Document:

Fourth amended and restated securityholders agreement

 Exhibit 10.13 
 FOURTH AMENDED AND RESTATED SECURITYHOLDERS AGREEMENT 
 THIS FOURTH AMENDED
AND RESTATED SECURITYHOLDERS AGREEMENT (the “Agreement”) is made as of the 10th day of January 2011, by and among Rib-X Pharmaceuticals, Inc. (the “Company”), the parties listed on Schedule 1 hereto (the
“Founders”), the parties listed on Schedule 2 hereto (the “Other Stockholders” and together with the Founders, the “Common Stockholders”), the parties listed on Schedule 3 hereto as
Series A-L Stockholders (the “Series A-L Holders”), the parties listed on Schedule 3 hereto as Series A-1 Stockholders (the “Series A-1 Holders”), the parties listed on Schedule 3 hereto as Series B
Stockholders (the “Series B Holders”), the parties listed on Schedule 3 hereto as Series C Stockholders (the “Series C Holders”), the parties listed on Schedule 4 hereto as Tier I Noteholders (the
“Tier I Noteholders”), the parties listed on Schedule 4 hereto as Tier II Noteholders (the “Tier II Noteholders”), the parties listed on Schedule 4 hereto as Senior Noteholders (the “Senior
Noteholders”, and together with the Tier I Noteholders and the Tier II Noteholders, the “Noteholders”) and the parties listed on Schedule 4 hereto as Warrantholders (the “Warrantholders”) (the Series
C Holders, the Series B Holders, the Series A-L Holders and the Series A-1 Holders being collectively referred to herein as the “Preferred Stockholders” and the Common Stockholders, the Preferred Stockholders, the Noteholders and
the Warrantholders being collectively referred to herein as the “Securityholders”). 
 RECITALS

 WHEREAS, the Company and the Senior Noteholders have entered into that certain Senior Convertible Demand
Promissory Note Purchase Agreement, dated as of January 10, 2011 (the “Senior Note Purchase Agreement”); 
 WHEREAS, as a condition to entering into the Senior Note Purchase Agreement, the Senior Noteholders purchasing Senior Convertible Demand Promissory Notes pursuant to the Senior Note Purchase
Agreement (the “Senior Notes”) have required that the Company and the Securityholders enter into this Agreement; 
 WHEREAS, the Company and the parties hereto are bound by a Third Amended and Restated Stockholders Agreement dated as of June 8, 2006, among the Company and the Stockholders thereunder, as
amended by that certain Amendment to Third Amended and Restated Stockholders Agreement dated as of January 7, 2009 and that certain Amendment No. 2 to Third Amended and Restated Stockholders Agreement, dated as of May 28, 2010 (the
“Prior Agreement”); 
 WHEREAS, the Company and such parties to the Prior Agreement believe that it is
in the best interests of the Company and each of them to amend and restate that Prior Agreement in its entirety; 

WHEREAS, pursuant to Section 7.4 of the Prior Agreement, the parties hereto that are (i) holders of at least a majority
of the outstanding shares of Stock (calculated on an as-if-converted and as-if-exercised basis), (ii) holders of at least a majority of the outstanding shares of Series B Convertible Preferred Stock (as defined below) and Series C Convertible
Preferred Stock (as defined below) and (iii) the Eligible Securities Majority (as defined below) desire to 

 
terminate the Prior Agreement and to accept the rights and obligations created pursuant hereto in lieu of the rights and obligations granted to them under the Prior Agreement; 

WHEREAS, pursuant to Section 9.09 of the Series B Stock Purchase Agreement (as defined below), the Company and at least 60%
of the holders of outstanding shares of Series B Convertible Preferred Stock wish to amend certain terms of the Series B Stock Purchase Agreement; 
 WHEREAS, pursuant to Section 7.09 of the Series C Stock Purchase Agreement (as defined below), the Company and a majority of the holders of outstanding shares of Series C Convertible Preferred
Stock wish to amend certain terms of the Series C Stock Purchase Agreement; and 
 WHEREAS, the Board of Directors of the
Company (the “Board of Directors”) has determined that it is in the best interests of the Company that the Company enter into this Agreement. 
 AGREEMENT 
 NOW, THEREFORE, in consideration of the foregoing, of
the mutual promises hereinafter set forth and of other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto, intending to be bound, hereby agree that the Prior Agreement shall be
terminated and replaced in its entirety by this Agreement, and the parties hereto further agree as follows: 
 SECTION 1

 DEFINITIONS 
 1.1 Definitions. The following terms shall have the following meanings whenever used in this Agreement: 
 (a) “Affiliate” shall mean with respect to any party, any partner or other equity holder of such party, or any person that, directly or indirectly, controls, is controlled by, or is under
common control with, such party. 
 (b) “as-if-converted and as-if-exercised basis” shall mean assuming
(i) conversion of each share of Series A Convertible Preferred Stock, the Series B Convertible Preferred Stock and the Series C Convertible Preferred Stock (collectively, the “Convertible Preferred Stock”), into the number of
shares of Common Stock into which such share of Convertible Preferred Stock would convert if such share then converted pursuant to Section 3(a) of the Charter (subject to adjustment as provided in Section 3(d) thereof),
(ii) conversion of the Notes into (A) the number of shares of Common Stock into which such Notes would convert by dividing (x) the Outstanding Amount (as defined in the applicable Notes) by (y) the Base Conversion Price (as
defined in the applicable Notes) as of the date of determination or (B) if in connection with, or subsequent to, an equity financing (as defined in the applicable Notes) or IPO (as defined in the applicable Notes), the number of shares of
Common Stock into which such Notes would convert pursuant to the terms of the Notes or pursuant to the terms of New Securities (as defined in the applicable Notes) in connection with such equity financing or IPO and (iii) exercise of the

  
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Warrants and issuance of the maximum number of shares of Common Stock then issuable thereunder in exchange therefor. 
 (c) “Bona Fide Offer” shall mean a legally enforceable offer in writing for the purchase of Shares owned by any of the Securityholders, made and signed by an offeror or offerors (the
“Offeror”) who is (or who are) a person or persons or entity or entities financially capable of carrying out the terms of such Bona Fide Offer. 
 (d) “Charter” shall mean the Company’s Seventh Amended and Restated Certificate of Incorporation, filed with the Secretary of State of the State of Delaware, as may be amended or
amended and restated from time to time after the date hereof. 
 (e) “Common Stock” shall mean the common stock
of the Company, par value $0.001 per share. 
 (f) “Drag-Along Event” shall mean any transaction (including,
without limitation, any change of control transaction, joint venture, partnership, liquidation or Repayment Event (as defined in the Notes)) approved by the Senior Eligible Securities Majority. 

(g) “Eligible Securities” shall have the definition ascribed to such term in the Charter. 

(h) “Eligible Securities Majority” shall have the definition ascribed to such term in the Charter. 

(i) “Investor Securityholder” shall, subject to Section 4.5 hereof, mean any Securityholder (including any such
Securityholder’s Permitted Notes Transferees) that beneficially owns Senior Notes. 
 (j) “Junior Notes”
means the Tier I Notes and the Tier II Notes. 
 (k) “Junior Note Purchase Agreement” means the Subordinated
Convertible Promissory Note Purchase Agreement, dated as of January 7, 2009, by and among the Company and the Purchasers listed therein (as the same may be amended from time to time). 

(l) “Notes” means the Junior Notes and the Senior Notes. 

(m) “Offered Shares” shall mean the Shares owned by a Securityholder of the Company (herein referred to as a
“Selling Securityholder”) that are proposed to be purchased from such Selling Securityholder in a Bona Fide Offer. 
 (n) “Permitted Notes Transferees” means any transferee of Senior Notes approved by the Eligible Securities Majority and designated as an “Investor Securityholder” for purposes
of this Agreement. 
 (o) “Preferred Stock” shall mean the Series A-1 Convertible Preferred Stock, Series A-L
Convertible Preferred Stock, Series B Convertible Preferred Stock and Series C Convertible Preferred Stock. 

  
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 (p) “Qualified Offering” shall have the definition ascribed to such term in
the Charter. 
 (q) “Registered Notice” shall mean all notices, consents and other communications made
hereunder, which shall be in writing and shall be: (i) delivered in person; (ii) mailed by certified or registered mail, return receipt requested; (iii) sent by a recognized overnight courier service; or (iv) sent by e-mail,
facsimile or other means or electronic communication, for which evidence of delivery is automatically generated (provided that if notice is provided pursuant to this clause (iv), such communication is followed promptly by a communication in the form
provided under clauses (i), (ii) or (iii)), addressed as follows: 
  

	 	(a)	if to the Company or any other party hereto, at the address of such party set forth in the applicable Schedule hereto, with a copy to the Company’s counsel;

  

	 	(b)	if to any subsequent Securityholder, to it at such address as may have been furnished to the Company in writing by such holder; 

or, in any case, at such other address as shall have been furnished in writing by the addressee to the others. Registered Notices shall be effective:
(i) upon delivery, if delivered in person; (ii) three (3) days after deposit in the U.S. mails, if mailed; (iii) on the day following deposit with the courier service, if sent by overnight courier; and (iv) upon
transmission, if sent by e-mail, facsimile or other means of electronic communication. If such Registered Notice is sent with respect to a Bona Fide Offer, such Registered Notice shall contain a true and complete copy of the Bona Fide Offer, setting
forth the number of Shares proposed to be sold by the Selling Securityholder, the price thereof and all of the terms and conditions thereof, with the name(s), address(es) (both home and office) and business(es) or other occupation(s) of the offeror
or offerors. Any notice which does not contain all such requisite information shall not be considered a “Registered Notice” for the purposes of Section 3 hereof. 

(r) “Securities Act” shall mean the United States Securities Act of 1933, as amended. 

(s) “Senior Eligible Securities” shall have the definition ascribed to such term in the Charter. 

(t) “Senior Eligible Securities Majority” shall have the definition ascribed to such term in the Charter. 

(u) “Senior Note Purchase Agreement” means the Senior Convertible Demand Promissory Note Purchase Agreement, dated as of
January 10, 2011, by and among the Company and the Purchasers listed therein. 
 (v) “Senior Notes” means
the Senior Convertible Demand Promissory Notes issued pursuant to the Senior Note Purchase Agreement. 
 (w) “Senior
Subordinated Note Purchase Agreement” means the Senior Subordinated Convertible Demand Promissory Note Purchase Agreement, dated as of May 28, 

  
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2010, by and among the Company and the Purchasers listed therein (as the same may be amended from time to time). 
 (x) “Series A-1 Convertible Preferred Stock” shall mean those shares of Preferred Stock which have been designated Series A-1 Convertible Preferred Stock and any subseries of the Series
A-1 Convertible Preferred Stock now or hereafter created thereunder (including but not limited to the Series A-1(A) Convertible Preferred Stock). 
 (y) “Series A-L Convertible Preferred Stock” shall mean those shares of Preferred Stock which have been designated Series A-L Convertible Preferred Stock. 

(z) “Series B Convertible Preferred Stock” shall have the meaning given to such term in the recitals hereto and shall
include any subseries of the Series B Convertible Preferred Stock now or hereafter created thereunder (including, but not limited to the Series B-1 Convertible Preferred Stock). 

(aa) “Series B Stock Purchase Agreement” shall mean that certain Amended and Restated Series B Convertible Preferred
Stock Purchase Agreement, dated as of April 28, 2003, between the Company and certain Preferred Stockholders. 
 (bb)
“Series C Convertible Preferred Stock” shall have the meaning given to such term in the recitals hereto and shall include any subseries of the Series C Convertible Preferred Stock now or hereafter created thereunder (including, but
not limited to the Series C-1 Convertible Preferred Stock). 
 (cc) “Series C Stock Purchase Agreement” shall
mean that certain Series C Convertible Preferred Stock Purchase Agreement, dated as of June 8, 2006, between the Company and certain Preferred Stockholders. 
 (dd) “Shares” shall mean all shares of capital Stock of the Company now beneficially owned or hereafter acquired by the Securityholders (including, without limitation, any Warrants, Notes
or other security exercisable or convertible into Shares now beneficially owned or hereafter acquired by the Securityholders). 

(ee) “Stock” shall mean the Common Stock and the Preferred Stock. 

(ff) “Stockholders” shall mean the Preferred Stockholders and the Common Stockholders. 

(gg) “Tier I Notes” shall mean the Subordinated Convertible Promissory Notes issued pursuant to the Junior Note Purchase
Agreement. 
 (hh) “Tier II Notes” shall mean the Senior Subordinated Convertible Demand Promissory Notes
issued pursuant to the Senior Subordinated Note Purchase Agreement. 
 (ii) “Warrants” means the Warrants to
Purchase Common Stock of the Company issued pursuant to (i) the Junior Note Purchase Agreement, (ii) the Senior Subordinated Note Purchase Agreement and (iii) the Senior Note Purchase Agreement. 

  
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 (jj) “WP” means WP VIII Finance, L.P. 

SECTION 2 

RESTRICTION OF STOCK 
 2.1 Scope of Agreement. This Agreement shall apply to all transfers of Shares by the Securityholders, whether voluntary, involuntary or by operation of law, whether resulting from bankruptcy,
insolvency or otherwise. 
 2.2 Restrictions on Transfer and Issuance. Except as otherwise provided in this Agreement, or
except in the event of a sale of all or substantially all of the Company’s voting securities or assets, as approved by the Board of Directors and (i) the Eligible Securities Majority or (ii) if there are no Eligible Securities
outstanding, the holders of at least a majority of the outstanding Preferred Stock, no Securityholder shall sell, exchange, deliver or assign, dispose of, or give, pledge, mortgage, hypothecate or otherwise encumber, transfer or permit to be
transferred, whether voluntarily, involuntarily or by operation of law (including, without limitation, the laws of bankruptcy, insolvency, intestacy, descent and distribution and succession), any or all of its Shares. If requested by the Company,
each Registered Notice relating to a proposed transfer of Shares shall be accompanied by an opinion of counsel reasonably satisfactory to the Company to the effect that the proposed transfer may be effected without registration under the Securities
Act and any applicable state securities laws. 
 2.3 Agreement Binding Upon Transferees. If at any time or from time to
time any Shares are transferred by a Securityholder to any party (other than the Company) pursuant to any provision hereof, the transferee shall take such Shares pursuant to all provisions, conditions and covenants of this Agreement and, as a
condition precedent to such transfer of Shares and to the right to have the transfer of such shares of Stock registered in the Company’s stock transfer record, the transferee shall agree (for and on behalf of the transferee, the
transferee’s legal representatives, permitted transferees and assigns) in writing to be bound by all provisions of this Agreement as a party hereto and in the capacity of Securityholder hereunder. If there shall be any transfer to any person or
entity pursuant to any provision of this Agreement and in compliance with the provisions of this Section 2.3, all references herein to the Securityholders shall thereafter be deemed to include such transferee or transferees. 

2.4 Stock Transfer Record. The Company shall keep a stock transfer book in which shall be recorded the name and address of each
Stockholder. No transfer or issuance of any shares of Stock shall be effective or valid unless and until recorded in such stock transfer book. The Company agrees not to record any transfer or issuance of shares of Stock in such stock transfer book
unless the transfer or issuance is in strict compliance with all provisions of this Agreement. The parties agree that in the event a Securityholder desires to make a transfer within the provisions hereof, such Securityholder shall furnish to the
Company such evidence of compliance with this Agreement as may be reasonably required by the Board of Directors, or by counsel for the Company. 
 2.5 Endorsement on Stock Certificates. Each certificate representing shares of Stock of the Company now or hereafter held by a Stockholder or any of his, her or its transferees shall bear legends
in substantially the following form: 

  
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 “THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933 OR APPLICABLE STATE SECURITIES LAWS. THESE SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO DISTRIBUTION OR RESALE, AND MAY NOT BE SOLD MORTGAGED, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED WITHOUT AN
EFFECTIVE REGISTRATION STATEMENT FOR SUCH SECURITIES UNDER THE SECURITIES ACT OF 1933 AND APPLICABLE STATE SECURITIES LAWS, OR THE AVAILABILITY OF AN EXEMPTION FROM THE REGISTRATION PROVISIONS OF THE SECURITIES ACT OF 1933 AND APPLICABLE STATE
SECURITIES LAWS.” 
 “THE VOLUNTARY OR INVOLUNTARY ENCUMBERING, TRANSFER OR OTHER DISPOSITION (INCLUDING WITHOUT
LIMITATION, ANY DISPOSITION PURSUANT TO THE LAWS OF BANKRUPTCY, INTESTACY, DESCENT AND DISTRIBUTION OR SUCCESSION) OF THE SHARES OF STOCK EVIDENCED BY THIS CERTIFICATE IS RESTRICTED UNDER THE TERMS OF A SECURITYHOLDERS AGREEMENT, AS AMENDED FROM
TIME TO TIME, TO WHICH THE HOLDER OF THIS CERTIFICATE IS A PARTY, A COPY OF WHICH AGREEMENT IS ON FILE AT THE PRINCIPAL OFFICE OF RIB-X PHARMACEUTICALS, INC. UPON WRITTEN REQUEST OF ANY SECURITYHOLDER OF THE COMPANY, THE COMPANY SHALL FURNISH,
WITHOUT CHARGE TO SUCH SECURITYHOLDER, A COPY OF SUCH AGREEMENT.” 
 A certificate shall not bear the first such legend if in the opinion
of counsel reasonably satisfactory to the Company the securities being sold thereby may be publicly sold without registration under the Securities Act. 
 2.6 Agreements by the Company. The Company agrees, for and on behalf of itself and its successors and assigns, that: (a) it hereby consents to this Agreement; (b) it shall not issue,
transfer or reissue any Shares in violation of the provisions of this Agreement; and (c) all certificates representing shares of capital Stock of the Company issued by the Company and held by a Securityholder or any of its transferees shall
bear an endorsement in substantially the form specified in Section 2.5 hereof. 
 2.7 Specific Performance. Strict
compliance shall be required with each and every provision of this Agreement, it being understood and agreed that no Securityholder shall, as set forth in Section 2.2 hereof, have the right or power to sell or assign any of his, her or its
Shares except in strict compliance with this Agreement. The parties hereto agree that the Shares are 

  
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unique, that failure to perform the obligations provided by this Agreement shall result in irreparable damage and that specific performance of these obligations may be obtained by suit in equity.

 2.8 Permitted Transfer in Event of Death. Notwithstanding the provisions of Section 2.2 hereof and subject to the
requirements of this Agreement, with respect to Securityholders that are individuals, in the event of a Securityholder’s death, all of the Shares registered on the books of the Company in the name of such deceased Securityholder may be
transferred to the executor, administrator, personal representative or estate (collectively, the “Securityholder’s Estate”) of such deceased Securityholder (and such transfers shall be registered on the books of the Company);
provided, however, that, as conditions precedent to the transfer of such Shares, the Securityholder’s Estate shall: (a) provide (or cause to be provided) to the Company (if requested by the Company) sufficient evidence of the
legal right and authority of such prospective transferee to have such Shares so transferred and registered; and (b) comply with the provisions of this Agreement. 
 2.9 Permitted Transfers to Family Members and Affiliates. Notwithstanding the provisions of Section 2.2 hereof and subject to the requirements of this Agreement, a Securityholder may transfer
any or all of his or her Shares to his or her spouse or children or to a trust established for the benefit of his or her spouse, children or himself or herself, in the case of Securityholders that are individuals, or to any Affiliate, in the case of
Securityholders that are not individuals (each such transferee being herein referred to as a “Permitted Transferee”); provided, however, that, as conditions precedent to the transfer of such Shares, the Permitted
Transferee shall: (a) provide (or cause to be provided) to the Company (if requested by the Company) sufficient evidence of the legal right and authority of such prospective transferee to have such Shares so transferred and registered; and
(b) comply with the provisions of this Agreement. 
 SECTION 3 

RIGHTS OF FIRST REFUSAL 
 AND TAG ALONG RIGHTS IN SALES BY SECURITYHOLDERS 
 3.1 Notice of Bona Fide
Offer. If a Selling Securityholder shall receive a Bona Fide Offer and in the further event that the Selling Securityholder shall desire to accept such Bona Fide Offer, then the Selling Securityholder shall promptly send Registered Notice
(i) to the Company and (ii) if the Selling Securityholder is a Founder, Preferred Stockholder, Noteholder or Warrantholder, to the Investor Securityholders (“Notice of Proposed Sale”), offering to sell the Offered Shares
to the Company and the Investor Securityholders at the same price and upon the same terms and conditions as are contained in the Bona Fide Offer in the manner set forth in Section 3.2 hereof. Upon compliance with the provisions of this section,
the Company and the Investor Securityholders shall then have such rights and privileges, for the prescribed time period, as are set forth in Section 3.2 hereof. 
 3.2 Procedure Relating to Receipt of a Bona Fide Offer. Whenever under Section 3.1 hereof a Bona Fide Offer has been received by the Selling Securityholder and Notice of Proposed Sale has been
sent by the Selling Securityholder to the Company and, if applicable, the Investor Securityholders, the following procedure shall be complied with: 

  
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 (a) Company Option. For a period of thirty (30) days after receipt of a Notice
of Proposed Sale, the Company shall have the right to purchase all or any part of the Offered Shares at the monetary value per Share designated in the Notice of Proposed Sale. Not later than thirty (30) days after delivery of the Notice of
Proposed Sale, the Company shall deliver to the Selling Securityholder and, if the Selling Securityholder is a Founder, Preferred Stockholder, Noteholder or Warrantholder, the Investor Securityholders, a Registered Notice (the “Company
Notice”) stating the number of Offered Shares (if any) for which the Company has accepted the offer stated in the Notice of Proposed Sale, or that the Company does not desire to purchase any of the Offered Shares. The closing of any
purchase of Offered Shares by the Company shall take place no later than fifteen (15) days after the end of the thirty (30) day period set forth above if the Company is purchasing all of the Offered Shares and no later than fifteen
(15) days after the end of the thirty (30) day period set forth in Subsection (b) below if the Company is purchasing less than all of the Offered Shares. Notwithstanding the foregoing, the requirements of this Section 3.2(a) and
the notice requirement of Section 3.1, as it applies to notice to the Company, may be waived by the Senior Eligible Securities Majority. 
 (b) Securityholder Option. If the Company has not elected to purchase all of the Offered Shares pursuant to Section 3.2(a) and the Selling Securityholder is a Founder, Preferred Stockholder,
Noteholder or Warrantholder, the procedures of this Section 3.2(b) shall be complied with. For a period of thirty (30) days after receipt of the Company Notice, each Investor Securityholder shall have the right to purchase all or any part
of its Proportionate Percentage (as defined below) of the Offered Shares not purchased by the Company at the monetary value per Share designated in the Notice of Proposed Sale, pursuant to the terms of this Section 3.2. Not later than thirty
(30) days after delivery of the Company Notice, each Investor Securityholder desiring to purchase all or any part of its Proportionate Percentage of the Offered Shares not purchased by the Company (each, a “Buying
Securityholder”) shall deliver to the Company, the other Investor Securityholders and the Selling Securityholder Registered Notice (the “Buying Securityholder’s Notice”) stating that the Buying Securityholder has
accepted the offer stated in the Notice of Proposed Sale with respect to all or any part of its Proportionate Percentage of the Offered Shares not purchased by the Company. If one or more of the Buying Securityholders elects not to purchase all of
the Offered Shares not purchased by the Company which it is entitled to purchase pursuant to this Section 3.2(b), the other Investor Securityholders, by written notice to the Company and the Selling Securityholder within five (5) days
after the end of the thirty (30) day period set forth above, may elect to purchase all or a part of such unpurchased Offered Shares pro rata between or among them or in such other manner as they may agree. The closing of any purchase of the
Offered Shares by the Buying Securityholders shall take place no later than fifteen (15) days after the end of the thirty (30) day period set forth above, and shall take place on the same day as the closing of the purchase of Offered
Shares by the Company pursuant to Section 3.2(a) if the Company is purchasing Offered Shares. As used in this Section 3.2(b), the term “Proportionate Percentage” shall mean, with respect to each Buying Securityholder, a
fraction, the numerator of which is the number of shares of Common Stock into which the Senior Notes held by such Buying Securityholder are convertible as of the date of the Notice of Proposed Sale, and the denominator of which is the total number
of shares of Common Stock into which the Senior Notes held by all Investor Securityholders (other than the Selling Securityholder if such Selling Securityholder is an Investor Securityholder) on such date. Notwithstanding the foregoing, the
requirements of this Section 3.2(b) and the notice 

  
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requirement of Section 3.1, as it applies to notice to the Investor Securityholders may be waived by the Senior Eligible Securities Majority. 

(c) Closing. The place for the closing of any purchase and sale described in Sections 3.2(a) and 3.2(b) shall be the principal
office of the Company or at such other place as the parties shall agree. At the closing, the Selling Securityholder shall accept payment on the terms offered by the proposed transferee named in the Notice of Proposed Sale; provided,
however, that the Company and Buying Securityholders, as applicable, shall not be required to meet any non-monetary terms of the proposed transfer, including, without limitation, delivery of other securities in exchange for the Shares
proposed to be sold. If the terms of the Notice of Proposed Sale provide for non-monetary consideration, the Company and Buying Securityholder(s), as applicable, shall pay the fair market value of such non-cash consideration, as determined in good
faith by the Board of Directors. At the closing, the Selling Securityholder shall deliver to the Company and Buying Securityholders, as applicable, in exchange for Shares purchased and sold at the closing, certificates for the number of Shares
stated in the Selling Securityholder’s Notice, accompanied by duly executed instruments of transfer. 
 (d) Failure to
Purchase All Offered Shares; Transfers to Third Parties. If the Company and Buying Securityholders in aggregate fail to accept the offer stated in the Notice of Proposed Sale with respect to all of the Offered Shares in accordance with the
procedures set forth in this Section 3.2, the Selling Securityholder shall be free to sell all, but not less than all, of the Offered Shares not purchased by the Company and the Buying Securityholders to the designated transferee at a price and
on terms no less favorable to the Selling Securityholder than described in the Notice of Proposed Sale; provided, however, that: (i) the Selling Securityholder must provide Registered Notice of its intent to proceed with the sale
(the “Second Notice of Transfer”); and (ii) such sale must be consummated no later than ninety (90) days after the giving of the Notice of Proposed Sale pursuant to Section 3.2(a). As a condition precedent to the
effectiveness of a transfer pursuant to this Section 3.2(d), the proposed transferee(s) shall agree in writing prior to such transfer to become a party to this Agreement and shall thereafter be permitted to transfer Shares only in accordance
with this Agreement. 
 3.3 Participation in Sales. 

(a) Tag-Along Right. In the event that: (i) any Securityholder (the “Offeree”) receives a Bona Fide Offer
from a third party or parties other than the Company or any other Securityholder (the “Third Party Buyer”) to purchase Shares owned by the Offeree; (ii) the Company and the Investor Securityholders do not exercise their
respective rights of first refusal under Section 3.2 hereof with respect to all of the Offered Shares; and (iii) the Offeree proposes to sell or otherwise transfer the Offered Shares not purchased by the Company and the Investor
Securityholders (the “Tag-Along Shares”) to the Third Party Buyer pursuant to the Bona Fide Offer, then each Investor Securityholder shall have the right to sell to the Third Party Buyer, at the same price per share and on the same
terms and conditions as stated in the Bona Fide Offer, that portion of the Tag-Along Shares as the number of shares of Common Stock into which the Senior Notes held by such Investor Securityholder are convertible as of the date of the Bona Fide
Offer bears to the total number of shares of Common Stock into which the Senior Notes held by all Investor Securityholders (other than the Offeree, if the Offeree is an Investor Securityholder) are convertible as of the date thereof. Notwithstanding
the foregoing, the requirements of this 

  
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Section 3.3(a) may be waived by the Senior Eligible Securities Majority. Notwithstanding the foregoing, this Section 3.3 shall not apply to any transfers in connection with a
transaction that results in a termination of this Agreement pursuant to Section 7.8(d). 
 (b) Notice of Offer and
Intent to Participate. If an Investor Securityholder wishes to participate in any sale pursuant to Section 3.3(a) it shall provide a Registered Notice to the Offeree stating such intention and the number of Shares it wishes to sell pursuant
to this Section 3.3 not later than fifteen (15) days after delivery of the Second Notice of Transfer (as described in Section 3.2(d) above). If the Offeree does not receive such Registered Notice from an Investor Securityholder within
such fifteen (15) day period, the Offeree shall be free to consummate the proposed transaction without any obligation to include such Investor Securityholders’ Shares in such transaction; provided, however, that such sale
must be consummated within the ninety (90) day period described in Section 3.2(d). 
 (c) Sale of Tag-Along
Shares. The Offeree and each Investor Securityholder that provided timely notice in accordance with Section 3.3(b) above shall sell to the Third Party Buyer all, or at the option of the Third Party Buyer, any part of the Shares proposed to
be sold by them at not less than the price and upon other terms and conditions, if any, not more favorable to the Third Party Buyer than those stated in the Bona Fide Offer; provided, however, that any purchase of less than all of such
Shares by the Third Party Buyer shall be made from the Offeree and each Investor Securityholder pro rata based upon the relative amount of the shares that the Offeree and such Investor Securityholder is entitled to sell pursuant to
Section 3.3(a). 
 3.4 Certain Arrangements. 

(a) Drag-Along Rights. So long as any Senior Eligible Securities remain outstanding, if the Senior Eligible Securities Majority
approves or otherwise elects to pursue a transaction that is a Drag-Along Event, then each Securityholder shall consent to, and vote its Shares (including, without limitation, any Shares in respect of any warrants, notes or other security
exercisable or convertible into Shares held by such Securityholder) in favor of, the Drag-Along Event and take such action necessary to comply herewith and facilitate the Drag-Along Event, and if the Drag-Along Event is structured as (a) a
merger or consolidation of the Company, or a sale of all or substantially all of the Company’s assets, each Securityholder hereby waives any dissenters’ rights, appraisal rights or similar rights in connection with such merger,
consolidation or asset sale, or (b) a sale of the stock of the Company, the Securityholders hereby agree to sell their Shares and, to the extent applicable, other Company securities (including, without limitation, any Shares issuable in respect
of any warrants, notes or other security exercisable or convertible into Shares held by such Securityholder) on the terms and conditions approved by the Senior Eligible Securities Majority, provided that the proceeds available for distribution to
the Company’s stockholders shall be distributed in accordance with the terms of the Charter. 
 (b) Other Voting
Arrangements. So long as any Senior Eligible Securities remain outstanding, in connection with any public offering of securities by the Company (a “Public Offering”) requested by the Senior Eligible Securities Majority to be
pursued by the Company, each Securityholder (i) will, at the request of the Senior Eligible Securities Majority, consent to and vote its Shares and, to the extent applicable, other securities in respect of the Company

  
 - 11 -

 
(including, without limitation, any Shares issuable in respect of any warrants, notes or other security exercisable or convertible into Shares held by such Securityholder) in favor of such Public
Offering and (ii) hereby consents to the conversion of, and hereby elects to convert, all Preferred Stock and Notes then held by such Securityholder into Common Stock (subject to the consummation of the public offering). 

(c) Further Assurances. Each Securityholder shall take, and cause to be taken, all such further actions as may be reasonably
requested to evidence or effectuate the provisions of subsections (a) and (b) of this Section 3.4. 
 3.5
Grant of Proxy. Each Securityholder hereby irrevocably constitutes and appoints the Company, on the one hand, and Senior Eligible Securities Majority, on the other hand, acting jointly and any representative or agent thereof with full power
of substitution, as its true and lawful attorney-in-fact with full irrevocable power and authority in the place and stead of such Securityholder and in the name of such Securityholder or in its own name, for the purpose of carrying out the terms of
Section 3.4 or the terms of the last paragraph of Section 5.1 hereof, to take any and all appropriate action and to execute any and all documents and instruments which may be necessary or desirable to accomplish the purposes of such
provisions, including without limitation any amendment to this Agreement in respect thereof or relating thereto. This proxy is coupled with an interest and is irrevocable, and each Securityholder will take such further action and execute such other
instruments as may be necessary to effect the intent of this proxy and hereby revokes any proxy previously granted by it with respect to its Shares. Each Securityholder hereby ratifies all that said attorneys shall lawfully do or cause to be done by
virtue hereof. 
 SECTION 4 
 RIGHT OF PARTICIPATION IN SALES BY THE COMPANY 
 4.1 Right of
Participation. Except as provided in Section 4.3(e) or 4.4 of this Agreement, the Company shall not issue, sell or exchange, agree or obligate itself to issue, sell or exchange, or reserve or set aside for issuance, sale or exchange,
(a) any equity security of the Company, including without limitation, shares of Stock, (b) any debt security of the Company which by its terms is convertible into or exchangeable for any equity security of the Company, or (c) any
option, warrant or other right to subscribe for, purchase or otherwise acquire any such equity security or any such debt security of the Company, unless in each case the Company shall have first offered to sell such securities (the “Offered
Securities”) to the Investor Securityholders as follows: the Company shall offer to sell to each Investor Securityholder (i) that portion of the Offered Securities as the number of shares of Common Stock into which the Senior Notes
then held by such Investor Securityholder can be converted bears to the total number of shares of Common Stock into which the Senior Notes then held by all Investor Securityholders can be converted on such date (the “Basic Amount”),
and (ii) such additional portion of the Offered Securities as such Investor Securityholder shall indicate it will purchase should the other Investor Securityholders subscribe for less than their Basic Amounts (the “Undersubscription
Amount”), at a price and on such other terms as shall have been specified by the Company in writing delivered to such Investor Securityholder (the “Offer”), which Offer by its terms shall remain open and irrevocable for a
period of twenty (20) business days from 

  
 - 12 -

 
receipt of the offer. For purposes of this Section 4, an Investor Securityholder shall include any fund managed by the principals of that Investor Securityholder. 

4.2 Notice of Acceptance. Notice of each Investor Securityholder’s intention to accept, in whole or in part, any Offer made
pursuant to Section 4.1 shall be evidenced by a writing signed by such Investor Securityholder and delivered to the Company prior to the end of the 20 business day period of such offer, setting forth such of the Investor Securityholder’s
Basic Amount as such Investor Securityholder elects to purchase and, if such Investor Securityholder shall elect to purchase all of its Basic Amount, such Undersubscription Amount, if any, as such Investor Securityholder shall offer to purchase (the
“Notice of Acceptance”). If the Basic Amounts subscribed for by all Investor Securityholders are less than the total portion of the Offered Securities offered to the Investor Securityholders, then each Investor Securityholder who
has set forth Undersubscription Amounts in its Notice of Acceptance shall be entitled to purchase, in addition to the Basic Amount is has subscribed for, the Undersubscription Amount it has offered to purchase; provided, however, that
should the Undersubscription Amounts subscribed for exceed the difference between the Offered Securities and the Basic Amounts subscribed for (the “Available Undersubscription Amount”), each Investor Securityholder who has offered
to purchase any Undersubscription Amount shall be entitled to purchase only that portion of the Available Undersubscription Amount as the Undersubscription Amount that such Investor Securityholder has offered to purchase bears to the total
Undersubscription Amounts that all Investor Securityholders have offered to purchase, subject to rounding by the Board of Directors to the extent it reasonably deems necessary. 

4.3 Conditions to Acceptances and Purchase. 
 (a) Permitted Sales of Refused Securities. If Notices of Acceptance are not given by the Investor Securityholders in respect of all the Offered Securities, the Company shall have ninety
(90) days from the expiration of the period set forth in Section 4.1 to close the sale of all or any part of such Offered Securities as to which a Notice of Acceptance has not been given by the Investor Securityholders (the
“Refused Securities”) to the person or persons specified in the Offer, but only for cash and otherwise in all respects upon terms and conditions, including, without limitation, unit price and interest rates, which are no more
favorable, in the aggregate, to such other person or persons than those set forth in the Offer. 
 (b) Reduction in Amount of
Offered Securities. If the Company shall propose to sell less than all the Refused Securities (any such sale to be in the manner and on the terms specified in Section 4.3(a) above), then each Investor Securityholder may, at its sole option
and in its sole discretion, reduce the number of, or other units of the Offered Securities specified in its respective Notices of Acceptance to an amount which shall be not less than the amount of the Offered Securities which it elected to purchase
pursuant to Section 4.2 multiplied by a fraction, (i) the numerator of which shall be the amount of Offered Securities which the Company actually proposes to sell, and (ii) the denominator of which shall be the amount of all Offered
Securities. If any Investor Securityholder so elects to reduce the number or amount of Offered Securities specified in its Notice of Acceptance, the Company may not sell or otherwise dispose of more than the reduced amount of the Offered Securities
until such securities have again been offered to the Investor Securityholders in accordance with Section 4.1. 

  
 - 13 -

 (c) Closing. Upon the closing, which shall include full payment to the Company, of
the sale to such other person or persons of all or less than all the Refused Securities, the Investor Securityholders shall purchase from the Company, and the Company shall sell to the Investor Securityholders, the number of Offered Securities
specified in the Notices of Acceptance, as reduced pursuant to Section 4.3(b) if the Investor Securityholders have so elected, upon the terms and conditions specified in the Offer. 

(d) Further Sale. In each case, any Offered Securities not purchased by the Investor Securityholders or other person or persons in
accordance with Section 4.3 may not be sold or otherwise disposed of until they are again offered to the Investor Securityholders under the procedures specified in Sections 4.1, 4.2 and 4.3. 

(e) Exception. The rights of the Investor Securityholders under this Section 4 shall not apply to the issuance of:

 (i) Common Stock issued as a stock dividend to holders of Common Stock or upon any subdivision or combination
of shares of Common Stock; 
 (ii) shares of a particular series of convertible Preferred Stock issued as a
dividend to holders of such series of convertible Preferred Stock upon any subdivision or combination of shares of such series of convertible Preferred Stock or shares of Preferred Stock issued pursuant to Article Fourth, Section 3(d)(iii)(D)
of the Charter; 
 (iii) the Conversion Shares (as defined in the Series C Stock Purchase Agreement); 

(iv) Common Stock issued pursuant to the acquisition of another corporation by the Company by merger or purchase of
substantially all of its stock or assets, if such acquisition is approved by (a) the majority vote or written consent of the Board of Directors (which majority shall include, if there are no Eligible Securities outstanding, at least two of the
Preferred Designees (as defined below)) and (b) for so long as any Senior Eligible Securities are outstanding, the Senior Eligible Securities Majority; 
 (v) Common Stock offered to the public pursuant to an underwritten registration statement filed under the Securities Act resulting in an automatic conversion of all outstanding shares of Preferred Stock;

 (vi) up to 48,498,196 shares of Common Stock, issued or issuable to officers, Founders, employees or directors
of, or consultants to, the Company pursuant to a stock purchase or option plan or other compensatory stock arrangements approved by the Board of Directors; provided, that such plans or arrangements are approved by (a) the majority vote
or written consent of the Board of Directors (which majority shall include, if there are no Eligible Securities outstanding, at least two of the Preferred Designees) and (b) for so long as any Senior Eligible Securities are outstanding, the
Senior Eligible Securities Majority; 
 (vii) shares of Stock issued or issuable upon conversion of any
convertible securities (including the Notes) or exercise of any options outstanding on the date on 

  
 - 14 -

 
which shares of Preferred Stock are first issued, including the issuance of any replacement or balance security issued in respect thereof; and 

(viii) grants or issuances of Stock or of rights, options or warrants (including the Warrants) to purchase Stock
outstanding from time to time, granted or issued to strategic partners, lenders, equipment lessors or other financing sources who have entered into a strategic relationship with the Company or provided the Company with financing and the shares of
Common Stock issued or issuable upon exercise of such rights, options and warrants (including the Warrants); provided, that such arrangements are approved by (a) the majority vote or written consent of the Board of Directors (which
majority shall include, if there are no Eligible Securities outstanding, at least two of the Preferred Designees) and (b) for so long as any Senior Eligible Securities are outstanding, the Senior Eligible Securities Majority. 

4.4 Waiver. The rights of the Investor Securityholders under this Section 4 may be waived in any instance, on behalf of all
of the Investor Securityholders, prospectively or retroactively, by the Senior Eligible Securities Majority. 
 SECTION 5

 BOARD OF DIRECTORS 
 5.1 Election of Directors. The Securityholders and the Company agree that they shall at all times and from time to time, if lawfully permitted to do so and as provided in the Company’s
Charter, take any and all actions necessary or required (including, without limitation, voting their shares of Stock, and, if applicable, causing their designees to the Board of Directors, if any, to vote as directors) in a manner so that
(1) the Board of Directors shall consist of at least ten (10) members, (2) if WP exercises its rights pursuant to Section 4.06 of the Junior Note Purchase Agreement, the Board of Directors shall consist of eleven
(11) members and (3) that the Board of Directors shall include the following members: 
 (a) one (1) individual
(the “Series C Designee”) elected by the holders of Series C Convertible Preferred Stock; 
 (b) one
(1) individual (the “Oxford Designee”) designated by Oxford Bioscience Partners IV L.P. (“Oxford”); 
 (c) one (1) individual (the “EuclidSR Designee”, and, together with the Oxford Designee, the “Series A Designees”) designated by EuclidSR Partners, L.P. and EuclidSR
Biotechnology Partners, L.P. (collectively, “EuclidSR”); 
 (d) one (1) individual who is the Chief
Executive Officer of the Company, who shall initially be Mark Leuchtenberger; 
 (e) one (1) individual elected by the
Common Stockholders in accordance with the Company’s Charter and by-laws, with Mr. Harry Penner, Jr. to be the initial representative of the Common Stockholders; 

  
 - 15 -

 (f) two (2) individuals (the “Series B Designees” and, together with
the Series A Designees and the Series C Designee, the “Preferred Designees”) designated by WP for as long as it continues to hold at least 40% of the shares of Series B Convertible Preferred Stock originally purchased by it;

 (g) in the event that WP exercises its rights pursuant to Section 4.06 of the Junior Note Purchase Agreement, one
(1) individual (the “Noteholder Designee”) designated by WP; and 
 (h) three (3) individuals with
relevant industry experience jointly designated by the directors appointed pursuant to Sections 5.1(a) through (g) above; 

provided, however, that notwithstanding the foregoing, for so long as any of the Eligible Securities remain outstanding, the Board of
Directors shall include at least a majority of individuals designated by the Eligible Securities Majority. In such event, (I) the members of the Board of Directors specified in clauses (a), (b), (c), (f) and (g) of this
Section 5.1 shall instead be designated by the Eligible Securities Majority, voting together as a single class and (II) any reference herein to “Preferred Designees” shall mean and refer to the designees appointed pursuant to
clause (I) of this paragraph. Furthermore, for so long as any of the Eligible Securities remain outstanding, the Eligible Securities Majority shall be entitled, upon written notice to the Company, to elect to decrease the number of directors on
the Board of Directors of the Company to no less than seven (7) members, and in the event of such a decrease, the Board of Directors shall consist of (i) a majority of individuals designated by the Eligible Securities Majority,
(ii) one individual designated as contemplated by Section 5.1(d) above and (iii) 2 individuals designated as contemplated by Section 5.1(h) (provided that such individuals shall be designated jointly by the directors appointed
pursuant to the foregoing clauses (i) and (ii)) and the obligations of the Company and the Securityholders to take any and all actions necessary or required (including, without limitation, voting their shares of Stock, and, if applicable,
causing their designees to the Board of Directors, if any, to vote as directors) in a manner so that the Board includes such individuals in this Section 5.1 shall apply. The parties acknowledge that such an election has been made prior to the
date hereof. 
 5.2 WP Rights After Conversion. 
 (a) After the conversion of the Series B Convertible Preferred Stock in accordance with the Charter, for so long as WP owns beneficially at least 40% of the shares of Common Stock issuable upon
conversion of the Series B Convertible Preferred Stock initially purchased by it, the Company will nominate and use its best efforts to elect to the Board of Directors two individuals designated by WP, and (ii) for so long as WP owns
beneficially at least 20% (but less than 40%) of such shares of Common Stock, the Company will nominate and use its best efforts to elect to the Board of Directors one individual designated by WP. 

(b) After the conversion of the Notes, for so long as WP owns beneficially at least 40% of the shares of Common Stock issuable upon
conversion of the Notes (or upon conversion of the securities issued upon conversion of the Notes) initially purchased by WP, the Company will nominate and use its best efforts to elect to the Board of Directors one (1) individual (in addition
to and not in lieu of the individuals contemplated by Section 5.2(b)) designated by WP. 

  
 - 16 -

 5.3 Vacancy; Removal. So long as the Securityholders are entitled to elect directors
pursuant to this Agreement, any vacancy in the position of a director may be filled only by a person designated by the Securityholders entitled by this Agreement to designate the individual whose position has become vacant. A director may, during
such director’s term of office, be removed at any time, with or without cause, only by the affirmative vote of the holders of Stock entitled to designate such director pursuant to this Agreement; provided, that, either individual
appointed pursuant to Section 5.1(f) above may be removed by a majority of the Preferred Designees. 
 5.4 Observation
Rights. With respect to any meeting of the Board of Directors or any committee thereof, at the invitation of the Board of Directors or any such committee, any or all of (a) CHP II, L.P., (b) Connecticut Innovations, Inc.,
(c) Axiom Venture Partners III, L.P., (d) Vox Equity Partners, L.P., (e) collectively, ABS Ventures VII, L.P. and ABS Investors L.L.C., (f) WP, (g) MedImmune Ventures, Inc., (h) Radius Venture Partners II, L.P.,
(i) Oxford, (j) EuclidSR, (k) SR One, Limited, and (l) Saints Capital VI, L.P. may designate an observer to attend such meeting of the Board of Directors or any committee thereof, so long as such entity is an Investor
Securityholder. With respect to any meeting of the Board of Directors or any committee thereof, at the invitation of the Board of Directors or such committee, the Common Stockholders may designate an observer to attend such meeting of the Board of
Directors or any committee thereof, so long as such designee is Thomas Steitz. The participation of any observer shall be conditioned upon such observer entering into a confidentiality agreement reasonably satisfactory to the Company. 

SECTION 6 

REMEDIES REGARDING PURCHASES 
 6.1 Delivery of Stock and Documents. Upon the closing of any purchase of any shares of Stock pursuant to this Agreement, the Securityholder shall deliver to the Company the following: (a) the
certificate or certificates representing the shares of such Stock being sold, duly endorsed for transfer; and (b) bearing such documentary stamps, if any, as are necessary, and such assignments, certificates of authority, tax releases, consents
to transfer, instruments and evidences of title of the Securityholder and of such Securityholder’s compliance with this Agreement as may be reasonably required by the Company or by counsel for the Company. 

6.2 Remedy for Failure to Transfer Shares. In the event that a Securityholder is required to sell or assign any Shares to the
Company pursuant to this Agreement, and the Securityholder that is required to sell or assign his, her or its Shares is unable to, or for any reason does not, deliver the certificate or certificates evidencing such Shares to the Company in
accordance with the applicable provisions of this Agreement, the Company may deposit the purchase price for such Shares (by good check, promissory note or both, as the case may be under the applicable provisions of this Agreement) with any bank
doing business within fifty (50) miles of the Company’s principal office, or with the Company’s certified public accountant, as agent or trustee, or in escrow, for such Securityholder, to be held by such bank or accountant until
withdrawn by such Securityholder. Upon such deposit by the Company and upon notice to the Securityholder that was required to sell or assign his, her or its Shares, such Shares shall at such time be deemed to have been sold, assigned, transferred
and conveyed to the Company, and 

  
 - 17 -

 
such Securityholder shall have no further rights thereto and the Company shall record such transfer in its stock transfer book. 

SECTION 7 

MISCELLANEOUS 

7.1 Notices. Any and all notices, requests or other communications hereunder provided for herein shall be given in writing as
Registered Notices, and such notices shall be addressed: (a) if to the Company, to the principal office of the Company; (b) if to a Securityholder, to the address of such Securityholder as reflected in the stock records of the Company or
in the Schedules to this Agreement, unless notice of a change of address is furnished to all parties in the manner provided in this Section 7.1. Any notice which is required to be made within a stated period of time shall be considered timely
if delivered or mailed before midnight of the last day of such period. 
 7.2 Invalid or Unenforceable Provisions. The
invalidity or unenforceability of any particular provision of this Agreement shall not affect the other provisions hereof, and this Agreement shall be construed in all respects as if such invalid or unenforceable provision were omitted. 

7.3 Benefit and Burden. This Agreement shall inure to the benefit of, and shall be binding upon, the parties hereto and their
successors and assigns, and other legal representatives. In the event that any Securityholder transfers any of his or her Shares hereunder, as and to the extent permitted pursuant to this Agreement, such designee shall take such Shares subject to
all of the terms and provisions of this Agreement. 
 7.4 Waiver; Amendment. Except as otherwise set forth herein, no
waiver of any provision of this Agreement shall be valid unless in writing and signed by the person against whom it is sought to be enforced. The failure of any party at any time to insist upon strict performance of any condition, promise, agreement
or understanding set forth herein shall not be construed as a waiver or relinquishment of the right to insist upon strict performance of the same or any other condition, promise, agreement or understanding at a future time. Any of the terms or
provisions of this Agreement may be amended, modified, terminated or waived with and only with the written consent or affirmative vote of the Senior Eligible Securities Majority; provided, however, that any amendment or modification of
any provision of this Agreement that materially adversely affects the express rights or obligations of the Common Stockholders or the Preferred Stockholders shall require the written consent or affirmative vote of the holders of a majority of the
outstanding Stock (calculated on an as-if-converted and as-if-exercised basis). 
 7.5 Information and Inspection; Amendment
to Stock Purchase Agreements. Notwithstanding any other agreement between any Securityholder and the Company, no Securityholder shall be entitled to any information rights, inspection rights or similar rights with respect to the Company except
as required by law or as agreed in writing on or after the date of this Agreement. In furtherance, and not in limitation, of the foregoing, (i) the Company and the holders of 60% of the outstanding Series B Convertible Preferred Stock hereby
amend the Series B Stock Purchase Agreement to delete Article VIII thereof in its entirety, except for Section 8.02 thereof, which shall remain in full force and effect; and (ii) the Company and the holders of a

  
 - 18 -

 
majority of the outstanding Series C Convertible Preferred Stock hereby amend the Series C Stock Purchase Agreement to delete Article VI thereof in its entirety, except for Section 6.02
thereof, which shall remain in full force and effect. 
 7.6 Governing Law. This Agreement shall be construed and
enforced in accordance with the laws of the State of Delaware, without reference to its conflict of laws or choice of law principles. 
 7.7 Headings. The headings, subheadings and other captions of this Agreement are for convenience and reference only and shall not be used in interpreting, construing or enforcing any of the
provisions of this Agreement. 
 7.8 Term of Agreement. This Agreement shall be effective as of the date first
hereinabove set forth and shall terminate upon the earliest to occur of any one of the following events: 
 (a) The liquidation,
dissolution or indefinite cessation of the business operations of the Company; 
 (b) The execution by the Company of a general
assignment for the benefit of creditors or the appointment of a receiver or trustee to take possession of the property and assets of the Company; 
 (c) A Qualified Offering resulting in the automatic conversion to Common Stock of all outstanding shares of Preferred Stock; provided, however, that Section 5.2 shall survive and shall not be
terminated upon a Qualified Offering; 
 (d) The sale, conveyance or disposal of all or substantially all of the Company’s
property or business or the Company’s merger into or consolidation with any other corporation (other than a wholly-owned subsidiary corporation) for cash or if the Company effects any transaction or series of related transactions in which more
than fifty percent (50%) of the voting power of the Company is disposed of, provided that this Section 7.8(d) shall not apply to a merger effected exclusively for the purpose of changing the domicile of the Company; or 

(e) With respect to the obligations of any party of this agreement, when such party no longer owns any Common Stock, any options to
purchase Common Stock, warrants or other securities exercisable for Common Stock or securities convertible into Common Stock. 

7.9 No Sale Period. If requested in writing by the underwriters for an underwritten public offering of securities of the Company,
the Company and each Securityholder agree not to sell, make any short sale of, grant any option to buy or otherwise transfer any interest in its shares of Common Stock or Common Stock issuable upon the conversion of Preferred Stock or Notes or
exercise of Warrants (other than shares of Common Stock being registered in such offering), without the consent of such underwriters, for a period of not more than one hundred eighty (180) days following the consummation of such public
offering; provided, however, that all executive officers, directors and holders of at least three percent (3%) of the outstanding equity securities of the Company shall also have agreed not to sell publicly their stock of the
Company under the circumstances and pursuant to the terms set forth in this Section 7.9. The 

  
 - 19 -

 
Company may impose stop-transfer instructions with respect to the securities subject to the foregoing restriction until the end of such 180 day period. 

7.10 Counterparts. This Agreement may be executed in any number of counterparts, all of which together shall constitute one
instrument. 
 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK] 

  
 - 20 -

 IN WITNESS WHEREOF, the parties hereto have caused this Fourth Amended and Restated
Securityholders Agreement to be executed by their duly authorized representatives, as of the date first above written. 
  

							
	THE COMPANY:    	 	
			
		 		 	RIB-X PHARMACEUTICALS, INC.
				
		 		 	By:	 	 /s/ Mark Leuchtenberger

		 		 	Name:	 	Mark Leuchtenberger
		 		 	Title:	 	President and Chief Executive Officer

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement 

 
					
	SECURITYHOLDERS
	
	WP VIII FINANCE, L.P.
		
	By:	 	WPVIII GP, L.P., its General Partner
	By:	 	Warburg Pincus Private Equity VIII, L.P.,
		 	its General Partner
	By:	 	 Warburg Pincus Partners, LLC, its General
 Partner

	By:	 	Warburg Pincus & Co., its Managing Member
		
	By:	 	 /s/ Jonathan Leff

		 	Name:	 	Jonathan Leff
		 	Title:	 	Partner
	
	AXIOM VENTURE PARTNERS III, LP
		
	By:	 	 /s/ Alan Mendelson

		 	Name:	 	Alan Mendelson
		 	Title:	 	General Partner
	
	CHP II L.P.
		
	By:	 	CHP II Management, LLC, its General Partner
		
	By:	 	 /s/ John J. Park

		 	Name:	 	John J. Park
		 	Title:	 	Managing Member

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement

 
					
	RADIUS VENTURE PARTNERS II L.P.
	By: Radius Venture Partners II, LLC, its General Partner
		
	By:	 	 /s/ Jordan S. Davis

		 	Name:	 	Jordan S. Davis
		 	Title:	 	Managing Member
	
	ABS VENTURES VII L.P.
	By:	 	Calvert Capital Caymans I L.L.C.
		
	By:	 	 /s/ Bruns H. Grayson

		 	Name:	 	Bruns H. Grayson
		 	Title:	 	Managing Member
	
	VOX EQUITY PARTNERS, L.P.
		
	By:	 	 /s/ Matthew K. Kelley

		 	Name:	 	M. Kelley
		 	Title:	 	MGP
	
	VOX EQUITY PARTNERS II, L.P.
	By:	 	Vox II GENERAL PARTNER, LLC, its General Partner
	By:	 	Omega Fund III, LP, its member
	By:	 	Omega Fund III GP LP, its General Partner
	By:	 	Omega Fund III, GP Limited, its General partner
		
	By:	 	 /s/ Kevin Brennan

		 	Name:	 	Mr. Kevin Brennan
		 	Title:	 	Director

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement

 
					
	S.R. ONE, LIMITED
		
	By:	 	 /s/ Kent Gossett

		 	Name:	 	Kent Gossett
		 	Title:	 	Vice President & Partner
	
	CONNECTICUT INNOVATIONS, INCORPORATED
		
	By:	 	 /s/ Peter Longo

		 	Name:	 	Peter Longo
		 	Title:	 	President & Executive Director
	
	 /s/ C. Boyd Clarke

	C. Boyd Clarke

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement

 
					
	OXFORD BIOSCIENCE PARTNERS IV L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

		 	Name:	 	Jonathan Fleming
		 	Title:	 	Managing General Partner
	
	MRNA FUND II L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

		 	Name:	 	Jonathan Fleming
		 	Title:	 	Managing General Partner

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement

 
					
	 Managing Member of

Saints Capital VI, LLC
 the General Partner
of
 SAINTS CAPITAL VI, L.P.

		
	By:	 	 /s/ David Quinlivan

		 	Name:	 	David Quinlivan
		 	Title:	 	Managing Member

 Counterpart Signature Page to Fourth Amended and Restated Securityholders Agreement

 Exhibit A 

Instrument of Accession 
 Fourth Amended and Restated Securityholders Agreement 
 The undersigned,
                    , in order to become the owner or holder of              shares of
             Stock, par value $0.001 per share of Rib-X Pharmaceuticals, Inc., a Delaware corporation (the “Company”), hereby agrees to become a party to that certain
Fourth Amended and Restated Securityholders Agreement dated as of January 10, 2011 (the “Agreement”), by and among the Company and the other parties thereto, and to be bound by all provisions thereof. The undersigned
agrees to become a Securityholder (as defined in the Agreement) under the terms of the Agreement. This Instrument of Accession shall take effect and shall become a part of said Agreement immediately upon execution by the undersigned hereto and
acceptance thereof by the Company. 
 Executed as a contract under seal as of the date set forth below: 

 

			
	Signature:	 	  

 

			
		
	Name:	 	  

 

			
		
	By:	 	  

 

			
		
	Address:	 	  

	
	  

	
	  

			
		
	Date:	 	  

	
	Accepted:
	
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	  

	Name:
	Title:
		
	Date:Third amended and restated registration rights

 Exhibit 10.14 
 Execution Copy 
 THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

 This THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT (this “Agreement”) is
made as of this 8th day of June, 2006, by and among Rib-X
Pharmaceuticals, Inc., a Delaware corporation (the “Company”), and the persons and entities named in Schedule 1 hereto, as amended from time to time (the “Purchasers”). 

RECITALS 

WHEREAS, the Company and certain of the Purchasers are entering into that certain Series C Convertible Preferred Stock Purchase
Agreement, dated as of the date hereof (the “Stock Purchase Agreement”); 
 WHEREAS, under the terms of the
Stock Purchase Agreement, certain of the Purchasers have agreed to purchase from the Company and the Company has agreed to sell to the Purchasers, shares of the Company’s Series C Convertible Preferred Stock, par value $0.001 per share (the
“Series C Preferred Stock”); 
 WHEREAS, as a condition to entering into the Stock Purchase Agreement, the
Purchasers have requested that the Company grant to the Purchasers registration rights and certain other rights and covenants as set forth herein; 
 WHEREAS, the Company and certain of the parties hereto are bound by a Second Amended and Restated Registration Rights Agreement dated as of April 28, 2003 among the Company and the Purchasers
thereunder (the “Prior Agreement”) and believe that it is in the best interests of the Company and each of them to amend and restate that Prior Agreement in its entirety; and 

WHEREAS, pursuant to Section 13(d) of the Prior Agreement, the Company and the parties hereto that are holders of a majority of the
outstanding shares of Restricted Stock and the holders of at least 60% of all of the outstanding shares of Series B Convertible Preferred Stock, par value $0.001 per share (the “Series B Preferred Stock”), desire to terminate the
Prior Agreement and to accept the rights created pursuant hereto in lieu of the rights granted to them under the Prior Agreement; and 
 WHEREAS, the Board of Directors of the Company has determined that it is in the best interests of the Company that the Company enter into this Agreement. 

AGREEMENT 

NOW, THEREFORE, in consideration of the covenants and agreements set forth herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby mutually acknowledged, the parties hereto agree that the Prior Agreement shall be terminated and replaced in its entirety by this Agreement, and the parties hereto further covenant and agree as follows:

 1. Certain Definitions. As used in this Agreement, the following terms shall have the
following respective meanings: 
 “Affiliate” shall mean with respect to any Purchaser, any partner or other
equity holder of such Purchaser, or any person that, directly or indirectly, controls, is controlled by, or is under common control with, such Purchaser. 
 “Commission” shall mean the Securities and Exchange Commission, or any other federal agency at the time administering the Securities Act and the Exchange Act. 

“Common Stock” shall mean the common stock, par value $0.001 per share, of the Company, as constituted as of the date of
this Agreement. 
 “Company” shall mean Rib-X Pharmaceuticals, Inc. 

“Conversion Stock” shall mean shares of Common Stock issued or issuable to a party hereto upon (i) conversion of
the Preferred Stock or (ii) exercise of warrants, options or other rights to purchase Common Stock of the Company approved by the Board of Directors in accordance with Section 4.3(e)(viii) of the Stockholders Agreement (including a warrant
for the purchase of 500,000 shares of Common Stock issued by the Company to Connecticut Innovations Inc.), and any shares of capital stock issued or distributed in respect thereof. 

“Exchange Act” shall mean the Securities Exchange Act of 1934 or any similar federal statute, and the rules and
regulations of the Commission thereunder, all as the same shall be in effect at the time. 
 “Preferred Stock”
shall mean the Series A Preferred Stock, the Series B Preferred Stock and the Series C Preferred Stock. 

“Purchasers” shall mean the persons and/or entities identified in Schedule 1 hereto. 

“Registration Expenses” shall mean the expenses so described in Section 8(a). 

“Restricted Stock” shall mean the Conversion Stock and any other shares of Common Stock held or otherwise acquired by a
Purchaser after the date hereof, excluding Conversion Stock or Common Stock which (a) has been registered under the Securities Act pursuant to an effective registration statement filed thereunder and disposed of in accordance with the
registration statement covering them, (b) has been sold pursuant to Rule 144 under the Securities Act, (c) is eligible to be sold or distributed pursuant to Rule 144(k) under the Securities Act or (d) has ceased to be
outstanding. 
 “Securities Act” shall mean the Securities Act of 1933 or any similar federal statute, and the
rules and regulations of the Commission thereunder, all as the same shall be in effect at the time. 
 “Selling
Expenses” shall mean the expenses so described in Section 8(b). 

  
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 “Series A Preferred Stock” shall mean the Company’s Series A-1
Convertible Preferred Stock, par value $0.001 per share, Series A-1(A) Convertible Preferred Stock, par value $0.001 per share, and Series A-L Convertible Preferred Stock, par value $0.001 per share. 

“Series B Preferred Stock” shall have the meaning ascribed to that term in the recitals to this Agreement. 

“Series C Preferred Stock” shall have the meaning ascribed to that term in the recitals to this Agreement. 

“Stockholders Agreement” shall mean that certain Third Amended and Restated Stockholders Agreement, dated as of the date
hereof, among the Company, the Purchasers, and the certain holders of Common Stock of the Company, as amended from time to time. 
 “Stockholders’ Counsel” shall have the meaning ascribed to that term in Section 8(a). 
 When a reference is made in this Agreement to a Section, such reference shall be to a Section of this Agreement unless otherwise indicated. Unless the context otherwise requires, the terms defined
hereunder shall have the meanings therein specified for all purposes of this Agreement, applicable to both the singular and plural forms of any of the terms defined herein. Whenever the words “include,” “includes” or
“including” are used in this Agreement, they shall be deemed to be followed by the words “without limitation.” The use of a gender herein shall be deemed to include the neuter, masculine and feminine genders whenever necessary or
appropriate. Whenever the word “herein” or “hereof” is used in this Agreement, it shall be deemed to refer to this Agreement and not to a particular Section of this Agreement unless expressly stated otherwise. 

2. Required Registration. 
 (a) Demand Registration. Subject to the conditions of this Section 2 of this Agreement, each of (i) the holders of Restricted Stock constituting not less than 40% of the total
number of shares of Restricted Stock then outstanding (excluding for this purpose, the Restricted Stock issued as a result of the conversion of the Series C Preferred Stock) and (ii) the holders of not less than 40% of the total number of
shares of Restricted Stock outstanding and issued upon conversion of the Series C Preferred (excluding for this purpose, the Restricted Stock issued as a result of the conversion of the Series A Preferred Stock and Series B Preferred Stock), in each
case, taken together as a single class on an as-converted basis, may request the Company to register on Form S-1 (or any successor form) under the Securities Act all or any portion of the shares of Restricted Stock held by such requesting holder or
holders having an aggregate value of at least $1,000,000 (based on the then current market price or fair value). For purposes of this Agreement, the term “Restricted Stock”, with respect to any holder of Preferred Stock, shall be
deemed to include the number of shares of Restricted Stock which would be issuable to such holder upon conversion of all shares of Preferred Stock held by such holder at such time; provided, however, that the only securities that the
Company shall be required to register pursuant hereto shall be shares of Common Stock. 
 (b) Notification of
Registration. Following receipt of any notice under this Section 2, the Company shall promptly notify all holders of Restricted Stock from whom notice 

  
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has not been received and such holders shall then be entitled, upon written notice received by the Company within thirty (30) days after the giving of any such notice by the Company, to
request the Company to include in the requested registration all or any portion of their shares of Restricted Stock. The Company shall use its best reasonable efforts to register under the Securities Act, for public sale in accordance with the
method of disposition described in paragraph (a) above, the number of shares of Restricted Stock specified in such notice (and in all notices received by the Company from other holders within thirty (30) days after the giving of such
notice by the Company). 
 (c) Conditions to Registration. Notwithstanding anything to the contrary contained herein, the
Company shall not be required to effect a registration pursuant to this Section 2: 
 (i) prior to
one hundred eighty (180) days after the effective date of a registration statement filed by the Company covering a firm commitment underwritten public offering by the Company of Common Stock pursuant to a registration statement under the
Securities Act; or 
 (ii) after the Company has effected two (2) registrations pursuant to
Section 2(a)(i), and such registrations have been declared or ordered effective; or 
 (iii) after
the Company has effected two (2) registrations pursuant to Section 2(a)(ii), and such registrations have been declared or ordered effective. 
 (d) Withdrawal. At any time before the registration statement covering such Restricted Stock becomes effective, the holders of a majority of such shares may request the Company to withdraw or not
to file the registration statement. In that event, unless such request of withdrawal was caused by, or made in response to, a material adverse effect or a similar event related to the business, properties, condition, or operations of the Company not
known (without imputing the knowledge of any other person to such holders) by the holders initiating such request at the time their request was made, or other material facts not known to such holders at the time their request was made, the Company
shall be deemed to have effected one registration in satisfaction of the requirements of Section 2(c)(ii). 
 3.
Incidental Registration. 
 (a) If the Company at any time (other than pursuant to Section 2 or
Section 4) proposes to register any of its securities under the Securities Act for sale to the public, whether for its own account or for the account of other security holders or both (except with respect to registration statements on
Forms S-4 (or any successor thereto), S-8 (or any successor thereto) or another form not available for registering the Restricted Stock for sale to the public), each such time it will give written notice to all holders of outstanding Restricted
Stock of its intention so to do. Upon the written request of any such holder, received by the Company within thirty (30) days after the giving of any such notice by the Company, to register any of its Restricted Stock, the Company will use its
reasonable best efforts to cause the Restricted Stock as to which registration shall have been so requested to be included in the securities to be covered by the registration statement proposed to be filed by the Company, all to the extent requisite
to permit 

  
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the sale or other disposition by the holder (in accordance with its written request) of such Restricted Stock so registered. If any registration pursuant to this Section 3 shall be,
in whole or in part, an underwritten public offering of Common Stock, the number of shares of Restricted Stock to be included in such an underwriting may be reduced (pro rata among the requesting holders based upon the number of shares of Restricted
Stock held by such requesting holders) if and to the extent that the managing underwriter shall have advised the Company in writing that such inclusion would adversely affect the marketing of the securities to be sold by the Company therein;
provided that, no shares of Restricted Stock shall be excluded from any such registration until all shares held by any other Stockholder of the Company have been so excluded. Notwithstanding the foregoing provisions, the Company may withdraw any
registration statement referred to in this Section 3 without thereby incurring any liability to the holders of Restricted Stock. 
 (b) If the Company desires that any securities of the Company held by officers, directors or founders of the Company (the “Other Holders”) be included in any registration for an
underwritten offering requested pursuant to Sections 2 or 4, the Company may include the securities of such Other Holders in such registration and underwriting on the terms set forth herein. The Company shall (together with all Other Holders
proposing to distribute their securities through such underwriting) enter into an underwriting agreement in customary form (including, without limitation, customary indemnification and contribution provisions on the part of the Company) with the
managing underwriter. Notwithstanding any other provision of this Section 3(b) if the managing underwriter advises the Company that the inclusion of all shares requested to be registered under this Section 3(b) would adversely
affect the offering, the securities of the Company held by Other Holders (other than Restricted Stock) shall be excluded from such registration and underwriting to the extent deemed advisable by the managing underwriter. If the managing underwriter
has not limited the number of shares of Restricted Stock or other securities to be underwritten, the Company may include securities for its own account in such registration if the managing underwriter so agrees and if the number of shares of
Restricted Stock and other securities which would otherwise have been included in such registration and underwriting will not thereby be limited. 
 4. Registration on Form S-3. If at any time: (i) a holder or holders of Restricted Stock then outstanding request that the Company file a registration statement on Form S-3 or any
successor thereto for a public offering of all or any portion of the shares of Restricted Stock held by such requesting holder or holders having an aggregate value of at least $500,000 (based on the then current market price or fair value); and
(ii) the Company is a registrant entitled to use Form S-3 or any successor thereto to register such share for resale, then the Company shall use its reasonable best efforts to register under the Securities Act on Form S-3 or any
successor thereto, the number of shares of Restricted Stock specified in such notice. Whenever the Company is required by this Section 4 to use its reasonable best efforts to effect the registration of Restricted Stock, each of the
procedures and requirements of Section 2 (including but not limited to the requirement that the Company notify all holders of Restricted Stock from whom notice has not been received and provide them with the opportunity to participate in
the offering) shall apply to such registration. The holders of Restricted Stock shall be entitled to request an unlimited number of registrations on Form S-3 pursuant to this Section 4; provided that, the Company shall not be required to affect
more than two (2) registrations pursuant to this Section 4 in any twelve (12) month period and the Company shall not be required to effect a registration 

  
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pursuant to this Section 4 within 180 days of the effective date of any registration referred to in Section 2 above. 

5. Suspension of Registration. Notwithstanding anything to the contrary set forth in this Agreement, the Company’s obligation
under this Agreement to register Restricted Stock under the Securities Act on registration statements (“Registration Statements”) may, upon the reasonable determination of the Board of Directors made not more than once during any
period of twelve consecutive months, be suspended in the event and during such period as circumstances (including without limitation: (a) an underwritten primary offering by the Company (which includes no secondary offering) if the Company is
advised in writing by its underwriters that the registration of the Restricted Stock would have a material adverse effect on the Company’s offering; or (b) pending negotiations relating to, or consummation of, a transaction or the
occurrence of an event which would require additional disclosure of material information by the Company in Registration Statements or such other filings, as to which the Company has a bona fide business purpose for preserving confidentiality or
which renders the Company unable to comply with Commission requirements exist) (such circumstances being hereinafter referred to as “Suspension Events”) which would make it impractical or unadvisable for the Company to file the
Registration Statements or such other filings or to cause such to become effective. Such suspension shall continue only for so long as such event is continuing but in no event for a period longer than one hundred and twenty (120) days. The
Company shall notify the Purchasers of the existence and nature of any Suspension Event. 
 6. Registration Procedures.

 (a) Registration Procedures. If and whenever the Company is required by the provisions of Sections 2,
3 or 4 to use its reasonable best efforts to effect the registration of any shares of Restricted Stock under the Securities Act, the Company will, as expeditiously as possible: 

(i) Preparation/Filing of Statement. Prepare and file with the Commission a registration statement (which, in the
case of an underwritten public offering pursuant to Section 2, shall be on Form S-1 or other form of general applicability satisfactory to the managing underwriter selected as therein provided) with respect to such securities and use its
reasonable best efforts to cause such registration statement to become and remain effective for the period of the distribution contemplated thereby (determined as hereinafter provided); 

(ii) Amend/Supplement; Retain Effectiveness. Use its reasonable best efforts to prepare and file with the
Commission such amendments and supplements to such registration statement and the prospectus used in connection therewith as may be necessary to keep such registration statement effective for the period specified in paragraph (i) above and
comply with the provisions of the Securities Act with respect to the disposition of Restricted Stock covered by such registration statement in accordance with the sellers’ intended method of disposition set forth in such registration statement
for such period; 

  
 -6-

 (iii) Furnish Copies. Furnish to each seller of Restricted Stock and
to each underwriter such number of copies of the registration statement and each such amendment and supplement thereto (in each case including all exhibits) and the prospectus included therein (including each preliminary prospectus) as such persons
reasonably may request in order to facilitate the public sale or other disposition of the Restricted Stock covered by such registration statement; provided, however that if the Prospectus is amended to comply with the requirements of
the Securities Act, the Company shall promptly notify the sellers of Restricted Stock of such amendment and, if necessary, request that such sellers immediately cease making offers of Restricted Stock and return all prospectuses to the Company;

 (iv) Compliance with Blue Sky Laws. Use its best efforts to register or qualify the Restricted Stock
covered by such registration statement under the securities or “blue sky” laws of such jurisdictions as the sellers of Restricted Stock or, in the case of an underwritten public offering, the managing underwriter reasonably shall request;
provided, however, that the Company shall not for any such purpose be required to qualify generally to transact business as a foreign corporation in any jurisdiction where it is not so qualified or to consent to general service of
process or to subject itself to taxation in any such jurisdiction; 
 (v) List on Exchange. Use
commercially reasonable efforts to list the Restricted Stock covered by such registration statement with any securities exchange or automated quotation system on which the Common Stock of the Company is then listed; 

(vi) Notice and Remedy of Material Misstatements or Omissions. Immediately notify each seller of Restricted Stock
and each underwriter under such registration statement, at any time when a prospectus relating thereto is required to be delivered under the Securities Act, of the happening of any event of which the Company has knowledge as a result of which the
prospectus contained in such registration statement, as then in effect, includes an untrue statement of a material fact or omits to state a material fact required to be stated therein or necessary to make the statements therein not misleading in
light of the circumstances then existing, and, if necessary request that the sellers and underwriters immediately cease making offers of Restricted Stock and use reasonable best efforts to promptly prepare and furnish to such seller a reasonable
number of copies of a prospectus supplemented or amended so that, as thereafter delivered to the purchasers of such Restricted Stock, such prospectus shall not include an untrue statement of a material fact or omit to state a material fact required
to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing; 
 (vii) Legal/Accounting Opinions. If the offering is underwritten, at the request of the underwriters or any seller of Restricted Stock, use its reasonable best efforts to furnish on the date that
Restricted Stock is delivered to the underwriters for sale pursuant to such registration: (i) an opinion dated such date of counsel representing the Company for the purposes of such registration, addressed to the underwriters and to such
seller, to such effect as reasonably may be requested by counsel for the underwriters; and (ii) a letter dated such date from the independent public accountants retained by the 

  
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Company, addressed to the underwriters and to such seller, stating that they are independent public accountants within the meaning of the Securities Act and that, in the opinion of such
accountants, the financial statements of the Company included in the registration statement or the prospectus, or any amendment or supplement thereof, comply as to form in all material respects with the applicable accounting requirements of the
Securities Act, and such letter shall additionally cover such other financial matters (including information as to the period ending no more than five (5) business days prior to the date of such letter) with respect to such registration as such
underwriters reasonably may request; 
 (viii) Access to Attorneys, Accountants and Records. Make
available upon reasonable notice and during normal business hours for inspection by each seller of Restricted Stock, any underwriter participating in any distribution pursuant to such registration statement, and any attorney, accountant or other
agent retained by such seller or underwriter (each an “Inspector” and collectively the “Inspectors”) provided that such seller or underwriter enters into a non-disclosure agreement reasonably satisfactory to the
Company, reasonable access to all financial and other records, pertinent corporate documents and properties of the Company, as the Inspectors may reasonably request to enable them to exercise their due diligence responsibility, and cause the
Company’s officers, directors and employees to supply all information reasonably requested by the Inspectors in connection with such registration statement; provided, however, that any documents, records or information (the
“Information”) which the Company determines in good faith to be confidential, and of which determination the Inspectors are so notified, shall not be disclosed by the Inspectors unless (i) the disclosure of such Information is
necessary to avoid or correct a material misstatement or omission in the registration statement, (ii) the release of such Information is ordered pursuant to a subpoena or other order from a court or governmental agency or authority of competent
jurisdiction, (iii) such Information has been made generally available to the public through no breach of the nondisclosure obligations of the Inspectors or their Affiliates or (iv) such disclosure is required to be made under applicable
law; 
 (ix) Preparation of Certificates. Cooperate with the selling holders of Restricted Stock and the
managing underwriters, if any, to facilitate the timely preparation and delivery of certificates representing Restricted Stock to be sold, such certificates to be in such denominations and registered in such names as such holders or the managing
underwriters may request at least two (2) business days prior to any sale of Restricted Stock; and 
 (x)
Participation of Controlling Stockholders. Permit any holder of Restricted Stock which holder, in the sole and exclusive judgment, exercised in good faith, of such holder, might be deemed to be a controlling person of the Company, to
participate in good faith in the preparation of such registration or comparable statement and to require the insertion therein of material, furnished to the Company in writing, which in the reasonable judgment of such holder and its counsel should
be included. 
 (b) Duration of Distributions. For purposes of this Agreement, the period of distribution of Restricted
Stock for any registration shall be deemed to extend until the earlier of 

  
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the sale of all Restricted Stock covered thereby and one hundred eighty (180) days after the effective date thereof. 
 (c) Information to be Provided by Purchasers. In connection with each registration hereunder, the sellers of Restricted Stock will furnish to the Company in writing such information requested by
the Company with respect to themselves and the proposed distribution by them as reasonably shall be necessary in order to assure compliance with federal and applicable state securities laws; provided, however, that this requirement
shall not be deemed to limit any disclosure obligation arising out of any seller’s relationship to the Company if one of such seller’s agents or affiliates is an officer, director or control person of the Company. In addition, the sellers
shall, if requested by the Company, execute such other agreements, which are reasonably satisfactory to them and which shall contain such provisions as may be customary and reasonable in order to accomplish the registration of the Restricted Stock.

 (d) Agreements with Underwriters. In connection with each registration pursuant to Sections 2, 3 or
4 covering an underwritten public offering, the Company and each seller agree to enter into a written agreement with the managing underwriter selected, in the case of a registration pursuant to Sections 2 or 4 hereof, by the sellers with a
reasonable consent of the Company in such form and containing such provisions as are customary in the securities business for such an arrangement between such underwriter and companies of the Company’s size and investment stature and each
seller’s participation in such registration shall be conditioned upon entering into such agreement. No seller may sell shares pursuant to a registration covering an underwritten offering other than to the underwriters for such offering. If any
Purchaser disapproves of the terms of any such underwriting, such Purchaser may elect to withdraw therefrom by written notice to the Company and the underwriter. Any Restricted Stock excluded or withdrawn from such underwriting shall be withdrawn
from such registration. 
 7. Reserved. 
 8. Expenses. 
 (a) Registration Expenses. The term
“Registration Expenses” as used in this Agreement means all expenses incurred by the Company in complying with Sections 2, 3 or 4, including, without limitation: (i) all registration fees, filing fees
and printing expenses; (ii) fees and disbursements of counsel and independent public accountants for the Company; (iii) fees and expenses incurred by sellers of Restricted Stock in connection with the registration of such stock, including
fees and expenses of one designated counsel for all sellers of Restricted Stock (“Stockholders’ Counsel”); (iv) transfer taxes; (v) fees of transfer agents and registrars; and (vi) costs of any insurance which
might be obtained in connection with the registration; but excluding any Selling Expenses (as defined in Section 8(b)). 
 (b) Selling Expenses. The term “Selling Expenses” as used in this Agreement includes: (i) all underwriting discounts and selling commissions applicable to the sale of
Restricted Stock; and (ii) the fees and expenses of any other counsel to holders of Restricted Stock, other than Stockholders’ Counsel, in connection with the registration of such stock. 

  
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 (c) Payment of Expenses. The Company will pay all Registration Expenses in connection
with each registration statement under Sections 2, 3 or 4, provided, that the Company shall not be required to pay for the Registration Expenses of any registration of shares of Restricted Stock which is withdrawn, prior to
effectiveness, at the request of the holders of a majority of such shares unless (i) such request of withdrawal was caused by, or made in response to, a material adverse effect or a similar event related to the business, properties, condition,
or operations of the Company not known (without imputing the knowledge of any other person to such holders) by the holders initiating such request at the time their request was made, or other material facts not known to such holders at the time
their request was made, or (ii) in connection with such withdrawal the Company shall be deemed to have effected one registration in satisfaction of the requirements of Section 2(c)(ii), as provided in Section 2(d). All Selling
Expenses in connection with each registration statement under Sections 2, 3 or 4 shall be borne by the participating sellers in proportion to the number of shares sold by each, or by such participating sellers other than
the Company (except to the extent the Company shall be a seller) as they may agree. 
 9. Indemnification. 

(a) Company’s Indemnification. In the event of a registration of any of the Restricted Stock under the Securities Act
pursuant to Sections 2, 3 or 4, the Company will indemnify and hold harmless each holder of Restricted Stock, its officers and directors, each underwriter of such Restricted Stock thereunder and each other person, if any,
who controls such seller or underwriter within the meaning of the Securities Act, against any losses, claims, damages or liabilities, joint or several, to which such holder, officer, director, underwriter or controlling person may become subject
under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement of any material fact contained in
any registration statement under which such Restricted Stock was registered under the Securities Act pursuant to Sections 2, 3 or 4, any preliminary prospectus or final prospectus contained therein, any amendment or
supplement thereof or any issuer free-writing prospectus; (ii) any untrue statement or alleged untrue statement of any material fact contained in any blue sky application or based upon written information furnished by the Company filed in any
state or other jurisdiction in order to qualify any or all of the Restricted Stock under the securities laws thereof (any such application, document or information herein called a “Blue Sky Application”); (iii) the omission or
alleged omission to state a material fact required to be stated in any filing referenced in items (i) and (ii) of this Section 9(a) or necessary to make the statements therein not misleading; (iv) any violation by the
Company or its agents of any rule or regulation promulgated under the Securities Act applicable to the Company or its agents and relating to action or inaction required of the Company in connection with such registration; or (v) any failure to
register or qualify the Restricted Stock in any state where the Company or its agents has affirmatively undertaken or agreed in writing that the Company (the undertaking of any underwriter chosen by the Company being attributed to the Company) will
undertake such registration or qualification on the seller’s behalf (provided that in such instance the Company shall not be so liable if it has undertaken its reasonable best efforts to so register or qualify the Restricted Stock), and will
reimburse each such holder, and such officer and director, each such underwriter and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage,
liability or 

  
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action; provided, however, that the Company will not be liable in any such case if and to the extent that any such loss, claim, damage or liability arises out of or is based upon
(i) an untrue statement or alleged untrue statement or omission or alleged omission so made in conformity with information furnished by any such seller, any such underwriter or any such controlling person, in writing, specifically for use in
such registration statement or prospectus, (ii) the failure of any such person to comply with the provisions of Section 6(a)(iii) or Section 6(a)(vi) hereof or (iii) any statement or omission in any prospectus that is corrected
by any subsequent prospectus or amendment that was delivered to such person prior to the pertinent sale or sales by or on behalf of such person. 
 (b) Seller’s Indemnification. In the event of a registration of any of the Restricted Stock under the Securities Act pursuant to Sections 2, 3 or 4, each seller of
such Restricted Stock thereunder, severally and not jointly, will indemnify and hold harmless the Company, each person, if any, who controls the Company within the meaning of the Securities Act, each officer of the Company who signs the registration
statement, each director of the Company, each other holder of Restricted Stock, each underwriter and each person who controls any underwriter within the meaning of the Securities Act, against all losses, claims, damages or liabilities, joint or
several, to which the Company or such officer, director, other seller, underwriter or controlling person may become subject under the Securities Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any registration or Blue Sky Application statement under which such Restricted Stock was registered under the Securities Act pursuant
to Sections 2, 3 or 4, any preliminary prospectus or final prospectus contained therein, or any amendment or supplement thereof or any issuer free-writing prospectus, or arise out of or are based upon the omission or
alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse the Company and each such officer, director, other seller, underwriter and controlling
person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that such seller will be liable hereunder in any
such case if and only to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission made in reliance upon and in conformity with
information pertaining to such seller, as such, furnished in writing to the Company by such seller specifically for use in such registration statement or prospectus. 
 (c) Indemnification Procedure. Promptly after receipt by an indemnified party hereunder of notice of the commencement of any action, such indemnified party shall, if a claim in respect thereof is
to be made against the indemnifying party hereunder, notify the indemnifying party in writing thereof, but the omission so to notify the indemnifying party shall not relieve it from any liability which it may have to such indemnified party other
than under this Section 9 and shall only relieve it from any liability which it may have to such indemnified party under this Section 9 if and to the extent the indemnifying party is prejudiced by such omission. In case any
such action shall be brought against any indemnified party and it shall notify the indemnifying party of the commencement thereof, the indemnifying party shall be entitled to participate in and, to the extent it shall wish, to assume and undertake
the defense thereof with counsel satisfactory to such indemnified party, and, after notice from the indemnifying party to such indemnified party of its election so to assume and undertake the defense thereof, the

  
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indemnifying party shall not be liable to such indemnified party under this Section 9 for any legal expenses subsequently incurred by such indemnified party in connection with the
defense thereof other than reasonable costs of investigation and of liaison with counsel so selected; provided, however, that, if the defendants in any such action include both the indemnified party and the indemnifying party and the
indemnified party shall have reasonably concluded that the interests of the indemnified party reasonably may be deemed to conflict with the interests of the indemnifying party, the indemnified party shall have the right to select a separate counsel
and to assume such legal defenses and otherwise to participate in the defense of such action, with the expenses and fees of such separate counsel and other expenses related to such participation to be reimbursed by the indemnifying party as
incurred. In no event shall an indemnifying party be liable for any settlement or compromise made by an indemnified party that the indemnifying party does not consent to in writing. 

(d) Survival of Indemnification. The indemnities provided in this Section 9 shall survive the transfer of any
Restricted Stock. 
 10. Changes in Common Stock or Preferred Stock. If, and as often as, there is any change in the
Common Stock or the Preferred Stock by way of a stock split, stock dividend, combination or reclassification, or through a merger, consolidation, reorganization or recapitalization, or by any other means, appropriate adjustment shall be made in the
provisions hereof so that the rights and privileges granted hereby shall continue with respect to the Common Stock or the Preferred Stock as so changed. 
 11. Rule 144 Reporting. With a view to making available the benefits of certain rules and regulations of the Commission which may at any time permit the sale of the Restricted Stock to the public
without registration, at all times after ninety (90) days after the initial registration statement covering a public offering of securities of the Company under the Securities Act shall have become effective, the Company agrees to use
reasonable best efforts to: 
 (a) make and keep public information available, as those terms are understood and defined in
Rule 144 under the Securities Act; 
 (b) file with the Commission 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 if has become subject to such reporting requirements); and 
 (c) furnish to each holder of Restricted Stock upon request a written statement by the Company as to its compliance with the reporting requirements of Rule 144 and of the Securities Act and the
Exchange Act (at any time after if has become subject to such reporting requirements), a copy of the most recent annual or quarterly report of the Company, and such other reports and documents so filed by the Company as such holder may reasonably
request in availing itself of any rule or regulation of the Commission allowing such holder to sell any Restricted Stock without registration. 

  
 -12-

 12. Representations and Warranties of the Company. The Company represents and
warrants to the Purchasers as follows: 
 (a) No Conflicts; Authorizations. The execution, delivery and performance of
this Agreement by the Company have been duly authorized by all requisite corporate action and will not violate any applicable provision of law, any applicable order of any court or other agency of government, the Certificate of Incorporation or
By-laws of the Company or any provision of any indenture, agreement or other instrument to which it or any of its properties or assets is bound, conflict with, result in a breach of or constitute (with due notice or lapse of time or both) a default
under any such indenture, agreement or other instrument or result in the creation or imposition of any lien, charge or encumbrance of any nature whatsoever upon any of the properties or assets of the Company. 

(b) Binding Effect. This Agreement has been duly executed and delivered by the Company and constitutes the legal, valid and
binding obligation of the Company, enforceable in accordance with its terms. 
 13. Miscellaneous. 

(a) Assignment. The registration rights granted to the Purchasers under this Agreement may only be assigned to a transferee which
acquires at least 20% of the Preferred Stock held by such Purchaser; provided, that (A) such transferee agrees to be bound by the provisions of this Agreement; and (B) at the time of transfer the Company is given written notice of
the name and address of the transferee and the number and type of Restricted Stock being transferred. 
 (b) Notices. All
notices, consents and other communications hereunder shall be in writing and shall be: (i) delivered in person; (ii) mailed by certified or registered mail, return receipt requested; (iii) sent by a recognized overnight courier
service; or (iv) sent by e-mail, facsimile or other means or electronic communication, for which evidence of delivery is automatically generated (provided that if notice is provided pursuant to this clause (iv), such communication is followed
promptly by a communication in the form provided under clauses (i), (ii) or (iii)), addressed as follows: 

(i) if to the Company or any other party hereto, at the address of such party set forth in Schedule 1 hereto, with a copy
to the Company’s counsel as indicated therein; 
 (ii) if to any subsequent holder of Preferred Stock or
Restricted Stock, to it at such address as may have been furnished to the Company in writing by such holder; 
 or, in any case, at such other
address as shall have been furnished in writing by the addressee to the others. Notices shall be effective: (i) upon delivery, if delivered in person; (ii) three (3) days after deposit in the U.S. mails, if mailed; (iii) on the
day following deposit with the courier service, if sent by overnight courier; and (iv) upon transmission, if sent by e-mail, facsimile or other means of electronic communication. 

  
 -13-

 (c) Governing Law. This Agreement shall be construed and enforced in accordance with
and governed by the laws of the State of Delaware, without regard to its principles of conflicts of laws. 
 (d) Modification
or Amendment. This Agreement may not be amended or modified, and no provision hereof may be waived, without the written consent of the Company and the holders of at least a majority of the outstanding shares of the Restricted Stock held by all
of the Purchasers. Notwithstanding the foregoing, no such amendment or modification shall be effective if and to the extent that such amendment or modification grants to any one or more Purchasers any rights more favorable than any rights granted to
all other Purchasers or otherwise treats any one or more Purchasers differently than all other Purchasers. 
 (e)
Counterparts. 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. 

(f) Successors and Assigns. All covenants and agreements contained in this Agreement by or on behalf of any of the parties hereto
shall bind and inure to the benefit of the respective successors and permitted assigns of the parties hereto (including without limitation transferees of any Preferred Stock or Restricted Stock), whether so expressed or not. 

(g) Senior Registration Rights. After the date of this Agreement, the Company shall not, without the prior written consent of
holders of a majority of the outstanding shares of Restricted Stock, enter into any agreement with any holder or prospective holder of any securities of the Company which would grant such holder registration rights senior or pari passu to the rights
of the holders of Restricted Stock under this Agreement. 
 (h) Severability. If any provision of this Agreement shall be
held to be illegal, invalid or unenforceable, such illegality, invalidity or unenforceability shall attach only to such provision and shall not in any manner affect or render illegal, invalid or unenforceable any other provision of this Agreement,
and this Agreement shall be carried out as if any such illegal, invalid or unenforceable provision were not contained herein. 

(i) Headings and Captions. The headings and captions of the various subdivisions of this Agreement are for convenience of
reference only and shall in no way modify or affect the meaning or construction of any of the terms or provisions hereof. 
 (j)
No Waiver of Rights, Powers and Remedies. No failure or delay by a party hereto in exercising any right, power or remedy under this Agreement, and no course of dealing among the parties hereto, shall operate as a waiver of any such right,
power or remedy of the party. No single or partial exercise of any right, power or remedy under this Agreement by a party hereto, nor any abandonment or discontinuance of steps to enforce any such right, power or remedy, shall preclude such party
from any other or further exercise thereof or the exercise of any other right, power or remedy hereunder. The election of any remedy by a party hereto shall not constitute a waiver of the right of such party to pursue other available remedies. No
notice to or demand on a party not expressly required under this Agreement shall entitle the party receiving such notice or demand to any other or further notice or demand in similar or other 

  
 -14-

 
circumstances or constitute a waiver of the rights of the party giving such notice or demand to any other or further action in any circumstances without such notice or demand. 

(k) Additional Parties. A purchaser of shares of Preferred Stock of the Company, if not already a party hereto, shall be required,
as a condition to such purchase, to execute and deliver an instrument of accession to this Agreement in the form of Exhibit A hereto (an “Instrument of Accession”) whereby such purchaser shall agree to be bound by this
Agreement and become a “Purchaser” for all purposes hereunder, and Schedule 1 hereto shall be amended by the Company to reflect the investments made by such Purchaser without the necessity of procuring a consent to such amendment to this
Agreement by the other parties hereto. 
 14. Termination. All of the Company’s obligations to register Restricted
Stock under this Agreement shall terminate five years after the initial registration statement covering a public offering of securities of the Company under the Securities Act shall have become effective. 

15. Affiliates. For purposes of determining the number of shares owned by each Purchaser, a Purchaser shall be deemed to be the
owner of all shares owned by all affiliates of the Purchaser who control, are controlled by or are under common control with such Purchaser 
 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK] 

  
 -15-

 IN WITNESS WHEREOF, the parties hereto have executed this Third Amended and Restated
Registration Rights Agreement or caused this Agreement to be executed by their duly authorized representatives, as of the date first above written. 
  

			
	THE COMPANY:
	
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Susan Froshauer

		 	Susan Froshauer
		 	President

 
					
	 THE PURCHASERS:

	
	 MEDIMMUNE VENTURES, INC.

		
	By:	 	 /s/ Edward T. Mathers

	Name:	 	 Edward T. Mathers

	Title:	 	 Authorized Person

	
	RADIUS VENTURE PARTNERS II, L.P.
	
	 By: Radius Venture Partners II, LLC,
 its General Partner

		
	By:	 	 /s/ Jordan Davis

		 	Name:	 	Jordan Davis
		 	Title: 	 	Managing Member
	
	 WARBURG PINCUS PRIVATE EQUITY VIII, L.P.

	
	 By: Warburg Pincus Partners LLC,

its General Partner

		
	By:	 	Warburg Pincus & Co., its Managing Member
		
	By:	 	 /s/ Stewart J. Hen

		 	Name:	 	Stewart J. Hen
		 	Title: 	 	Partner
	
	 AXIOM VENTURE PARTNERS III, LP

		
	By:	 	 /s/ Alan Mendelson

		 	Alan Mendelson
		 	General Partner
	
	 CHP II, L.P.

	
	By: CHP II Management, LLC, its General Partner
		
	By:	 	 /s/ John J. Park

	Name:	 	 John J. Park

	Title:	 	 Managing Member

  

[Counterpart Signature Page to Third Amended and Restated Registration Rights Agreement] 

 
			
	OXFORD BIOSCIENCE PARTNERS IV L.P.
		
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Michael Lytton

		 	Michael Lytton – General Partner
	
	MRNA FUND II L.P.
		
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Michael Lytton

		 	Michael Lytton – General Partner
	
	 EUCLIDSR BIOTECHNOLOGY PARTNERS, L.P.

		
	By:	 	EuclidSR Associates, L.P.
		
	Its:	 	General Partner
		
	By:	 	 /s/ Barbara J. Dalton

		 	Barbara J. Dalton
		 	General Partner
	
	EUCLIDSR PARTNERS, L.P.
		
	By:	 	EuclidSR Associates, L.P.
		
	Its:	 	General Partner
		
	By:	 	 /s/ Barbara J. Dalton

		 	Barbara J. Dalton
		 	General Partner
	
	S.R. ONE, LIMITED
		
	By:	 	 /s/ Philip L. Smith

	Name:	 	 Philip L. Smith

	Title:	 	 Vice President

	
	ABS VENTURES VII L.P.
	
	By Calvert Capital Caymans I L.L.C.
		
	By:	 	 /s/ Bruns Grayson

	Name:	 	Bruns Grayson
	Title:	 	Senior Manager

  

[Counterpart Signature Page to Third Amended and Restated Registration Rights Agreement] 

 
			
	ABS INVESTORS L.L.C.
		
	By:	 	 /s/ Bruns Grayson

	Name:	 	Bruns Grayson
	Title:	 	Senior Manager
	
	 /s/ Thomas Steitz

	Thomas Steitz
	
	 /s/ Peter Moore

	Peter Moore
	
	 /s/ John Abelson

	John Abelson
	
	 /s/ C. Boyd Clarke

	C. Boyd Clarke

  

[Counterpart Signature Page to Third Amended and Restated Registration Rights Agreement] 

 Instrument of Accession 

Third Amended and Restated Registration Rights Agreement 
 The undersigned,                     , in order to become the owner or holder of
             shares of the Series C Convertible Preferred Stock, par value $0.001 per share (the “Series C Preferred Stock”), of Rib-X Pharmaceuticals, Inc., a Delaware
corporation (the “Company”), hereby agrees to become a party to that certain Third Amended and Restated Registration Rights Agreement dated as of June 8, 2006 (the “Agreement”), by and among the Company
and the other parties thereto, and to be bound by all provisions thereof. The undersigned agrees to become a Purchaser (as defined in the Agreement) under the terms of the Agreement. This Instrument of Accession shall take effect and shall become a
part of said Agreement immediately upon execution by the undersigned hereto and acceptance thereof by the Company. 
 Executed
as a contract under seal as of the date set forth below: 
  

			
	Signature:	 	  

			
		
	Name:	 	  

			
		
	By:	 	  

			
		
	Address:	 	  

					
	
	  

	
	  

		
	 Date:
	 	  

	
	Accepted:
	
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	  

		 	Name:	 	Susan Froshauer
		 	Title:	 	President
		
	Date:	 	  

 AMENDMENT TO THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT 

This AMENDMENT, dated as of January 7, 2009 (this “Amendment”), to the Third Amended and Restated Registration
Rights Agreement, dated as of June 8, 2006, as amended (the “Registration Rights Agreement”), by and among Rib-X Pharmaceuticals, Inc., a Delaware corporation (the “Company”) and the Purchasers (as defined
therein). 
 W I T N E S S E T H : 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Subordinated Convertible Promissory Note Purchase
Agreement, dated as of January 7, 2009, pursuant to which certain of the Purchasers agreed to purchase Subordinated Convertible Promissory Notes (the “Notes”) and Warrants to purchase shares of Common Stock (the
“Warrants”) from the Company (collectively, the “Note Financing”); 
 WHEREAS,
Section 13(d) of the Registration Rights Agreement provides that the Registration Rights Agreement may be amended with the written consent of the Company and the holders of at least a majority of the outstanding shares of Restricted Stock held
by all of the Purchasers (the “Required Purchasers”); and 
 WHEREAS, in connection with the Note Financing,
the Company and the Required Purchasers desire to amend certain provisions of the Registration Rights Agreement as more fully set forth herein. 
 NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, and in consideration of the agreements herein, the parties hereto agree as follows:

 1. Definition of Conversion Stock. The definition of “Conversion Stock” shall be amended and restated
in its entirety to read as follows: 
 ‘“Conversion Stock” shall mean shares of Common Stock issued or issuable to
a party hereto upon (i) conversion of the Preferred Stock or the Notes or exercise of the Warrants or (ii) exercise of warrants, options or other rights to purchase Common Stock of the Company approved by the Board of Directors in
accordance with Section 4.3(e)(viii) of the Stockholders Agreement (including, a warrant for the purchase of 500,000 shares of Common Stock issued by the Company to Connecticut Innovations Inc.), and any shares of capital stock issued or
distributed in respect thereof.’ 
 2. Defined Terms. Capitalized terms used but not defined herein shall
have the meaning set forth in the Registration Rights Agreement. 
 3. No Other Amendment. Except as expressly
amended hereby, the Registration Rights Agreement shall remain in full force and effect in accordance with its terms, without any waiver, amendment or modification of any provision thereof. All references in the

 
Registration Rights Agreement to “this Agreement” shall be deemed to refer to the Registration Rights Agreement as amended by this Amendment. 

4. Governing Law; Jurisdiction. This Amendment shall be construed, performed and enforced in accordance with, and governed
by, the laws of the State of Delaware, without giving effect to the principles of conflicts of laws thereof. The parties hereto irrevocably elect as the sole judicial forum for the adjudication of any matters arising under or in connection with this
Amendment, and consent to the jurisdiction of, the courts of the State of Delaware or the corresponding United States federal court in the State of Delaware. 
 5. Section and Paragraph Headings. The section and paragraph headings in this Amendment are for reference purposes only and shall not affect the meaning or interpretation of this Amendment.

 6. Counterparts. This Amendment may be executed in counterparts, each of which shall be deemed an original, but
all of which shall constitute the same instrument. 
 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK] 

  
 -2-

 IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed as of the
date first above written. 
  

			
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Susan Froshauer

	Name:	 	Susan Froshauer
	Title:	 	Chief Executive Officer
	
	WP VIII FINANCE, L.P.
	By:	 	WPVIII GP, L.P., its General Partner
	By:	 	Warburg Pincus Private Equity VIII, L.P., its
		 	General Partner
	By:	 	Warburg Pincus Partners, LLC, its General
		 	Partner
	By:	 	Warburg Pincus & Co., its Managing Member
		
	By:	 	 /s/ Stewart J. Hen

		 	Stewart J. Hen
		 	Partner
	
	ABS VENTURES VII L.P.
	By Calvert Capital Caymans I L.L.C.
		
	By:	 	 /s/ Bruns Grayson

		 	Bruns Grayson
		 	Senior Manager
	
	AXIOM VENTURE PARTNERS III, LP
		
	By:	 	 /s/ Alan Mendelson

		 	Alan Mendelson
		 	General Partner

 Amendment to Third Amended and Restated Registration Rights Agreement 

 
			
	EUCLIDSR BIOTECHNOLOGY PARTNERS, L.P.
	By:	 	EuclidSR Associates, L.P.
	Its:	 	General Partner
		
	By:	 	 /s/ Raymond J. Whitaker

		 	Raymond J. Whitaker
		 	General Partner
	
	EUCLIDSR PARTNERS, L.P.
	By:	 	EuclidSR Associates, L.P.
	Its:	 	General Partner
		
	By:	 	 /s/ Raymond J. Whitaker

		 	Raymond J. Whitaker
		 	General Partner
	
	MEDIMMUNE VENTURES, INC.
		
	By:	 	 /s/ Joseph L. Amprey

	Name:	 	Joseph L. Amprey
	Title:	 	Sr. Managing Director
	
	OXFORD BIOSCIENCE PARTNERS IV L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Michael Lytton

		 	Michael Lytton
		 	General Partner
	
	MRNA FUND II L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Michael Lytton

		 	Michael Lytton
		 	General Partner

 Amendment to Third Amended and Restated Registration Rights Agreement 

 
			
	S.R. ONE, LIMITED
		
	By:	 	 /s/ Kent Gossett

	Name:	 	Kent Gossett
	Title:	 	Vice President
	
	VOX EQUITY PARTNERS, L.P.
		
	By:	 	 /s/ Matthew Kaup Kelley

	its	 	  

		
	By:	 	Matthew Kaup Kelley
	Name:	 	Managing General Partner
	Title:	 	Vox Equity Partners, LP

 Amendment to Third Amended and Restated Registration Rights Agreement 

 EXECUTION VERSION 

AMENDMENT NO. 2 TO 

THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT 
 This AMENDMENT NO. 2, dated as of May 28, 2010 (this “Amendment”), to the Third Amended and Restated Registration Rights Agreement, dated as of June 8, 2006, as amended (the
“Registration Rights Agreement”), by and among Rib-X Pharmaceuticals, Inc., a Delaware corporation (the “Company”) and the Purchasers (as defined therein). 

W I T N E S S E T H : 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Subordinated Convertible Promissory Note
Purchase Agreement, dated as of January 7, 2009, pursuant to which certain of the Purchasers agreed to purchase Subordinated Convertible Promissory Notes (the “Junior Notes”) and Warrants to purchase shares of Common Stock (the
“Prior Warrants”) from the Company (collectively, the “Junior Note Financing”); 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Senior Subordinated Convertible Promissory Note
Purchase Agreement, dated as of May 28, 2010, pursuant to which certain of the Purchasers agreed to purchase Senior Subordinated Convertible Demand Promissory Notes (the “Senior Notes”) and Warrants to purchase shares of Common
Stock (the “New Warrants”) from the Company (collectively, the “Senior Note Financing”); 

WHEREAS, Section 13(d) of the Registration Rights Agreement provides that the Registration Rights Agreement may be amended
with the written consent of the Company and the holders of at least a majority of the outstanding shares of Restricted Stock held by all of the Purchasers (the “Required Purchasers”); and 

WHEREAS, in connection with the Senior Note Financing, the Company and the Required Purchasers desire to amend certain provisions
of the Registration Rights Agreement as more fully set forth herein. 
 NOW, THEREFORE, for good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, and in consideration of the agreements herein, the parties hereto agree as follows: 
 1. Definition of Note. The definition of “Notes” shall be inserted in Section 1 reading in its entirety as follows: 

‘“Notes” shall mean (i) those certain Subordinated Convertible Promissory Notes issued by the Company pursuant to the
Subordinated Convertible Promissory Note Purchase Agreement, dated as of January 7, 2009, by and among the Company and the Purchasers listed therein and (ii) those certain Senior Subordinated Convertible Demand Promissory Notes issued by
the Company from time to time pursuant to the Senior Subordinated Convertible Demand Promissory Note Purchase Agreement, dated as of May 28 2010, by and among the Company and the Purchasers listed therein.’ 

 2. Definition of Warrants. The definition of “Warrants” shall be
inserted in Section 1 reading in its entirety as follows: 
 ‘“Warrants” shall mean (i) those certain
Warrants to Purchase Common Stock issued by the Company pursuant to the Subordinated Convertible Promissory Note Purchase Agreement, dated as of January 7, 2009, by and among the Company and the Purchasers listed therein and (ii) those
certain Warrants to Purchase Common Stock issued by the Company from time to time pursuant to the Senior Subordinated Convertible Demand Promissory Note Purchase Agreement, dated as of May 28, 2010, by and among the Company and the Purchasers
listed therein.’ 
 3. Definition of Conversion Stock. The definition of “Conversion Stock” in
Section 1 shall be amended and restated in its entirety to read as follows: 
 ‘“Conversion Stock” shall mean
shares of Common Stock issued or issuable to a party hereto upon (i) conversion of the Preferred Stock or the Notes or exercise of the Warrants or (ii) exercise of warrants, options or other rights to purchase Common Stock of the Company
approved by the Board of Directors in accordance with Section 4.3(e)(viii) of the Stockholders Agreement (including, a warrant for the purchase of 500,000 shares of Common Stock issued by the Company to Connecticut Innovations, Incorporated),
and any shares of capital stock issued or distributed in respect thereof.’ 
 4. Defined Terms. Capitalized
terms used but not defined herein shall have the meaning set forth in the Registration Rights Agreement. 
 5. No Other
Amendment. Except as expressly amended hereby, the Registration Rights Agreement shall remain in full force and effect in accordance with its terms, without any waiver, amendment or modification of any provision thereof. All references in
the Registration Rights Agreement to “this Agreement” shall be deemed to refer to the Registration Rights Agreement as amended by this Amendment. 
 6. Governing Law; Jurisdiction. This Amendment shall be construed, performed and enforced in accordance with, and governed by, the laws of the State of Delaware, without giving effect to the
principles of conflicts of laws thereof. The parties hereto irrevocably elect as the sole judicial forum for the adjudication of any matters arising under or in connection with this Amendment, and consent to the jurisdiction of, the courts of the
State of Delaware or the corresponding United States federal court in the State of Delaware. 
 7. Section and Paragraph
Headings. The section and paragraph headings in this Amendment are for reference purposes only and shall not affect the meaning or interpretation of this Amendment. 
 8. Counterparts. This Amendment may be executed in counterparts, each of which shall be deemed an original, but all of which shall constitute the same instrument. 

[REMAINDER OF PAGE INTENTIONALLY LEFT BLANK] 

  
 -2-

 IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed as
of the date first above written. 
  

			
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Mark Leuchtenberger

	 Name:
 Title:
	 	 Mark Leuchtenberger

President and Chief Executive Officer

	
	WP VIII FINANCE, L.P.
	By:	 	WPVIII GP, L.P., its General Partner
	By:	 	Warburg Pincus Private Equity VIII, L.P., its General Partner
	By:	 	Warburg Pincus Partners LLC, its General Partner
	By:	 	Warburg Pincus & Co., its Managing Member
		
	By:	 	 /s/ Jonathan Leff

	Name:	 	Jonathan Leff
	Title:	 	Partner
	
	EUCLIDSR BIOTECHNOLOGY PARTNERS, L.P.
	By:	 	EuclidSR Associates, L.P.
	Its:	 	General Partner
		
	By:	 	 /s/ Raymond J. Whitaker

	Name:	 	Raymond J. Whitaker
	Title:	 	General Partner
	
	EUCLIDSR PARTNERS, L.P.
	By:	 	EuclidSR Associates, L.P.
	Its:	 	General Partner
		
	By:	 	 /s/ Raymond J. Whitaker

	Name:	 	Raymond J. Whitaker
	Title:	 	General Partner

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
			
	OXFORD BIOSCIENCE PARTNERS IV L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

	Name:	 	Jonathan Fleming
	Title:	 	General Partners
	
	MRNA FUND II L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

	Name:	 	Jonathan Fleming
	Title:	 	General Partners
	
	RADIUS VENTURE PARTNERS II L.P.
	By:	 	Radius Venture Partners II, LLC
		 	its General Partner
		
	By:	 	 /s/ Jordan Davis

	Name:	 	Jordan Davis
	Title:	 	Managing Partner
	
	S.R. ONE, LIMITED
		
	By:	 	 /s/ John Keller

	Name:	 	John Keller
	Title:	 	Vice President
	
	VOX EQUITY PARTNERS, L.P.
		
	By:	 	 /s/ Matthew K. Kelley

	Name:	 	M. Kelley
	Title:	 	MGP

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
			
	 /s/ C. Boyd Clarke

	C. Boyd Clarke
	
	 /s/ Elaine Jones

	Elaine Jones
	
	CHP II L.P.
	By:	 	CHP II Management, LLC
		 	    its General Partner

		
	By:	 	 /s/ John J. Park

	Name:	 	John J. Park
	Title:	 	Managing Member

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
			
	ABS VENTURES VII L.P.
		
	By	 	Calvert Capital Caymans I L.L.C.
		
	By:	 	  

	Name:	 	Bruns Grayson
	Title:	 	Senior Manager
	
	AXIOM VENTURE PARTNERS III, LP
		
	By:	 	 /s/ Alan Mendelson

	Name:	 	Alan Mendelson
	Title:	 	General Partner
	
	MEDIMMUNE VENTURES, INC.
		
	By:	 	  

	Name:	 	
	Title:	 	

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
			
	 /s/ Barbara Dalton

	Barbara Dalton

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
					
	 /s/ Thomas Steitz
	 		 	 /s/ Joan Steitz

	Thomas Steitz	 		 	Joan Steitz

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
	
	 /s/ Susan Froshauer

	Susan Froshauer

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 
					
	VOX EQUITY PARTNERS II, L.P.
		
	By:	 	 /s/ Sharon Alvarez

		 	Name:	 	Sharon Alvarez
		 	Title:	 	Director
		
	By:	 	VOX II GENERAL PARTNER LLC
		 	Its GENERAL PARTNER.
	By:	 	OMEGA FUND III G.P. LP
		 	Its MEMBER.
	By:	 	OMEGA FUND III G.P. LTD
		 	Its GENERAL PARTNER

  
 Amendment No.
2 to Third Amended and Restated Registration Rights Agreement 

 AMENDMENT NO. 3 TO 
 THIRD AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT 
 This AMENDMENT NO. 3,
dated as of January 10, 2011 (this “Amendment”), to the Third Amended and Restated Registration Rights Agreement, dated as of June 8, 2006, as amended (the “Registration Rights Agreement”), by and among
Rib-X Pharmaceuticals, Inc., a Delaware corporation (the “Company”) and the Purchasers (as defined therein). 

W I T N E S S E T H : 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Subordinated Convertible Promissory Note
Purchase Agreement, dated as of January 7, 2009, pursuant to which certain of the Purchasers agreed to purchase Subordinated Convertible Promissory Notes and Warrants to purchase shares of Common Stock from the Company; 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Senior Subordinated Convertible Promissory Note
Purchase Agreement, dated as of May 28, 2010, pursuant to which certain of the Purchasers agreed to purchase Senior Subordinated Convertible Demand Promissory Notes and Warrants to purchase shares of Common Stock from the Company; 

WHEREAS, the Company and certain of the Purchasers have entered into that certain Senior Convertible Promissory Note Purchase
Agreement, of even date herewith, pursuant to which certain of the Purchasers agreed to purchase Senior Convertible Demand Promissory Notes and Warrants to purchase shares of Common Stock from the Company (collectively, the “Senior Note
Financing”); 
 WHEREAS, Section 13(d) of the Registration Rights Agreement provides that the Registration
Rights Agreement may be amended with the written consent of the Company and the holders of at least a majority of the outstanding shares of Restricted Stock held by all of the Purchasers (the “Required Purchasers”); and 

WHEREAS, in connection with the Senior Note Financing, the Company and the Required Purchasers desire to amend certain provisions
of the Registration Rights Agreement as more fully set forth herein. 
 NOW, THEREFORE, for good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, and in consideration of the agreements herein, the parties hereto agree as follows: 
 1. Definition of Note. The definition of “Notes” in Section 1 shall be amended and restated in its entirety to read as follows: 

‘“Notes” shall mean (i) those certain Subordinated Convertible Promissory Notes issued by the Company pursuant to the
Subordinated Convertible Promissory Note Purchase Agreement, dated as of January 7, 2009, by and among the Company and the Purchasers listed therein, (ii) those certain Senior Subordinated Convertible Demand Promissory Notes issued by the
Company from time to time 

 
pursuant to the Senior Subordinated Convertible Demand Promissory Note Purchase Agreement, dated as of May 28 2010, by and among the Company and the Purchasers listed therein, and
(iii) those certain Senior Convertible Demand Promissory Notes issued by the Company from time to time pursuant to the Senior Convertible Demand Promissory Note Purchase Agreement, dated as of January 10, 2011, by and among the Company and
the Purchasers listed therein.’ 
 2. Definition of Warrants. The definition of “Warrants” in
Section 1 shall be amended and restated in its entirety to read as follows: 
 ‘“Warrants” shall mean
(i) those certain Warrants to Purchase Common Stock issued by the Company pursuant to the Subordinated Convertible Promissory Note Purchase Agreement, dated as of January 7, 2009, by and among the Company and the Purchasers listed therein,
(ii) those certain Warrants to Purchase Common Stock issued by the Company from time to time pursuant to the Senior Subordinated Convertible Demand Promissory Note Purchase Agreement, dated as of May 28, 2010, by and among the Company and
the Purchasers listed therein, and (iii) those certain Warrants to Purchase Common Stock issued by the Company from time to time pursuant to the Senior Convertible Demand Promissory Note Purchase Agreement, dated as of January 10, 2011, by
and among the Company and the Purchasers listed therein.’ 
 3. Definition of Conversion Stock. The
definition of “Conversion Stock” in Section 1 shall be amended and restated in its entirety to read as follows: 

‘“Conversion Stock” shall mean shares of Common Stock issued or issuable to a party hereto upon (i) conversion of the
Preferred Stock or the Notes or exercise of the Warrants or (ii) exercise of warrants, options or other rights to purchase Common Stock of the Company approved by the Board of Directors in accordance with Section 4.3(e)(viii) of the
Stockholders Agreement (including, a warrant for the purchase of 500,000 shares of Common Stock issued by the Company to Connecticut Innovations, Incorporated), and any shares of capital stock issued or distributed in respect thereof.’

 4. Defined Terms. Capitalized terms used but not defined herein shall have the meaning set forth in the
Registration Rights Agreement. 
 5. No Other Amendment. Except as expressly amended hereby, the Registration
Rights Agreement shall remain in full force and effect in accordance with its terms, without any waiver, amendment or modification of any provision thereof. All references in the Registration Rights Agreement to “this Agreement” shall be
deemed to refer to the Registration Rights Agreement as amended by this Amendment. 
 6. Governing Law;
Jurisdiction. This Amendment shall be construed, performed and enforced in accordance with, and governed by, the laws of the State of Delaware, without giving effect to the principles of conflicts of laws thereof. The parties hereto
irrevocably elect as the sole judicial forum for the adjudication of any matters arising under or in connection 

  
 -2-

 
with this Amendment, and consent to the jurisdiction of, the courts of the State of Delaware or the corresponding United States federal court in the State of Delaware. 

7. Section and Paragraph Headings. The section and paragraph headings in this Amendment are for reference purposes only and
shall not affect the meaning or interpretation of this Amendment. 
 8. Counterparts. This Amendment may be
executed in counterparts, each of which shall be deemed an original, but all of which shall constitute the same instrument. 

[REMAINDER OF PAGE INTENTIONALLY LEFT BLANK] 

  
 -3-

 IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed as
of the date first above written. 
  

					
	RIB-X PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Mark Leuchtenberger

		 	Name:	 	Mark Leuchtenberger
		 	Title:	 	President and Chief Executive Officer

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement 

 
					
	WP VIII FINANCE, L.P.
		
	By:	 	WPVIII GP, L.P., its General Partner
	By:	 	Warburg Pincus Private Equity VIII, L.P., its General Partner
	By:	 	Warburg Pincus Partners, LLC, its General Partner
	By:	 	Warburg Pincus & Co., its Managing Member
		
	By:	 	 /s/ Jonathan Leff

		 	Name:	 	Jonathan Leff
		 	Title:	 	Partner
	
	AXIOM VENTURE PARTNERS III, LP
		
	By:	 	 /s/ Alan Mendelson

		 	Name:	 	Alan Mendelson
		 	Title:	 	General Partner
	
	CHP II L.P.
		
	By:	 	CHP II Management, LLC, its General Partner
		
	By:	 	 /s/ John J. Park

		 	Name:	 	John J. Park
		 	Title:	 	Managing Member

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement 

 
					
	RADIUS VENTURE PARTNERS II L.P.
	By:	 	Radius Venture Partners II, LLC, its General Partner
		
	By:	 	 /s/ Jordan S. Davis

		 	Name:	 	Jordan S. Davis
		 	Title:	 	Managing Member
	
	ABS VENTURES VII L.P.
	By:	 	Calvert Capital Caymans I L.L.C.
		
	By:	 	 /s/ Bruns H. Grayson

		 	Name:	 	Bruns H. Grayson
		 	Title:	 	Managing Member
	
	VOX EQUITY PARTNERS, L.P.
		
	By:	 	 /s/ Matthew K. Kelley

		 	Name:	 	M. Kelley
		 	Title:	 	MGP
	
	VOX EQUITY PARTNERS II, L.P.
	By:	 	Vox II GENERAL PARTNER, LLC, its General Partner
	By:	 	Omega Fund III, LP, its member
	By:	 	Omega Fund III GP LP, its General Partner
	By:	 	Omega Fund III, GP Limited, its General partner
		
	By:	 	 /s/ Kevin Brennan

		 	Name:	 	Mr. Kevin Brennan
		 	Title:	 	Director

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement 

 
					
	S.R. ONE, LIMITED
		
	By:	 	 /s/ Kent Gossett

		 	Name:	 	Kent Gossett
		 	Title:	 	Vice President & Partner
	
	CONNECTICUT INNOVATIONS, INCORPORATED
		
	By:	 	 /s/ Peter Longo

		 	Name:	 	Peter Longo
		 	Title:	 	President & Executive Director
	
	 /s/ C. Boyd Clarke

	C. Boyd Clarke

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement 

 
					
	OXFORD BIOSCIENCE PARTNERS IV L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

		 	Name:	 	Jonathan Fleming
		 	Title:	 	Managing General Partner
	
	MRNA FUND II L.P.
	By:	 	OBP Management IV L.P.
		
	By:	 	 /s/ Jonathan Fleming

		 	Name:	 	Jonathan Fleming
		 	Title:	 	Managing General Partner

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement 

 
					
	 Managing Member of Saints Capital VI, LLC
 the General Partner of

	SAINTS CAPITAL VI, L.P.
		
	By:	 	 /s/ David Quinlivan

		 	Name:	 	David Quinlivan
		 	Title:	 	Managing Member

  
 Signature Page
to Amendment No. 3 to Third Amended and Restated Registration Rights Agreement

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