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Share-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2023
Share-Based Compensation |
Schedule of share-based compensation expense category | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended September 30, | ​ | Nine Months Ended September 30,
(in thousands) |  | 2023 |  | 2022 | ​ | 2023 |  | 2022
Research and development | ​ | $ | 1,429 | ​ | $ | 568 | ​ | $ | 4,788 | ​ | $ | 6,528
General and administrative | ​ |  | 1,395 | ​ |  | 2,294 | ​ |  | 4,563 | ​ |  | 8,949
​ | ​ | $ | 2,824 | ​ | $ | 2,862 | ​ | $ | 9,351 | ​ | $ | 15,477
Summary of stock option activity plan | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted | ​
​ | ​ | ​ | ​ | Weighted | ​ | average | ​
​ | ​ | ​ | ​ | average | ​ | remaining | ​
​ | ​ | Number of | ​ | exercise price | ​ | contractual | ​
​ | ​ | shares | ​ | per share | ​ | term (years) | ​
Outstanding at January 1, 2023 |  | 11,411,390 |  | $ | 9.01 |  | 7.1 | ​
Granted |  | 3,348,982 | ​ | ​ | 1.06 |  |  | ​
Exercised |  | — | ​ | ​ | — |  |  | ​
Forfeited |  | (2,256,315) | ​ | ​ | 8.58 |  |  | ​
Expired |  | (2,264,006) | ​ | ​ | 12.50 |  |  | ​
Outstanding at September 30, 2023 |  | 10,240,051 | ​ | $ | 5.73 |  | 8.2 | ​
Vested and exercisable at September 30, 2023 |  | 4,935,214 | ​ | $ | 8.43 |  | 7.4 | ​
Vested or expected to vest at September 30, 2023 |  | 10,240,051 | ​ | $ | 5.73 |  | 8.2 | ​
Schedule of weighted average assumptions applied to options | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Nine Months Ended September 30,
​ | ​ | 2023 | ​ | 2022
Expected volatility | ​ | 92.6 | % | ​ | 92.3 | %
Risk‑free interest rate | ​ | 3.6 | % | ​ | 2.6 | %
Expected term | ​ | 6.0 | years | ​ | 5.8 | years
Expected dividend yield | ​ | — | ​ | ​ | — | ​
Summary of activity related to restricted stock unit | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ |  | ​ |  | ​ | Weighted average
​ | ​ |  | Number of shares |  | ​ | grant date fair value
Unvested balance at January 1, 2022 | ​ |  | 1,229,166 |  | $ | 2.98
Granted | ​ |  | 195,000 |  | $ | 1.01
Vested | ​ | ​ | (98,042) | ​ | ​ | 5.82
Forfeited | ​ |  | (179,625) |  | $ | 2.13
Unvested balance at September 30, 2023 | ​ |  | 1,146,499 |  | $ | 2.58

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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