Document:

EX-10.3

 Exhibit 10.3 
  

 
 REGENXBIO INC. 

2015 EQUITY INCENTIVE PLAN 

(AS ADOPTED ON JUNE 17, 2015) 

 REGENXBIO INC. 

2015 EQUITY INCENTIVE PLAN 

ARTICLE 1. INTRODUCTION. 
 The Board
adopted the Plan to become effective immediately, although no Awards may be granted prior to the Registration Date. The purpose of the Plan is to promote the long-term success of the Company and the creation of stockholder value by
(a) encouraging Service Providers to focus on critical long-range corporate objectives, (b) encouraging the attraction and retention of Service Providers with exceptional qualifications and (c) linking Service Providers directly to
stockholder interests through increased stock ownership. The Plan seeks to achieve this purpose by providing for Awards in the form of Options (which may constitute ISOs or NSOs), SARs, Restricted Shares, Stock Units and Performance Cash Awards.

 ARTICLE 2. ADMINISTRATION. 
 2.1
General. The Plan may be administered by the Board or one or more Committees. Each Committee shall have the authority and be responsible for such functions as have been assigned to it. 

2.2 Section 162(m). To the extent an Award is intended to qualify as “performance-based compensation” within the meaning
of Code Section 162(m), the Plan will be administered by a Committee of two or more “outside directors” within the meaning of Code Section 162(m). 

2.3 Section 16. To the extent desirable to qualify transactions hereunder as exempt under Exchange Act Rule 16b-3, the
transactions contemplated hereunder will be approved by the entire Board or a Committee of two or more “non-employee directors” within the meaning of Exchange Act Rule 16b-3. 

2.4 Powers of Administrator. Subject to the terms of the Plan, and in the case of a Committee, subject to the specific duties delegated
to the Committee, the Administrator shall have the authority to (a) select the Service Providers who are to receive Awards under the Plan, (b) determine the type, number, vesting requirements and other features and conditions of such
Awards, (c) determine whether and to what extent any Performance Goals have been attained, (d) interpret the Plan and Awards granted under the Plan, (e) make, amend and rescind rules relating to the Plan and Awards granted under the
Plan, including rules relating to sub-plans established for the purposes of satisfying applicable foreign laws or for qualifying for favorable tax treatment under applicable foreign laws, (f) impose such restrictions, conditions or limitations
as it determines appropriate as to the timing and manner of any resales by a Participant of any Common Shares issued pursuant to an Award, including restrictions under an insider trading policy and restrictions as to the use of a specified brokerage
firm for such resales, and (g) make all other decisions relating to the operation of the Plan and Awards granted under the Plan. 

 2.5 Effect of Administrator’s Decisions. The Administrator’s decisions,
determinations and interpretations shall be final and binding on all Participants and any other holders of Awards. 
 2.6 Governing
Law. The Plan shall be governed by, and construed in accordance with, the laws of the State of Delaware (except its choice-of-law provisions). 

ARTICLE 3. SHARES AVAILABLE FOR GRANTS. 

3.1 Basic Limitation. Common Shares issued pursuant to the Plan may be authorized but unissued shares or treasury shares. The aggregate
number of Common Shares issued under the Plan shall not exceed the sum of (a) 2,025,000 shares (subject to adjustment pursuant to a stock split to be effected prior to the IPO Date), (b) the number of Common Shares reserved under the
Predecessor Plan that are not issued or subject to outstanding awards under the Predecessor Plan on the Registration Date, (c) any Common Shares subject to outstanding options under the Predecessor Plan on the Registration Date that
subsequently expire or lapse unexercised and Common Shares issued pursuant to awards granted under the Predecessor Plans that are outstanding on the Registration Date and that are subsequently forfeited to or repurchased by the Company and
(d) the additional Common Shares described in Articles 3.2 and 3.3; provided, however, that no more than 6,015,300 Common Shares (subject to adjustment pursuant to a stock split to be effected prior to the IPO Date), in the aggregate,
shall be added to the Plan pursuant to clauses (b) and (c). The number of Common Shares that are subject to Stock Awards outstanding at any time under the Plan may not exceed the number of Common Shares that then remain available for issuance
under the Plan. The numerical limitations in this Article 3.1 shall be subject to adjustment pursuant to Article 9. 
 3.2
Annual Increase in Shares. As of the first business day of each fiscal year of the Company during the term of the Plan, commencing on January 1, 2016, the aggregate number of Common Shares that may be issued under the Plan shall
automatically increase by a number equal to the least of (a) 4% of the total number of Common Shares outstanding on December 31 of the prior year, or (b) a number of Common Shares determined by the Board. 

3.3 Shares Returned to Reserve. To the extent that Options, SARs or Stock Units granted under this Plan are forfeited or expire for any
other reason before being exercised or settled in full, the Common Shares subject to such Options, SARs or Stock Units shall again become available for issuance under the Plan. If SARs are exercised, then only the number of Common Shares (if any)
actually issued to the Participant in settlement of such SARs shall reduce the number available under Article 3.1 and the balance shall again become available for issuance under the Plan. If Stock Units are settled, then only the number of
Common Shares (if any) actually issued to the Participant in settlement of such Stock Units shall reduce the number available under Article 3.1 and the balance shall again become available for issuance under the Plan. If Restricted Shares or
Common Shares issued upon the exercise of Options or otherwise under the Plan are reacquired by the Company pursuant to a forfeiture provision, repurchase right or for any other reason prior to the shares having become vested, then such Common
Shares shall again become available for issuance under the Plan. Common Shares applied to pay 

  
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the Exercise Price of Options or to satisfy tax withholding obligations related to any Award shall again become available for issuance under the Plan. To the extent that an Award is settled in
cash rather than Common Shares, the cash settlement shall not reduce the number of Shares available for issuance under the Plan. 
 3.4
Awards Not Reducing Share Reserve in Article 3.1. Any dividend equivalents paid or credited under the Plan with respect to Stock Units shall not be applied against the number of Common Shares that may be issued under the Plan, whether or not
such dividend equivalents are converted into Stock Units. In addition, Common Shares subject to Substitute Awards granted by the Company shall not reduce the number of Common Shares that may be issued under Article 3.1, nor shall shares subject to
Substitute Awards again be available for Awards under the Plan in the event of any forfeiture, expiration or cash settlement of such Substitute Awards. 

3.5 Share Limits. Subject to adjustment in accordance with Article 9: 

(a) The aggregate number of Common Shares subject to Options and SARs that may be granted under this Plan during any calendar
year to any one Participant shall not exceed 1,500,000 Common Shares (subject to adjustment pursuant to a stock split to be effected prior to the IPO Date), except that the Company may grant to a new Employee in the calendar year in which his or her
Service as an Employee first commences Options and/or SARs that cover (in the aggregate) up to an additional 500,000 Common Shares (subject to adjustment pursuant to a stock split to be effected prior to the IPO Date); 

(b) The aggregate number of Common Shares subject to Restricted Share awards and Stock Units that may be granted under this
Plan during any calendar year to any one Participant shall not exceed 1,500,000 Shares (subject to adjustment pursuant to a stock split to be effected prior to the IPO Date), except that the Company may grant to a new Employee in the calendar year
in which his or her Service as an Employee first commences Restricted Share awards and Stock Units that cover (in the aggregate) up to an additional 500,000 Common Shares (subject to adjustment pursuant to a stock split to be effected prior to the
IPO Date); 
 (c) No Participant shall be paid more than $1 million in cash in any calendar year pursuant to Performance
Cash Awards granted under the Plan; 
 (d) No more than 6,015,300 Common Shares (subject to adjustment pursuant to a stock
split to be effected prior to the IPO Date) plus the additional Common Shares described in Article 3.2 may be issued under the Plan upon the exercise of ISOs; and 

(e) The maximum aggregate grant date fair value (as determined in accordance with Financial Accounting Standards Board
Accounting Standards Codification Topic 718, or any successor thereto) of Options and SARs that may be granted under this Plan to an Outside Director as compensation for services as an Outside Director during a calendar year shall not exceed
$500,000. 

  
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 ARTICLE 4. ELIGIBILITY. 

4.1 Incentive Stock Options. Only Employees who are common-law employees of the Company, a
Parent or a Subsidiary shall be eligible for the grant of ISOs. In addition, an Employee who owns more than 10% of the total combined voting power of all classes of outstanding stock of the Company or any of its Parents or Subsidiaries shall not be
eligible for the grant of an ISO unless the additional requirements set forth in Code Section 422(c)(5) are satisfied. 
 4.2 Other
Awards. Awards other than ISOs may only be granted to Service Providers. 
 ARTICLE 5. OPTIONS. 

5.1 Stock Option Agreement. Each grant of an Option under the Plan shall be evidenced by a Stock Option Agreement between the Optionee
and the Company. Such Option shall be subject to all applicable terms of the Plan and may be subject to any other terms that are not inconsistent with the Plan. The Stock Option Agreement shall specify whether the Option is intended to be an ISO or
an NSO. The provisions of the various Stock Option Agreements entered into under the Plan need not be identical. 
 5.2 Number of
Shares. Each Stock Option Agreement shall specify the number of Common Shares subject to the Option, which number shall adjust in accordance with Article 9. 

5.3 Exercise Price. Each Stock Option Agreement shall specify the Exercise Price, which shall not be less than 100% of the Fair Market
Value of a Common Share on the date of grant. The preceding sentence shall not apply to an Option that is a Substitute Award granted in a manner that would satisfy the requirements of Code Section 409A and, if applicable, Code
Section 424(a). 
 5.4 Exercisability and Term. Each Stock Option Agreement shall specify the date or event when all or any
installment of the Option is to become vested and/or exercisable. The Stock Option Agreement shall also specify the term of the Option; provided that, except to the extent necessary to comply with applicable foreign law, the term of an Option shall
in no event exceed 10 years from the date of grant. A Stock Option Agreement may provide for accelerated vesting and/or exercisability upon certain specified events and may provide for expiration prior to the end of its term in the event of the
termination of the Optionee’s Service. 
 5.5 Death of Optionee. After an Optionee’s death, any vested and exercisable
Options held by such Optionee may be exercised by his or her beneficiary or beneficiaries. Each Optionee may designate one or more beneficiaries for this purpose by filing the prescribed form with the Company. A beneficiary designation may be
changed by filing the prescribed form with the Company at any time before the Optionee’s death. If no beneficiary was designated or if no designated beneficiary survives the Optionee, then any vested and exercisable Options held by the Optionee
may be exercised by his or her estate. 

  
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 5.6 Modification or Assumption of Options. Within the limitations of the Plan, the
Administrator may modify, reprice, extend or assume outstanding options or may accept the cancellation of outstanding options (whether granted by the Company or by another issuer) in return for the grant of new Options for the same or a different
number of shares and at the same or a different exercise price or in return for the grant of a different type of Award. The foregoing notwithstanding, no modification of an Option shall, without the consent of the Optionee, impair his or her rights
or obligations under such Option. 
 5.7 Buyout Provisions. The Administrator may at any time (a) offer to buy out for a payment
in cash or cash equivalents an Option previously granted or (b) authorize an Optionee to elect to cash out an Option previously granted, in either case at such time and based upon such terms and conditions as the Administrator shall establish.

 5.8 Payment for Option Shares. The entire Exercise Price of Common Shares issued upon exercise of Options shall be payable in cash
or cash equivalents at the time when such Common Shares are purchased. In addition, the Administrator may, in its sole discretion and to the extent permitted by applicable law, accept payment of all or a portion of the Exercise Price through any one
or a combination of the following forms or methods: 
 (a) Subject to any conditions or limitations established by the
Administrator, by surrendering Common Shares that are already owned by the Optionee with a Fair Market Value on the date of surrender equal to the aggregate exercise price of the Common Shares as to which such Option will be exercised; 

(b) By delivering (on a form prescribed by the Company) an irrevocable direction to a securities broker approved by the Company
to sell all or part of the Common Shares being purchased under the Plan and to deliver all or part of the sales proceeds to the Company; 

(c) Subject to such conditions and requirements as the Administrator may impose from time to time, through a net exercise
procedure; or 
 (d) Through any other form or method consistent with applicable laws, regulations and rules. 

ARTICLE 6. STOCK APPRECIATION RIGHTS. 

6.1 SAR Agreement. Each grant of a SAR under the Plan shall be evidenced by a SAR Agreement between the Optionee and the Company. Such
SAR shall be subject to all applicable terms of the Plan and may be subject to any other terms that are not inconsistent with the Plan. The provisions of the various SAR Agreements entered into under the Plan need not be identical. 

  
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 6.2 Number of Shares. Each SAR Agreement shall specify the number of Common Shares to
which the SAR pertains, which number shall adjust in accordance with Article 9. 
 6.3 Exercise Price. Each SAR Agreement shall
specify the Exercise Price, which shall in no event be less than 100% of the Fair Market Value of a Common Share on the date of grant. The preceding sentence shall not apply to a SAR that is a Substitute Award granted in a manner that would satisfy
the requirements of Code Section 409A. 
 6.4 Exercisability and Term. Each SAR Agreement shall specify the date when all or any
installment of the SAR is to become vested and exercisable. The SAR Agreement shall also specify the term of the SAR; provided that except to the extent necessary to comply with applicable foreign law, the term of a SAR shall not exceed 10 years
from the date of grant. A SAR Agreement may provide for accelerated vesting and exercisability upon certain specified events and may provide for expiration prior to the end of its term in the event of the termination of the Optionee’s Service.

 6.5 Exercise of SARs. Upon exercise of a SAR, the Optionee (or any person having the right to exercise the SAR after his or her
death) shall receive from the Company (a) Common Shares, (b) cash or (c) a combination of Common Shares and cash, as the Administrator shall determine. The amount of cash and/or the Fair Market Value of Common Shares received upon
exercise of SARs shall, in the aggregate, not exceed the amount by which the Fair Market Value (on the date of surrender) of the Common Shares subject to the SARs exceeds the Exercise Price. If, on the date when a SAR expires, the Exercise Price is
less than the Fair Market Value on such date but any portion of such SAR has not been exercised or surrendered, then such SAR shall automatically be deemed to be exercised as of such date with respect to such portion. A SAR Agreement may also
provide for an automatic exercise of the SAR on an earlier date. 
 6.6 Death of Optionee. After an Optionee’s death, any vested
and exercisable SARs held by such Optionee may be exercised by his or her beneficiary or beneficiaries. Each Optionee may designate one or more beneficiaries for this purpose by filing the prescribed form with the Company. A beneficiary designation
may be changed by filing the prescribed form with the Company at any time before the Optionee’s death. If no beneficiary was designated or if no designated beneficiary survives the Optionee, then any vested and exercisable SARs held by the
Optionee at the time of his or her death may be exercised by his or her estate. 
 6.7 Modification or Assumption of SARs. Within the
limitations of the Plan, the Administrator may modify, reprice, extend or assume outstanding SARs or may accept the cancellation of outstanding SARs (whether granted by the Company or by another issuer) in return for the grant of new SARs for the
same or a different number of shares and at the same or a different exercise price or in return for the grant of a different type of Award. The foregoing notwithstanding, no modification of a SAR shall, without the consent of the Optionee, impair
his or her rights or obligations under such SAR. 
 ARTICLE 7. RESTRICTED SHARES. 

7.1 Restricted Stock Agreement. Each grant of Restricted Shares under the Plan shall be evidenced by a Restricted Stock Agreement
between the recipient and the Company. 

  
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Such Restricted Shares shall be subject to all applicable terms of the Plan and may be subject to any other terms that are not inconsistent with the Plan. The provisions of the various Restricted
Stock Agreements entered into under the Plan need not be identical. 
 7.2 Payment for Awards. Restricted Shares may be sold or
awarded under the Plan for such consideration as the Administrator may determine, including (without limitation) cash, cash equivalents, property, cancellation of other equity awards, full-recourse promissory notes, past services and future
services, and such other methods of payment as are permitted by applicable law. 
 7.3 Vesting Conditions. Each Award of Restricted
Shares may or may not be subject to vesting and/or other conditions as the Administrator may determine. Vesting shall occur, in full or in installments, upon satisfaction of the conditions specified in the Restricted Stock Agreement. Such
conditions, at the Administrator’s discretion, may include one or more Performance Goals. A Restricted Stock Agreement may provide for accelerated vesting upon certain specified events. 

7.4 Voting and Dividend Rights. The holders of Restricted Shares awarded under the Plan shall have the same voting, dividend and other
rights as the Company’s other stockholders, unless the Administrator otherwise provides. A Restricted Stock Agreement, however, may require that any cash dividends paid on Restricted Shares (a) be accumulated and paid when such Restricted
Shares vest, or (b) be invested in additional Restricted Shares. Such additional Restricted Shares shall be subject to the same conditions and restrictions as the shares subject to the Stock Award with respect to which the dividends were paid.
In addition, unless the Administrator provides otherwise, if any dividends or other distributions are paid in Common Shares, such Common Shares shall be subject to the same restrictions on transferability and forfeitability as the Restricted Shares
with respect to which they were paid. 
 ARTICLE 8. STOCK UNITS. 

8.1 Stock Unit Agreement. Each grant of Stock Units under the Plan shall be evidenced by a Stock Unit Agreement between the recipient
and the Company. Such Stock Units shall be subject to all applicable terms of the Plan and may be subject to any other terms that are not inconsistent with the Plan. The provisions of the various Stock Unit Agreements entered into under the Plan
need not be identical. 
 8.2 Payment for Awards. To the extent that an Award is granted in the form of Stock Units, no cash
consideration shall be required of the Award recipients. 
 8.3 Vesting Conditions. Each Award of Stock Units may or may not be
subject to vesting, as determined by the Administrator. Vesting shall occur, in full or in installments, upon satisfaction of the conditions specified in the Stock Unit Agreement. Such conditions, at the Administrator’s discretion, may include
one or more Performance Goals. A Stock Unit Agreement may provide for accelerated vesting upon certain specified events. 
 8.4 Voting
and Dividend Rights. The holders of Stock Units shall have no voting rights. Prior to settlement or forfeiture, Stock Units awarded under the Plan may, at the Administrator’s discretion, provide for a right to dividend equivalents. Such
right entitles the 

  
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holder to be credited with an amount equal to all cash dividends paid on one Common Share while the Stock Unit is outstanding. Dividend equivalents may be converted into additional Stock Units.
Settlement of dividend equivalents may be made in the form of cash, in the form of Common Shares, or in a combination of both. Prior to distribution, any dividend equivalents shall be subject to the same conditions and restrictions as the Stock
Units to which they attach. 
 8.5 Form and Time of Settlement of Stock Units. Settlement of vested Stock Units may be made in the
form of (a) cash, (b) Common Shares or (c) any combination of both, as determined by the Administrator. The actual number of Stock Units eligible for settlement may be larger or smaller than the number included in the original Award,
based on predetermined performance factors, including Performance Goals. Methods of converting Stock Units into cash may include (without limitation) a method based on the average Fair Market Value of Common Shares over a series of trading days.
Vested Stock Units shall be settled in such manner and at such time(s) as specified in the Stock Unit Agreement. Until an Award of Stock Units is settled, the number of such Stock Units shall be subject to adjustment pursuant to Article 9. 

8.6 Death of Recipient. Any Stock Units that become payable after the recipient’s death shall be distributed to the
recipient’s beneficiary or beneficiaries. Each recipient of Stock Units under the Plan may designate one or more beneficiaries for this purpose by filing the prescribed form with the Company. A beneficiary designation may be changed by filing
the prescribed form with the Company at any time before the Award recipient’s death. If no beneficiary was designated or if no designated beneficiary survives the Award recipient, then any Stock Units that become payable after the
recipient’s death shall be distributed to the recipient’s estate. 
 8.7 Modification or Assumption of Stock Units. Within
the limitations of the Plan, the Administrator may modify or assume outstanding stock units or may accept the cancellation of outstanding stock units (whether granted by the Company or by another issuer) in return for the grant of new Stock Units
for the same or a different number of shares or in return for the grant of a different type of Award. The foregoing notwithstanding, no modification of a Stock Unit shall, without the consent of the Participant, impair his or her rights or
obligations under such Stock Unit. 
 8.8 Creditors’ Rights. A holder of Stock Units shall have no rights other than those of a
general creditor of the Company. Stock Units represent an unfunded and unsecured obligation of the Company, subject to the terms and conditions of the applicable Stock Unit Agreement. 

ARTICLE 9. ADJUSTMENTS; DISSOLUTIONS AND LIQUIDATIONS; CORPORATE TRANSACTIONS. 

9.1 Adjustments. In the event of a subdivision of the outstanding Common Shares, a declaration of a dividend payable in Common Shares or
a combination or consolidation of the outstanding Common Shares (by reclassification or otherwise) into a lesser number of Common Shares, corresponding proportionate adjustments shall automatically be made in each of the following: 

(a) The number and kind of shares available for issuance under Article 3, including the numerical share limits in Articles
3.1, 3.2 and 3.5; 

  
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 (b) The number and kind of shares covered by each outstanding Option, SAR and
Stock Unit; and 
 (c) The Exercise Price applicable to each outstanding Option and SAR, and the repurchase price, if any,
applicable to Restricted Shares. 
 In the event of a declaration of an extraordinary dividend payable in a form other than Common Shares in an amount that
has a material effect on the price of Common Shares, a recapitalization, a spin-off or a similar occurrence, the Administrator shall make such adjustments as it, in its sole discretion, deems appropriate in one or more of the foregoing. Any
adjustment in the number of and kind of shares subject to an Award under this Article 9.1 shall be rounded down to the nearest whole share, although the Administrator in its sole discretion may make a cash payment in lieu of a fractional share.
Except as provided in this Article 9, a Participant shall have no rights by reason of any issuance by the Company of stock of any class or securities convertible into stock of any class, any subdivision or consolidation of shares of stock of
any class, the payment of any stock dividend or any other increase or decrease in the number of shares of stock of any class. 
 9.2
Dissolution or Liquidation. To the extent not previously exercised or settled, Options, SARs and Stock Units shall terminate immediately prior to the dissolution or liquidation of the Company. 

9.3 Corporate Transactions. In the event that the Company is a party to a merger, consolidation, or a Change in Control (other than one
described in Article 14.6(d)), all Common Shares acquired under the Plan and all Awards outstanding on the effective date of the transaction shall be treated in the manner described in the definitive transaction agreement (or, in the event the
transaction does not entail a definitive agreement to which the Company is party, in the manner determined by the Administrator, with such determination having final and binding effect on all parties), which agreement or determination need not treat
all Awards (or portions thereof) in an identical manner. Unless an Award Agreement provides otherwise, the treatment specified in the transaction agreement or by the Administrator shall include (without limitation) one or more of the following with
respect to each outstanding Award: 
 (a) The continuation of such outstanding Awards by the Company (if the Company is the
surviving entity); 
 (b) The assumption of such outstanding Awards by the surviving entity or its parent, provided that the
assumption of an Option or a SAR shall comply with applicable tax requirements; 
 (c) The substitution by the surviving
entity or its parent of an equivalent award for outstanding Awards (including, but not limited to, an award to acquire the same consideration paid to the holders of Common Shares in the transaction), provided that the substitution of an Option or a
SAR shall comply with applicable tax requirements; 

  
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 (d) The cancellation of outstanding Options and SARs without payment of any
consideration. The Optionees shall be able to exercise such Options and SARs (to the extent the Options and SARs are vested or become vested as of the effective date of the transaction) during a period of not less than five full business days
preceding the closing date of the transaction, unless (i) a shorter period is required to permit a timely closing of the transaction and (ii) such shorter period still offers the Optionees a reasonable opportunity to exercise such Options
and SARs. Any exercise of such Options and SARs during such period may be contingent on the closing of the transaction; 

(e) Full exercisability of outstanding Options and SARs and full vesting of the Common Shares subject to Options and SARs,
followed by cancellation of such Options and SARs. The full exercisability of such Options and SARs and full vesting of such Common Shares may be contingent on the closing of the transaction. The Optionees shall be able to exercise such Options and
SARs during a period of not less than five full business days preceding the closing date of such merger or consolidation, unless (i) a shorter period is required to permit a timely closing of such merger or consolidation and (ii) such
shorter period still offers the Optionees a reasonable opportunity to exercise such Options and SARs. Any exercise of such Options and SARs during such period may be contingent on the closing of such merger or consolidation; 

(f) The cancellation of the Options and SARs and a payment to the Optionee with respect to each Share subject to the portion of
the Award that is vested as of the transaction date equal to the excess of (A) the value, as determined by the Administrator in its absolute discretion, of the property (including cash) received by the holder of a Common Share as a result
of the transaction, over (B) the per-share Exercise Price of the Option or SAR (such excess, the “Spread”). Such payment shall be made in the form of cash, cash equivalents, or securities of the surviving entity or its
parent having a value equal to the Spread. In addition, any escrow, holdback, earn-out or similar provisions in the transaction agreement may apply to such payment to the same extent and in the same manner as such provisions apply to the
holders of Common Shares, but only to the extent the application of such provisions does not adversely affect the status of the Option or SAR as exempt from Code Section 409A. If the Spread applicable to an Option or SAR is zero
or a negative number, then the Option or SAR may be cancelled without making a payment to the Optionee; 
 (g) The
cancellation of outstanding Stock Units and a payment to the holder thereof with respect to each Common Share subject to the Stock Unit (whether or not such Stock Unit is then vested) equal to the value, as determined by the Administrator in its
absolute discretion, of the property (including cash) received by the holder of a Common Share as a result of the transaction (the “Transaction Value”). Such payment shall be made in the form of cash, cash equivalents, or securities
of the surviving entity or its parent having a value equal to the Transaction Value. In addition, such payment may be subject to vesting based on the Participant’s continuing Service, provided that the vesting schedule shall not be less
favorable to the Participant than the schedule under which such Stock Units would have vested, and if required under applicable tax rules, such payment may be deferred until the settlement date specified in the Stock Unit Agreement. In addition, any
escrow, holdback, earn-out or similar provisions in the transaction agreement may apply to such payment to the 

  
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same extent and in the same manner as such provisions apply to the holders of Common Shares. In the event that a Stock Unit is subject to Code Section 409A, the payment described in this
clause (g) shall be made on the settlement date specified in the applicable Stock Unit Agreement, provided that settlement may be accelerated in accordance with Treasury Regulation Section 1.409A-3(j)(4); or 

(h) The assignment of any reacquisition or repurchase rights held by the Company in respect of an Award of Restricted Shares to
the surviving entity or its parent, with corresponding proportionate adjustments made to the price per share to be paid upon exercise of any such reacquisition or repurchase rights. 

For avoidance of doubt, the Administrator shall have the discretion, exercisable either at the time an Award is granted or at any time while the Award remains
outstanding, to provide for the acceleration of vesting upon the occurrence of a Change in Control, whether or not the Award is to be assumed or replaced in the transaction, or in connection with a termination of the Participant’s Service
following a transaction. 
 Any action taken under this Article 9.3 shall either preserve an Award’s status as exempt from Code Section 409A or
comply with Code Section 409A. 
 ARTICLE 10. OTHER AWARDS. 

10.1 Performance Cash Awards. A Performance Cash Award is a cash award that may be granted subject to the attainment of specified
Performance Goals during a Performance Period. A Performance Cash Award may also require the completion of a specified period of continuous Service. The length of the Performance Period, the Performance Goals to be attained during the Performance
Period, and the degree to which the Performance Goals have been attained shall be determined conclusively by the Administrator. Each Performance Cash Award shall be set forth in a written agreement or in a resolution duly adopted by the
Administrator which shall contain provisions determined by the Administrator and not inconsistent with the Plan. The terms of various Performance Cash Awards need not be identical. 

10.2 Awards Under Other Plans. The Company may grant awards under other plans or programs. Such awards may be settled in the form of
Common Shares issued under this Plan. Such Common Shares shall be treated for all purposes under the Plan like Common Shares issued in settlement of Stock Units and shall, when issued, reduce the number of Common Shares available under
Article 3. 
 ARTICLE 11. LIMITATION ON RIGHTS. 

11.1 Retention Rights. Neither the Plan nor any Award granted under the Plan shall be deemed to give any individual a right to remain a
Service Provider. The Company and its Parents, Subsidiaries and Affiliates reserve the right to terminate the Service of any Service Provider at any time, with or without cause, subject to applicable laws, the Company’s certificate of
incorporation and by-laws and a written employment agreement (if any). 
 11.2 Stockholders’ Rights. Except as set forth in
Article 7.4 or 8.4 above, a Participant shall have no dividend rights, voting rights or other rights as a stockholder with 

  
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respect to any Common Shares covered by his or her Award prior to the time when a stock certificate for such Common Shares is issued or, if applicable, the time when he or she becomes entitled to
receive such Common Shares by filing any required notice of exercise and paying any required Exercise Price. No adjustment shall be made for cash dividends or other rights for which the record date is prior to such time, except as expressly provided
in the Plan. 
 11.3 Regulatory Requirements. Any other provision of the Plan notwithstanding, the obligation of the Company to issue
Common Shares under the Plan shall be subject to all applicable laws, rules and regulations and such approval by any regulatory body as may be required. The Company reserves the right to restrict, in whole or in part, the delivery of Common Shares
pursuant to any Award prior to the satisfaction of all legal requirements relating to the issuance of such Common Shares, to their registration, qualification or listing or to an exemption from registration, qualification or listing. The inability
of the Company to obtain authority from any regulatory body having jurisdiction, which authority is deemed necessary by the Company’s counsel to be necessary to the lawful issuance and sale of any Common Shares hereunder, will relieve the
Company of any liability in respect of the failure to issue or sell such Common Shares as to which such requisite authority will not have been obtained. 

11.4 Transferability of Awards. The Administrator may, in its sole discretion, permit transfer of an Award in a manner consistent with
applicable law. Unless otherwise determined by the Administrator, Awards shall be transferable by a Participant only by (a) beneficiary designation, (b) a will or (c) the laws of descent and distribution. An ISO may only be
transferred by will or by the laws of descent and distribution and may be exercised during the lifetime of the Optionee only by the Optionee or by the Optionee’s guardian or legal representative. 

11.5 Other Conditions and Restrictions on Common Shares. Any Common Shares issued under the Plan shall be subject to such forfeiture
conditions, rights of repurchase, rights of first refusal, other transfer restrictions and such other terms and conditions as the Administrator may determine. Such conditions and restrictions shall be set forth in the applicable Award Agreement and
shall apply in addition to any restrictions that may apply to holders of Common Shares generally. In addition, Common Shares issued under the Plan shall be subject to such conditions and restrictions imposed either by applicable law or by Company
policy, as adopted from time to time, designed to ensure compliance with applicable law or laws with which the Company determines in its sole discretion to comply including in order to maintain any statutory, regulatory or tax advantage. 

ARTICLE 12. TAXES. 
 12.1 General.
As a condition to an Award under the Plan, a Participant or his or her successor shall make arrangements satisfactory to the Company for the satisfaction of any federal, state, local or foreign withholding tax obligations that arise in connection
with any Award granted under the Plan. The Company shall not be required to issue any Common Shares or make any cash payment under the Plan until such obligations are satisfied. 

12.2 Share Withholding. To the extent that applicable law subjects a Participant to tax withholding obligations, the Administrator may
permit such Participant to satisfy all or part 

  
 12 

 
of such obligations by having the Company withhold all or a portion of any Common Shares that otherwise would be issued to him or her or by surrendering all or a portion of any Common Shares that
he or she previously acquired. Such Common Shares shall be valued at their Fair Market Value on the date when they are withheld or surrendered. Any payment of taxes by assigning Common Shares to the Company may be subject to restrictions including
any restrictions required by SEC, accounting or other rules. 
 12.3 Section 162(m) Matters. The Administrator, in its sole
discretion, may determine whether an Award is intended to qualify as “performance-based compensation” within the meaning of Code Section 162(m). The Administrator may grant Awards that are based on Performance Goals but that are not
intended to qualify as performance-based compensation. With respect to any Award that is intended to qualify as performance-based compensation, the Administrator shall designate the Performance Goal(s) applicable to, and the formula for calculating
the amount payable under, an Award within 90 days following commencement of the applicable Performance Period (or such earlier time as may be required under Code Section 162(m)), and in any event at a time when achievement of the applicable
Performance Goal(s) remains substantially uncertain. Prior to the payment of any Award that is intended to constitute performance-based compensation, the Administrator shall certify in writing whether and the extent to which the Performance Goal(s)
were achieved for such Performance Period. The Administrator shall have the right to reduce or eliminate (but not to increase) the amount payable under an Award that is intended to constitute performance-based compensation. 

12.4 Section 409A Matters. Except as otherwise expressly set forth in an Award Agreement, it is intended that Awards granted under
the Plan either be exempt from, or comply with, the requirements of Code Section 409A. To the extent an Award is subject to Code Section 409A (a “409A Award”), the terms of the Plan, the Award and any written agreement
governing the Award shall be interpreted to comply with the requirements of Code Section 409A so that the Award is not subject to additional tax or interest under Code Section 409A, unless the Administrator expressly provides otherwise. A
409A Award shall be subject to such additional rules and requirements as specified by the Administrator from time to time in order for it to comply with the requirements of Code Section 409A. In this regard, if any amount under a 409A Award is
payable upon a “separation from service” to an individual who is considered a “specified employee” (as each term is defined under Code Section 409A), then no such payment shall be made prior to the date that is the earlier
of (i) six months and one day after the Participant’s separation from service or (ii) the Participant’s death, but only to the extent such delay is necessary to prevent such payment from being subject to Code
Section 409A(a)(1). 
 12.5 Limitation on Liability. Neither the Company nor any person serving as Administrator shall have any
liability to a Participant in the event an Award held by the Participant fails to achieve its intended characterization under applicable tax law. 

ARTICLE 13. FUTURE OF THE PLAN. 
 13.1
Term of the Plan. The Plan, as set forth herein, shall become effective on the Registration Date. The Plan shall remain in effect until the earlier of (a) the date when the Plan is terminated under Article 13.2 or (b) the 10th
anniversary of the date when the Board adopted the Plan. 

  
 13 

 13.2 Amendment or Termination. The Board may, at any time and for any reason, amend or
terminate the Plan. No Awards shall be granted under the Plan after the termination thereof. The termination of the Plan, or any amendment thereof, shall not affect any Award previously granted under the Plan. 

13.3 Stockholder Approval. An amendment of the Plan shall be subject to the approval of the Company’s stockholders only to the
extent required by applicable laws, regulations or rules. 
 ARTICLE 14. DEFINITIONS. 

14.1 “Administrator” means the Board or any Committee administering the Plan in accordance with Article 2. 

14.2 “Affiliate” means any entity other than a Subsidiary, if the Company and/or one or more Subsidiaries own not less than
50% of such entity. 
 14.3 “Award” means any award granted under the Plan, including as an Option, a SAR, a Restricted
Share, a Stock Unit or a Performance Cash Award. 
 14.4 “Award Agreement” means a Stock Option Agreement, an SAR
Agreement, a Restricted Stock Agreement, a Stock Unit Agreement or such other agreement evidencing an Award granted under the Plan. 
 14.5
“Board” means the Company’s Board of Directors, as constituted from time to time. 
 14.6 “Change in
Control” means: 
 (a) Any “person” (as such term is used in Sections 13(d) and 14(d) of the Exchange Act)
becomes the “beneficial owner” (as defined in Rule 13d-3 of the Exchange Act), directly or indirectly, of securities of the Company representing more than fifty percent (50%) of the total voting power represented by the Company’s
then-outstanding voting securities; 
 (b) The consummation of the sale or disposition by the Company of all or substantially
all of the Company’s assets; 
 (c) The consummation of a merger or consolidation of the Company with or into any other
entity, other than a merger or consolidation which would result in the voting securities of the Company outstanding immediately prior thereto continuing to represent (either by remaining outstanding or by being converted into voting securities of
the surviving entity or its parent) more than fifty percent (50%) of the total voting power represented by the voting securities of the Company or such surviving entity or its parent outstanding immediately after such merger or consolidation;
or 

  
 14 

 (d) Individuals who are members of the Board (the “Incumbent
Board”) cease for any reason to constitute at least a majority of the members of the Board over a period of 12 months; provided, however, that if the appointment or election (or nomination for election) of any new Board member was approved
or recommended by a majority vote of the members of the Incumbent Board then still in office, such new member shall, for purposes of this Plan, be considered as a member of the Incumbent Board. 

A transaction shall not constitute a Change in Control if its sole purpose is to change the state of the Company’s incorporation or to create a holding
company that will be owned in substantially the same proportions by the persons who held the Company’s securities immediately before such transaction. In addition, if a Change in Control constitutes a payment event with respect to any Award
which provides for a deferral of compensation and is subject to Code Section 409A, then notwithstanding anything to the contrary in the Plan or applicable Award Agreement the transaction with respect to such Award must also constitute a
“change in control event” as defined in Treasury Regulation Section 1.409A-3(i)(5) to the extent required by Code Section 409A. 

14.7 “Code” means the Internal Revenue Code of 1986, as amended. 

14.8 “Committee” means a committee of one or more members of the Board, or of other individuals satisfying applicable laws,
appointed by the Board to administer the Plan. 
 14.9 “Common Share” means one share of the common stock of the Company.

 14.10 “Company” means Histogenics Corporation, a Delaware corporation. 

14.11 “Consultant” means a consultant or adviser who provides bona fide services to the Company, a Parent, a
Subsidiary or an Affiliate as an independent contractor and who qualifies as a consultant or advisor under Instruction A.1.(a)(1) of Form S-8 under the Securities Act of 1933, as amended. 

14.12 “Employee” means a common-law employee of the Company, a Parent, a Subsidiary
or an Affiliate. 
 14.13 “Exchange Act” means the Securities Exchange Act of 1934, as amended. 

14.14 “Exercise Price,” in the case of an Option, means the amount for which one Common Share may be purchased upon exercise
of such Option, as specified in the applicable Stock Option Agreement. “Exercise Price,” in the case of a SAR, means an amount, as specified in the applicable SAR Agreement, which is subtracted from the Fair Market Value of one Common
Share in determining the amount payable upon exercise of such SAR. 
 14.15 “Fair Market Value” means the closing price of
a Common Share on any established stock exchange or a national market system on the applicable date or, if the applicable date is not a trading day, on the last trading day prior to the applicable date, as reported in a source that the Administrator
deems reliable. If Common Shares are no longer traded on an established stock exchange or a national market system, the Fair Market Value shall be determined by the Administrator in good faith on such basis as it deems appropriate. The
Administrator’s determination shall be conclusive and binding on all persons. 

  
 15 

 14.16 “ISO” means an incentive stock option described in Code
Section 422(b). 
 14.17 “NSO” means a stock option not described in Code Sections 422 or 423. 

14.18 “Option” means an ISO or NSO granted under the Plan and entitling the holder to purchase Common Shares. 

14.19 “Optionee” means an individual or estate holding an Option or SAR. 

14.20 “Outside Director” means a member of the Board who is not an Employee. 

14.21 “Parent” means any corporation (other than the Company) in an unbroken chain of corporations ending with the Company,
if each of the corporations other than the Company owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation that attains the status of a Parent on a
date after the adoption of the Plan shall be considered a Parent commencing as of such date. 
 14.22 “Participant” means
an individual or estate holding an Award. 
 14.23 “Performance Cash Award” means an award of cash granted under Article
10.1 of the Plan. 
 14.24 “Performance Goal” means a goal established by the Administrator for the applicable Performance
Period based on one or more of the performance criteria set forth in Appendix A. Depending on the performance criteria used, a Performance Goal may be expressed in terms of overall Company performance or the performance of a business unit,
division, Subsidiary, Affiliate or an individual. A Performance Goal may be measured either in absolute terms or relative to the performance of one or more comparable companies or one or more relevant indices. The Administrator may adjust the
results under any performance criterion to exclude any of the following events that occurs during a Performance Period: (a) asset write-downs, (b) litigation, claims, judgments or settlements, (c) the effect of changes in tax laws,
accounting principles or other laws or provisions affecting reported results, (d) accruals for reorganization and restructuring programs, (e) extraordinary, unusual or non-recurring items, (f) exchange rate effects for non-U.S. dollar
denominated net sales and operating earnings, or (g) statutory adjustments to corporate tax rates; provided, however, that if an Award is intended to qualify as “performance-based compensation” within the meaning of Code
Section 162(m), such adjustment(s) shall only be made to the extent consistent with Code Section 162(m). 
 14.25 “Performance
Period” means a period of time selected by the Administrator over which the attainment of one or more Performance Goals will be measured for the purpose of determining a Participant’s right to a Performance Cash Award or an Award of
Restricted Shares or Stock Units that vests based on the achievement of Performance Goals. Performance Periods may be of varying and overlapping duration, at the discretion of the Administrator. 

  
 16 

 14.26 “Plan” means this REGENXBIO Inc. 2015 Equity Incentive Plan, as amended
from time to time. 
 14.27 “Predecessor Plan” means the Company’s 2014 Stock Plan, as amended. 

14.28 “Registration Date” means the effective date of the registration statement filed by the Company with the Securities and
Exchange Commission pursuant to Form S-1. 
 14.29 “Restricted Share” means a Common Share awarded under the Plan. 

14.30 “Restricted Stock Agreement” means the agreement between the Company and the recipient of a Restricted Share that
contains the terms, conditions and restrictions pertaining to such Restricted Share. 
 14.31 “SAR” means a stock
appreciation right granted under the Plan. 
 14.32 “SAR Agreement” means the agreement between the Company and an Optionee
that contains the terms, conditions and restrictions pertaining to his or her SAR. 
 14.33 “Service” means service as an
Employee, Outside Director or Consultant. 
 14.34 “Service Provider” means any individual who is an Employee, Outside
Director or Consultant. 
 14.35 “Stock Award” means any award of an Option, a SAR, a Restricted Share or a Stock Unit
under the Plan. 
 14.36 “Stock Option Agreement” means the agreement between the Company and an Optionee that contains the
terms, conditions and restrictions pertaining to his or her Option. 
 14.37 “Stock Unit” means a bookkeeping entry
representing the equivalent of one Common Share, as awarded under the Plan. 
 14.38 “Stock Unit Agreement” means the
agreement between the Company and the recipient of a Stock Unit that contains the terms, conditions and restrictions pertaining to such Stock Unit. 

14.39 “Subsidiary” means any corporation (other than the Company) in an unbroken chain of corporations beginning with the
Company, if each of the corporations other than the last corporation in the unbroken chain owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation
that attains the status of a Subsidiary on a date after the adoption of the Plan shall be considered a Subsidiary commencing as of such date 

  
 17 

 14.40 “Substitute Awards” means Awards or Common Shares issued by the Company in
assumption of, or substitution or exchange for, Awards previously granted, or the right or obligation to make future awards, in each case by a corporation acquired by the Company or any Affiliate or with which the Company or any Affiliate combines
to the extent permitted by NASDAQ Marketplace Rule 5635 or any successor thereto. 

  
 18 

 APPENDIX A 

PERFORMANCE CRITERIA 

The Administrator may establish Performance Goals derived from one or more of the following criteria when it makes Awards of Restricted Shares or Stock Units
that vest entirely or in part on the basis of performance or when it makes Performance Cash Awards: 
  

			
		
	 •    Earnings (before or after taxes)
	  	 •    Sales or revenue (using a measure thereof that complies with Section 162(m))

		
	 •    Earnings per share
	  	 •    Expense or cost reduction

		
	 •    Earnings before interest, taxes and depreciation
	  	 •    Working capital

		
	 •    Earnings before interest, taxes, depreciation and amortization
	  	 •    Economic value added (or an equivalent metric)

		
	 •    Total stockholder return
	  	 •    Market share

		
	 •    Return on equity or average stockholders’ equity
	  	 •    Cash measures including cash flow and cash balance

		
	 •    Return on assets, investment or capital employed
	  	 •    Operating cash flow

		
	 •    Operating income
	  	 •    Cash flow per share

		
	 •    Gross margin
	  	 •    Share price

		
	 •    Operating margin
	  	 •    Debt reduction

		
	 •    Net operating income
	  	 •    Customer satisfaction

		
	 •    Net operating income after tax
	  	 •    Stockholders’ equity

		
	 •    Return on operating revenue
	  	 •    Contract awards or backlog

		
	 •    Objective corporate or individual strategic goals
	  	 •    Objective individual performance goals

	
	 •    To the extent that an Award is not intended to comply with Code Section 162(m), other
measures of performance selected by the Administrator

  
 19EX-10.4

 Exhibit 10.4 
  

 
 REGENXBIO INC. 

2015 EMPLOYEE STOCK PURCHASE PLAN 

(AS ADOPTED ON JUNE 17, 2015) 

 REGENXBIO INC. 

2015 EMPLOYEE STOCK PURCHASE PLAN 

SECTION 1. PURPOSE OF THE PLAN. 
 The
Board adopted the Plan effective as of the IPO Date. The purpose of the Plan is to provide Eligible Employees with an opportunity to increase their proprietary interest in the success of the Company by purchasing Stock from the Company on favorable
terms and to pay for such purchases through payroll deductions or other approved contributions. 
 SECTION 2. ADMINISTRATION OF THE PLAN. 

(a) Committee Composition. The Committee shall administer the Plan. The Committee shall consist exclusively of one or more members of
the Board, who shall be appointed by the Board. 
 (b) Committee Responsibilities. The Committee shall interpret the Plan and make
all other policy decisions relating to the operation of the Plan. The Committee may adopt such rules, guidelines and forms as it deems appropriate to implement the Plan. The Committee’s determinations under the Plan shall be final and binding
on all persons. 
 SECTION 3. STOCK OFFERED UNDER THE PLAN. 

(a) Authorized Shares. The number of shares of Stock available for purchase under the Plan shall be 254,000 of the Company’s Stock
(subject to adjustment pursuant to Subsection (c) below), plus the additional shares described in Subsection (b) below. Shares of Stock issued pursuant to the Plan may be authorized but unissued shares or treasury shares. 

(b) Annual Increase in Shares. As of the first business day of each fiscal year of the Company during the term of the Plan, commencing
on January 1, 2016, the aggregate number of shares of Stock that may be issued under the Plan shall automatically increase by a number equal to the least of (i) 1% of the total number of shares of Stock actually issued and outstanding on
the last business day of the prior fiscal year (excluding any rights to purchase shares of common shares that may be outstanding, such as options or warrants), or (ii) a number of shares of Stock determined by the Board. 

(c) Anti-Dilution Adjustments. In the event that any dividend or other distribution (whether in the form of cash, stock or other
securities or other property), recapitalization, stock split, reverse stock split, reorganization, merger, consolidation, split-up, spin-off, combination, repurchase, or exchange of Stock or other securities of the Company, or other similar change
in the corporate structure of the Company affecting the Stock and effected without receipt or payment of consideration by the Company occurs, then in order to prevent dilution or enlargement of the benefits or potential benefits intended to be made
available under 

 
the Plan, there will be a proportionate adjustment of the number and class of Stock that may be delivered under the Plan, the Purchase Price per share and the number of shares of Stock covered by
each option under the Plan which has not yet been exercised, and the numerical limits of Sections 3(a), 3(b)(ii) and 9(c). 
 (d)
Reorganizations. Any other provision of the Plan notwithstanding, in the event of a Corporate Reorganization, the Plan may be continued or assumed by the surviving corporation or its parent corporation. If such acquirer refuses to continue or
assume the Plan, then, immediately prior to the effective time of the Corporate Reorganization, any Offering Period then in progress shall terminate, and, a new Purchase Date for each such Offering Period will be set, immediately prior to the
effective time of the Corporate Reorganization. In the event a new Purchase Date is set under this Section 3(d), Participants will be given notice of the new Purchase Date. The Plan shall in no event be construed to restrict in any way the
Company’s right to undertake a dissolution, liquidation, merger, consolidation or other reorganization. 
 SECTION 4. ENROLLMENT AND PARTICIPATION.

 (a) Offering Periods and Purchase Periods. 

(i) Base Offering Periods. The Committee may establish Offering Periods of such frequency and duration as it may from
time to time determine as appropriate (the “Base Offering Periods”); provided that a Base Offering Period shall in no event be longer than 27 months (or such other period as may be imposed under applicable tax law). The Base
Offering Periods are intended to qualify under Code Section 423. Unless changed by the Committee, the Plan shall operate such that two Base Offering Periods, each of six months’ duration and each including a single six-month Purchase
Period, will commence on July 1 and January 1 of each year, except that the first Base Offering Period will commence on the IPO Date and shall end on or about December 31, 2015. The Committee may determine that the first Base Offering
Period applicable to the Eligible Employees of a new Participating Company shall commence on any later date specified by the Committee. 

(ii) Additional Offering Periods. At the discretion of the Committee, additional Offering Periods (the “Additional
Offering Periods”) may be conducted under the Plan or, if necessary or advisable, in the sole discretion of the Committee, under a separate sub-plan or sub-plans permitting grants to Eligible Employees of certain Participating Companies (each,
a “Sub-Plan”). Such Additional Offering Periods may, but need not, qualify under Code Section 423, and may be designed to achieve desired tax or other objectives in particular locations outside the United States of America or to
comply with local laws applicable to offerings in such foreign jurisdictions. The Committee shall determine the commencement and duration of each Additional Offering Period, and Additional Offering Periods may be consecutive or overlapping. The
other terms and conditions of each Additional Offering Period shall be those set forth in this Plan document or in the applicable Sub-Plan, with such changes or additional features as the Committee determines necessary to comply with local law. Each
Sub-Plan shall be considered a separate plan from the Plan (the “Statutory Plan”). The total number of Shares authorized to be issued under the Plan as provided in Section 3 above applies in the aggregate to both the Statutory Plan
and any Sub-Plan. Unless otherwise superseded by the terms of such Sub-Plan, the provisions of this Plan document shall govern the operation of such Sub-Plan. 

  
 2 

 (iii) Separate Offerings. Each Base Offering Period and Additional
Offering Period conducted under the Plan or any Sub-Plan is intended to constitute a separate “offering” for purposes of Code Section 423. 

(iv) Equal Rights and Privileges. To the extent an Offering Period is intended to qualify under Code Section 423,
all participants in such Offering Period shall have the same rights and privileges with respect to their participation in such Offering Period in accordance with Code Section 423 and the regulations thereunder except for differences that may be
mandated by local law and are consistent with the requirements of Code Section 423(b)(5). 
 (b) Enrollment At IPO. Each individual
who, on the IPO Date, qualifies as an Eligible Employee shall automatically become a Participant on such day, and shall be considered to have been granted an option to participate in the first Offering Period under the Plan at the maximum applicable
participation rate. Each Participant who was automatically enrolled on the IPO Date shall file the prescribed enrollment form with the Company. The enrollment form shall be filed at the prescribed location by a date specified by the Company, but in
no event later than 30 days after the IPO Date. If a Participant who was automatically enrolled on the IPO Date fails to file such form in a timely manner, then such Participant shall be deemed to have withdrawn from the Plan under
Section 6(a). A former Participant who is deemed to have withdrawn from the Plan shall not be a Participant until he or she re-enrolls in the Plan under Subsection (c) below. Re-enrollment may be effective only at the commencement of an
Offering Period. 
 (c) Enrollment After IPO. Any individual who qualifies as an Eligible Employee on the first day of any Offering
Period other than the first Offering Period may elect to become a Participant on such day by filing the prescribed enrollment form with the Company. The enrollment form shall be filed at the prescribed location at least 10 business days (or such
other period as the Committee or its designee may designate) prior to such day. 
 (d) Duration of Participation. Once enrolled in
the Plan, a Participant shall continue to participate in the Plan until he or she: 
 (i) Reaches the end of the Offering
Period or Purchase Period, as applicable, in which his or her employee contributions were discontinued under Section 5(c) or 9(b); 

(ii) Is deemed to withdraw from the Plan under Subsection (b) above; 

(iii) Withdraws from the Plan under Section 6(a); or 

(iv) Ceases to be an Eligible Employee. 

  
 3 

 A Participant whose employee contributions were discontinued automatically under Section 9(b) shall
automatically resume participation at the beginning of the earliest Offering Period ending in a later calendar year, if he or she then is an Eligible Employee. In all other cases, a former Participant may again become a Participant, if he or she
then is an Eligible Employee, by following the procedure described in Subsection (b) above. 
 SECTION 5. EMPLOYEE CONTRIBUTIONS. 

(a) Commencement of Payroll Deductions. A Participant may purchase shares of Stock under the Plan by means of payroll deductions or
other approved contributions in form and substance satisfactory to the Committee. Payroll deductions or other approved contributions shall commence as soon as reasonably practicable after the Company has received the prescribed enrollment form. In
jurisdictions where payroll deductions are not permitted under local law, Participants may purchase shares of Stock by making contributions in the form that is acceptable and approved by the Committee. 

(b) Amount of Payroll Deductions. An Eligible Employee shall designate on the prescribed enrollment form the portion of his or her
Compensation that he or she elects to have withheld for the purchase of Stock. Such portion shall be a whole percentage of the Eligible Employee’s Compensation, but not less than 1% nor more than 15%. 

(c) Reducing Withholding Rate or Discontinuing Payroll Deductions. If a Participant wishes to reduce his or her rate of payroll
withholding, such Participant may do so by filing a new enrollment form with the Company at the prescribed location at any time. The new withholding rate shall be effective as soon as reasonably practicable after the Company has received such form.
The new withholding rate may be 0% or any whole percentage of the Participant’s Compensation, but not more than his or her old withholding rate. No Participant shall make more than two elections under this Subsection (c) during any
Purchase Period. (In addition, employee contributions may be discontinued automatically pursuant to Section 9(b).) 
 (d) Increasing
Withholding Rate. If a Participant wishes to increase his or her rate of payroll withholding, such Participant may do so by filing a new enrollment form with the Company at the prescribed location at any time. The new withholding rate may be
effective on the first day of the next-upcoming Offering Period in which the Participant participates, provided that the Participant has filed the enrollment form with the Company at the prescribed location at least 10 business days (or such other
period as the Committee or its designee may designate) prior to such day. The new withholding rate may be any whole percentage of the Participant’s Compensation, but not less than 1% nor more than 15%. An increase in a Participant’s rate
of payroll withholding may not take effect during an Offering Period. 
 SECTION 6. WITHDRAWAL FROM THE PLAN. 

(a) Withdrawal. A Participant may elect to withdraw from the Plan (or, if applicable, from an Offering Period) by filing the prescribed
form with the Company at the prescribed location at any time before a Purchase Date. As soon as reasonably practicable 

  
 4 

 
thereafter, payroll deductions or other approved contributions shall cease and the entire amount credited to the Participant’s Plan Account with respect to such Offering Period shall be
refunded to him or her in cash, without interest (except as otherwise required by the laws of the local jurisdiction). No partial withdrawals from an Offering Period shall be permitted. 

(b) Re-Enrollment After Withdrawal. A former Participant who has withdrawn from the Plan shall not be a Participant until he or she
re-enrolls in the Plan under Section 4(b). Re-enrollment may be effective only at the commencement of an Offering Period. 
 SECTION 7. CHANGE IN
EMPLOYMENT STATUS. 
 (a) Termination of Employment. Termination of employment as an Eligible Employee for any reason, including
death, shall be treated as an automatic withdrawal from the Plan under Section 6(a). (A transfer from one Participating Company to another shall not be treated as a termination of employment provided that each Participating Company is then
participating in the same Offering Period.) 
 (b) Leave of Absence. For purposes of the Plan, employment shall not be deemed to
terminate when the Participant goes on a military leave, a sick leave or another bona fide leave of absence, if the leave was approved by the Company in writing. Employment, however, shall be deemed to terminate on the first day following three
months after the Participant goes on a leave, unless a contract or statute guarantees his or her right to return to work. Employment shall be deemed to terminate in any event when the approved leave ends, unless the Participant immediately returns
to work. 
 (c) Death. In the event of the Participant’s death, the amount credited to his or her Plan Account shall be paid to
a beneficiary designated by him or her for this purpose on the prescribed form or, if none, to the Participant’s estate. Such form shall be valid only if it was filed with the Company at the prescribed location before the Participant’s
death. 
 SECTION 8. PLAN ACCOUNTS AND PURCHASE OF SHARES. 

(a) Plan Accounts. The Company shall maintain a Plan Account on its books in the name of each Participant. Whenever an amount is
deducted from the Participant’s Compensation under the Plan, such amount shall be credited to the Participant’s Plan Account. Amounts credited to Plan Accounts shall not be trust funds and may be commingled with the Company’s general
assets and applied to general corporate purposes. Unless otherwise required by the laws of the local jurisdiction, no interest shall be credited to Plan Accounts. 

(b) Purchase Price. The Purchase Price for each share of Stock purchased on a Purchase Date shall be the lower of: 

(i) 85% of the Fair Market Value of such share on the first day of such Offering Period or, in the case of the first Offering
Period under the Plan, 85% of the price at which one share of Stock is offered to the public in the IPO; or 
 (ii) 85% of
the Fair Market Value of such share on the Purchase Date. 

  
 5 

 (c) Number of Shares Purchased. On each Purchase Date, each Participant shall be deemed to
have elected to purchase the number of shares of Stock calculated in accordance with this Subsection (c), unless the Participant has previously elected to withdraw from the Offering Period in accordance with Section 6(a). The amount then
in the Participant’s Plan Account shall be divided by the Purchase Price, and the number of shares that results shall be purchased from the Company with the funds in the Participant’s Plan Account. The foregoing number of shares of Stock
purchasable by a Participant are subject to the limitations set forth in Section 9. The Committee may determine with respect to all Participants that any fractional share, as calculated under this Subsection (c), shall be (i) rounded
down to the next lower whole share or (ii) credited as a fractional share. 
 (d) Available Shares Insufficient. In the event
that the aggregate number of shares that all Participants elect to purchase with respect to a particular Purchase Period exceeds (i) the number of shares of Stock that were available under Section 3 above for sale under the Plan on the
first day of the applicable Offering Period, or (ii) the number of shares that were available under Section 3 above for sale under the Plan on the applicable Purchase Date, then the number of shares to which each Participant is entitled
shall be determined by multiplying the number of shares available for issuance by a fraction. The numerator of such fraction is the number of shares that such Participant has elected to purchase, and the denominator of such fraction is the number of
shares that all Participants have elected to purchase. The Company may make a pro rata allocation of the shares available on the first day of an applicable Offering Period pursuant to the preceding sentence, notwithstanding any authorization of
additional shares for issuance under the Plan by the Company’s stockholders subsequent to such date. In the event of a pro-rata allocation under this Section (d), the Committee may determine in its discretion to continue all Offering Periods
then in effect or terminate all Offering Periods then in effect pursuant to Section 14. 
 (e) Issuance of Stock. The shares of
Stock purchased by a Participant under the Plan may be registered in the name of such Participant, or jointly in the name of such Participant and his or her spouse as joint tenants with the right of survivorship or as community property (with or
without the right of survivorship). The Company may permit or require that shares be deposited directly with a broker designated by the Company or to a designated agent of the Company, and the Company may utilize electronic or automated methods of
share transfer. The Company may require that shares be retained with such broker or agent for a designated period of time and/or may establish other procedures to permit tracking of disqualifying dispositions of such shares. (The two preceding
sentences shall apply whether or not the Participant is required to pay income tax in the United States.) 
 (f) Tax Withholding. To
the extent required by applicable federal, state, local or foreign law, a Participant shall make arrangements satisfactory to the Company for the satisfaction of any withholding tax obligations that arise in connection with the Plan. The Company
shall not be required to issue any shares of Stock under the Plan until such obligations, if any, are satisfied. 
 (g) Unused Cash
Balances. Subject to the final sentence of Section 8(c), an amount remaining in the Participant’s Plan Account that represents the Purchase Price for any fractional share shall be carried over in the Participant’s Plan Account to
the next Purchase 

  
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Period. Any amount remaining in the Participant’s Plan Account that represents the Purchase Price for whole shares that could not be purchased by reason of Subsections (c) or
(d) above or Section 9(b) shall be refunded to the Participant in cash, without interest (except as otherwise required by the laws of the local jurisdiction). 

(h) Stockholder Approval. Any other provision of the Plan notwithstanding, no shares of Stock shall be purchased under the Plan unless
and until the Company’s stockholders have approved the adoption of the Plan. 
 SECTION 9. PLAN LIMITATIONS. 

(a) Five Percent Limit. Any other provision of the Plan notwithstanding, no Participant shall be granted a right to purchase Stock under
the Plan if such Participant, immediately after his or her election to purchase such Stock, would own stock possessing more than 5% of the total combined voting power or value of all classes of stock of the Company or any parent or Subsidiary of the
Company, determined in accordance with applicable tax law. 
 (b) Dollar Limit. Any other provision of the Plan notwithstanding, no
Participant shall purchase Stock with a Fair Market Value in excess of the following limit: 
 (i) In the case of Stock
purchased during an Offering Period that commenced in the current calendar year, the limit shall be equal to (A) $25,000 minus (B) the Fair Market Value of the Stock that the Participant previously purchased under the Plan in the current
calendar year. 
 (ii) In the case of Stock purchased during an Offering Period that commenced in the immediately preceding
calendar year, the limit shall be equal to (A) $50,000 minus (B) the Fair Market Value of the Stock that the Participant previously purchased under the Plan in the current calendar year and in the immediately preceding calendar year. 

(iii) In the case of Stock purchased during an Offering Period that commenced in the second calendar year before the current
calendar year, the limit shall be equal to (A) $75,000 minus (B) the Fair Market Value of the Stock that the Participant previously purchased under the Plan in the current calendar year and in the immediately preceding two calendar years.

 For all purposes under this Subsection (b), (A) the Fair Market Value of Stock shall be determined as of the beginning of the Offering Period
in which such Stock is purchased; and (B) this Plan shall be aggregated with any other employee stock purchase plans of the Company (or any parent or Subsidiary of the Company) described in Code Section 423. If a Participant is precluded
by this Subsection (b) from purchasing additional Stock under the Plan, then his or her employee contributions shall automatically be discontinued and shall automatically resume at the beginning of the next Offering Period with a scheduled
Purchase Date in the next calendar year, provided that he or she is an Eligible Employee at the beginning of such Offering Period. 

  
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 (c) Purchase Period Share Purchase Limit. Any other provision of the Plan notwithstanding,
no Participant shall purchase more than 1,600 shares of Stock with respect to any Purchase Period; provided that the Committee may, for future Offering Periods, increase or decrease in its absolute discretion, the maximum number of shares of Stock
that a Participant may purchase during each Purchase Period. 
 SECTION 10. RIGHTS NOT TRANSFERABLE. 

The rights of any Participant under the Plan, or any Participant’s interest in any Stock or moneys to which he or she may be entitled
under the Plan, shall not be transferable by voluntary or involuntary assignment or by operation of law, or in any other manner other than by beneficiary designation or the laws of descent and distribution. If a Participant in any manner attempts to
transfer, assign or otherwise encumber his or her rights or interest under the Plan, other than by beneficiary designation or the laws of descent and distribution, then such act shall be treated as an election by the Participant to withdraw from the
Plan under Section 6(a). 
 SECTION 11. NO RIGHTS AS AN EMPLOYEE. 

Nothing in the Plan or in any right granted under the Plan shall confer upon the Participant any right to continue in the employ of a
Participating Company for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Participating Companies or of the Participant, which rights are hereby expressly reserved by each, to terminate his or her
employment at any time and for any reason, with or without cause. 
 SECTION 12. NO RIGHTS AS A STOCKHOLDER. 

A Participant shall have no rights as a stockholder with respect to any shares of Stock that he or she may have a right to purchase under the
Plan until such shares have been purchased on the applicable Purchase Date. 
 SECTION 13. Securities Law Requirements. 

Shares of Stock shall not be issued, and the Company shall have no liability for failure to issue shares of Stock, under the Plan unless the
issuance and delivery of such shares comply with (or are exempt from) all applicable requirements of law, including (without limitation) the Securities Act of 1933, as amended, the rules and regulations promulgated thereunder, state securities laws
and regulations, and the regulations of any stock exchange or other securities market on which the Company’s securities may then be traded. 

SECTION 14. AMENDMENT OR DISCONTINUANCE. 

(a) General Rule. The Committee, in its sole discretion, may amend, suspend, or terminate the Plan, or any part thereof, at any time and
for any reason. If the Plan is terminated, the Committee, in its discretion, may elect to terminate all outstanding Offering Periods either immediately or upon completion of the purchase of shares of Stock on the next Purchase Date, or may elect to
permit Offering Periods to expire in accordance with their terms 

  
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(and subject to any adjustment pursuant to Section 3(c) or (d)). If the Offering Periods are terminated prior to expiration, all amounts then credited to Participants’ accounts which
have not been used to purchase shares of Stock will be returned to the Participants (without interest thereon, except as otherwise required by the laws of the local jurisdiction) as soon as administratively practicable. 

(b) Committee’s Discretion. Without stockholder consent and without limiting Section 14(a), the Committee will be entitled to
change the Offering Periods, limit the frequency and/or number of changes in the amount withheld during an Offering Period, establish the exchange ratio applicable to amounts withheld in a currency other than U.S. dollars, permit payroll withholding
in excess of the amount designated by a Participant in order to adjust for delays or mistakes in the Company’s processing of properly completed withholding elections, establish reasonable waiting and adjustment periods and/or accounting and
crediting procedures to ensure that amounts applied toward the purchase of Stock for each Participant properly correspond with amounts withheld from the Participant’s Compensation, and establish such other limitations or procedures as it
determines in its sole discretion advisable which are consistent with the Plan. 
 (c) Accounting Consideration. In the event the
Committee determines that the ongoing operation of the Plan may result in unfavorable financial accounting consequences, the Committee may, in its discretion and, to the extent necessary or desirable, modify, amend or terminate the Plan to reduce or
eliminate such accounting consequence including, but not limited to: 
 (i) Amending the Plan to conform with the safe harbor
definition under Financial Accounting Standards Board Accounting Standards Codification Topic 718, including with respect to an Offering Period underway at the time; 

(ii) Altering the Purchase Price for any Offering Period including an Offering Period underway at the time of the change in
Purchase Price; 
 (iii) Shortening any Offering Period by setting a new Purchase Date, including an Offering Period underway
at the time of the Committee’s action; 
 (iv) Reducing the maximum percentage of Compensation a Participant may elect
to set aside as payroll deductions; and 
 (v) Reducing the maximum number of shares of Stock a Participant may purchase
during any Purchase Period. 
 Such modifications or amendments will not require stockholder approval or the consent of any Plan Participants. 

(d) Stockholder Approval. Except as provided in Section 3, any increase in the aggregate number of shares of Stock that may be
issued under the Plan shall be subject to the approval of the Company’s stockholders. In addition, any other amendment of the Plan shall be subject to the approval of the Company’s stockholders to the extent required under
Section 14(e) or by any applicable law or regulation. 

  
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 (e) Plan Termination. The Plan shall terminate automatically 20 years after its adoption
by the Board, unless (i) the Plan is extended by the Board and (ii) the extension is approved within 12 months by a vote of the stockholders of the Company. 

SECTION 15. DEFINITIONS. 
 (a)
“Board” means the Board of Directors of the Company, as constituted from time to time. 
 (b) “Code” means
the Internal Revenue Code of 1986, as amended. 
 (c) “Committee” means a committee of the Board, as described in
Section 2. 
 (d) “Company” means REGENXBIO Inc., a Delaware corporation. 

(e) “Compensation” means (i) the total compensation paid in cash to a Participant by a Participating Company, including
salaries, wages, bonuses, incentive compensation, commissions, overtime pay and shift premiums, plus (ii) any pre-tax contributions made by the Participant under Code Sections 401(k) or 125. “Compensation” shall exclude all
non-cash items, moving or relocation allowances, cost-of-living equalization payments, car allowances, tuition reimbursements, imputed income attributable to cars or life insurance, severance pay, fringe benefits, contributions or benefits received
under employee benefit plans, income attributable to equity compensation awards of the Company, and similar items. The Committee shall determine whether a particular item is included in Compensation. 

(f) “Corporate Reorganization” means: 

(i) The consummation of a merger or consolidation of the Company with or into another entity or any other corporate
reorganization; or 
 (ii) The sale, transfer or other disposition of all or substantially all of the Company’s assets
or the complete liquidation or dissolution of the Company. 
 (g) “Eligible Employee” means a common law employee of a
Participating Company who is customarily employed for more than five months per calendar year and at least 20 hours per week. The foregoing notwithstanding, an individual shall not be considered an Eligible Employee if his or her participation in
the Plan is prohibited by the law of any country that has jurisdiction over him or her. In addition, the Committee may determine prior to the commencement of an Offering Period not to exclude part-time employees or exclude employees whose customary
employment is for fewer hours per week or fewer months in a calendar year; provided that such terms are applied in an identical manner to all employees of every Participating Company in such Offering Period. 

(h) “Exchange Act” means the Securities Exchange Act of 1934, as amended. 

(i) “Fair Market Value” means the price at which Stock was last sold in the principal U.S. market for the Stock on the
applicable date or, if the applicable date was not a trading day, on the last trading day prior to the applicable date. If Stock is no longer traded on a 

  
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public U.S. securities market, the Fair Market Value shall be determined by the Committee in good faith on such basis as it deems appropriate. The Committee’s determination shall be
conclusive and binding on all persons. 
 (j) “IPO” means the Company’s initial offering of Stock to the public. 

(k) “IPO Date” means the effective date of the registration statement filed by the Company with the Securities and Exchange
Commission for its initial offering of Stock to the public. 
 (l) “Offering Period” means any period, including as the
context requires Base Offering Periods and Additional Offering Periods, with respect to which the right to purchase Stock may be granted under the Plan, as determined pursuant to Section 4(a). 

(m) “Participant” means an Eligible Employee who participates in the Plan or any Sub-Plan, as provided in Section 4.

 (n) “Participating Company” means (i) the Company and (ii) each present or future Subsidiary designated by the
Committee as a Participating Company. 
 (o) “Plan” means this REGENXBIO Inc. 2015 Employee Stock Purchase Plan, as it may
be amended from time to time. 
 (p) “Plan Account” means the account established for each Participant pursuant to
Section 8(a). 
 (q) “Purchase Date” means the last trading day of a Purchase Period. 

(r) “Purchase Period” means a period within an Offering Period (which for an Offering Period with only a single Purchase
Period would be coterminous with the Offering Period) during which contributions may be made toward the purchase of Stock under the Plan, as determined pursuant to Section 4(a). 

(s) “Purchase Price” means the price at which Participants may purchase Stock under the Plan, as determined pursuant to
Section 8(b). 
 (t) “Stock” means the Common Stock of the Company. 

(u) “Subsidiary” means any corporation (other than the Company) in an unbroken chain of corporations beginning with the
Company, if each of the corporations other than the last corporation in the unbroken chain owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. 

  
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