The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:


	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
(in thousands)	2021		2020		2021		2020
Research and development		535		522		2,115		1,587
General and administrative		1,836		1,270		7,742		3,806
Stock-based compensation expense	$	2,371	$	1,792	$	9,857	$	5,393

The Company granted an aggregate of 2,755,000 and 7,150,438 stock options during the three and nine months ended September 30, 2021, with a weighted-average grant date fair value of $1.08 and $1.91 per share, respectively. The Company granted an aggregate of 203,178 and 1,252,178 stock options during the three and nine months ended September 30, 2020, with a weighted-average grant date fair value of $1.96 and $2.45 per share, respectively.

On March 4, 2021, the Company extended the contractual life of 216,700 fully vested stock options held by a former director of the Company. On April 5, 2021, the Company extended the contractual life of 751,371 stock options and accelerated the vesting of 226,889 shares of restricted stock held by a former officer of the Company. On April 29, 2021, the Company extended the contractual life of 10,417 vested and 167,023 unvested stock options and accelerated the vesting of 4,137 shares of restricted stock held by a former director. On May 17, 2021, the Company extended the contractual life of 347,267 vested stock options held by a former officer of the Company. These extensions resulted in additional stock compensation expense of approximately $2.0 million during the nine months ended September 30, 2021.

For the three and nine months ended September 30, 2021 and 2020, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:


	For the Three Months Ended September 30,						For the Nine Months Ended September 30,
	2021			2020			2021			2020
Risk-free interest rate	0.89 - 0.96%			0.36 - 0.39%			0.50 - 1.15%			0.36 - 1.68%
Expected life in years	6.00 - 6.25			5.75 - 6.25			5.50 - 6.25			5.75 - 6.25
Expected volatility	72.53 - 72.84%			73.59 - 74.18%			72.53 - 74.80%			71.11 - 74.18%
Expected dividend yield		—	%		—	%		—	%		—	%

At September 30, 2021, there were 97,500 stock options that had been issued outside the 2012 Equity Incentive Plan, or the 2012 Plan and the 2020 Equity Incentive Plan, or the 2020 Plan. These options are excluded from the schedule below.

Stock option activity under the Company’s stock option plans for the nine months ended September 30, 2021 is as follows:


(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2020		6,840,719		$	3.81
Granted		7,150,438			2.97
Exercised		(363,109	)		2.86
Cancelled		(2,555,154	)		3.54
Outstanding, September 30, 2021		11,072,894		$	3.36		8.32	$	473
Options exercisable, September 30, 2021		5,743,820		$	4.08		7.24	$	—
Options exercisable, December 31, 2020		3,596,315		$	4.17		6.90	$	598
Options available for future grant		2,224,159

At September 30, 2021, total unrecognized compensation costs related to unvested stock options outstanding amounted to $8.0 million. The cost is expected to be recognized over a weighted-average period of 2.03 years.

A summary of the status of unvested restricted stock for the nine months ended September 30, 2021 is as follows:


	Number of Shares			Weighted-Average Grant Date Fair Value
Unvested, December 31, 2020		786,280		$	3.08
Granted		1,601,224			2.60
Vested		(466,436	)		3.68
Cancelled		(410,413	)		3.46
Unvested, September 30, 2021		1,510,655		$	2.28

At September 30, 2021, total unrecognized compensation costs related to unvested restricted stock outstanding amounted to $2.4 million. The cost is expected to be recognized over a weighted-average period of 2.19 years.

At the Company’s annual meeting held on June 29, 2020, the shareholders approved the 2020 Equity Incentive Plan, or the 2020 Plan, which is a successor to and continuation of the 2012 Plan. The 2020 Plan had 21 million shares authorized, plus the shares remaining for issuance under the 2012 Plan. Our ability to utilize the total shares authorized under the 2020 Plan will be limited by the total number of shares authorized in our certificate of incorporation. As a result, as of September 30, 2021, there are 2,224,159 shares available to grant from the 2020 Plan. Additionally, 2,625,000 stock options with an exercise price of $1.64 were granted on August 30, 2021 to the Company's Chief Executive Officer, as part of his compensation package. These options are subject to a vesting schedule. None of these options have vested and do not currently impact the shares available to grant from the 2020 Plan. No additional awards can be granted from the 2012 Plan or the Company's 2003 Stock Option Plan.