options (Narratives) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award
Granted (shares)	1,651,740
Non-employee compensation expense	$ 50	$ 100
Stock options
Share-based Compensation Arrangement by Share-based Payment Award
Weighted average grant date fair value (usd per share)	$ 20.04	$ 8.55	$ 4.04

Share Based Compensation - Restricted Ordinary Shares Valuation Assumptions (Details) - Restricted Ordinary Shares	May 31, 2018	Mar. 31, 2018	Sep. 25, 2017	Apr. 26, 2017	Mar. 02, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected term (in years)	1 year 9 months 18 days	1 year 9 months 18 days	9 months 18 days	1 year 2 months 12 days	2 years 9 months 18 days
Risk-free interest rate (percentage)	2.10%	2.10%	1.30%	1.00%	1.00%
Expected volatility (percentage)	71.00%	71.00%	71.00%	76.60%	73.20%
Expected dividend yield (percentage)	0.00%	0.00%	0.00%	0.00%	0.00%

Share Based Compensation - Restricted Ordinary Shares Rollforward (Details) - Restricted Ordinary Shares - $ / shares	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Unvested and outstanding beginning balance (shares)	815,632
Granted (shares)	0	0
Vested (shares)	(106,233)
Canceled or forfeited (shares)	(565)
Unvested and outstanding ending balance (shares)	708,834	815,632
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Unvested and outstanding beginning balance (weighted average grant date fair value) (usd per share)	$ 4.17
Granted (weighted average grant date fair value) (usd per share)	0.00
Vested (weighted average grant date fair value) (usd per share)	3.97
Canceled or forfeited (weighted average grant date fair value) (usd per share)	2.99
Unvested and outstanding ending balance (weighted average grant date fair value) (usd per share)	$ 4.10	$ 4.17

Share Based Compensation - Restricted Ordinary Shares (Narratives) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award
Share based compensation expense	$ 3,393	$ 6,765	$ 3,153	$ 2,257
Non-employee compensation expense	$ 50	$ 100
Restricted Ordinary Shares
Share-based Compensation Arrangement by Share-based Payment Award
Granted (shares)	0	0
Vested (shares)	106,233
Unrecognized stock based compensation	$ 1,100
Non-employee compensation expense	$ 100	$ 1,000	$ 200
Restricted Ordinary Shares \| Service Based
Share-based Compensation Arrangement by Share-based Payment Award
Granted (shares)			439
Restricted Ordinary Shares \| Service and Performance Based
Share-based Compensation Arrangement by Share-based Payment Award
Granted (shares)			641,711
Restricted Ordinary Shares \| Performance Based
Share-based Compensation Arrangement by Share-based Payment Award
Vested (shares)		159,490	24,896
Share based compensation expense		$ 1,000	$ 800

Share Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	$ 3,393	$ 6,765	$ 3,153	$ 2,257
Unrecognized stock based compensation	$ 42,000
Period for recognition of share based compensation (years)	3 years 9 months 18 days
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	$ 1,906	3,116	1,145	916
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Total share-based compensation	$ 1,487	$ 3,649	$ 2,008	$ 1,341

License Agreements (Details) £ in Thousands, $ in Thousands	1 Months Ended
License Agreements (Details) £ in Thousands, $ in Thousands	Mar. 31, 2018 GBP (£)	Mar. 31, 2016 shares	Sep. 30, 2014 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)
Schedule Of License Agreements [Line Items]
Accrued license fees payable \| $				$ 638		$ 653	$ 500	$ 0
UCLB
Schedule Of License Agreements [Line Items]
Shares issued (shares) \| shares		313,971	1,497,643
Payment of upfront fees	£ 1,500		$ 300
Annual license fee payments					£ 30
UCLB \| Regulatory Approval
Schedule Of License Agreements [Line Items]
Conditional payment, regulatory approval					35,500
UCLB \| Net Sales Levels
Schedule Of License Agreements [Line Items]
Conditional payment, regulatory approval					51,000
UCLB \| Product Sales
Schedule Of License Agreements [Line Items]
Conditional payment, regulatory approval					18,000
UCLB \| Product Sales \| Minimum
Schedule Of License Agreements [Line Items]
Conditional payment, regulatory approval					1,000
UCLB \| Product Sales \| Maximum
Schedule Of License Agreements [Line Items]
Conditional payment, regulatory approval					£ 18,500

Income Taxes - (Narratives) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax benefit	$ 2,605	$ 1,397	$ 7,280	$ 3,653	$ 1,777
Effective rate of income tax (percentage)	11.20%		14.00%	15.60%	12.40%
Decrease in deferred tax assets	$ (1,300)
Operating loss carryforward, foreign	46,200
Deferred tax asset valuation allowances	$ 11,342		$ 10,040	$ 4,987

Income Taxes - Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Net loss before taxes	$ (23,253)	$ (8,921)	$ (52,031)	$ (23,380)	$ (14,327)
U.K. statutory tax rate (percentage)	19.00%		19.00%	19.50%	20.00%
Income tax benefit at U.K. statutory tax rate	$ (4,423)		$ (9,886)	$ (4,559)	$ (2,865)
Tax incentives / credits	(3,234)		(7,296)	(3,702)	(1,837)
Non-deductible expenses	127		1,553	609	694
Non-deductible expenses	265		(13)	13	57
Operating losses	3,605		7,317	3,754	2,168
Tax on property, plant, equipment and intangibles	140		233	113	0
Other, net	915		812	119	6
Total income tax benefit	$ (2,605)	$ (1,397)	$ (7,280)	$ (3,653)	$ (1,777)
Effective rate of income tax (percentage)	11.20%		14.00%	15.60%	12.40%

Income Taxes - Deferred Tax Assets Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Deferred tax assets:
Other differences	$ 2,870	$ 1,785	$ 11
Tax losses	7,851	6,515	3,878
Fixed assets	621	1,740	1,098
Total deferred tax assets	11,342	10,040	4,987
Valuation allowances	(11,342)	(10,040)	(4,987)
Net deferred tax asset (liability)	$ 0	$ 0	$ 0

Commitments and Contingencies - (Narratives) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Loss Contingencies
Rent expense	$ 500,000	$ 900,000	$ 600,000
Catapult Limited
Loss Contingencies
Rent free period (in months)	6 months
Whitewood Media Village GP Limited and Whitewood Media Village Nominee Limited
Loss Contingencies
Leasehold improvements	$ 6,600,000	2,500,000
The Mutual Insurance Society Limited
Loss Contingencies
Lease term (in years)	15 years
Sucampo Pharmaceuticals, Inc.
Loss Contingencies
Rent free period (in months)	4 months
Operating lease
Loss Contingencies
Leasehold improvements		100,000	2,100,000
Operating lease \| Imperial (Forest House) Limited
Loss Contingencies
Lease term (in years)	10 years
Period to exercise option for additional space (in months)	15 months
Licensing agreements
Loss Contingencies
Loss Contingency Accrual	$ 600,000	$ 0	$ 0

Commitments and Contingencies - Future Minimum Lease Payment (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity
2019	$ 2,244
2020	2,332
2021	1,934
2022	1,324
2023	1,196
Thereafter	1,121
Total	$ 10,151

Related Party Transactions (Details)	3 Months Ended		12 Months Ended
Related Party Transactions (Details)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2018 GBP (£)
Related Party Transaction
Professional fees	$ 200,000		$ 1,000,000	$ 500,000
Affiliated Entity \| Syncona LLP
Related Party Transaction
Related party expense			60,000	56,000	$ 200,000
Due to related party			13,000	3,000
Affiliated Entity \| University College London and Related Entities
Related Party Transaction
Due to related party				200,000
Related party transactions				700,000	2,400,000
Affiliated Entity \| University College London and Related Entities \| License fees
Related Party Transaction
Related party transactions				40,000	1,500,000
Affiliated Entity \| Arix Bioscience
Related Party Transaction
Related party expense	0		18,000	20,000	$ 11,000
Due to related party	0		0	2,000
Affiliated Entity \| Kapil Dhingra, M.D.
Related Party Transaction
Due to related party	$ 3,000		$ 46,000	$ 32,000
Professional fees \| £		£ 10,000
Incremental rate for professional fees \| £						£ 1,111

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Retirement Benefits [Abstract]
Employer contributions to defined benefit pension schemes	$ 200	$ 500	$ 300	$ 100
Employer contribution (percent)		4.00%
Employer contributions	$ 18

Selected Financial Data for the Three Months Ended December 31, 2017 (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Results of Operations
Grant income	$ 296	$ 231	$ 1,407	$ 1,693	$ 1,212
Operating expenses:
Research and development	(17,713)	(5,564)	(36,150)	(16,012)	(10,436)
General and administrative	(7,593)	(3,084)	(22,790)	(9,099)	(5,152)
Total operating expenses, net	(25,010)	(8,417)	(57,533)	(23,418)	(14,376)
Other income (expense):
Interest income	660	181	1,532	84	75
Other income (expense)	1,097	(685)	3,970	(46)	(26)
Total other income, net	1,757	(504)	5,502	38	49
Net loss before income tax	(23,253)	(8,921)	(52,031)	(23,380)	(14,327)
Income tax benefit	2,605	1,397	7,280	3,653	1,777
Net loss attributable to ordinary shareholders	(20,648)	(7,524)	(44,751)	(19,727)	(12,550)
Cash Flows
Net cash used in operating activities	(19,785)	(8,797)	(31,537)	(16,360)	(9,849)
Net cash used in investing activities	(4,422)	(764)	(9,531)	(2,876)	(1,855)
Net cash provided by financing activities	0	433	156,920	127,686	32,222
Effect of exchange rate changes on cash		1,042
Net decrease in cash		(8,086)
Balance Sheet Data
Cash	217,450	128,984	246,984	137,070	28,059
Working capital		131,576
Net assets		137,515
Total assets	254,210	142,715	273,205	148,662
Ordinary shares		1
Additional paid-in capital	361,311	195,644	357,918	194,351
Total shareholders' equity	$ 232,642	$ 137,515	$ 255,465	$ 142,601	$ 30,687	$ 10,501

Subsequent Events	3 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company evaluated subsequent events through February 25, 2019, the date on which these financial statements were issued.

Summary of Significant Accounting Policies - Intangible Assets Subject to Amortization (Details) $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($)
Software
Finite-Lived Intangible Assets
Impairment of finite lived intangible	$ 0.4

Summary of Significant Accounting Policies - Segment Information (Details)	3 Months Ended
	Dec. 31, 2018 segment region
Accounting Policies [Abstract]
Number of reportable segments \| segment	1
Number of geographic regions \| region	2

Employee Benefit Plans	3 Months Ended
Employee Benefit Plans	Dec. 31, 2018
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 $0.2 million, $0.5 million, $0.3 million and $0.1 million in contributions for the three months ended December 31, 2018 and years ended September 30, 2018, 2017 and 2016, 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. For the three months ended December 31, 2018, the Company incurred $18,000 in matching expenses. The Company pays all administrative fees related to the 401(k) plan.

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Restricted cash	$ 105,000	$ 105,000	$ 0	$ 0