Document:

EX-4.3

 Exhibit 4.3 

November 8, 2019 
 RTW Master Fund, Ltd. 

RTW Innovation Master Fund, Ltd. 
 RTW Venture Fund Limited 

c/o RTW Investments, LP 
 412 West 15th Street, Floor 9, 

New York, NY, 10011 USA 
 Attn: Roderick Wong, M.D. 

Re: IPO Participation Right 
 This letter
agreement (this “Agreement”) memorializes the agreement and understanding between RTW Master Fund, Ltd., RTW Innovation Master Fund, Ltd. and RTW Venture Fund Limited (collectively, “RTW”), on the one hand, and
Avidity Biosciences, Inc., a Delaware corporation (the “Company”), on the other hand, regarding the Company’s grant to RTW of the right to participate in the Company’s future initial public offering of its equity
securities on the terms, and subject to the conditions, set forth below. 
 The Company is entering into this Agreement as a material
inducement to cause RTW to enter into that certain Series C Preferred Stock Purchase Agreement, dated as of the date hereof, by and among the Company, RTW and the other purchasers named therein (the “Purchase Agreement”).
Capitalized terms not otherwise defined herein shall have the meanings ascribed to such terms in the Purchase Agreement and, to the extent not defined therein, such terms shall have the meanings ascribed to them in that certain Registration Rights
Agreement, dated as of the date hereof, by and among the Company, RTW and the parties named therein. 
 In consideration of the foregoing
and the mutual promises and covenants hereinafter set forth and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, by execution of this Agreement, the parties hereto hereby agree as follows: 

1.    In connection with the Company’s sale of shares of its common stock (“Common Stock”) to the
public in a firm-commitment underwritten public offering pursuant to an effective registration statement under the Securities Act (the “IPO”), the Company shall, within a reasonable period of time preceding the consummation of the
IPO and in compliance with all applicable laws and regulations, use commercially reasonable efforts to provide RTW with the opportunity to purchase shares of Common Stock to be sold in the IPO (including any over-allotment option by the underwriters
to the IPO, if any) at the same price per share at which the Common Stock offered in the IPO are being offered to the public (the “IPO Price”) (such right, the “Public Offering Participation Right”). If RTW
exercises its Public Offering Participation Right, RTW shall have the right to purchase up to a number of shares of Common Stock to be sold in the IPO equal to (a) the Participation Right Percentage (as defined below), multiplied by,
(b) the aggregate number of shares of Common Stock to be sold in the IPO (including any overallotment option by the underwriters to the IPO, if any). RTW may assign its Public Offering Participation Right to any of its Affiliates. For the
avoidance of doubt, nothing in this Section 1 is intended to limit the number of shares that RTW or its Affiliates may acquire in the IPO outside of its Public Offering Participation Right. For purposes of this Agreement, the
“Participation Right Percentage” shall mean a fraction, the numerator of which shall be equal to 150% of the number of shares of Common Stock held by RTW and its Affiliates immediately prior to the IPO (including all shares of
Common Stock then issuable (directly or indirectly) upon conversion and/or exercise, as applicable, of any shares of the Company’s preferred stock (“Preferred Stock”) held by RTW and its Affiliates immediately prior to the
IPO), and the denominator of which shall be the total number of outstanding shares of Common Stock (including all shares of Common Stock issuable (directly or indirectly) upon conversion and/or exercise, as applicable, of the Preferred Stock or
other convertible securities then outstanding). 

  
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 2.    Notwithstanding Section 1 above, in the event that either
(a) the Company is advised by its outside legal counsel, the Securities and Exchange Commission (the “SEC”), the Financial Industry Regulatory Authority (“FINRA”) or any stock exchange on which the Common Stock
is to be traded (the “Exchange”) that the offering or sale of the Company’s securities to RTW as described above in Section 1 would violate any federal or state securities laws or the rules or regulations of the SEC, FINRA
or the Exchange, or (b) the managing underwriter(s) reasonably determines that marketing factors require a limitation on the number of shares of Common Stock to be underwritten in connection with the IPO and request(s) that RTW’s Public
Offering Participation Right be subject to carve-backs, restrictions or other limitations (each of the events described in the foregoing clauses (a) or (b), a “Cutback”), then, in each case, the Company shall offer to RTW the
right to purchase in a separate private placement (the “Private Placement”) (which shall be conducted concurrently with the IPO and the closing of which shall be contingent on the closing of the IPO), at the IPO Price, up to that
number of shares of Common Stock equal to the difference between the number of shares of Common Stock that RTW would have been able to purchase pursuant to Section 1 above but for the applicable Cutback, and the number of shares of Common Stock
that RTW was actually permitted to purchase in the IPO pursuant to Section 1, if any (the “Private Sale Participation Right,” and together with the Public Offering Participation Right, the “Rights”).
Notwithstanding anything to the contrary set forth above, if any Cutback shall be imposed on RTW, such Cutback shall apply equally to any other individual or entity to which the Company has granted rights similar to the Public Offering Participation
Rights (the “Other Participating Investors”), if any, with respect to the number of shares of Common Stock that RTW and such Other Participating Investors are prohibited from purchasing upon exercise of their respective rights. Any
shares of Common Stock that RTW purchases in a Private Placement shall be exempt from the registration requirements of the Securities Act. 

3.    Notwithstanding the foregoing, RTW agrees that (a) in no event shall the Private Sale Participation Right be
exercised in such a manner that, in the reasonable determination of the managing underwriter(s), would materially and adversely affect the IPO and (b) the number of shares RTW is entitled to purchase may be reduced or modified only to the
extent reasonably requested by the Company’s underwriter(s) as to not cause such material and adverse effect on the IPO, which reduction or modification shall be applied equally to each of RTW and the Other Participating Investors, if any, with
respect to the number of shares of Common Stock that RTW and such Other Participating Investors are prohibited from purchasing upon exercise of their respective rights. 

4.    If RTW exercises its Private Sale Participation Right, the Company and RTW shall execute and deliver such documents
that are (a) customary for a transaction structured as a concurrent private placement with a public offering and (b) reasonably satisfactory to the Company, RTW and the managing underwriter(s), if applicable. 

5.    The invalidity or unenforceability of any provision hereof shall in no way affect the validity or enforceability of
any other provision. 
 6.    For the avoidance of doubt, the rights described in this Agreement shall apply only to the
IPO and shall not apply to any subsequent offering of the Company’s securities. This Agreement shall be binding upon and inure to the benefit of the parties hereto and their respective successors and assigns. This Agreement may not be modified,
amended or terminated, in whole or in part, except by an agreement in 

  
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writing signed by the parties hereto; provided, that, whether or not RTW exercises the Public Offering Participation Right or the Private Sale Participation Right, this Agreement shall
automatically terminate and be of no further force or effect upon the consummation of the IPO and, if applicable, the Private Placement. 

7.    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. Counterparts may be delivered via facsimile, electronic mail (including pdf or any electronic signature complying with the U.S. federal ESIGN Act of 2000, Uniform Electronic Transactions
Act or other applicable law) or other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes. 

8.    The governing law and dispute resolution provisions set forth in Section 6.3 and 6.15 of the Purchase Agreement
are incorporated by reference herein, mutatis mutandis. 
 (The remainder of this page left intentionally blank.)

  
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 Please confirm your agreement to the terms of this Agreement by counter-signature where indicated below.

  

			
	Sincerely,
	
	AVIDITY BIOSCIENCES, INC.
		
	By:	 	/s/ Sarah Boyce
	Name:	 	Sarah Boyce
	Title:	 	Chief Executive Officer

  

			
	Accepted by:
	
	RTW MASTER FUND, LTD.
		
	By:	 	 /s/ Roderick Wong, M.D.

	Name:	 	Roderick Wong, M.D.
	Title:	 	Director
	
	RTW INNOVATION MASTER FUND, LTD.
		
	By:	 	 /s/ Roderick Wong, M.D.

	Name:	 	Roderick Wong, M.D.
	Title:	 	Director
	
	RTW VENTURE FUND LIMITED
	By: RTW Investments, LP, its Investment Manager
		
	By:	 	 /s/ Roderick Wong, M.D.

	Name:	 	Roderick Wong, M.D.
	Title:	 	Managing PartnerEX-4.4

 Exhibit 4.4 

THIS WARRANT AND THE UNITS ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR
THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN SECTIONS 5.3 AND 5.4 BELOW, MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND
SUBSTANCE SATISFACTORY TO THE ISSUER, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS EXEMPT FROM SUCH REGISTRATION. 
 WARRANT TO PURCHASE
LIMITED LIABILITY COMPANY SERIES A PREFERRED UNITS 
  

			
	Company:	  	AVIDITY NANOMEDICINES LLC, a Delaware limited liability company
	Number of Units:	  	16,474
	Type/Series of Units:	  	Series A Preferred Units
	Warrant Price:	  	2.2615 per Unit
	Issue Date:	  	August 7, 2015
	Expiration Date:	  	August 7, 2025            See also Section 5.1(b). 
	Credit Facility:	  	 This Warrant to Purchase Limited Liability Company Series A Preferred

Units (“Warrant”) is issued in connection with that certain Loan and Security Agreement of even date herewith between Silicon Valley
Bank and the Company (as amended and/or modified and in effect from time to time, the “Loan Agreement”).

 THIS WARRANT CERTIFIES THAT, for good and valuable consideration, SILICON VALLEY BANK (together with any
successor or permitted assignee or transferee of this Warrant or of any units issued upon exercise hereof, “Holder”) is entitled to purchase the number of fully paid and non-assessable
units of limited liability company interest (the “Units”) of the Class (as defined below) of the above-named company (the “Company”) at the above-stated Warrant Price per Unit, all as set forth above
and as adjusted pursuant to Section 2 of this Warrant, subject to the provisions and upon the terms and conditions set forth in this Warrant. Reference is made to Section 5.4 of this Warrant whereby Silicon Valley Bank shall transfer this
Warrant to its parent company, SVB Financial Group. 
 This Warrant shall be exercisable for Series A Preferred Units (as may be adjusted
from time to time pursuant to the provisions of this Warrant, the “Class”) as further described and defined in, and having the relative rights, powers, preferences and privileges as set forth in, the Company’s Amended
and Restated Operating Agreement dated as of January 31, 2014, as amended and/or restated and in effect from time to time (the “Operating Agreement”). As used herein, “units” refers generally to
limited liability company interests in the Company, whether such interests be styled as units, percentage interests, units or otherwise in the Operating Agreement. 

 SECTION 1.  EXERCISE. 

1.1 Method of Exercise. Holder may at any time and from time to time exercise this Warrant, in whole or in part, by delivering to the
Company the original of this Warrant together with a duly executed Notice of Exercise in substantially the form attached hereto as Appendix 1 and, unless Holder is exercising this Warrant pursuant to a cashless exercise set forth in
Section 1.2, a check, wire transfer of same-day funds (to an account designated by the Company), or other form of payment acceptable to the Company for the aggregate Warrant Price for the Units being
purchased. 
 1.2 Cashless Exercise. On any exercise of this Warrant, in lieu of payment of the aggregate Warrant Price in the manner
as specified in Section 1.1 above, but otherwise in accordance with the requirements of Section 1.1, Holder may elect to receive Units equal to the value of this Warrant, or portion hereof as to which this Warrant is being exercised.
Thereupon, the Company shall issue to the Holder such number of fully paid and non-assessable Units as are computed using the following formula: 

 

			
	X =	  	Y(A-B)/A
		
	where:                          	  	
		
	X =	  	the number of Units to be issued to the Holder;
		
	Y =	  	the number of Units with respect to which this Warrant is being exercised (inclusive of the Units surrendered to the Company in payment of the aggregate Warrant Price);
		
	A =	  	the Fair Market Value (as determined pursuant to Section 1.3 below) of one Unit; and
		
	B =	  	the Warrant Price.

 1.3 Fair Market Value. If the Company’s common or ordinary units are then traded or quoted on a
nationally recognized securities exchange, inter-dealer quotation system or over-the-counter market (a “Trading Market”) and the Class is
common or ordinary units, the fair market value of a Unit shall be the closing price or last sale price of a common or ordinary unit reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its
Notice of Exercise to the Company. If the Company’s common or ordinary units are then traded in a Trading Market and the Class is a series of convertible preferred units or other units convertible into common or ordinary units, the fair
market value of a Unit shall be the closing price or last sale price of a common or ordinary unit reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its Notice of Exercise to the Company
multiplied by the number of common or ordinary units into which a unit of the Class is then convertible. If the Company’s common or ordinary units are not then traded in a Trading Market, the Manager or Managers of the Company shall
determine the fair market value of a Unit in its, his or their reasonable good faith judgment. 

 1.4 Delivery of Certificate and New Warrant. Within a reasonable time after Holder
exercises this Warrant in the manner set forth in Section 1.1 or 1.2 above, if units of the Class are then certificated by the Company, the Company shall deliver to Holder a certificate representing the Units issued to Holder upon such
exercise and, if this Warrant has not been fully exercised and has not expired, a new warrant of like tenor representing the Units not so acquired. If units of the Class are not then certificated by the Company, the Company will deliver to
Holder such evidence of the issuance of such Units to Holder as required or permitted under the Operating Agreement or, if there be none, such evidence as Holder may reasonably request. 

1.5 Replacement of Warrant. On receipt of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation
of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form, substance and amount to the Company or, in the case of mutilation, on surrender of this Warrant to the Company for
cancellation, the Company shall, within a reasonable time, execute and deliver to Holder, in lieu of this Warrant, a new warrant of like tenor and amount. 

1.6    Treatment of Warrant Upon Acquisition of Company. 

(a)    Acquisition. For the purpose of this Warrant, “Acquisition” means any transaction or
series of related transactions involving: (i) the sale, lease, exclusive license, or other disposition of all or substantially all of the assets of the Company; (ii) any merger or consolidation of the Company into or with another person or
entity (other than a merger or consolidation effected exclusively to change the Company’s domicile), or any other corporate reorganization, in which the members and other holders of units of the Company in their capacity as such immediately
prior to such merger, consolidation or reorganization, own less than a majority of the Company’s (or the surviving or successor entity’s) outstanding voting power (even if such voting power be limited solely to such matters as required by
applicable law) immediately after such merger, consolidation or reorganization (or, if such Company members and other holders of units beneficially own a majority of the outstanding voting power (even if such voting power be limited solely to such
matters as required by applicable law) of the surviving or successor entity as of immediately after such merger, consolidation or reorganization, such surviving or successor entity is not the Company); or (iii) any sale or other transfer by the
members and/or other holders of units of the Company of units representing at least a majority of the Company’s then-total outstanding combined voting power (even if such voting power be limited solely to such matters as required by applicable
law). 
 (b)    Treatment of Warrant at Acquisition. In the event of an Acquisition in which the consideration to
be received by the Company’s members and other holders of units consists solely of cash, solely of Marketable Securities or a combination of cash and Marketable Securities (a “Cash/Public Acquisition”), either
(i) Holder shall exercise this Warrant pursuant to Section 1.1 and/or 1.2 and such exercise will be deemed effective immediately prior to and contingent upon the consummation of such Acquisition or (ii) if Holder elects not to
exercise the Warrant, this Warrant will expire immediately prior to the consummation of such Acquisition. 

 (c)    The Company shall provide Holder with written notice of its
request relating to the Cash/Public Acquisition (together with such reasonable information as Holder may reasonably require regarding the treatment of this Warrant in connection with such contemplated Cash/Public Acquisition giving rise to such
notice), which is to be delivered to Holder not less than seven (7) Business Days prior to the closing of the proposed Cash/Public Acquisition. In the event the Company does not provide such notice, then if, immediately prior to the Cash/Public
Acquisition, the fair market value of one Unit (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above would be greater than the Warrant Price in effect on such date, then this Warrant shall
automatically be deemed on and as of such date to be exercised pursuant to Section 1.2 above as to all Units (or such other securities) for which it shall not previously have been exercised, and the Company shall promptly notify the Holder of
the number of Units (or such other securities) issued upon such exercise to the Holder and Holder shall be deemed to have restated each of the representations and warranties in Section 4 of the Warrant as the date thereof. 

(d)    Upon the closing of any Acquisition other than a Cash/Public Acquisition defined above, the acquiring, surviving or
successor entity shall assume the obligations of this Warrant, and this Warrant shall thereafter be exercisable for the same securities and/or other property as would have been paid for the Units issuable upon exercise of the unexercised portion of
this Warrant as if such Units were outstanding on and as of the closing of such Acquisition, subject to further adjustment from time to time in accordance with the provisions of this Warrant. 

(e)    As used in this Warrant, “Marketable Securities” means securities meeting all of the
following requirements: (i) the issuer thereof is then subject to the reporting requirements of Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and is then
current in its filing of all required reports and other information under the Act and the Exchange Act; (ii) the class and series of shares or other security of the issuer that would be received by Holder in connection with the Acquisition were
Holder to exercise this Warrant on or prior to the closing thereof is then traded in Trading Market, and (iii) Holder would be able to publicly re-sell, within six (6) months and one day following
the closing of such Acquisition, all of the issuer’s shares and/or other securities that would be received by Holder in such Acquisition were Holder to exercise this Warrant in full on or prior to the closing of such Acquisition. 

SECTION 2.  ADJUSTMENTS TO THE SHARES AND WARRANT PRICE. 

2.1    Unit Dividends, Splits, Etc. If the Company declares or pays a dividend or distribution on
the outstanding units of the Class payable in additional units of the Class or other units, securities or property (other than cash), then upon exercise of this Warrant, for each Unit acquired, Holder shall receive, without additional cost
to Holder, the total number and kind of units, securities and property which Holder would have received had Holder owned the Units of record as of the date the dividend or distribution occurred. If the Company subdivides the outstanding units of the
Class by reclassification or otherwise into a greater number of units, the number of Units purchasable hereunder shall be proportionately increased and the Warrant Price shall be proportionately decreased. If the outstanding units of the
Class are combined or consolidated, by reclassification or otherwise, into a lesser number of units, the Warrant Price shall be proportionately increased and the number of Units shall be proportionately decreased. 

 2.2    Reclassification, Exchange, Combinations or
Substitution. Upon any event whereby all of the outstanding units of the Class are reclassified, exchanged, combined, substituted, or replaced for, into, with or by Company securities of a different class and/or series, then from and after
the consummation of such event, this Warrant will be exercisable for the number, class and series of Company securities that Holder would have received had the Units been outstanding on and as of the consummation of such event, and subject to
further adjustment thereafter from time to time in accordance with the provisions of this Warrant. The provisions of this Section 2.2 shall similarly apply to successive reclassifications, exchanges, combinations substitutions, replacements or
other similar events. 
 2.3    Conversion of Convertible Units. If the Class is a class,
type series or other designation of convertible preferred units or other units convertible into common or ordinary units, in the event that all outstanding units of the Class are converted, automatically or by action of the holders thereof,
into common or ordinary units pursuant to the provisions of the Operating Agreement, including, without limitation, in connection with the Company’s initial, underwritten public offering and sale of its units pursuant to an effective
registration statement under the Act (the “IPO”), then from and after the date on which all outstanding units of the Class have been so converted, this Warrant shall be exercisable for such number of common or ordinary
units into which the Units would have been converted had the Units been outstanding on the date of such conversion, and the Warrant Price shall equal the Warrant Price in effect as of immediately prior to such conversion divided by the number of
common or ordinary units into which one Unit would have been converted, all subject to further adjustment thereafter from time to time in accordance with the provisions of this Warrant. 

2.4    Adjustments for Diluting Issuances. Without duplication of any adjustment otherwise provided
for in this Section 2, the number of common or ordinary units issuable upon conversion of the Units shall be subject to anti-dilution adjustment from time to time in the manner set forth in Section 3.03(d)(iv) of the Operating Agreement as
if the Units were issued and outstanding on and as of the date of any such required adjustment. 

2.5    No Fractional Unit. No fractional Unit shall be issuable upon exercise of this Warrant and
the number of Units to be issued shall be rounded down to the nearest whole Unit. If a fractional Unit interest arises upon any exercise of the Warrant, the Company shall eliminate such fractional Unit interest by paying Holder in cash the amount
computed by multiplying the fractional interest by (i) the fair market value (as determined in accordance with Section 1.3 above) of a full Unit, less (ii) the then-effective Warrant Price. 

2.6    Notice/Certificate as to Adjustments. Upon each adjustment of the Warrant Price,
Class and/or number of Units, the Company, at the Company’s expense, shall notify Holder in writing within a reasonable time setting forth the adjustments to the Warrant Price, Class and/or number of Units and facts upon which such
adjustment is based. The 

 
Company shall, upon written request from Holder, furnish Holder with a certificate of its Manager, including computations of such adjustment and the Warrant Price, Class and number of Units
in effect upon the date of such adjustment. 
 SECTION 3.  REPRESENTATIONS AND COVENANTS OF THE COMPANY. 

3.1 Representations and Warranties. The Company represents and warrants to, and agrees with, the Holder as follows: 

(a)    The initial Warrant Price referenced on the first page of this Warrant is not greater than the price per unit at
which units of the Class were last sold and issued prior to the Issue Date hereof in an arms-length transaction in which at least $500,000 of such units were sold. 

(b)    All Units which may be issued upon the exercise of this Warrant, and all units and/or other securities, if any,
issuable upon conversion of the Units, shall, upon issuance, be duly authorized, validly issued, fully paid and non-assessable, and free of any liens and encumbrances except for restrictions on transfer
provided for herein, under the Operating Agreement or under applicable federal and state securities laws. The Company covenants that it shall at all times cause to be reserved and kept available out of its authorized and unissued units such number
of units of the Class, common or ordinary units and other securities as will be sufficient to permit the exercise in full of this Warrant and the conversion of the Units into common or ordinary units or such other securities, if any. 

(c)    The Company’s capitalization table attached hereto as Schedule 1 is true and complete, in all material
respects, as of the Issue Date. 
 3.2 Notice of Certain Events. If the Company proposes at any time to: 

(a)    declare any dividend or distribution upon the outstanding units of the Class or, if units of
the Class are then convertible into common or ordinary units, such common or ordinary units, whether in cash, property, units, or other securities and whether or not a regular or periodic cash dividend or distribution (other than a distribution
of cash upon the outstanding units of the Class and/or common or ordinary units made solely for the purpose of permitting the holders thereof to satisfy their respective federal and state tax obligations in respect of the taxable income of the
Company); 
 (b)    offer for subscription or sale pro rata to all holders of the outstanding units of
the Class any additional Company units of any type, class, series or other designation (other than pursuant to contractual pre-emptive rights); 

(c)    effect any reclassification, exchange, combination, substitution, reorganization or recapitalization
of the outstanding units of the Class; 
 (d)    effect an Acquisition or to liquidate, dissolve or wind
up; or 
 (e)    effect an IPO; 

 then, in connection with each such event, the Company shall give Holder: 

(1)    in respect of the matters referred to in (a) and (b) above, at least seven (7) Business Days
prior written notice of the earlier to occur of (i) the date on which a record will be taken for such dividend, distribution, or subscription rights (and specifying the date on which the holders of outstanding units of the Class will be
entitled thereto) or for determining rights to vote, if any, or (ii) the closing or effective date of such event; 

(2)    in the case of the matters referred to in (c) and (d) above at least seven (7) Business
Days prior written notice of the date when the same will take place (and specifying the date on which the holders of outstanding units of the Class will be entitled to exchange their units for the securities or other property deliverable upon
the occurrence of such event); and 
 (3)    with respect to the IPO, at least seven (7) Business
Days prior written notice of the date on which the Company proposes to file its registration statement in connection therewith. 
 Reference is made to
Section 1.6(c) whereby this Warrant will be deemed to be exercised pursuant to Section 1.2 hereof if the Company does not give written notice to Holder of a Cash/Public Acquisition as required by the terms hereof. Company will also provide
information requested by Holder that is reasonably necessary to enable Holder to comply with Holder’s accounting or reporting requirements. 

SECTION 4.  REPRESENTATIONS, WARRANTIES OF THE HOLDER. 

The Holder represents and warrants to the Company as follows: 

4.1    Purchase for Own Account. This Warrant and the securities to be acquired upon exercise of
this Warrant by Holder are being acquired for investment for Holder’s account, not as a nominee or agent, and not with a view to the public resale or distribution within the meaning of the Act. Holder also represents that it has not been formed
for the specific purpose of acquiring this Warrant or the Units. 
 4.2    Disclosure of
Information. Holder is aware of the Company’s business affairs and financial condition and has received or has had full access to all the information it considers necessary or appropriate to make an informed investment decision with respect
to the acquisition of this Warrant and its underlying securities. Holder further has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the offering of this Warrant and its underlying
securities and to obtain additional information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify any information furnished to Holder or to which Holder has access.

 4.3    Investment Experience. Holder understands
that the purchase of this Warrant and its underlying securities involves substantial risk. Holder has experience as an investor in securities of companies in the development stage and acknowledges that Holder can bear the economic risk of such
Holder’s investment in this Warrant and its underlying securities and has such knowledge and experience in financial or business matters that Holder is capable of evaluating the merits and risks of its investment in this Warrant and its
underlying securities and/or has a preexisting personal or business relationship with the Company and certain of its officers, directors or controlling persons of a nature and duration that enables Holder to be aware of the character, business
acumen and financial circumstances of such persons. 
 4.4    Accredited Investor Status. Holder
is an “accredited investor” within the meaning of Regulation D promulgated under the Act. 

4.5    The Act. Holder understands that this Warrant and the Units issuable upon exercise hereof
have not been registered under the Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of the Holder’s investment intent as expressed herein. Holder understands that this
Warrant and the Units issued upon any exercise hereof must be held indefinitely unless subsequently registered under the Act and qualified under applicable state securities laws, or unless exemption from such registration and qualification are
otherwise available. Holder is aware of the provisions of Rule 144 promulgated under the Act. 

4.6    Market Stand-off Agreement. Holder hereby agrees that Holder shall not sell, dispose of,
transfer, make any short sale of, grant any option for the purchase of, or enter into any hedging or similar transaction with the same economic effect as a sale, any common units or other securities of Company held by Holder (other than those
included in the registration) during the 180-day period following the effective date of the IPO (or such longer period not to exceed 34 days after the expiration of the
180-day period, as the underwriters or the Company shall request in order to facilitate compliance with NASD Rule 2711 or NYSE Member Rule 472 or any successor or similar rule or regulation) (the
“Market Standoff Provision”); provided, that all officers and managers of the Company and holders of at least one percent (1%) of the Company’s voting securities are bound by and have entered into similar agreements. The Market
Stand-Off Provision may not be amended, modified or waived without the prior written consent of Holder unless such amendment, modification or waiver affects the rights associated with the Units in the same
manner as such amendment, modification or waiver affects the rights associated with all other units of the same series and type as the Units granted pursuant to this Warrant. 

4.7    Rights as Member. Without limiting any provision of this Warrant, Holder agrees that, as a
Holder of this Warrant, it will not have any rights as a member of the Company unless and until the exercise of this Warrant, and then only with respect to the Units issued upon such exercise. Upon exercise of this Warrant, the Company agrees that
Holder shall automatically and without further action by any person be admitted as a member of the Company under the Operating Agreement with respect to the Units issued upon such exercise. 

 4.8    No Public Market. Holder understands that
no public market now exists for any of the securities issued by the Company, and that the Company has made no assurances that a public market will ever exist for the securities issuable upon exercise of this Warrant. 

SECTION 5.  MISCELLANEOUS. 

5.1    Term; Automatic Cashless Exercise Upon Expiration. 

(a)    Term. Subject to the provisions of Section 1.6 above, this Warrant is exercisable in whole or in part at
any time and from time to time on or before 6:00 PM, Pacific time, on the Expiration Date and shall be void thereafter. 

(b)    Automatic Cashless Exercise upon Expiration. In the event that, upon the Expiration Date, the fair market
value of one Unit (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above is greater than the Warrant Price in effect on such date, then this Warrant shall automatically be deemed on and as of
such date to be exercised pursuant to Section 1.2 above as to all Units (or such other securities) for which it shall not previously have been exercised, and the Company shall, within a reasonable time, deliver a certificate representing the
Units (or such other securities) issued upon such exercise to Holder. 
 5.2    Legends. Each
certificate evidencing Units (and each certificate evidencing securities issued upon conversion of any Units, if any) shall be imprinted with a legend in substantially the following form: 

THE UNITS EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
“ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN THAT CERTAIN WARRANT TO PURCHASE LIMITED LIABILITY COMPANY SERIES A PREFERRED UNITS ISSUED BY THE ISSUER TO SILICON VALLEY BANK DATED AUGUST 7,
2015, MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS
EXEMPT FROM SUCH REGISTRATION. 
 5.3    Compliance with Securities Laws on Transfer. This Warrant
and the Units issued upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Units, if any) may not be transferred or assigned in whole or in part except in compliance with applicable federal and
state securities laws by the transferor and the transferee (including, without limitation, the delivery of investment representation letters and legal opinions reasonably satisfactory to the Company, as reasonably requested by the Company). The
Company shall not require Holder to provide an opinion of counsel if the transfer is to SVB Financial Group (Silicon Valley Bank’s parent company) or any other 

 
affiliate of Holder, provided that any such transferee is an “accredited investor” as defined in Regulation D promulgated under the Act. Additionally, the Company shall also not require
an opinion of counsel if there is no material question as to the availability of Rule 144 promulgated under the Act. 

5.4    Transfer Procedure. After receipt by Silicon Valley Bank of the executed Warrant, Silicon
Valley Bank will transfer all of this Warrant to its parent company, SVB Financial Group. By its acceptance of this Warrant, SVB Financial Group hereby makes to the Company each of the representations and warranties set forth in Section 4
hereof and agrees to be bound by all of the terms and conditions of this Warrant as if the original Holder hereof. Subject to the provisions of Section 5.3 and upon providing the Company with written notice, SVB Financial Group and any
subsequent Holder may transfer all or part of this Warrant or the Units issued upon exercise of this Warrant (or the securities issued upon conversion of the Units, if any) to any transferee, provided, however, in connection with any such transfer,
SVB Financial Group or any subsequent Holder will give the Company notice of the portion of the Warrant and/or Units (and/or securities issued upon conversion of the Units, if any) being transferred with the name, address and taxpayer identification
number of the transferee and Holder will surrender this Warrant to the Company for reissuance to the transferee(s) (and Holder if applicable); and provided further, that any subsequent transferee other than SVB Financial Group shall agree in writing
with the Company to be bound by all of the terms and conditions of this Warrant; and provided, further, that any transfer of Units (or of securities issued upon conversion of the Units, if any), shall be subject to the provisions of the Operating
Agreement. Notwithstanding any contrary provision herein, at all times prior to the IPO, Holder may not, without the Company’s prior written consent, transfer this Warrant or any portion hereof, or any Units issued upon any exercise hereof, or
any units or other securities issued upon any conversion of any Units issued upon any exercise hereof, to any person or entity who directly competes with the Company, except in connection with an Acquisition of the Company by such a direct
competitor. 
 5.5    Notices. All notices and other communications hereunder from the Company to
the Holder, or vice versa, shall be deemed delivered and effective (i) when given personally, (ii) on the third (3rd) Business Day after being mailed by first-class registered or
certified mail, postage prepaid, (iii) upon actual receipt if given by facsimile or electronic mail and such receipt is confirmed in writing by the recipient, or (iv) on the first Business Day following delivery to a reliable overnight
courier service, courier fee prepaid, in any case at such address as may have been furnished to the Company or Holder, as the case may be, in writing by the Company or such Holder from time to time in accordance with the provisions of this
Section 5.5. All notices to Holder shall be addressed as follows until the Company receives notice of a change of address in connection with a transfer or otherwise: 

SVB Financial Group 

Attn: Treasury Department 

3003 Tasman Drive, HA 215 

Santa Clara, California 95054 

Telephone: 408-654-7400 

Facsimile: 408-988-8317 

Email: derivatives@svb.com 

 Notice to the Company shall be addressed as follows until Holder receives notice of a change
in address: 
 Avidity NanoMedicines LLC 

Attn: Troy Wilson 

10975 N. Torrey Pines Road, Suite 150 

La Jolla, California 92037 

With a copy (which shall not constitute notice) to: 

Cooley LLP 

Attn: Joshua Seidenfeld, Esq. 

3175 Hanover Street 

Palo Alto, California 94304 

5.6    Waiver. This Warrant and any term hereof may be changed, waived, discharged or terminated
(either generally or in a particular instance and either retroactively or prospectively) only by an instrument in writing signed by the party against which enforcement of such change, waiver, discharge or termination is sought. 

5.7    Attorneys’ Fees. In the event of any dispute between the parties concerning the terms
and provisions of this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorneys’ fees. 

5.8    Counterparts; Facsimile/Electronic Signatures. This Warrant may be executed in counterparts,
all of which together shall constitute one and the same agreement. Any signature page delivered electronically or by facsimile shall be binding to the same extent as an original signature page with regards to any agreement subject to the terms
hereof or any amendment thereto. 
 5.9    Governing Law. This Warrant shall be governed by and
construed in accordance with the laws of the State of California, without giving effect to its principles regarding conflicts of law. 

5.10    Headings. The headings in this Warrant are for purposes of reference only and shall not
limit or otherwise affect the meaning of any provision of this Warrant. 
 5.11    Business Days.
“Business Day” is any day that is not a Saturday, Sunday or a day on which Silicon Valley Bank is closed. 

 [Remainder of page left blank intentionally] 

[Signature page follows] 

 IN WITNESS WHEREOF, the parties have caused this Warrant to Purchase Limited Liability
Company Series A Preferred Units to be executed by their duly authorized representatives effective as of the Issue Date written above. 
  

			
	“COMPANY”
	
	AVIDITY NANOMEDICINES LLC
		
	By:	 	/s/ Troy Wilson
		 	Troy Wilson, President and Chief Executive Officer

  

			
	“HOLDER”
	
	SILICON VALLEY BANK
		
	By:	 	/s/ Anthony Flores
	Name:	 	Anthony Flores
	Title:	 	Vice President

 APPENDIX 1 

NOTICE OF EXERCISE 

1.    The undersigned Holder hereby exercises its right purchase
                     units of the Series A Preferred Units of Avidity NanoMedicines LLC (the “Company”) in accordance
with the attached Warrant To Purchase Limited Liability Company Series A Preferred Units, and tenders payment of the aggregate Warrant Price for such units as follows: 

[    ]    check in the amount of
$             payable to order of the Company enclosed herewith 

[    ]    Wire transfer of immediately available funds to the Company’s account 

[    ]    Cashless Exercise pursuant to Section 1.2 of the Warrant 

[    ]    Other [Describe]
                                         
                    

2.    If units of the above-stated Class are currently certificated by the Company, please issue a certificate or
certificates representing the Units in the name specified below: 
  

			
		 	      

		
		 	     Holder’s Name

		
		 	      

		
		 	      

		
		 	     (Address)

 3.    By its execution below and for the benefit of the Company, Holder hereby restates
each of the representations and warranties in Section 4 of the Warrant to Purchase Limited Liability Company Series A Preferred Units as of the date hereof. 

 

			
	
	HOLDER:
	
	      

		
	By:	 	      

		
	Name:	 	      

		
	Title:	 	      

		
	(Date):

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