In January 2023, the Company established the 2023 Inducement Plan (the “2023 Inducement Plan”), which provides for the granting of share-based awards to individuals who were not previously employees, or following a bona fide period of non-employment, as an inducement material to such individuals entering into employment with the Company. The Company reserved 1.0 million shares of common stock for grants under the 2023 Inducement Plan. As of June 30, 2023, there were 0.3 million shares available for issuance under the 2023 Inducement Plan.

The 2015 Stock Incentive Plan, as amended (“2015 Plan”), was approved at the Company's annual meeting of stockholders in June 2015. Under the 2015 Plan, equity awards may be granted to officers, directors, employees, and consultants of and advisors to the Company and any present or future subsidiary. The 2015 Plan authorizes the issuance of up to 14.8 million shares of common stock under equity awards granted under the 2015 Plan. All such shares authorized for issuance under the 2015 Plan have been reserved. The 2015 Plan will expire on March 4, 2025. As of June 30, 2023, there were 0.9 million shares available for issuance under the 2015 Plan.

The Amended and Restated 2005 Stock Incentive Plan (“2005 Plan”) expired in February 2015 and no new awards may be made under such plan, although awards will continue to be outstanding in accordance with their terms.

The 2023 Inducement Plan and the 2015 Plan permit and the 2005 Plan permitted the grant of stock options (including incentive stock options), restricted stock, stock appreciation rights (“SARs”), and restricted stock units (“RSUs”). In addition, under the 2023 Inducement Plan and the 2015 Plan, unrestricted stock, stock units, and performance awards may be granted. Stock options and SARs generally have a maximum term of ten years and may be or were granted with an exercise price that is no less than 100% of the fair market value of the Company's common stock at the time of grant. Grants of share-based awards are generally subject to vesting over periods ranging from one to four years.


	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Cost of sales	$	998	$	—	$	1,516	$	—
Research and development	9,946		19,695		23,804		36,582
Selling, general, and administrative	9,348		18,353		23,619		34,399
Total stock-based compensation expense	$	20,292	$	38,048	$	48,939	$	70,981

As of June 30, 2023, there was approximately $122 million of total unrecognized compensation expense related to unvested stock options, SARs, RSUs, and the Company’s Employee Stock Purchase Plan, as amended (“ESPP”). This unrecognized non-cash compensation expense is expected to be recognized over a weighted-average period of approximately one year. This estimate does not include the impact of other possible stock-based awards that may be made during future periods.

The aggregate intrinsic value represents the total intrinsic value (the difference between the Company’s closing stock price on the last trading day of the period and the exercise price, multiplied by the number of in-the-money stock options and SARs) that would have been received by the holders had all stock option and SAR holders exercised their stock options and SARs on June 30, 2023. This amount is subject to change based on changes to the closing price of the Company's common stock. The aggregate intrinsic value of stock options and SARs exercises and vesting of RSUs for the six months ended June 30, 2023 and 2022 was approximately $2 million and $8 million, respectively.


	2023 Inducement Plan			2015 Plan			2005 Plan
	Stock Options	Weighted-Average Exercise Price		Stock Options	Weighted-Average Exercise Price		Stock Options	Weighted-Average Exercise Price
Outstanding at December 31, 2022	—	$	—	4,053,290	$	46.07	63,725	$	112.94
Granted	358,600	10.96		860,872	7.29		—	—
Exercised	—	—		(5,031)	6.81		—	—
Canceled	—	—		(63,839)	51.41		(5,250)	36.60
Outstanding at June 30, 2023	358,600	$	10.96	4,845,292	$	39.15	58,475	$	119.80
Shares exercisable at June 30, 2023	—	$	—	3,295,810	$	40.62	58,475	$	119.80


	Three Months Ended June 30,		Six Months Ended June 30,
	2023	2022	2023	2022
Weighted average Black-Scholes fair value of stock options granted	$6.79	$43.21	$7.24	$62.52
Risk-free interest rate	3.5%-3.9%	2.7%-3.2%	3.5%-4.0%	1.4%-3.2%
Dividend yield	—%	—%	—%	—%
Volatility	120.4%-131.3%	120.5%-136.7%	120.4%-140.3%	120.5%-136.7%
Expected term (in years)	3.9-6.4	4.0-6.2	3.9-6.4	4.0-6.2

The total aggregate intrinsic value and weighted-average remaining contractual term of stock options and SARs outstanding under the 2023 Inducement Plan, 2015 Plan and 2005 Plan as of June 30, 2023 was approximately $1.7 million and 7.3 years, respectively. The total aggregate intrinsic value and weighted-average remaining contractual term of stock options and SARs exercisable under the 2023 Inducement Plan, 2015 Plan and 2005 Plan as of June 30, 2023 was approximately $1.1 million and 6.3 years, respectively.


	2023 Inducement Plan			2015 Plan
	Number of Shares	Per Share Weighted- Average Fair Value		Number of Shares	Per Share Weighted- Average Fair Value
Outstanding and unvested at December 31, 2022	—	$	—	2,034,574	$	61.67
Granted	308,390	$	10.96	2,767,475	7.23
Vested	—	$	—	(307,653)	82.94
Forfeited	—	$	—	(637,727)	29.46
Outstanding and unvested at June 30, 2023	308,390	$	10.96	3,856,669	$	26.23

The ESPP was approved at the Company's annual meeting of stockholders in June 2013. The ESPP currently authorized an aggregate of 1.2 million shares of common stock to be purchased, and the aggregate amount of shares will continue to increase 5% on each anniversary of its adoption up to a maximum of 1.65 million shares. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate). As of June 30, 2023, there were 0.6 million shares available for issuance under the ESPP.