EX-4.5



 Exhibit 4.5 
 EXECUTION COPY 
 AMENDED AND RESTATED INVESTORS’ RIGHTS
AGREEMENT 
 THIS AMENDED AND RESTATED INVESTORS’ RIGHTS AGREEMENT is made as of the 23rd day of July, 2012, by and
among bluebird bio, Inc., a Delaware corporation (the “Company”), each of the investors listed on Schedule A hereto, each of which is referred to in this Agreement as an “Investor”, and any additional
investor that becomes a party to this Agreement in accordance with Section 6.9 hereof. 
 RECITALS

 WHEREAS, certain of the Investors are parties to an Investors’ Rights Agreement dated as of
April 15, 2011 by and among the Company and such Investors (the “Prior Agreement” and such Investors, the “Existing Investors”); 
 WHEREAS, certain Investors (the “Series D Investors”) are entering into that certain Series D Preferred Stock Purchase Agreement of even date herewith between the Company and the
Series D Investors (the “Series D Purchase Agreement”), pursuant to which the Company is selling, and the Series D Investors are purchasing, shares of the Company’s newly designated Series D Convertible Preferred Stock, par
value $0.01 per share (the “Series D Preferred Stock”); and 
 WHEREAS, Existing Investors that
hold (i) a majority of the outstanding Series C Preferred Stock (as defined below), (ii) at least sixty percent (60%) of the outstanding Series B Preferred Stock (as defined below) and (iii) at least fifteen percent (15%) of
the outstanding Series A Preferred Stock (as defined below), desire to amend and restate the Prior Agreement as provided herein and to provide the Series D Investors with certain registration rights, information rights, rights of first offer, and
other rights in accordance with the terms of this Agreement. 
 NOW, THEREFORE, the Existing Investors hereby agree that
the Prior Agreement shall be superseded and replaced in its entirety by this Agreement, and the parties to this Agreement further agree as follows: 
 1. Definitions. For purposes of this Agreement: 
 1.1
“Affiliate” means, with respect to any specified Person, any other Person who or which, directly or indirectly, controls, is controlled by, or is under common control with such specified Person, including without limitation any
general partner, officer, director or manager of such Person and any venture capital fund now or hereafter existing that is controlled by or under common control with one or more general partners or managing members of, or shares the same management
company with, such Person. 
 1.2 “Common Stock” means shares of the Company’s common stock, par value
$0.01 per share. 
 1.3 “Damages” means any loss, damage, or liability (joint or several) to which a party
hereto may become subject under the Securities Act, the Exchange Act, or other federal or state law, insofar as such loss, damage, or liability (or any action in respect thereof) arises out of or is based upon (i) any untrue statement or
alleged untrue statement of a material 







 
fact contained in any registration statement of the Company, including any preliminary prospectus or final prospectus contained therein or any amendments or supplements thereto; (ii) an
omission or alleged omission to state therein a material fact required to be stated therein, or necessary to make the statements therein not misleading; or (iii) any violation or alleged violation by the indemnifying party (or any of its agents
or Affiliates) of the Securities Act, the Exchange Act, any state securities law, or any rule or regulation promulgated under the Securities Act, the Exchange Act, or any state securities law. 

1.4 “Derivative Securities” means any securities or rights convertible into, or exercisable or exchangeable for (in each
case, directly or indirectly), Common Stock, including options and warrants. 
 1.5 “Exchange Act” means the
Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder. 
 1.6 “Excluded
Registration” means (i) a registration relating to the sale of securities to employees of the Company or a subsidiary pursuant to a stock option, stock purchase, or similar plan; (ii) a registration relating to an SEC Rule 145
transaction; (iii) a registration on any form that does not include substantially the same information as would be required to be included in a registration statement covering the sale of the Registrable Securities; or (iv) a registration
in which the only Common Stock being registered is Common Stock issuable upon conversion of debt securities that are also being registered. 
 1.7 “Form S-1” means such form under the Securities Act as in effect on the date hereof or any successor registration form under the Securities Act subsequently adopted by the SEC.

 1.8 “Form S-3” means such form under the Securities Act as in effect on the date hereof or any registration
form under the Securities Act subsequently adopted by the SEC that permits incorporation of substantial information by reference to other documents filed by the Company with the SEC. 

1.9 “GAAP” means generally accepted accounting principles in the United States. 

1.10 “Holder” means any holder of Registrable Securities, or holder of Derivative Securities convertible into, or
exercisable or exchangeable for, Registrable Securities, who is a party to this Agreement. For purposes hereof, a holder of Derivative Securities convertible into, or exercisable or exchangeable for, Registrable Securities, shall be deemed to hold
such Registrable Securities. 
 1.11 “Immediate Family Member” means a child, stepchild, grandchild, parent,
stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, of a natural person referred to herein. 

1.12 “Initiating Holders” means, collectively, Holders who properly initiate a registration request under this
Agreement. 

  
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 1.13 “IPO” means the Company’s first underwritten public offering of
its Common Stock under the Securities Act. 
 1.14 “Key Employee” means any executive-level employee (including
division director and vice president-level positions). 
 1.15 “New Securities” means, collectively, equity or
debt securities of the Company, whether or not currently authorized, as well as rights, options, or warrants to purchase such equity or debt securities, or securities of any type whatsoever that are, or may become, convertible or exchangeable into
or exercisable for such equity or debt securities. 
 1.16 “Person” means any individual, corporation,
partnership, trust, limited liability company, association or other entity. 
 1.17 “Preferred Stock” means,
collectively, shares of the Company’s Series A Preferred Stock, Series B Preferred Stock, Series C Preferred Stock and Series D Preferred Stock. 
 1.18 “Qualified Public Offering” shall have the meaning ascribed to such term in the Company’s Certificate of Incorporation, as amended from time to time. 

1.19 “Preferred Directors” means the director(s) of the Company that the holders of record of the Series A Preferred
Stock, Series B Preferred Stock and Series C Preferred Stock, respectively, are entitled to elect pursuant to the Company’s Certificate of Incorporation. 
 1.20 “Registrable Securities” means (i) the Common Stock issuable or issued upon conversion of the Preferred Stock and (ii) any Common Stock issued as (or issuable upon the
conversion or exercise of any warrant, right, or other security that is issued as) a dividend or other distribution with respect to, or in exchange for or in replacement of, the shares referenced in clause (i) above; excluding in all
cases, however, any Registrable Securities sold by a Person in a transaction in which the applicable rights under this Agreement are not assigned pursuant to Section 6.1, and excluding for purposes of Section 2 any shares for
which registration rights have terminated pursuant to Section 2.13 of this Agreement. 
 1.21 “Registrable
Securities then outstanding” means the number of shares at a point in time determined by adding the number of shares of outstanding Common Stock that are Registrable Securities at such time and the number of shares of Common Stock issuable
(directly or indirectly) at such time pursuant to outstanding Derivative Securities. 
 1.22 “Requisite
Holders” means the holders of (i) a majority of the then outstanding shares of Preferred Stock, voting together as a single class and on an as-converted basis. 
 1.23 “Requisite Preferred Directors” means a majority of the Preferred Directors. 

  
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 1.24 “Restricted Securities” means the securities of the Company required
to bear the legend set forth in Section 2.12(b) hereof. 
 1.25 “SEC” means the Securities and
Exchange Commission. 
 1.26 “SEC Rule 144” means Rule 144 promulgated by the SEC under the Securities Act, or
any successor provisions. 
 1.27 “SEC Rule 145” means Rule 145 promulgated by the SEC under the Securities
Act, or any successor provisions. 
 1.28 “Securities Act” means the Securities Act of 1933, as amended, and
the rules and regulations promulgated thereunder. 
 1.29 “Selling Expenses” means all underwriting discounts,
selling commissions, and stock transfer taxes applicable to the sale of Registrable Securities, and fees and disbursements of counsel for any Holder, except for the fees and disbursements of the Selling Holder Counsel borne and paid by the Company
as provided in Section 2.6. 
 1.30 “Series A Preferred Stock” means shares of the Company’s Series
A-1 Convertible Preferred Stock and Series A-2 Convertible Preferred Stock, par value $0.01 per share. 
 1.31 “Series A
Registrable Securities” means the Common Stock issuable or issued upon conversion of the Series A Preferred Stock. 

1.32 “Series B Preferred Stock” means shares of the Company’s Series B Convertible Preferred Stock, par value $0.01
per share. 
 1.33 “Series B Registrable Securities” means the Common Stock issuable or issued upon conversion
of the Series B Preferred Stock. 
 1.34 “Series C Preferred Stock” means shares of the Company’s Series C
Convertible Preferred Stock, par value $0.01 per share. 
 1.35 “Series C Registrable Securities” means the
Common Stock issuable or issued upon conversion of the Series C Preferred Stock. 
 1.36 “Series D Registrable
Securities” means the Common Stock issuable or issued upon conversion of the Series D Preferred Stock. 
 2.
Registration Rights. The Company covenants and agrees as follows: 
 2.1 Demand Registration. 

(a) Form S-1 Demand. Beginning upon the earlier of (i) five (5) years after the date of this Agreement or (ii) one
hundred eighty (180) days after the effective date of the registration statement for the IPO, the Company receives a request from Holders of at least a majority of the Registrable Securities then outstanding, voting together as a single class
and on 

  
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an as-converted basis (the “Demand Holders”) that the Company file a Form S-1 registration statement with respect to the Registrable Securities then outstanding, which
Registrable Securities represent an anticipated aggregate offering price of at least $5 million, then the Company shall (i) within ten (10) days after the date such request is given, give notice thereof (the “Demand
Notice”) to all Holders other than the Initiating Holders; and (ii) as soon as practicable, and in any event within sixty (60) days after the date such request is given by the Initiating Holders, file a Form S-1 registration
statement under the Securities Act covering all Registrable Securities that the Initiating Holders requested to be registered and any additional Registrable Securities requested to be included in such registration by any other Holders, as specified
by notice given by each such Holder to the Company within twenty (20) days of the date the Demand Notice is given, and in each case, subject to the limitations of Section 2.1(c) and Section 2.3. 

(b) Form S-3 Demand. If at any time when it is eligible to use a Form S-3 registration statement and the Company receives a
request from any Holder or Holders that the Company file a Form S-3 registration statement with respect to outstanding Registrable Securities of such Holders having an anticipated aggregate offering price of at least $1 million, then the Company
shall (i) within ten (10) days after the date such request is given, give a Demand Notice to all Holders other than the Initiating Holders; and (ii) as soon as practicable, and in any event within forty-five (45) days after the
date such request is given by the Initiating Holders, file a Form S-3 registration statement under the Securities Act covering all Registrable Securities requested to be included in such registration by any other Holders, as specified by notice
given by each such Holder to the Company within twenty (20) days of the date the Demand Notice is given, and in each case, subject to the limitations of Section 2.1(c) and Section 2.3. 

(c) Notwithstanding the foregoing obligations, if the Company furnishes to Holders requesting a registration pursuant to this
Section 2.1 a certificate signed by the Company’s chief executive officer stating that in the good faith judgment of the Company’s Board of Directors it would be materially detrimental to the Company and its stockholders for
such registration statement to either become effective or remain effective for as long as such registration statement otherwise would be required to remain effective, because such action would (i) materially interfere with a significant
acquisition, corporate reorganization, or other similar transaction involving the Company; (ii) require premature disclosure of material information that the Company has a bona fide business purpose for preserving as confidential; or
(iii) render the Company unable to comply with requirements under the Securities Act or Exchange Act, then the Company shall have the right to defer taking action with respect to such filing, and any time periods with respect to filing or
effectiveness thereof shall be tolled correspondingly, for a period of not more than ninety (90) days after the request of the Initiating Holders is given; provided, however, that the Company may not invoke this right more than once in
any twelve (12) month period; and provided further that the Company shall not register any securities for its own account or that of any other stockholder during such ninety (90) day period other than an Excluded Registration.

 (d) The Company shall not be obligated to effect, or to take any action to effect, any registration pursuant to
Section 2.1(a) (i) during the period that is sixty (60) days before the Company’s good faith estimate of the date of filing of, and ending on a date that is one 

  
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hundred eighty (180) days after the effective date of, a Company-initiated registration, provided, that the Company is actively employing its good faith commercially reasonable
efforts to cause such registration statement to become effective; (ii) after the Company has effected two (2) registrations pursuant to Section 2.1(a), provided that a registration pursuant to Section 2.1(a)
shall only be considered “effected” for purposes of this Section 2.1(d)(ii) if the registration statement registers all the Registrable Securities requested to be registered; or (iii) if the requesting Holders propose to
dispose of shares of Registrable Securities that may be immediately registered on Form S-3 pursuant to a request made pursuant to Section 2.1(b). The Company shall not be obligated to effect, or to take any action to effect, any
registration pursuant to Section 2.1(b), (i) during the period that is thirty (30) days before the Company’s good faith estimate of the date of filing of, and ending on a date that is ninety (90) days after the
effective date of, a Company-initiated registration relating to shares to be sold by the Company, provided, that the Company is actively employing its good faith commercially reasonable efforts to cause such registration statement to become
effective; or (ii) if the Company has effected two registration statements pursuant to Section 2.1(b) within the twelve (12) month period immediately preceding the date of such request. A registration shall not be counted as
“effected” for purposes of this Section 2.1(d) until such time as the applicable registration statement has been declared effective by the SEC, unless the Initiating Holders withdraw their request for such registration (other
than as a result of a material adverse change to the Company), elect not to pay the registration expenses therefor, and forfeit their right to one demand registration statement pursuant to Section 2.6, in which case such withdrawn
registration statement shall be counted as “effected” for purposes of this Section 2.1(d). 
 2.2
Company Registration. If the Company proposes to register (including, for this purpose, a registration effected by the Company for stockholders other than the Holders) any of its Common Stock under the Securities Act in connection with the
public offering of such securities solely for cash (other than in an Excluded Registration), the Company shall, at such time, promptly give each Holder notice of such registration. Upon the request of each Holder given within twenty (20) days
after such notice is given by the Company, the Company shall, subject to the provisions of Section 2.3, cause to be registered all of the Registrable Securities that each such Holder has requested to be included in such registration. The
Company shall have the right to terminate or withdraw any registration initiated by it under this Section 2.2 before the effective date of such registration, whether or not any Holder has elected to include Registrable Securities in such
registration. The expenses (other than Selling Expenses) of such withdrawn registration shall be borne by the Company in accordance with Section 2.6. 
 2.3 Underwriting Requirements. 
 (a) If, pursuant to
Section 2.1, the Initiating Holders intend to distribute the Registrable Securities covered by their request by means of an underwriting, they shall so advise the Company as a part of their request made pursuant to
Section 2.1, and the Company shall include such information in the Demand Notice. The underwriter(s) will be selected by the Company and shall be reasonably acceptable to a majority in interest of the Initiating Holders. In such event,
the right of any Holder to include such Holder’s Registrable Securities in such registration shall be conditioned upon such Holder’s participation in such underwriting and the inclusion of such Holder’s Registrable Securities in the
underwriting to the extent provided herein. All Holders proposing to distribute their securities through such 

  
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underwriting shall (together with the Company as provided in Section 2.4(e)) enter into an underwriting agreement in customary form with the underwriter(s) selected for such
underwriting. Notwithstanding any other provision of this Section 2.3, if the managing underwriter(s) advise(s) the Initiating Holders in writing that marketing factors require a limitation on the number of shares to be underwritten,
then the Initiating Holders shall so advise all Holders of Registrable Securities that otherwise would be underwritten pursuant hereto, and the number of Registrable Securities that may be included in the underwriting shall be allocated among such
Holders of Registrable Securities, including the Initiating Holders, in proportion (as nearly as practicable) to the number of Registrable Securities owned by each Holder or in such other proportion as shall mutually be agreed to by all such selling
Holders; provided, however, that the number of Registrable Securities held by the Holders to be included in such underwriting shall not be reduced unless all other securities are first entirely excluded from the underwriting. To facilitate
the allocation of shares in accordance with the above provisions, the Company or the underwriters may round the number of shares allocated to any Holder to the nearest 100 shares. 

(b) In connection with any offering involving an underwriting of shares of the Company’s capital stock pursuant to
Section 2.2, the Company shall not be required to include any of the Holders’ Registrable Securities in such underwriting unless the Holders accept the terms of the underwriting as agreed upon between the Company and its
underwriters, and then only in such quantity as the underwriters in their sole discretion determine will not jeopardize the success of the offering by the Company. If the total number of securities, including Registrable Securities, requested by
stockholders to be included in such offering exceeds the number of securities to be sold (other than by the Company) that the underwriters in their reasonable discretion determine is compatible with the success of the offering, then the Company
shall be required to include in the offering only that number of such securities, including Registrable Securities, which the underwriters and the Company in their sole discretion determine will not jeopardize the success of the offering. If the
underwriters determine that less than all of the Registrable Securities requested to be registered can be included in such offering, then the Registrable Securities that are included in such offering shall be allocated among the selling Holders in
proportion (as nearly as practicable to) the number of Registrable Securities owned by each selling Holder or in such other proportions as shall mutually be agreed to by all such selling Holders. To facilitate the allocation of shares in accordance
with the above provisions, the Company or the underwriters may round the number of shares allocated to any Holder to the nearest 100 shares. Notwithstanding the foregoing, in no event shall (i) the number of Registrable Securities included in
the offering be reduced unless all other securities (other than securities to be sold by the Company) are first entirely excluded from the offering (in which case the number of Series B Registrable Securities, Series C Registrable Securities and
Series D Registrable Securities included in the offering (A) shall not be reduced unless all Series A Registrable Securities are first excluded from the offering and (B) shall be reduced on a pari passu basis), or (ii) the
number of Registrable Securities included in the offering be reduced below thirty percent (30%) of the total number of securities included in such offering, unless such offering is the IPO, in which case the selling Holders may be excluded
further if the underwriters make the determination described above and no other stockholder’s securities are included in such offering For purposes of the provision in this Section 2.3(b) concerning apportionment, for any selling
Holder that is a partnership, limited liability company, or corporation, the partners, members, retired partners, retired members, stockholders, and 

  
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Affiliates of such Holder, or the estates and Immediate Family Members of any such partners, retired partners, members, and retired members and any trusts for the benefit of any of the foregoing
Persons, shall be deemed to be a single “selling Holder,” and any pro rata reduction with respect to such “selling Holder” shall be based upon the aggregate number of Registrable Securities owned by all Persons included in such
“selling Holder,” as defined in this sentence. 
 (c) For purposes of Section 2.1, a registration shall
not be counted as “effected” if, as a result of an exercise of the underwriter’s cutback provisions in Section 2.3(a), fewer than all of the Registrable Securities that Holders have requested to be included in such
registration statement are actually included. 
 2.4 Obligations of the Company. Whenever required under this
Section 2 to effect the registration of any Registrable Securities, the Company shall, as expeditiously as reasonably possible: 
 (a) prepare and file with the SEC a registration statement with respect to such Registrable Securities and use its commercially reasonable efforts to cause such registration statement to become effective
and, upon the request of the Holders of a majority of the Registrable Securities registered thereunder, keep such registration statement effective for a period of up to one hundred twenty (120) days or, if earlier, until the distribution
contemplated in the registration statement has been completed; provided, however, that such one hundred twenty (120) day period shall be extended for a period of time equal to the period the Holder refrains, at the request of an
underwriter of Common Stock (or other securities) of the Company, from selling any securities included in such registration; 

(b) prepare and file with the SEC such amendments and supplements to such registration statement, and the prospectus used in connection
with such registration statement, as may be necessary to comply with the Securities Act in order to enable the disposition of all securities covered by such registration statement; 

(c) furnish to the selling Holders such numbers of copies of a prospectus, including a preliminary prospectus, as required by the
Securities Act, and such other documents as the Holders may reasonably request in order to facilitate their disposition of their Registrable Securities; 
 (d) use its commercially reasonable efforts to register and qualify the securities covered by such registration statement under such other securities or blue-sky laws of such jurisdictions as shall be
reasonably requested by the selling Holders; provided that the Company shall not be required to qualify to do business or to file a general consent to service of process in any such states or jurisdictions, unless the Company is already
subject to service in such jurisdiction and except as may be required by the Securities Act; 
 (e) in the event of any
underwritten public offering, enter into and perform its obligations under an underwriting agreement, in usual and customary form, with the underwriter(s) of such offering; 
 (f) use its commercially reasonable efforts to cause all such Registrable Securities covered by such registration statement to be listed on a national securities exchange or trading system and each
securities exchange and trading system (if any) on which similar securities issued by the Company are then listed; 

  
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 (g) provide a transfer agent and registrar for all Registrable Securities registered
pursuant to this Agreement and provide a CUSIP number for all such Registrable Securities, in each case not later than the effective date of such registration; 
 (h) promptly make available for inspection by the selling Holders, any managing underwriter(s) participating in any disposition pursuant to such registration statement, and any attorney or accountant or
other agent retained by any such underwriter or selected by the selling Holders, all financial and other records, pertinent corporate documents, and properties of the Company, and cause the Company’s officers, directors, employees, and
independent accountants to supply all information reasonably requested by any such seller, underwriter, attorney, accountant, or agent, in each case, as necessary or advisable to verify the accuracy of the information in such registration statement
and to conduct appropriate due diligence in connection therewith; 
 (i) notify each selling Holder, promptly after the Company
receives notice thereof, of the time when such registration statement has been declared effective or a supplement to any prospectus forming a part of such registration statement has been filed and in each case supply each selling Holder with a copy
thereof; and 
 (j) after such registration statement becomes effective, notify each selling Holder of any request by the SEC
that the Company amend or supplement such registration statement or prospectus. 
 2.5 Furnish Information. It shall be a
condition precedent to the obligations of the Company to take any action pursuant to this Section 2 with respect to the Registrable Securities of any selling Holder that such Holder shall furnish to the Company such information regarding
itself, the Registrable Securities held by it, and the intended method of disposition of such securities as is reasonably required to effect the registration of such Holder’s Registrable Securities. 

2.6 Expenses of Registration. All expenses (other than Selling Expenses) incurred in connection with registrations, filings, or
qualifications pursuant to Section 2, including all registration, filing, and qualification fees; printers’ and accounting fees; fees and disbursements of counsel for the Company; and the reasonable fees and disbursements of one
counsel for the selling Holders (“Selling Holder Counsel”) selected by the Demand Holders, shall be borne and paid by the Company; provided, however, that the Company shall not be required to pay for any expenses of any
registration proceeding begun pursuant to Section 2.1 if the registration request is subsequently withdrawn at the request of the Holders of a majority of the Registrable Securities to be registered (in which case all selling Holders
shall bear such expenses pro rata based upon the number of Registrable Securities that were to be included in the withdrawn registration), unless the Holders of a majority of the Registrable Securities agree to forfeit their right to one
registration pursuant to Section 2.1(a); provided further that if, at the time of such withdrawal, the Holders shall have learned of a material adverse change in the condition, business or prospects of the Company from that known
to the Holders at the time of their request and have withdrawn the request with reasonable promptness after learning of such 

  
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information then the Holders shall not be required to pay any of such expenses and shall not forfeit their right to one registration pursuant to Section 2.1(a). All Selling Expenses
relating to Registrable Securities registered pursuant to this Section 2 shall be borne and paid by the Holders pro rata on the basis of the number of Registrable Securities registered on their behalf. 

2.7 Delay of Registration. No Holder shall have any right to obtain or seek an injunction restraining or otherwise delaying any
registration pursuant to this Agreement as the result of any controversy that might arise with respect to the interpretation or implementation of this Section 2. 
 2.8 Indemnification. If any Registrable Securities are included in a registration statement under this Section 2: 

(a) To the extent permitted by law, the Company will indemnify and hold harmless each selling Holder, and the partners, members,
officers, directors, and stockholders of each such Holder; legal counsel and accountants for each such Holder; any underwriter (as defined in the Securities Act) for each such Holder; and each Person, if any, who controls such Holder or underwriter
within the meaning of the Securities Act or the Exchange Act, against any Damages, and the Company will pay to each such Holder, underwriter, controlling Person, or other aforementioned Person any legal or other expenses reasonably incurred thereby
in connection with investigating or defending any claim or proceeding from which Damages may result, as such expenses are incurred; provided, however, that the indemnity agreement contained in this Section 2.8(a) shall not apply
to amounts paid in settlement of any such claim or proceeding if such settlement is effected without the consent of the Company, which consent shall not be unreasonably withheld, nor shall the Company be liable for any Damages to the extent that
they arise out of or are based upon actions or omissions made in reliance upon and in conformity with written information furnished by or on behalf of any such Holder, underwriter, controlling Person, or other aforementioned Person expressly for use
in connection with such registration. 
 (b) To the extent permitted by law, each selling Holder, severally and not jointly,
will indemnify and hold harmless the Company, and each of its directors, each of its officers who has signed the registration statement, each Person (if any), who controls the Company within the meaning of the Securities Act, legal counsel and
accountants for the Company, any underwriter (as defined in the Securities Act), any other Holder selling securities in such registration statement, and any controlling Person of any such underwriter or other Holder, against any Damages, in each
case only to the extent that such Damages arise out of or are based upon actions or omissions made in reliance upon and in conformity with written information furnished by or on behalf of such selling Holder expressly for use in connection with such
registration; and each such selling Holder will pay to the Company and each other aforementioned Person any legal or other expenses reasonably incurred thereby in connection with investigating or defending any claim or proceeding from which Damages
may result, as such expenses are incurred; provided, however, that the indemnity agreement contained in this Section 2.8(b) shall not apply to amounts paid in settlement of any such claim or proceeding if such settlement is
effected without the consent of the Holder, which consent shall not be unreasonably withheld; and provided further that in no event shall any indemnity under this Section 2.8(b) exceed the proceeds from the offering received by
such Holder (net of any Selling Expenses paid by such Holder), except in the case of fraud or willful misconduct by such Holder. 

  
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 (c) Promptly after receipt by an indemnified party under this Section 2.8 of
notice of the commencement of any action (including any governmental action) for which a party may be entitled to indemnification hereunder, such indemnified party will, if a claim in respect thereof is to be made against any indemnifying party
under this Section 2.8, give the indemnifying party notice of the commencement thereof. The indemnifying party shall have the right to participate in such action and, to the extent the indemnifying party so desires, participate jointly
with any other indemnifying party to which notice has been given, and to assume the defense thereof with counsel mutually satisfactory to the parties; provided, however, that an indemnified party (together with all other indemnified parties
that may be represented without conflict by one counsel) shall have the right to retain one separate counsel, with the fees and expenses to be paid by the indemnifying party, if representation of such indemnified party by the counsel retained by the
indemnifying party would be inappropriate due to actual or potential differing interests between such indemnified party and any other party represented by such counsel in such action. The failure to give notice to the indemnifying party within a
reasonable time of the commencement of any such action shall relieve such indemnifying party of any liability to the indemnified party under this Section 2.8, to the extent that such failure materially prejudices the indemnifying
party’s ability to defend such action. The failure to give notice to the indemnifying party will not relieve it of any liability that it may have to any indemnified party otherwise than under this Section 2.8. 

(d) Notwithstanding anything else herein to the contrary, the foregoing indemnity agreements of the Company and the selling Holders are
subject to the condition that, insofar as they relate to any Damages arising from any untrue statement or alleged untrue statement of a material fact contained in, or omission or alleged omission of a material fact from, a preliminary prospectus (or
necessary to make the statements therein not misleading) that has been corrected in the form of prospectus included in the registration statement at the time it becomes effective, or any amendment or supplement thereto filed with the SEC pursuant to
Rule 424(b) under the Securities Act (the “Final Prospectus”), such indemnity agreement shall not inure to the benefit of any Person if a copy of the Final Prospectus was furnished to the indemnified party within a reasonable period
prior to the applicable sale and such indemnified party failed to deliver, at or before the confirmation of the sale of the shares registered in such offering, a copy of the Final Prospectus to the Person asserting the loss, liability, claim, or
damage in any case in which such delivery was required by the Securities Act. 
 (e) To provide for just and equitable
contribution to joint liability under the Securities Act in any case in which either (i) any party otherwise entitled to indemnification hereunder makes a claim for indemnification pursuant to this Section 2.8 but it is judicially
determined (by the entry of a final judgment or decree by a court of competent jurisdiction and the expiration of time to appeal or the denial of the last right of appeal) that such indemnification may not be enforced in such case, notwithstanding
the fact that this Section 2.8 provides for indemnification in such case, or (ii) contribution under the Securities Act may be required on the part of any party hereto for which indemnification is provided under this
Section 2.8, then, and in each such case, such parties will contribute to the aggregate losses, claims, damages, liabilities, or expenses to which they may be subject (after contribution from others) in such proportion as is appropriate
to reflect the relative fault of each of the indemnifying party and the indemnified party in connection with the statements, omissions, or other actions that resulted in such loss, claim, damage, liability, or expense, as well as to reflect


  
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any other relevant equitable considerations. The relative fault of the indemnifying party and of the indemnified party shall be determined by reference to, among other things, whether the untrue
or allegedly untrue statement of a material fact, or the omission or alleged omission of a material fact, relates to information supplied by the indemnifying party or by the indemnified party and the parties’ relative intent, knowledge, access
to information, and opportunity to correct or prevent such statement or omission; provided, however, that, in any such case, (x) no Holder will be required to contribute any amount in excess of the public offering price of all such
Registrable Securities offered and sold by such Holder pursuant to such registration statement, and (y) no Person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) will be entitled to
contribution from any Person who was not guilty of such fraudulent misrepresentation; and provided further that in no event shall a Holder’s liability pursuant to this Section 2.8(e), when combined with the amounts paid or
payable by such Holder pursuant to Section 2.8(b), exceed the proceeds from the offering received by such Holder (net of any Selling Expenses paid by such Holder), except in the case of willful misconduct or fraud by such Holder.

 (e) Notwithstanding the foregoing, to the extent that the provisions on indemnification and contribution contained in the
underwriting agreement entered into in connection with the underwritten public offering are in conflict with the foregoing provisions, the provisions in the underwriting agreement shall control. 

(f) Unless otherwise superseded by an underwriting agreement entered into in connection with the underwritten public offering, the
obligations of the Company and Holders under this Section 2.8 shall survive the completion of any offering of Registrable Securities in a registration under this Section 2, and otherwise shall survive the termination of this
Agreement. 
 2.9 Reports Under Exchange Act. With a view to making available to the Holders the benefits of SEC Rule 144
and any other rule or regulation of the SEC that may at any time permit a Holder to sell securities of the Company to the public without registration or pursuant to a registration on Form S-3, the Company shall: 

(a) make and keep available adequate current public information, as those terms are understood and defined in SEC Rule 144, at all times
after the effective date of the registration statement filed by the Company for the IPO; 
 (b) use commercially reasonable
efforts to file with the SEC in a timely manner all reports and other documents required of the Company under the Securities Act and the Exchange Act (at any time after the Company has become subject to such reporting requirements); and 

(c) furnish to any Holder, so long as the Holder owns any Registrable Securities, forthwith upon request (i) to the extent
accurate, a written statement by the Company that it has complied with the reporting requirements of SEC Rule 144 (at any time after ninety (90) days after the effective date of the registration statement filed by the Company for the IPO), the
Securities Act, and the Exchange Act (at any time after the Company has become subject to such reporting requirements), or that it qualifies as a registrant whose securities may be resold pursuant to Form S-3 (at any time after the Company so
qualifies); (ii) a copy of the most recent 

  
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annual or quarterly report of the Company and such other reports and documents so filed by the Company; and (iii) such other information as may be reasonably requested in availing any Holder
of any rule or regulation of the SEC that permits the selling of any such securities without registration (at any time after the Company has become subject to the reporting requirements under the Exchange Act) or pursuant to Form S-3 (at any time
after the Company so qualifies to use such form). 
 2.10 Limitations on Subsequent Registration Rights. From and after
the date of this Agreement, the Company shall not, without the prior written consent of the Requisite Holders, enter into any agreement with any holder or prospective holder of any securities of the Company that would allow such holder or
prospective holder (i) to include such securities in any registration unless, under the terms of such agreement, such holder or prospective holder may include such securities in any such registration only to the extent that the inclusion of
such securities will not reduce the number of the Registrable Securities of the Holders that are included or (ii) to demand registration of any securities held by such holder or prospective holder; provided that this limitation shall not
apply to any additional Investor who becomes a party to this Agreement in accordance with Section 6.9. 
 2.11
“Market Stand-off” Agreement. Each Holder hereby agrees that, if required by the managing underwriter and the Company, it will not, without the prior written consent of the managing underwriter, during the period commencing on the
date of the final prospectus relating to the IPO and ending on the date specified by the Company and the managing underwriter (such period not to exceed one hundred eighty (180) days, which period may be extended upon the request of the
managing underwriter, for an additional period of up to thirty-four (34) days in order to address FINRA Rule 2711(f) to the extent then applicable or any similar successor provision, (i) lend; offer; pledge; sell; contract to sell; sell
any option or contract to purchase; purchase any option or contract to sell; grant any option, right, or warrant to purchase; or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any Derivative Securities
(whether such shares or any such Derivative Securities are then owned by the Holder or are thereafter acquired but specifically excluding any shares of Common Stock or Derivative Securities that are purchased in the IPO or in the open market after
the IPO, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be made during the 180-day period referred to above (and any extension thereof as provided above) in connection with subsequent sales of such
shares of Common Stock or any Derivative Securities so purchased in the IPO or in the open market after the IPO) or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences
of ownership of such securities, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or other securities, in cash, or otherwise. The foregoing provisions of this
Section 2.11 shall apply only to the IPO, shall not apply to the sale of any shares to an underwriter pursuant to an underwriting agreement, and shall be applicable to the Holders only if all officers and directors, and all stockholders
individually owning more than one percent (1%) of the Company’s outstanding Common Stock (after giving effect to conversion into Common Stock of all outstanding Preferred Stock) are subject to substantially similar restrictions. The
underwriters in connection with such registration are intended third-party beneficiaries of this Section 2.11 and shall have the right, power, and authority to enforce the provisions hereof as though they were a party hereto. Each Holder
further agrees to execute such agreements as may be reasonably requested by the 

  
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underwriters in connection with such registration that are consistent with this Section 2.11 or that are necessary to give further effect thereto. Notwithstanding the foregoing, the
Company shall use commercially reasonable best efforts to obtain from the managing underwriter(s) an agreement to waive these restrictions in order to provide for periodic early releases of portions of the aforesaid securities upon the occurrence of
certain specified events, any such release to apply pro rata to all Holders subject to this Section 2.11, based on the number of securities (determined on an as-converted basis) subject to the restrictions set forth in this
Section 2.11. 
 2.12 Restrictions on Transfer. 

(a) The Preferred Stock and the Registrable Securities shall not be sold, pledged, or otherwise transferred, and the Company shall not
recognize any such sale, pledge, or transfer, except upon the conditions specified in this Agreement, which conditions are intended to ensure compliance with the provisions of the Securities Act. A transferring Holder will cause any proposed
purchaser, pledgee, or transferee of the Preferred Stock and the Registrable Securities held by such Holder to agree to take and hold such securities subject to the provisions and upon the conditions specified in this Agreement. 

(b) Each certificate or instrument representing (i) the Preferred Stock, (ii) the Registrable Securities, and (iii) any
other securities issued in respect of the securities referenced in clauses (i) and (ii), upon any stock split, stock dividend, recapitalization, merger, consolidation, or similar event, shall (unless otherwise permitted by the provisions
of Section 2.12(c)) be stamped or otherwise imprinted with a legend substantially in the following form: 
 THE
SECURITIES REPRESENTED HEREBY HAVE BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. SUCH SHARES MAY NOT BE SOLD, PLEDGED, OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR A VALID EXEMPTION FROM THE
REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SAID ACT. 
 THE SECURITIES REPRESENTED HEREBY MAY BE TRANSFERRED ONLY IN
ACCORDANCE WITH THE TERMS OF AN AGREEMENT BETWEEN THE COMPANY AND THE STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE SECRETARY OF THE COMPANY. 
 The Holders consent to the Company making a notation in its records and giving instructions to any transfer agent of the Restricted Securities in order to implement the restrictions on transfer set forth
in this Section 2.12. 
 (c) The holder of each certificate representing Restricted Securities, by acceptance
thereof, agrees to comply in all respects with the provisions of this Section 2. Before any proposed sale, pledge, or transfer of any Restricted Securities, unless there is in effect a registration statement under the Securities Act
covering the proposed transaction, the Holder thereof shall give notice to the Company of such Holder’s intention to effect such sale, pledge, or transfer. Each such notice shall describe the manner and circumstances of the proposed sale,
pledge, or transfer in sufficient detail and, if reasonably requested by the Company, shall be 

  
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accompanied at such Holder’s expense by either (i) a written opinion of legal counsel who shall, and whose legal opinion shall, be reasonably satisfactory to the Company, addressed to
the Company, to the effect that the proposed transaction may be effected without registration under the Securities Act; (ii) a “no action” letter from the SEC to the effect that the proposed sale, pledge, or transfer of such
Restricted Securities without registration will not result in a recommendation by the staff of the SEC that action be taken with respect thereto; or (iii) any other evidence reasonably satisfactory to counsel to the Company to the effect that
the proposed sale, pledge, or transfer of the Restricted Securities may be effected without registration under the Securities Act, whereupon the Holder of such Restricted Securities shall be entitled to sell, pledge, or transfer such Restricted
Securities in accordance with the terms of the notice given by the Holder to the Company. The Company will not require such a legal opinion or “no action” letter (x) in any transaction in compliance with SEC Rule 144 or (y) in
any transaction in which such Holder distributes Restricted Securities to an Affiliate of such Holder for no consideration; provided that each transferee agrees in writing to be subject to the terms of this Section 2.12. Each certificate
or instrument evidencing the Restricted Securities transferred as above provided shall bear, except if such transfer is made pursuant to SEC Rule 144, the appropriate restrictive legend set forth in Section 2.12(b), except that such
certificate shall not bear such restrictive legend if, in the opinion of counsel for such Holder and the Company, such legend is not required in order to establish compliance with any provisions of the Securities Act. 

2.13 Termination of Registration Rights. The right of any Holder to request registration or inclusion of Registrable Securities in
any registration pursuant to Section 2.1 or Section 2.2 shall terminate upon the later to occur of: 

(a) the date on which all of such Holder’s Registrable Securities have been sold; or 

(b) the fifth anniversary of the Qualified Public Offering. 
 3. Information and Observer Rights. 
 3.1 Delivery of Financial
Statements. The Company shall deliver to each Investor: 
 (a) as soon as practicable, but in any event within one hundred
twenty (120) days after the end of each fiscal year of the Company, (i) a balance sheet as of the end of such year, (ii) statements of income and of cash flows for such year, and a comparison between (x) the actual amounts as of
and for such fiscal year and (y) the comparable amounts for the prior year and as included in the Budget (as defined in Section 3.1(e)) for such year, with an explanation of any material differences between such amounts and a
schedule as to the sources and applications of funds for such year, and (iii) a statement of stockholders’ equity as of the end of such year, all such financial statements audited and certified by independent public accountants of
regionally or nationally recognized standing selected by the Company and approved by the Board of Directors, which approval shall include the approval of the Requisite Preferred Directors. 

  
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 (b) as soon as practicable, but in any event within forty-five (45) days after the end
of each of the first three (3) quarters of each fiscal year of the Company, unaudited statements of income and of cash flows for such fiscal quarter, and an unaudited balance sheet and a statement of stockholders’ equity as of the end of
such fiscal quarter, all prepared in accordance with GAAP (except that such financial statements may (i) be subject to normal year-end audit adjustments and (ii) not contain all notes thereto that may be required in accordance with GAAP);

 (c) as soon as practicable, but in any event within forty-five (45) days after the end of each of the first three
(3) quarters of each fiscal year of the Company, a statement showing the number of shares of each class and series of capital stock and securities convertible into or exercisable for shares of capital stock outstanding at the end of the period,
the Common Stock issuable upon conversion or exercise of any outstanding securities convertible or exercisable for Common Stock and the exchange ratio or exercise price applicable thereto, and the number of shares of issued stock options and stock
options not yet issued but reserved for issuance, if any, all in sufficient detail as to permit the Investors to calculate their respective percentage equity ownership in the Company, and certified by the chief financial officer or chief executive
officer of the Company as being true, complete, and correct; 
 (d) as soon as practicable, but in any event within thirty
(30) days of the end of each month, an unaudited income statement and statement of cash flows for such month, and an unaudited balance sheet and statement of stockholders’ equity as of the end of such month, all prepared in accordance with
GAAP (except that such financial statements may (i) be subject to normal year-end audit adjustments and (ii) not contain all notes thereto that may be required in accordance with GAAP); and 

(e) as soon as practicable, but in any event thirty (30) days before the end of each fiscal year, a budget and business plan for
the next fiscal year (collectively, the “Budget”), approved by the Board of Directors, which approval shall include the approval of the Requisite Preferred Directors, and prepared on a monthly basis, including balance sheets, income
statements, and statements of cash flow for such months and, promptly after prepared, any other budgets or revised budgets prepared by the Company. 
 If, for any period, the Company has any subsidiary whose accounts are consolidated with those of the Company, then in respect of such period the financial statements delivered pursuant to the foregoing
sections shall be the consolidated and consolidating financial statements of the Company and all such consolidated subsidiaries. 

Notwithstanding anything else in this Section 3.1 to the contrary, the Company may cease providing the information set forth in this
Section 3.1 during the period starting with the date sixty (60) days before the Company’s good-faith estimate of the date of filing of a registration statement if it reasonably concludes it must do so to comply with the SEC
rules applicable to such registration statement and related offering; provided that the Company’s covenants under this Section 3.1 shall be reinstated at such time as the Company is no longer actively employing its commercially
reasonable efforts to cause such registration statement to become effective. 
 3.2 Inspection. The Company shall permit
each Investor, at such Investor’s expense, to visit and inspect the Company’s properties; examine its books of account and records; and discuss the Company’s affairs, finances, and accounts with its officers, upon providing reasonable
notice during normal business hours of the Company as may be reasonably 

  
 16 









 
requested by the Investor; provided, however, that the Company shall not be obligated pursuant to this Section 3.2 to provide access to any information that it reasonably and
in good faith considers to be a trade secret or confidential information (unless covered by an enforceable confidentiality agreement, in form acceptable to the Company) or the disclosure of which would adversely affect the attorney-client privilege
between the Company and its counsel. 
 3.3 Observer Rights. The Company shall invite a representative of
(i) Genzyme Corporation, (ii) Shire plc and (iii) Third Rock Ventures, LLC to attend all meetings of its Board of Directors in a nonvoting observer capacity and shall give such representatives copies of all notices, minutes, consents,
and other materials that it provides to its directors at the same time and in the same manner as provided to such directors; provided, however, that such Investor shall agree to hold (and cause its representative to hold) in confidence all
information so provided; provided further, that the Company reserves the right to withhold any information and to exclude such representatives from any meeting or portion thereof if the Company’s Board of Directors determines in good
faith that access to such information or attendance at such meeting could adversely affect the attorney-client privilege between the Company and its counsel or result in disclosure of trade secrets or a conflict of interest. The observer rights
provided by this Section 3.3, including the foregoing confidentiality obligations, shall be set forth in letter agreements in a form reasonably acceptable to the Company with each of the Investors named in this Section 3.3.

 3.4 Informational Meetings. Each Investor shall be entitled to participate in semi-annual informational meetings with
members of the Company’s management (the “Informational Meetings”). The Company shall provide reasonable notice to the Investors in advance of each Informational Meeting, which shall be held at a time and place determined by
the Company (which may include attendance in-person and by remote access at the option of the Investors). 
 3.5 Termination
of Information. The covenants set forth in Sections 3.1, 3.2, 3.3 and 3.4 shall terminate and be of no further force or effect (i) immediately before but subject to the consummation of a Qualified Public Offering or
(ii) when the Company first becomes subject to the periodic reporting requirements of Section 12(g) or 15(d) of the Exchange Act, whichever event occurs first. 
 3.6 Confidentiality. Each Investor agrees that such Investor will keep confidential and will not disclose, divulge, or use for any purpose (other than to monitor its investment in the Company) any
confidential information obtained from the Company pursuant to the terms of this Agreement (including notice of the Company’s intention to file a registration statement), unless such confidential information (a) is known or becomes known
to the public in general (other than as a result of a breach of this Section 3.6 by such Investor), (b) is or has been independently developed or conceived by the Investor without use of the Company’s confidential information,
or (c) is or has been made known or disclosed to the Investor by a third party without a breach of any obligation of confidentiality such third party may have to the Company; provided, however, that an Investor may disclose confidential
information (i) to its attorneys, accountants, consultants, investment advisors and other professionals to the extent necessary to obtain their services in connection with monitoring its investment in the Company; (ii) to any prospective
purchaser of any Registrable Securities from such Investor, if such prospective purchaser agrees to be bound by the provisions of this Section 3.6; (iii) to any existing or 

  
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prospective Affiliate, partner, member, stockholder, or wholly owned subsidiary of such Investor in the ordinary course of business, provided that such Investor informs such Person that
such information is confidential and directs such Person to maintain the confidentiality of such information except as may be (and solely to the extent) required by reporting obligations of the Investor or its investment advisor; or (iv) as may
otherwise be required by law, provided that the Investor promptly notifies the Company of such disclosure and takes reasonable steps to minimize the extent of any such required disclosure. 

4. Rights to Future Stock Issuances. 
 4.1 Right of First Offer. Unless waived by the Requisite Holders and subject to the terms and conditions of this Section 4.1 and applicable securities laws, if the Company proposes to
offer or sell any New Securities, the Company shall first offer such New Securities to each Investor. An Investor shall be entitled to apportion the right of first offer hereby granted to it among itself and its Affiliates in such proportions as it
deems appropriate. 
 (a) The Company shall give notice (the “Offer Notice”) to each Investor, stating
(i) its bona fide intention to offer such New Securities, (ii) the number of such New Securities to be offered, and (iii) the price and terms, if any, upon which it proposes to offer such New Securities. 

(b) By notification to the Company within twenty (20) days after the Offer Notice is given, each Investor may elect to purchase or
otherwise acquire, at the price and on the terms specified in the Offer Notice, up to that portion of such New Securities which equals the proportion that the Common Stock issued and held, or issuable (directly or indirectly) upon conversion,
exercise or exchange, as applicable, of Derivative Securities then held, by such Investor bears to the total Common Stock of the Company then outstanding (assuming full conversion, exercise or exchange, as applicable, of all Derivative Securities).
At the expiration of such twenty (20) day period, the Company shall promptly notify each Investor that elects to purchase or acquire all the shares available to it (each, a “Fully Exercising Investor”) of any other
Investor’s failure to do likewise. During the ten (10) day period commencing after the Company has given such notice, each Fully Exercising Investor may, by giving notice to the Company, elect to purchase or acquire, in addition to the
number of shares specified above, up to that portion of the New Securities for which Investors were entitled to subscribe but that were not subscribed for by the Investors which is equal to the proportion that the Common Stock issued and held, or
issuable (directly or indirectly) upon conversion, exercise or exchange, as applicable, of Derivative Securities then held, by such Fully Exercising Investor bears to the Common Stock issued and held, or issuable (directly or indirectly) upon
conversion, exercise or exchange, as applicable, of Derivative Securities then held, by all Fully Exercising Investors who wish to purchase such unsubscribed shares. The closing of any sale pursuant to this Section 4.1(b) shall occur
within the later of ninety (90) days of the date that the Offer Notice is given and the date of initial sale of New Securities pursuant to Section 4.1(c). 
 (c) If all New Securities referred to in the Offer Notice are not elected to be purchased or acquired as provided in Section 4.1(b), the Company may, during the ninety (90) day period
following the expiration of the periods provided in Section 4.1(b), offer and sell the remaining unsubscribed portion of such New Securities to any Person or Persons at a price not less than, and upon terms no more favorable to the
offeree than, those specified in the Offer 

  
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Notice. If the Company does not enter into an agreement for the sale of the New Securities within such period, or if such agreement is not consummated within thirty (30) days of the
execution thereof, the right provided hereunder shall be deemed to be revived and such New Securities shall not be offered unless first reoffered to the Investors in accordance with this Section 4.1. 

(d) The right of first offer in this Section 4.1 shall not be applicable to (i) Exempted Securities (as defined in the
Company’s Certificate of Incorporation); (ii) shares of Common Stock issued in the IPO; and (iii) the issuance of shares of Series D Preferred Stock pursuant to the Series D Purchase Agreement. 

4.2 Termination. The covenants set forth in Section 4.1 shall terminate and be of no further force or effect
(i) immediately before the consummation of the Qualified Public Offering, or (ii) when the Company first becomes subject to the periodic reporting requirements of Section 12(g) or 15(d) of the Exchange Act, whichever event occurs
first. 
 5. Additional Covenants. 
 5.1 Insurance. The Company shall use its commercially reasonable efforts to maintain from financially sound and reputable insurers Directors and Officers liability insurance in an amount and on
terms and conditions satisfactory to the Board of Directors, including the Requisite Preferred Directors, and will use commercially reasonable efforts to cause such insurance policy to be maintained until such time as the Board of Directors,
including the affirmative vote of the Requisite Preferred Directors, determines that such insurance should be discontinued. 

5.2 Employee Agreements. The Company will cause (i) each person now or hereafter employed by it or by any subsidiary (or
engaged by the Company or any subsidiary as a consultant or independent contractor, including any member of the Company’s scientific advisory board) with access to confidential information and/or trade secrets to enter into a nondisclosure and
proprietary rights assignment agreement and, to the extent permitted by law, (ii) each Key Employee to enter into a one (1) year noncompetition and nonsolicitation agreement, substantially in the form approved by the Board of Directors,
including the affirmative vote of the Requisite Preferred Directors, all subject to the policies of any academic or research institution with which any such person may be affiliated. In addition, the Company shall not amend, modify, terminate,
waive, or otherwise alter, in whole or in part, any of the above-referenced agreements or any restricted stock agreement between the Company and any employee, without the consent of the Requisite Preferred Directors. 

5.3 Employee Vesting. Unless otherwise approved by the Board of Directors, which approval must include the affirmative vote of the
Requisite Preferred Directors, all future employees and consultants of the Company who purchase, receive options to purchase, or receive awards of shares of the Company’s capital stock after the date hereof shall be required to execute
restricted stock or option agreements, as applicable, providing for (i) vesting of shares over a four (4) year period, with the first twenty-five percent (25%) of such shares vesting following twelve (12) months of continued
employment or service, and the remaining shares vesting in equal monthly installments over the following thirty-six (36) months and (ii) a one hundred eighty day (180) day lockup period in connection with the Company’s IPO. In
addition, 

  
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unless otherwise approved by the Board of Directors, including the affirmative vote of the Requisite Preferred Directors, the Company shall retain a “right of first refusal” on employee
transfers until the Company’s IPO and shall have the right to repurchase unvested shares at cost upon termination of employment of a holder of restricted stock. 
 5.4 [Reserved.] 
 5.5 Matters Requiring Investor Director Approval.
The Company hereby covenants and agrees with each of the Investors that it shall not, nor shall it permit any subsidiary to, without approval of the Board of Directors, which approval must include the affirmative vote of the Requisite Preferred
Directors: 
 (a) make any loan or advance to, or own any stock or other securities of, any subsidiary or other corporation,
partnership, or other entity unless it is wholly owned by the Company; 
 (b) make any loan or advance to any Person,
including, without limitation, any employee or director of the Company or any subsidiary, except advances and similar expenditures in the ordinary course of business or under the terms of an employee stock or option plan approved by the Board of
Directors; 
 (c) guarantee, directly or indirectly, any indebtedness except for trade accounts of the Company or any
subsidiary arising in the ordinary course of business; 
 (d) make any investment other than investments in prime commercial
paper, money market funds, certificates of deposit in any United States bank having a net worth in excess of $100,000,000, or obligations issued or guaranteed by the United States of America, in each case having a maturity not in excess of two
years; 
 (e) otherwise enter into or be a party to any transaction with any director, officer, or employee of the Company or
any “associate” (as defined in Rule 12b-2 promulgated under the Exchange Act) of any such Person, except for transactions contemplated by the Purchase Agreement; 
 (f) hire, terminate, or change the compensation of the executive officers, including approving any option grants or stock awards to executive officers. 

(g) change the principal business of the Company, enter new lines of business, or exit the current line of business; or 

(h) sell, assign, license, pledge, or encumber material technology or intellectual property, other than licenses granted in the ordinary
course of business. 
 5.6 Meetings of the Board of Directors. Unless otherwise determined by the vote of a majority of
the directors then in office, the Board of Directors shall meet at least quarterly in accordance with an agreed-upon schedule. 

  
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 5.7 Successor Indemnification. If the Company or any of its successors or assignees
consolidates with or merges into any other Person and is not the continuing or surviving corporation or entity of such consolidation or merger, then to the extent necessary, proper provision shall be made so that the successors and assignees of the
Company assume the obligations of the Company with respect to indemnification of members of the Board of Directors as in effect immediately before such transaction, whether such obligations are contained in the Company’s Bylaws, its Certificate
of Incorporation, or elsewhere, as the case may be. 
 5.8 Board Expenses. The Company shall reimburse nonemployee
directors and the observers appointed pursuant to Section 3.3 for all reasonable out-of-pocket travel expenses incurred in connection with attending meetings of the Board of Directors. 

5.9 Termination of Covenants. The covenants set forth in this Section 5, except for Section 5.8, shall
terminate and be of no further force or effect (i) immediately before the consummation of the Qualified Public Offering or (ii) when the Company first becomes subject to the periodic reporting requirements of Section 12(g) or 15(d) of
the Exchange Act, whichever event occurs first. 
 6. Miscellaneous. 

6.1 Successors and Assigns. The rights under this Agreement may be assigned (but only with all related obligations) by a Holder to
a transferee of Registrable Securities that (i) is an Affiliate, partner, member, limited partner, retired partner, retired member, or stockholder of a Holder; (ii) is a Holder’s Immediate Family Member or trust for the benefit of an
individual Holder or one or more of such Holder’s Immediate Family Members; or (iii) after such transfer, holds at least 50,000 shares of Registrable Securities (subject to appropriate adjustment for stock splits, stock dividends,
combinations, and other recapitalizations); provided, however, that (x) the Company is, within a reasonable time after such transfer, furnished with written notice of the name and address of such transferee and the Registrable Securities with
respect to which such rights are being transferred; and (y) such transferee agrees in a written instrument delivered to the Company to be bound by and subject to the terms and conditions of this Agreement, including the provisions of
Section 2.11. For the purposes of determining the number of shares of Registrable Securities held by a transferee, the holdings of a transferee (1) that is an Affiliate, partner, member, limited partner, retired partner, retired
member, or stockholder or stockholder of a Holder; (2) who is a Holder’s Immediate Family Member; or (3) that is a trust for the benefit of an individual Holder or such Holder’s Immediate Family Member shall be aggregated
together and with those of the transferring Holder; provided further that all transferees who would not qualify individually for assignment of rights shall have a single attorney-in-fact for the purpose of exercising any rights, receiving notices,
or taking any action under this Agreement. The terms and conditions of this Agreement inure to the benefit of and are binding upon the respective successors and permitted assignees of the parties. Nothing in this Agreement, express or implied, is
intended to confer upon any party other than the parties hereto or their respective successors and permitted assignees any rights, remedies, obligations or liabilities under or by reason of this Agreement, except as expressly provided herein.

 6.2 Governing Law. This Agreement and any controversy arising out of or relating to this Agreement shall be governed
by and construed in accordance with the General Corporation Law of the State of Delaware as to matters within the scope thereof, and as to all 

  
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other matters shall be governed by and construed in accordance with the internal laws of The Commonwealth of Massachusetts, without regard to conflict of law principles that would result in the
application of any law other than the law of The Commonwealth of Massachusetts. 
 6.3 Counterparts; Facsimile. This
Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed and delivered by facsimile or electronic
mail signature and in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. 
 6.4 Titles and Subtitles. The titles and subtitles used in this Agreement are for convenience only and are not to be considered in construing or interpreting this Agreement. 

6.5 Notices. All notices, requests, and other communications given or made pursuant to this Agreement shall be in writing and
shall be deemed effectively given, delivered and received (i) upon personal delivery to the party to be notified; (ii) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so
confirmed, then on the next business day; (iii) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid; or (iv) one (1) business day after the business day of deposit with
a nationally recognized overnight courier, specifying next-day delivery, with written verification of receipt. All communications shall be sent to the respective parties at their addresses as set forth on Schedule A hereto, or to the
principal office of the Company and to the attention of the Chief Executive Officer, in the case of the Company, or to such email address, facsimile number, or address as subsequently modified by written notice given in accordance with this
Section 6.5. If notice is given to the Company, a copy shall also be sent to Goodwin Procter LLP, 53 State Street, Boston, Massachusetts 02109, Attention: Michael H. Bison, Esq. 

6.6 Amendments and Waivers. Any term of this Agreement, including without limitation Section 4.1, may be amended and
the observance of any term of this Agreement may be waived (either generally or in a particular instance, and either retroactively or prospectively) only with the written consent of the Company and the Requisite Holders; provided that the
Company may in its sole discretion waive compliance with Section 2.12(c) (and the Company’s failure to object promptly in writing after notification of a proposed assignment allegedly in violation of Section 2.12(c)
shall be deemed to be a waiver); and provided further that any provision hereof may be waived by any waiving party on such party’s own behalf, without the consent of any other party. Notwithstanding the foregoing, this Agreement may not be
amended or terminated and the observance of any term hereof may not be waived with respect to any Investor without the written consent of such Investor, unless such amendment, termination, or waiver applies to all Investors in the same fashion (it
being agreed that a waiver of the provisions of Section 4 with respect to a particular transaction shall be deemed to apply to all Investors in the same fashion if such waiver does so by its terms, notwithstanding the fact that certain
Investors may nonetheless, by agreement with the Company, purchase securities in such transaction); provided that (a) Section 3.3 of this Agreement shall not be amended or waived without the written consent of the Investors
named therein, (b) no changes to Section 2.11 that make any provision therein more restrictive as to an Investor shall be enforceable against such Investor without its consent (and in the absence of such consent,
Section 2.11 in such form as it exists as of July 23, 2012 shall remain in effect with respect to 

  
 22 









 
such Investor), and (c) no changes to Sections 3.1, 3.2 or 3.4 that reduce the rights provided to any Investor thereunder shall be enforceable against such Investor
without its consent (and in the absence of such consent, the applicable Section in such form as it exists as of July 23, 2012 shall remain in effect with respect to such Investor). The Company shall give prompt notice of any amendment or
termination hereof or waiver hereunder to any party hereto that did not consent in writing to such amendment, termination, or waiver. Any amendment, termination, or waiver effected in accordance with this Section 6.6 shall be binding on
all parties hereto, regardless of whether any such party has consented thereto. No waivers of or exceptions to any term, condition, or provision of this Agreement, in any one or more instances, shall be deemed to be or construed as a further or
continuing waiver of any such term, condition, or provision. 
 6.7 Severability. In case any one or more of the
provisions contained in this Agreement is for any reason held to be invalid, illegal or unenforceable in any respect, such invalidity, illegality, or unenforceability shall not affect any other provision of this Agreement, and such invalid, illegal,
or unenforceable provision shall be reformed and construed so that it will be valid, legal, and enforceable to the maximum extent permitted by law. 
 6.8 Aggregation of Stock. All shares of Registrable Securities held or acquired by Affiliates or Investors with the same or affliated investment advisor shall be aggregated together for the purpose
of determining the availability of any rights under this Agreement and such Affiliated persons may apportion such rights as among themselves in any manner they deem appropriate. 

6.9 Additional Investors. Notwithstanding anything to the contrary contained herein, if the Company issues additional shares of
Series D Preferred Stock after the date hereof, any purchaser of such shares of Series D Preferred Stock may become a party to this Agreement by executing and delivering an additional counterpart signature page to this Agreement, and thereafter
shall be deemed an “Investor” for all purposes hereunder. No action or consent by the Investors shall be required for such joinder to this Agreement by such additional Investor, so long as such additional Investor has agreed in writing to
be bound by all of the obligations as an “Investor” hereunder. 
 6.10 Entire Agreement. This Agreement
(including the Schedule and Exhibit hereto) constitutes the full and entire understanding and agreement among the parties with respect to the subject matter hereof, and any other written or oral agreement relating to the subject matter hereof
existing between the parties is expressly canceled. Upon the effectiveness of this Agreement, the Prior Agreement shall be deemed superseded and replaced in its entirety by this Agreement, and shall be of no further force or effect. 

6.11 Jurisdiction; Venue. The parties (a) hereby irrevocably and unconditionally submit to the jurisdiction of the federal
and state courts located within the geographic boundaries of the United States District Court for the District of Massachusetts for the purpose of any suit, action or other proceeding arising out of or based upon this Agreement, (b) agree not
to commence any suit, action or other proceeding arising out of or based upon this Agreement except in the federal and state courts located within the geographic boundaries of the United States District Court for the District of Massachusetts, and
(c) hereby waive, and agree not to assert, by way of motion, as a defense, or otherwise, in any such suit, action or proceeding, any claim that it is not subject personally to the jurisdiction of the above-named courts, that its


  
 23 









 
property is exempt or immune from attachment or execution, that the suit, action or proceeding is brought in an inconvenient forum, that the venue of the suit, action or proceeding is improper or
that this Agreement or the subject matter hereof may not be enforced in or by such court. The prevailing party shall be entitled to reasonable attorney’s fees, costs, and necessary disbursements in addition to any other relief to which such
party may be entitled. Each of the parties to this Agreement consents to personal jurisdiction for any equitable action sought in the U.S. District Court for the District of Massachusetts or any court of The Commonwealth of Massachusetts having
subject matter jurisdiction. 
 6.12 Delays or Omissions. No delay or omission to exercise any right, power, or remedy
accruing to any party under this Agreement, upon any breach or default of any other party under this Agreement, shall impair any such right, power, or remedy of such nonbreaching or nondefaulting party, nor shall it be construed to be a waiver of or
acquiescence to any such breach or default, or to any similar breach or default thereafter occurring, nor shall any waiver of any single breach or default be deemed a waiver of any other breach or default theretofore or thereafter occurring. All
remedies, whether under this Agreement or by law or otherwise afforded to any party, shall be cumulative and not alternative. 

6.13 Acknowledgment. The Company acknowledges that the Investors are in the business of venture capital investing and therefore
review the business plans and related proprietary information of many enterprises, including enterprises which may have products or services which compete directly or indirectly with those of the Company. Nothing in this Agreement shall preclude or
in any way restrict the Investors from investing or participating in any particular enterprise whether or not such enterprise has products or services which compete with those of the Company. 

6.14 Waiver of Conflicts. Each party to this Agreement acknowledges that Goodwin Procter LLP, counsel for the Company, has in the
past and may continue to perform legal services for certain of the Investors in matters unrelated to the transactions described in this Agreement, including the representation of such Investors in venture capital financings and other matters.
Accordingly, each party to this Agreement hereby (a) acknowledges that they have had an opportunity to ask for information relevant to this disclosure; (b) acknowledges that Goodwin Procter LLP represented the Company in the transaction
contemplated by this Agreement and has not represented any individual Investor or any individual stockholder or employee of the Company in connection with such transaction; and (c) gives its informed written consent to Goodwin Procter
LLP’s representation of certain of the Investors in such unrelated matters and to Goodwin Procter LLP’s representation of the Company in connection with this Agreement and the transactions contemplated hereby. 

[Remainder of Page Intentionally Left Blank] 

  
 24 









 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 COMPANY:
  

BLUEBIRD BIO, INC.

		
	By:	 	/s/ Nick Leschly
	 Name:
 Title:
	 	 Nick Leschly
 President and
Chief Executive Officer



  

  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

ARCH VENTURE FUND VII, L.P.

		
	 By:
 Its:

By:
 Its:
	 	 ARCH Venture Partners VII, L.P.

General Partner
 ARCH Venture Partners VII,
LLC
 General Partner

		
	By:	 	/s/ Clinton W. Bybee
	 Name:
 Title:
	 	 Clinton Bybee
 Manager
Director




  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

THIRD ROCK VENTURES, L.P.
  

	By:	 	 Third Rock Ventures GP, L.P., its general partner

 

	By:	 	TRV GP, LLC, its general partner
		
	By:	 	/s/ Robert Tepper
	 Name:
 Title:
	 	 Robert Tepper

Manager




  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

TVM V LIFE SCIENCE VENTURES GMBH & CO. KG

		
	By:	 	/s/ Axel Polack
	 Name:

Title:
	 	 Dr. Axel Polack

Managing Limited Partner

		
	By:	 	/s/ Mark G. Cipriano
	 Name:
 Title:
	 	 Mark G. Cipriano
 Managing
Limited Partner




  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

COOPERATIVE AAC LS U.A.

		
	By:	 	/s/ Bart Bergstein
	 Name:
 Title:
	 	 Bart Bergstein
 Managing
Partner

		
	By:	 	/s/ Christina Takke
	 Name:
 Title:
	 	 Christina Takke

Partner




  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

SMALLCAP WORLD FUND, INC.

 
 By: Capital Research and Management Company

Its: Investment Advisor

		
	By:	 	/s/ Michael J. Downer
	Name:	 	Michael J. Downer
	Title:	 	Senior Vice President and Secretary


  

			
	 AMERICAN FUNDS INSURANCE SERIES –

GLOBAL SMALL CAPITALIZATION FUND

 
 By: Capital Research and Management Company

Its: Investment Advisor

		
	By:	 	/s/ Michael J. Downer
	Name:	 	Michael J. Downer
	Title:	 	Senior Vice President and Secretary



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

DEERFIELD SPECIAL SITUATIONS FUND, L.P.

	 By:
	 	 Deerfield Capital, L.P.

General Partner

		
	By:	 	 J.E. Flynn Capital, LLC

General Partner

		
	By:	 	/s/ James Flynn
	Name:	 	James Flynn
	Title:	 	General Partner


  

			
	 DEERFIELD SPECIAL SITUATIONS
 INTERNATIONAL MASTER FUND, L.P.
  

	By:	 	 Deerfield Capital, L.P.

General Partner
  

	By:	 	 J.E. Flynn Capital, LLC

General Partner

		
	By:	 	/s/ James Flynn
	Name:	 	James Flynn
	Title:	 	General Partner



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

RA CAPITAL HEALTHCARE FUND, LP

		
	By:	 	/s/ Peter Kolchinsky
	Name:	 	Peter Kolchinsky
	Title:	 	Manager



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

COWEN BLUEBIRD LLC

	  
 By: Ramius Advisors, LLC, its managing
member

		
	By:	 	/s/ Andrew Cohen
	Name:	 	Andrew Cohen
	Title:	 	Managing Director
		
	By:	 	/s/ Owen Littman
	Name:	 	Owen Littman
	Title:	 	Authorized Signatory



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

SHIRE LLC

		
	By:	 	/s/ Mike Chapman
	Name:	 	Mike Chapman
	Title:	 	President



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY CONTRAFUND: FIDELITY CONTRAFUND

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY CONTRAFUND: FIDELITY ADVISOR NEW INSIGHTS FUND

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY MT. VERNON STREET TRUST: FIDELITY GROWTH COMPANY FUND

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY SELECT PORTFOLIOS: BIOTECHNOLOGY PORTFOLIO

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY ADVISOR SERIES VII: FIDELITY ADVISOR BIOTECHNOLOGY FUND

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 IN WITNESS WHEREOF, the parties have executed this Amended and Restated Investors’
Rights Agreement as of the date first written above. 
  

			
	 INVESTORS:
  

FIDELITY MAGELLAN FUND: FIDELITY MAGELLAN FUND

		
	By:	 	/s/ Adrien Deberghes
	Name:	 	Adrien Deberghes
	Title:	 	Deputy Treasurer



  
 [Signature
Page to Amended and Restated Investors’ Rights Agreement] 








 SCHEDULE A 
 Investors 
 Series A Investors 

TVM V Life Science Ventures GmbH & Co. KG 
 c/o TVM Capital 
 Maximilianstr. 35 
 Entrance C 
 80539 Munich, Germany 
 Attn: Josef Moosholzer 
 Fax: 49-89-998-992-55 

With copies to: 
 c/o TVM Capital 

470 Atlantic Ave, 4th floor 
 Boston, MA 02210

 Attn: Mark G. Cipriano 
 Fax:
617-345-9377 
 Cooperative AAC LS U.A. 
 c/o Forbion Capital Partners 
 PO Box 5187 
 1410 AD Naarden 
 The Netherlands 
 Attn: Geert-Jan Mulder 
 Fax: 31.35.699.3001 

Easton Hunt Capital Partners, L.P. 
 767 Third Avenue, 7th Floor 
 New York, NY 10017 
 Attn: John Friedman 
 Fax: 212.702.0852 
 Series B Investors 
 Third Rock Ventures, L.P. 

29 Newbury Street 
 Boston, MA 02116 

Attn.: Kevin Starr 







 TVM V Life Science Ventures GmbH & Co. KG 

c/o TVM Capital 
 Maximilianstr. 35 

Entrance C 
 80539 Munich, Germany 

Attn: Josef Moosholzer 
 Fax: 49-89-998-992-55

 With copies to: 
 c/o TVM Capital

 470 Atlantic Ave, 4th floor 
 Boston,
MA 02210 
 Attn: Mark G. Cipriano 

Fax: 617-345-9377 
 Cooperative AAC LS U.A.

 c/o Forbion Capital Partners 
 PO
Box 5187 
 1410 AD Naarden 
 The
Netherlands 
 Attn: Geert-Jan Mulder 

Fax: 31.35.699.3001 
 Easton Hunt Capital
Partners, L.P. 
 767 Third Avenue, 7th Floor 
 New
York, NY 10017 
 Attn: John Friedman 

Fax: 212.702.0852 
 Genzyme Corporation

 500 Kendall Street 
 Cambridge,
Massachusetts 02142 
 Attn: Alan Walts 

Series C Investors 
 ARCH
Venture Fund VII, L.P. 
 c/o ARCH Venture Partners 
 8725 West Higgins Road 
 Suite 290 
 Chicago, IL 60631 
 Attn: Mark McDonnell 
 Fax: 773 380 6606 
 Email: mmcdonnell@archventure.com 

Copy to: 
 ARCH Venture Partners 

1000 Second Avenue 
 Suite 3700 

Seattle, WA 98104 
 Attn: Steve Gillis, Ph. D.

 Fax: 206-674-3026 
 Email:
sgillis@archventure.com 







 With a copy (which shall not constitute notice) to: 
 Proskauer Rose LLP 
 One International Place 

Boston, MA 02110 
 Attn: Ori Solomon 

Fax: 617-526-9899 
 Email: osolomon@proskauer.com

 Third Rock Ventures, L.P. 

29 Newbury Street 
 Boston, MA 02116 

Attn.: Kevin Starr 
 TVM V Life Science
Ventures GmbH & Co. KG 
 c/o TVM Capital 
 Maximilianstr. 35 
 Entrance C 
 80539 Munich, Germany 
 Attn: Josef Moosholzer 

Fax: 49-89-998-992-55 
 With copies to:

 c/o TVM Capital 
 470 Atlantic Ave,
4th floor 
 Boston, MA 02210 
 Attn:
Mark G. Cipriano 
 Fax: 617-345-9377 

Cooperative AAC LS U.A. 
 c/o Forbion
Capital Partners 
 PO Box 5187 
 1410
AD Naarden 
 The Netherlands 
 Attn:
Geert-Jan Mulder 
 Fax: 31.35.699.3001 

Easton Hunt Capital Partners, L.P. 
 767 Third Avenue, 7th Floor 
 New York, NY 10017 
 Attn: John Friedman 
 Fax: 212.702.0852 







 Series D Investors 
 ARCH Venture Fund VII, L.P. 
 c/o ARCH Venture Partners 

8725 West Higgins Road 
 Suite 290 

Chicago, IL 60631 
 Attn: Mark McDonnell

 Fax: 773 380 6606 
 Email:
mmcdonnell@archventure.com 
 Copy to: 

ARCH Venture Partners 
 1000 Second Avenue

 Suite 3700 
 Seattle, WA 98104

 Attn: Steve Gillis, Ph. D. 
 Fax:
206-674-3026 
 Email: sgillis@archventure.com 
 Third Rock Ventures, L.P. 
 29 Newbury Street 

Boston, MA 02116 
 Attn.: Kevin Starr 

TVM V Life Science Ventures GmbH & Co. KG 
 c/o TVM Capital 
 Maximilianstr. 35 
 Entrance C 
 80539 Munich, Germany 
 Attn: Josef Moosholzer 
 Fax: 49-89-998-992-55 

With copies to: 
 c/o TVM Capital 

470 Atlantic Ave, 4th floor 
 Boston, MA 02210

 Attn: Mark G. Cipriano 
 Fax:
617-345-9377 
 Cooperative AAC LS U.A. 
 c/o Forbion Capital Partners 
 PO Box 5187 
 1410 AD Naarden 
 The Netherlands 
 Attn: Geert-Jan Mulder 
 Fax: 31.35.699.3001 







 Mag & Co fbo Fidelity Contrafund: Fidelity Contrafund 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 
 Mag & Co fbo Fidelity Contrafund: Fidelity Advisor New Insights Fund 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 
 Ball &Co fbo Fidelity Mt. Vernon Street Trust: Fidelity Growth Company Fund 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 
 Mag & Co fbo Fidelity Select Portfolios: Biotechnology Portfolio 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 
 Bangle & Co fbo Fidelity Advisor Series VII: Fidelity Advisor Biotechnology Fund 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 
 SAILBOAT & CO. fbo Fidelity Magellan Fund: Fidelity Magellan Fund 

c/o Fidelity Investments 
 82 Devonshire Street,
V13H 
 Boston, MA 02109 
 Attn: Andrew
Boyd 







 Shire LLC 
 9200 Brookfield Court 
 Florence, Kentucky 41042 

SMALLCAP World Fund, Inc. 
 333 S. Hope
Street, 55th Floor 
 Los Angeles, CA 90017 
 Attn: Michael Triessl and Don Rolfe 
 Email: mcjt@capgroup.com; 

dhr@capgroup.com 
 Fax: 213-615-0430 

American Funds Insurance Series Global Small Capitalization Fund 
 333 S. Hope Street, 55th Floor 
 Los Angeles, CA 90017 

Attn: Michael Triessl and Don Rolfe 
 Email:
mcjt@capgroup.com; 
 dhr@capgroup.com 

Fax: 213-615-0430 
 Deerfield Special
Situations Fund, L.P. 
 780 Third Avenue, 37th Floor 
 New York, New York 10017 
 Attn: Howard Furst 

Deerfield Special Situations International Master Fund, L.P. 
 780 Third Avenue, 37th Floor 
 New York, New York 10017 

Attn: Howard Furst 
 Cowen Bluebird LLC

 c/o RAMIUS 
 599 Lexington Ave

 New York, NY 10022 
 Tel:
212.201.4860 
 Fax: 212.845.7999 

Attn: Andrew Cohen | Managing Director 
 Email:
acohen@ramius.com 
 RA Capital Healthcare Fund, LP 
 c/o RA Capital Management, LLC 
 20 Park Plaza, Suite 1200 

Boston, MA 02116 
 f: 617 778 2510