10. Stock‑based compensation

2015 Stock Option Plan

In October 2015, the Company’s board of directors and stockholders approved the 2015 Stock Option and Incentive Plan, or 2015 Stock Option Plan, which became effective upon the completion of the IPO. The 2015 Stock Option Plan provides the Company with the flexibility to use various equity-based incentive and other awards as compensation tools to motivate our workforce. These tools include stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance share awards and cash-based awards. The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Stock Option Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (i) 1,311,812 shares of common stock and (ii) the number of shares under the 2014 Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31.

Effective January 1, 2016 and 2017, an additional 1,069,971 and 1,070,635 shares, respectively, were added to the Company’s 2015 Stock Option Plan for future issuance. During the year ended December 31, 2016, the Company issued 966,060 stock options to employees and directors and 23,500 stock options to non‑employees. As of December 31, 2016, there were 1,825,174 shares available for future issuance under the 2015 Stock Option Plan.

2014 Stock Option and Grant Plan

In January 2014, the Company adopted the Voyager Therapeutics, Inc. 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it may grant incentive stock options, non‑qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of Common Stock to employees, officers, directors and consultants of the Company.

In April 2014, the Company amended the Plan to allow for the issuance of up to 1,411,764 shares of Common Stock. In August 2014, April 2015, August 2015 and October 2015 the Company further amended the Plan to allow for the issuance of up to 2,000,000, 2,047,058, 2,669,411 and 2,998,823 shares of Common Stock, respectively. During 2014 the Company issued only restricted stock awards under the Plan and during 2015 the Company only granted stock options.

The terms of stock awards agreements, including vesting requirements, are determined by the Board of Directors and are subject to the provisions of the 2014 Plan. Restricted Stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Awards granted to employees generally vest over four years, with 25% vesting on the one year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Awards granted to non‑employee consultants generally vest monthly over a period of one to four years.

During the year ended December 31, 2014, the Company granted a total of 1,597,988 shares of restricted stock to employees and 110,960 shares of restricted stock to non‑employee consultants at an original issuance price of $0.04 per share.

Founder Awards

In January 2014, the Company issued 1,188,233 shares of restricted stock to its Founders at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the Founders, 835,292 shares generally vest over one to four years, based on each Founder’s continued service to the Company in varying capacity as a Scientific Advisory Board member, consultant, director, officer or employee, as set forth in each grantee’s individual restricted stock purchase agreement. The remaining 352,941 of the shares issued will begin vesting upon the achievement of certain performance objectives as well as continued service to the Company, as set forth in the agreements.

These performance conditions are tied to certain milestone events specific to the Company’s corporate goals, including but not limited to preclinical and clinical development milestones related to the Company’s product candidates. Stock‑based compensation expense associated with these performance‑based awards will be recognized when the achievement of the performance condition is considered probable, using management’s best estimates. As of December 31, 2016, management has concluded that the achievement of the performance milestone for one of the three performance-based awards had been met during the year. Accordingly, stock‑based compensation expense in the amount of $1.1 million was recorded as of December 31, 2016.

2015 Employee Stock Purchase Plan

In October 2015, the Company’s board of directors and stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). Under the 2015 ESPP, all full-time employees of the Company are eligible to purchase common stock of the Company twice per year, at the end of each six-month payment period. During each payment period, eligible employees who so elect, may authorize payroll deductions in an amount of 1% to 10% (whole percentages only) of the employee’s base pay for each payroll period. At the end of each payment period, the accumulated deductions are used to purchase shares of common stock from the Company at a discount. A total of 262,362 shares of common stock were initially authorized for issuance under this plan. The 2015 ESPP became effective upon the completion of the IPO. Effective January 1, 2016 and 2017, 267,492 and 267,658 shares of common stock, respectively, were added to the 2015 ESPP.

Stock-based Compensation Expense

Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive loss is as follows:


	Year ended December 31,
	2016		2015		2014
	(in thousands)
Research and development	$	4,296	$	3,218	$	297
General and administrative		2,014		809		128
Total stock-compensation expense	$	6,310	$	4,027	$	425

Restricted Stock

A summary of the status of and changes in unvested restricted stock was as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	Per Share
Unvested restricted common stock as of December 31, 2015	1,818,261	$	0.76
Issued	—
Vested	(601,501)	$	0.79
Repurchased	(48,776)	$	1.11
Unvested restricted common stock as of December 31, 2016	1,167,984	$	0.76

The expense related to awards granted to employees and non‑employees was $0.5 million and $2.6 million, respectively, for the year ended December 31, 2016. The expense related to awards granted to employees and non-employees was $0.5 million and $2.6 million, respectively, for the year ended December 31, 2015. The expense related to awards granted to employees and non-employees was $0.2 million and $0.2 million, respectively, for the year ended December 31, 2014.

As of December 31, 2016, the Company had unrecognized stock‑based compensation expense related to its unvested restricted stock awards of $10.7 million, which is expected to be recognized over the remaining weighted average vesting period of 1.33 years.

Stock Options

A summary of the status of, and changes in, stock options was as follows:


		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2015	1,022,617	$	8.35
Granted	989,560	$	11.90
Exercised	(65,432)	$	7.85
Cancelled or forfeited	(75,508)	$	9.62
Outstanding at December 31, 2016	1,871,237	$	10.21	8.9	$	5,232
Exercisable at December 31, 2016	458,737	$	9.02	8.5	$	1,759
Vested and expected to vest at December 31, 2016	1,871,237	$	10.21	8.9	$	5,232

Using the Black‑Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the year ended December 31, 2016 was $7.66. The expense related to awards granted to employees and directors was $3.0 million and $0.7 million for the years ended December 31, 2016 and 2015, respectively. There were no stock options granted during the year ended December 31, 2014.

The fair value of each option issued to employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the following weighted‑average assumptions:


	Year ended December 31,
	2016		2015
Risk-free interest rate	1.5	%	1.6	%
Expected dividend yield	—	%	—	%
Expected term (in years)	6.0		6.0
Expected volatility	73.1	%	78.6	%

Using the Black‑Scholes option pricing model, the weighted average grant date fair value of options granted to non‑employees during the year ended December 31, 2016 was $9.98. Unvested options granted to non‑employees are revalued at each measurement period until they vest. The expense related to awards granted to non‑employees was $0.2 million and $0.3 million for the years ended December 31, 2016, and 2015, respectively. There were no stock options granted during the year ended December 31, 2014.

The fair value of each option issued to non‑employees was estimated at each vesting and reporting date using the Black‑Scholes option pricing model. The reporting date fair value was determined using the following weighted‑average assumptions:


	As of December 31,
	2016		2015
Risk-free interest rate	2.1	%	2.0	%
Expected dividend yield	—	%	—	%
Expected term (in years)	9.1		10.0
Expected volatility	83.3	%	84.0	%

As of December 31, 2016, the Company had unrecognized stock‑based compensation expense related to its unvested stock options of $8.7 million which is expected to be recognized over the remaining weighted average vesting period of 2.71 years.