Document:

EX-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
                 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), (ii)                  shares of Stock (subject to adjustment pursuant to Subsection (c) below), or (iii) 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. 

  
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 (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. 

  
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 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 

  
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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. 

  
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 (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                  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. 

  
 11EX-10.5

 Exhibit 10.5 
  

 
 This Employment Agreement (this “Agreement”) is entered into as of June 30, 2015, by and between Kenneth T.
Mills (the “Employee”) and REGENXBIO Inc., a Delaware corporation (the “Company”). 
  

	 	1.	Position. 

  

	 	(a)	During your employment with the Company pursuant to this Agreement, you will hold the title of President and Chief Executive Officer. As the President and Chief Executive Officer, you will report directly to the
Company’s Board of Directors (the “Board”). By signing this Agreement, you agree to perform the duties and fulfill the responsibilities normally inherent in the position of President and Chief Executive Officer and such other duties
and responsibilities as may from time to time reasonably be assigned to you. In addition, you shall serve on the Board. In the event that you cease to be employed by the Company, you shall promptly resign from the Board if requested to do so by a
majority of the Board. 

  

	 	(b)	You agree that, to the best of your ability and experience, you will at all times loyally and conscientiously perform all of the duties and obligations required of and from you pursuant to the express and implicit terms
hereof, and to the reasonable satisfaction of the Company. During the term of your employment with the Company, you further agree that (i) you will devote substantially all of your business time and attention to the business of the Company,
(ii) the Company will be entitled to all of the benefits and profits arising from or incident to all such business services, (iii) you will not render commercial or professional services of any nature to any person or organization outside
of the Company without the prior written approval of the Board, and (iv) you will not directly or indirectly engage or participate in any business that is competitive in any manner with the business of the Company. Notwithstanding the above,
you may continue, on your own time, at your own expense and so as to not interfere with your duties and responsibilities at the Company to (i) serve as a member of an advisory board or board of directors of other companies that are not
competitive in any manner with the Company, (ii) accept speaking or presentation engagements in exchange for honoraria, and (iii) participate in civic, educational, charitable or fraternal organizations. This Agreement does not prevent you
from owning no more than one percent (1%) of the outstanding equity securities of a corporation whose stock is listed on a national stock exchange and is a competitor or potential competitor of the Company. 

	 	2.	Offer Letter. Subject to the consummation of the initial public offering of the Company’s common stock (the “IPO”), this Agreement shall supersede and replace the offer letter you entered into with
the Company, dated February 1, 2015, other than the Proprietary Information and Inventions Agreement, which shall continue in full force and effect. If the IPO is not consummated, then this Agreement shall be null and void. 

 

	 	3.	Compensation. 

  

	 	(a)	Base Salary. You will be paid a monthly salary at a rate of $41,666.67, which is equivalent to $500,000 on an annualized basis, which will be paid semi-monthly in
accordance with the Company’s standard payroll procedures. 

  

	 	(b)	Incentive Bonus. You shall be eligible for an annual incentive bonus with a target amount equal to 50% of your Base Salary (the “Annual Target Bonus”). Any bonus for the fiscal year in which the
IPO is consummated shall be prorated between your pre-IPO and post- IPO target bonus percentages. Such bonus (if any) shall be awarded based on objective and/or subjective criteria established in advance by the Board or the Compensation Committee of
the Board (the “Compensation Committee”). The Company shall determine when to pay to you any earned incentive bonus, but shall in no event pay such bonus more than 2 1⁄2 months following the close of the fiscal year for which it is earned. Except as provided in Section 9, any earned incentive bonus shall be paid to you only if you are employed by the Company at the time of
payment. The determinations of the Board or the Compensation Committee with respect to such bonus shall be final and binding. 

  

	 	(c)	Annual Review. Your compensation will be reviewed by the Board or Compensation Committee annually. 

For purposes of this Agreement, “Cause” shall mean (i) the conviction of, or the entering a plea of guilty or no contest (or
pleading or accepting deferred adjudication or receiving unadjudicated probation) to or for, any felony or any crime involving moral turpitude, (ii) the commission of a material breach of any of the covenants, terms and provisions of this
Agreement or the Proprietary Information and Inventions Agreement you will enter into as a condition of your employment, (iii) the commission of an act of fraud, embezzlement, misappropriation, willful misconduct or breach of fiduciary duty
against the Company or other similar conduct materially harmful or potentially materially harmful to the Company’s best interest, as determined by the Board, in its reasonable sole discretion, (iv) the failure to perform assigned duties or
responsibilities as the President and Chief Executive Officer (other than a failure resulting from 

 
Disability (as defined below)); provided, however, that you shall be given written notice of, and shall have a ten (10) day period following such notice to cure a failure or
refusal under this subclause (iv)), or (v) the violation of any federal or state law or regulation applicable to the Company’s business. 

For purposes of this Agreement, “Good Reason” shall mean the occurrence of any of the following, without your written consent:
(i) a significant reduction in your duties or responsibilities or your removal from the position contemplated by this Agreement, unless you are assigned comparable duties or responsibilities or employed in a different position, respectively;
(ii) a significant reduction in the number of employees who report directly to you; (ii) a significant reduction (thirty percent (30%) or more) in your base salary as in effect immediately prior to such reduction; (iii) a
significant reduction in the type or level of employee benefits to which you are entitled that results in a significant reduction to your overall benefits package (other than a reduction of such employee benefits applicable to all Company
employees), as determined by the Board in its sole discretion; or (iv) relocation of your principal workplace by more than 35 miles. Good reason will not be deemed to occur unless you give the Company written notice of the condition within 90
days after the condition comes into existence and the Company fails to remedy the condition with 30 days after receiving said notice. 
  

	 	4.	Benefits. As an employee of the Company, you will also be eligible to receive certain employee benefits including paid time off and medical, dental, life, and long term disability insurance. You will also be
eligible to participate in our 401(k) savings plan. 

  

	 	5.	At-Will Employment; Proprietary Information and Inventions Agreement. Employment with the Company is for no specific period of time. Your employment with the Company is “at will,” meaning that either
you or the Company may terminate your employment at any time and for any reason, with or without cause. In addition, you should note that the Company may modify your job title, salary or benefits at its discretion. You agree and affirm that your
continued employment with the Company and this Agreement are contingent upon your agreement to comply with the Proprietary Information and Inventions Agreement, previously executed, a copy of which is attached hereto as Exhibit A.

  

	 	6.	Indemnification. The Company shall indemnify you to the fullest extent allowed by law, in accordance with the terms of the Company’s Certificate of Incorporation and Bylaws. You shall become a party to the
Company’s standard Indemnification Agreement. 

	 	7.	Evidence of Employment Eligibility. For purposes of federal immigration law, you will be required to provide to the Company documentary evidence of your identity and eligibility for employment in the United
States. Such documentation must be provided to us within three (3) business days of your Start Date, or our employment relationship with you may be terminated. 

 

	 	8.	Company Handbook. As a Company employee, you will be expected to abide by the Company’s rules of operation and standards of conduct. Specifically, you will be required to sign an acknowledgment that you have
read and that you understand such rules and standards, which are set forth in the Company Handbook. 

  

	 	9.	Termination of Employment and Severance Benefits. 

  

	 	(a)	Preconditions. Any other provision of this Agreement notwithstanding, the remaining Subsections of this Section 9 shall not apply unless each of the following requirements is satisfied:

  

	 	(i)	You have executed a general release of all known and unknown claims that you may then have against the Company or persons affiliated with the Company in a form prescribed by the Company, without alterations. You shall
execute and return the release on or before the date specified by the Company in the prescribed form (the “Release Deadline”). The Release Deadline shall in no event be later than sixty (60) days after your termination of employment.
If the 60 day period described in the prior sentence spans two calendar years, then the payments will begin on the first payroll period, following expiration of the revocation period, in the second calendar year. If you fail to return the release on
or before the Release Deadline, or if you revoke the release, then you shall not be entitled to the benefits described in this Section 9; and 

  

	 	(ii)	You have returned all property of the Company in your possession. 

  

	 	(b)	Termination of Employment. Except for the severance benefits provided below, the Company’s obligations under this Agreement may be terminated upon the occurrence of any of the following events:

  

	 	(i)	The Company’s determination in good faith that it is terminating you for Cause (“Termination for Cause”); 

  

	 	(ii)	The Company’s determination that it is terminating you without Cause, which determination may be made by the Company at any time at the Company’s sole discretion, for any or no reason (“Termination
Without Cause”); 

	 	(iii)	Thirty (30) days following delivery by you of a written notice to the Company stating that you are electing to terminate your employment with the Company (“Voluntary Termination”); 

 

	 	(iv)	Following your death or Disability (as defined below); or 

  

	 	(v)	Your determination in good faith that you are electing to terminate your employment with the Company for Good Reason. 

  

	 	(c)	Severance Benefits. You shall be entitled to receive severance benefits upon termination of employment only as set forth in this Section 9(c): 

 

	 	(i)	Voluntary Termination. In the event of a Voluntary Termination you shall not be entitled to receive payment of any severance benefits. You will receive payment(s) for all salary and unpaid vacation
accrued as of the date of your Voluntary Termination and your benefits will be continued under the Company’s then existing benefit plans and policies to the extent permitted under such plans and policies and in accordance with such plans and
policies in effect on the date of your Voluntary Termination and in accordance with applicable law. 

  

	 	(ii)	 Involuntary Termination/No Change in Control. If your employment is terminated under Section 9(b)(ii) or
(v) above (such termination, an “Involuntary Termination”), you, or your estate or representative, if applicable, will be entitled to receive payment of severance benefits on the date of your Involuntary Termination (the
“Severance Benefits”). The Severance Benefits shall consist of salary continuation for twelve (12) months of monthly Base Salary amounts; provided that if you become employed during this period, then the Company’s obligation to
pay Severance Benefits shall cease upon commencement of your new employment. If you elect to continue your health insurance coverage under the Consolidated Omnibus Budget Reconciliation Act (“COBRA”) following the Separation, then the
Company shall pay your monthly premium under COBRA until the earliest of (A) the date that is twelve (12) months following your Involuntary Termination (the “Continuation Period”), (B) the expiration of your continuation
coverage under COBRA and (C) the date when you are offered substantially equivalent health insurance coverage in connection with new employment or self-employment. Notwithstanding anything to the contrary above, if deemed necessary or advisable
by the Company in its sole discretion to 

	 	
avoid adverse tax consequences to the Company or any employee thereof, such COBRA premium payments will be treated as taxable compensation income to you, subject to all applicable withholdings.
If the Company decides to treat the COBRA premium payments as taxable income compensation to you, the Company will gross-up the amount of the payments to cover all applicable withholdings. 

 

	 	(iii)	Involuntary Termination/ Change in Control. If your employment is terminated in an Involuntary Termination immediately prior to or in the eighteen (18) months following a Change in
Control, you, or your estate or representative, if applicable, will be entitled to receive payment of severance benefits on the date of your Involuntary Termination (the “Change in Control Severance Benefits”). The Change in Control
Severance Benefits shall consist of (A) salary continuation for eighteen (18) months’ of monthly Base Salary and (B) a monthly amount equal to your Annual Target Bonus multiplied by 1.5 then divided by eighteen (18). If you elect
to continue your health insurance coverage under the Consolidated Omnibus Budget Reconciliation Act (“COBRA”) following the Separation, then the Company shall pay your monthly premium under COBRA until the earliest of (A) the date
that is eighteen (18) months following your Involuntary Termination (the “Continuation Period”), (B) the expiration of your continuation coverage under COBRA and (C) the date when you are offered substantially equivalent
health insurance coverage in connection with new employment or self-employment. Notwithstanding anything to the contrary above, if deemed necessary or advisable by the Company in its sole discretion to avoid adverse tax consequences to the Company
or any employee thereof, such COBRA premium payments will be treated as taxable compensation income to you, subject to all applicable withholdings. If the Company decides to treat the COBRA premium payments as taxable income compensation to you, the
Company will gross-up the amount of the payments to cover all applicable withholdings. If immediately prior to or following a Change in Control (as defined in the Company’s 2015 Equity Incentive Plan), your employment with the Company (or the
Company’s successor) is terminated in an Involuntary Termination during the remaining vesting period of the options then outstanding as of the date of closing of the Change in Control (the “Options”), then one hundred percent
(100%) of the unvested shares subject to the Options shall automatically vest. 

	 	(iv)	Termination for Cause. In the event of your Termination for Cause, you will receive payment(s) for all salary and unpaid vacation accrued as of the date of your Termination for Cause.

  

	 	(v)	Termination by Reason of Death or Disability. In the event that your employment with the Company terminates as a result of your death or Disability (as defined below), you or your estate or
representative will receive all salary and unpaid vacation accrued as of the date of your death or Disability, all severance benefits payable under Section 9(b)(ii) above and any other benefits payable under the Company’s then existing
benefit plans and policies, to the extent permitted under such plans and policies and in accordance with such plans and policies in effect on the date of death or Disability and in accordance with applicable law. For purposes of this Agreement,
“Disability” shall mean that you have been unable to perform your duties hereunder as the result of physical or mental incapacity lasting at least forty-five (45) consecutive calendar days or ninety (90) calendar days during any
consecutive twelve-month period, after which time such incapacity is determined to be permanent by a physician chosen by the Company and its insurers and acceptable to you or to your legal representative (with such agreement on acceptability not to
be unreasonably withheld). 

  

	 	10.	Tax Matters. 

  

	 	(a)	Withholding. All forms of compensation referred to in this Agreement are subject to reduction to reflect applicable withholding and payroll taxes and other deductions required by law. 

 

	 	(b)	Tax Advice. You are encouraged to obtain your own tax advice regarding your compensation from the Company. You agree that the Company does not have a duty to design its compensation policies in a manner
that minimizes your tax liabilities, and you will not make any claim against the Company or the Board related to tax liabilities arising from your compensation. 

  

	 	(c)	 280G. Notwithstanding anything contained in this Agreement to the contrary, if any of the payments or benefits received or to be
received by you pursuant to this Agreement when taken together with payments and benefits provided to you under any other plans, contracts, or arrangements with the Company (all such payments and benefits, the “Total Payments”), would be
subject to any excise tax imposed under Code Section 4999 (together with any interest or penalties, the “Excise Tax”), then such Total Payments will be reduced to the extent necessary so that no portion thereof will be subject to the
Excise Tax; 

	 	
provided, however, that if you would receive in the aggregate greater value (as determined under Code Section 280G and the regulations thereunder) on an after tax basis if the Total Payments
were not subject to such reduction, then no such reduction will be made. To effect the reduction described herein, if applicable, the Company will first reduce or eliminate the payments and benefits provided under this Agreement. All calculations
required to be made under this Section will be made by the Company’s independent public accountants, subject to the right of your representative to review the same. 

 

	 	11.	Miscellaneous Provisions. 

  

	 	(a)	Choice of Law. The validity, interpretation, construction and performance of this Agreement shall be governed by the laws of the State of Maryland, without giving effect to the principles of
conflicts of law. 

  

	 	(b)	Counterparts. This Agreement may be executed in counterparts, each of which shall be deemed an original, but all of which together will constitute one and the same instrument. 

 

	 	(c)	Severability. In the event that any provision hereof becomes or is declared by a court of competent jurisdiction to be illegal, unenforceable, or void, this Agreement shall continue in full force
and effect without such provision. 

  

	 	(d)	Acknowledgment. You acknowledge that you have had the opportunity to discuss this matter with and obtain advice from your private attorney, have had sufficient time to read, and have carefully read
and fully understand, all the provisions of this Agreement, and are knowingly and voluntarily entering into this Agreement. 

  

	 	(e)	 Arbitration. Any controversy or claim arising out of this Agreement and any and all claims relating to the Employee’s Employment with the
Company shall be settled by final and binding arbitration. The arbitration shall take place in Washington, D.C., or, at the Employee’s option, the County in which the Employee primarily worked when the arbitrable dispute or claim first arose.
The arbitration shall be administered by the American Arbitration Association under its National Rules for the Resolution of Employment Disputes. Any award or finding shall be confidential. The Employee and the Company agree to provide one another
with reasonable access to documents and witnesses in connection with the resolution of the dispute. The Employee and the Company shall share the costs of arbitration equally. Each party shall be responsible for its own attorneys’ fees, and the
arbitrator may not award attorneys’ fees unless 

	 	
a statute or contract at issue specifically authorizes such an award. This Section 11(e) shall not apply to claims for workers’ compensation benefits or unemployment insurance benefits.
This Section 11(e) also shall not apply to claims concerning the ownership, validity, infringement, misappropriation, disclosure, misuse or enforceability of any confidential information, patent right, copyright, mask work, trademark or any
other trade secret or intellectual property held or sought by either the Employee or the Company (whether or not arising under the Proprietary Information and Inventions Agreement between the Employee and the Company). 

[The remainder of this page intentionally left blank] 

 IN WITNESS WHEREOF, each of the parties has executed this Agreement, in the case of the Company by its
duly authorized officer, as of the day and year first above written. 
  

									
	REGENXBIO INC.				EMPLOYEE
					
	By:		 /s/ Vittal Vasista
				By:		 /s/ Kenneth T. Mills

					
	Name:		 Vittal Vasista
				Date:		 June 30, 2015

					
	Title:		CFO

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