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Organization and Operations - Additional Information (Details) |  |  |  |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 9 Months Ended | 12 Months Ended |
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Feb. 17, 2021 USD ($) shares | Oct. 23, 2020 USD ($) shares | Oct. 02, 2020 shares | Sep. 30, 2020 USD ($) | Jun. 16, 2020 shares | Aug. 05, 2019 $ / shares | Apr. 25, 2019 USD ($) | Apr. 24, 2019 USD ($) | Sep. 21, 2018 USD ($) | Sep. 30, 2019 $ / shares shares | Feb. 17, 2021 USD ($) shares | Sep. 30, 2020 USD ($) shares | Dec. 31, 2020 USD ($) Subsidiary $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Feb. 28, 2021 shares
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of wholly-owned subsidiaries | Subsidiary |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |
Proceeds from sale of business |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 5,637,000 |
Reverse stock split of common stock |  |  |  |  |  | 0.02 |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  |  |  |  | $ 0.001 |  |  |  |  |  |  | $ 0.001 | $ 0.001 |
Net loss |  |  |  |  |  |  |  |  |  |  |  |  | $ (8,241,000) | $ (10,887,000) |
Accumulated deficit |  |  |  |  |  |  |  |  |  |  |  |  | (433,511,000) | (425,270,000) |
Net cash used in operating activities |  |  |  |  |  |  |  |  |  |  |  |  | (8,434,000) | (5,906,000) |
Cash and cash equivalents |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,346,000 | 17,552,000 |
Substantial doubt about going concern, description |  |  |  |  |  |  |  |  |  |  |  |  | These factors raise substantial doubt about the Company’s ability to continue as a going concern |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,007,000 | 15,964,000 |
Sale of common stock, net |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,208,000 |
Reimbursement revenue recognized |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,600,000 |
Option granted | shares |  |  |  |  |  |  |  |  |  |  |  |  | 530,000 |  |
Warrant exercise price (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 2.25 |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option vesting period |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option vesting period |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |
Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 289,000 |  |
Common Class B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities called by warrant or right | shares |  |  |  |  |  |  |  |  |  |  |  |  | 2,711,000 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 184,666 |
Warrant exercised | shares |  |  |  |  |  |  |  |  |  |  |  |  | 487,521 | 65,114 |
Series U Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 3,450,000 |  |
Sale of Stock, Price Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 5.00 |  |
Representative Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities called by warrant or right | shares |  |  |  |  |  |  |  |  |  |  |  |  | 75,000 |  |
Warrant exercise price (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 6.25 |  |
2020 Repurchase Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  | 180,701 |  |  |  |  |  |  |  |  | 0 | 353,113 |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |
Sale of common stock, net |  |  |  |  |  |  |  |  |  |  |  | $ 25,000,000 |  |  |
Period exercisable from the date of issuance |  |  |  |  |  |  |  |  |  |  |  | 36 months |  |  |
2020 Repurchase Agreement [Member] | Common Stock [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  | 23,800,000 |  |  |  |  |  |  |  |  |  |
Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 1,616,331 |  |
Proceeds from sale of common stock |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  | $ 3,200,000 |  |
Remaining availability under financing facility |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 32,170 |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000 |
Remaining availability under financing facility |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |
Sale of common stock, net |  |  |  |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  |  |  |  |  |  | 24 months |  |  |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  | 353,113 |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |
Sale of common stock, net |  |  |  | $ 25,000,000 |  |  |  |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  | 36 months |  |  |  |  |  |  |  |  |  |  |
Underwriter [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwritten public offering description |  |  |  |  |  |  |  |  |  | pursuant to which the Company sold in an underwritten public offering an aggregate of (i) 289,000 Class A Units, each consisting of one share of common stock, par value $0.001 per share, of the Company and one Series U warrant to purchase one share of common stock, and (ii) 2,711,000 Class B Units, each consisting of one pre-funded Series V warrant to purchase one share of common stock and one Series U Warrant to purchase one share of common stock at a public offering price of $5.00 per Class A Unit and $4.9999 per Class B Unit (the “September 2019 Offering”). In addition, the Company granted the Underwriters a 45-day option to purchase up to an additional 450,000 shares of the Company’s common stock and/or Series U Warrants at the public offering price, less the underwriting discounts and commissions. The Underwriters exercised their option to purchase an additional 450,000 Series U warrants. The Company also issued to the Representative warrants (in the form of the Series U warrants) to purchase 75,000 shares of common stock with an exercise price of $6.25 per share of common stock (the “Representative Warrants”). |  |  |  |  |
Option vesting period |  |  |  |  |  |  |  |  |  | 45 days |  |  |  |  |
Warrant granted | shares |  |  |  |  |  |  |  |  |  | 450,000 |  |  |  |  |
Underwriter [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option granted | shares |  |  |  |  |  |  |  |  |  | 450,000 |  |  |  |  |
Underwriter [Member] | Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 0.001 |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  | 289,000 |  |  |  |  |
Underwriter [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  | 1,616,299 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock |  | $ 3,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriter [Member] | Series V Warrants | Common Class B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities called by warrant or right | shares |  |  |  |  |  |  |  |  |  | 2,711,000 |  |  |  |  |
Underwriter [Member] | Series U Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant exercised | shares |  |  |  |  |  |  |  |  |  | 450,000 |  |  |  |  |
Underwriter [Member] | Series U Warrants [Member] | Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of Stock, Price Per Share | $ / shares |  |  |  |  |  |  |  |  |  | $ 5.00 |  |  |  |  |
Underwriter [Member] | Series U Warrants [Member] | Common Class B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of Stock, Price Per Share | $ / shares |  |  |  |  |  |  |  |  |  | $ 4.9999 |  |  |  |  |
Underwriter [Member] | Representative Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities called by warrant or right | shares |  |  |  |  |  |  |  |  |  | 75,000 |  |  |  |  |
Warrant exercise price (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 6.25 |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities called by warrant or right | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 896,500
Subsequent Event [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares | 985,186 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock | $ 2,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares | 536,070 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  | 985,186 |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  | $ 2,900,000 |  |  |  |
Subsequent Event [Member] | Underwriter [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  | 536,070 |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  | $ 1,500,000 |  |  |  |
Sale of UK Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of business |  |  |  |  |  |  |  | $ 4,000,000 |  |  |  |  |  |  |
Payments for principal, interest and fees |  |  |  |  |  |  |  | 1,700,000 |  |  |  |  |  |  |
Sale of the Japanese Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of business |  |  |  |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |
Payments for principal, interest and fees |  |  |  |  |  |  | 1,400,000 |  |  |  |  |  |  |  |
UK Subsidiary and Cell Therapy Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of business |  |  |  |  |  |  |  | 3,300,000 |  |  |  |  |  |  |
UK Subsidiary and Cell Therapy Assets [Member] | Amendmend to Loan and Security Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for principal, interest and fees |  |  |  |  |  |  |  | $ 1,700,000 |  |  |  |  |  |  |
Japanese Subsidiary and Cell Therapy Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of business |  |  |  |  |  |  | 2,400,000 |  |  |  |  |  |  |  |
Japanese Subsidiary and Cell Therapy Assets [Member] | Amendmend to Loan and Security Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for principal, interest and fees |  |  |  |  |  |  | $ 1,400,000 |  |  |  |  |  |  |  |

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