EX-4.3





 Exhibit 4.3 

REGISTRATION RIGHTS AGREEMENT 
 This
Registration Rights Agreement (this “Agreement”) is made as of January 15, 2021 by and between TScan Therapeutics, Inc., a Delaware corporation (the “Company”), and the person(s) listed on the attached
Schedule A who are signatories to this Agreement (each, an “Investor”, and collectively, the “Investors”). Unless otherwise defined herein, capitalized terms used in this Agreement have the
respective meanings ascribed to them in Section 1. 
 RECITALS 

WHEREAS, the Company and the Investors wish to provide for certain arrangements with respect to the registration of the Registrable Securities (as
defined below) by the Company under the Securities Act (as defined below). 
 NOW, THEREFORE, in consideration of the mutual promises and covenants
set forth herein, and other consideration, the receipt and adequacy of which are hereby acknowledged, the parties hereto agree as follows: 

Section 1. 

Definitions 
 1.1. Certain
Definitions. In addition to the terms defined elsewhere in this Agreement, as used in this Agreement, the following terms have the respective meanings set forth below: 

(a) “Block Trade” shall mean an offering of Registrable Securities which requires both the Investors and the Company to enter into a sale
agreement and is limited in scope of selling efforts as compared to an Underwritten Offering. 
 (b) “Board” shall mean the Board of
Directors of the Company. 
 (c) “Commission” shall mean the Securities and Exchange Commission or any other federal agency at the time
administering the Securities Act. 
 (d) “Common Stock” shall mean the common stock of the Company, par value $0.0001 per share. 

(e) “Exchange Act” shall mean the Securities Exchange Act of 1934, as amended, or any similar successor federal statute and the rules and
regulations thereunder, all as the same shall be in effect from time to time. 
 (f) “Governmental Entity” shall mean any federal, state,
local or foreign government, or any department, agency, or instrumentality of any government; any public international organization, any transnational governmental organization; any court of competent jurisdiction, arbitral, administrative agency,
commission, or other governmental regulatory authority or quasi-governmental authority, any political party; and any national securities exchange or national quotation system. 












 (g) “Investors’ Rights Agreement” shall mean that certain Amended and Restated
Investors’ Rights Agreement, dated as of January [•], 2021, by and among the Company and the investors listed on Schedule A thereto, including the Investors, as the same may be amended and/or restated from time to time. 

(h) “Other Investors” shall mean the “Investors,” as defined in the Investors’ Rights Agreement. 

(i) “Other Securities” shall mean securities of the Company, other than Registrable Securities (as defined below). 

(j) “Person” shall mean any individual, partnership, corporation, company, association, trust, joint venture, limited liability company,
unincorporated organization, entity or division, or any government, governmental department or agency or political subdivision thereof. 
 (k)
“Registrable Securities” shall mean the shares of Common Stock and any Common Stock issued or issuable upon the exercise or conversion of any other securities (whether equity, debt or otherwise) of the Company now owned or hereafter
acquired by any of the Investors. 
 (l) The terms “register,” “registered” and “registration” shall
refer to a registration effected by preparing and filing a Registration Statement in compliance with the Securities Act, and such Registration Statement becoming effective under the Securities Act. 

(m) “Registration Expenses” shall mean all expenses incurred by the Company in effecting any registration pursuant to this Agreement,
including, without limitation, all registration, qualification, and filing fees, printing expenses, escrow fees, fees and disbursements of counsel for the Company, up to (1) $50,000 in aggregate of reasonable and documented out-of-pocket legal expenses of one outside counsel for Investors and one outside counsel for each of the Other Investors (in each case if different from the Company’s
counsel and if such counsel is reasonably approved by the Company) in connection with the preparation and filing of the Resale Registration Shelf (as defined below), and (2) up to $50,000 in aggregate of reasonable and documented out-of-pocket legal expenses of one outside counsel for the Investors and one outside counsel for each of the Other Investors (in each case if different from the
Company’s counsel and if such counsel is reasonably approved by the Company) per Underwritten Offering, blue sky fees and expenses, and expenses of any regular or special audits incident to or required by any such registration, but shall not
include Selling Expenses. For the avoidance of doubt, the Registration Expenses comprising legal expenses incurred by the Investors and Other Investors payable by the Company shall be allocated equally among the Investors and the Other Investors
participating in the applicable Resale Registration Shelf or underwritten public offering in the event the aggregate of such legal expenses exceeds $50,000. 

(n) “Registration Statement” means any registration statement of the Company filed with, or to be filed with, the Commission under the
Securities Act, including the related prospectus, amendments and supplements to such registration statement, including pre- and post-effective amendments, and all exhibits and all material incorporated by
reference in such registration statement as may be necessary to comply with applicable securities laws other than a registration statement (and related prospectus) filed on Form S-4 or Form S-8 or any successor forms thereto. 

  
 2 













 (o) “Rule 144” shall mean Rule 144 as promulgated by the Commission under the Securities
Act, as such rule may be amended from time to time, or any similar successor rule that may be promulgated by the Commission. 
 (p) “Securities
Act” shall mean the Securities Act of 1933, as amended, or any similar successor federal statute and the rules and regulations thereunder, all as the same shall be in effect from time to time. 

(q) “Selling Expenses” shall mean all underwriting discounts and selling commissions applicable to the sale of Registrable Securities, the
fees and expenses of any legal counsel (except as provided in the definition of “Registration Expenses”) and any other advisors any of the Investors engage and all similar fees and commissions relating to the Investors’ disposition of
the Registrable Securities. 
 (r) “Underwritten Offering” shall mean a public offering of Registrable Securities pursuant to an effective
registration statement under the Securities Act (other than pursuant to a registration statement on Form S-4 or S-8 or any similar or successor form) which requires the
Investors and the Company to enter into an underwriting agreement. 
 Section 2. 

Resale Registration Rights 
 2.1. Resale
Registration Rights. 
 (a) Following demand by any Investor the Company shall file with the Commission a Registration Statement on Form S-3 (except if the Company is not then eligible to register for resale the Registrable Securities on Form S-3, in which case such registration shall be on another appropriate
form in accordance with the Securities Act) covering the resale of the Registrable Securities by the Investors (the “Resale Registration Shelf”), and the Company shall file such Resale Registration Shelf as promptly as reasonably
practicable following such demand, and in any event within sixty (60) days of such demand; provided, however, that the Company shall not be obligated to make any such filing until one year following the date of the Company’s initial public
offering (the “Demand Effective Date”). Such Resale Registration Shelf shall include a “final” prospectus, including the information required by Item 507 of Regulation S-K of the
Securities Act, as provided by the Investors in accordance with Section 2.7. Notwithstanding the foregoing, before filing the Resale Registration Shelf, the Company shall furnish to the Investors a copy of the Resale
Registration Shelf and afford the Investors an opportunity to review and comment on the Resale Registration Shelf. The Company’s obligation pursuant to this Section 2.1(a) is conditioned upon the Investors providing
the information contemplated in Section 2.7. Notwithstanding anything contained herein to the contrary, any demand made by an Investor pursuant to this Agreement that the Company file with the Commission a Registration
Statement shall be deemed to be a demand for registration of the same nature (i.e., Form S-3 or Form S-1, underwritten or not) pursuant to the Investor Rights Agreement
to the extent such rights are, at the relative time, available pursuant to the Investor Rights Agreement. 

  
 3 













 (b) The Company shall use its reasonable best efforts to cause the Resale Registration Shelf and related
prospectuses to become effective as promptly as practicable after filing, but in any event by the earlier of: (A) 120 days following the demand that the Company file the Resale Registration Shelf, and (B) five trading days after the date the
Company receives written notification from the Commission that such Resale Registration Shelf will not be reviewed. The Company shall use its reasonable best efforts to cause such Registration Statement to remain effective under the Securities Act,
including by filing any necessary post-effective amendments and prospectus supplements, or alternatively, by filing one or more new Registration Statements, continuously until the earlier of the date (i) all Registrable Securities covered by
the Resale Registration Shelf have been sold or may be sold freely without limitations or restrictions as to volume or manner of sale pursuant to Rule 144 or (ii) all Registrable Securities covered by the Resale Registration Shelf otherwise
cease to be Registrable Securities pursuant to Section 2.10 hereof. The Company shall promptly, and within two (2) business days after the Company confirms the effectiveness of the Resale Registration Shelf with the
Commission, notify the Investors of the effectiveness of the Resale Registration Shelf. 
 (c) Notwithstanding anything contained herein to the contrary,
the Company shall not be obligated to effect, or to take any action to effect, a registration pursuant to Section 2.1(a): 
 (i) if
the Company has and maintains an effective Registration Statement on Form S-3ASR that provides for the resale of an unlimited number of securities by selling stockholders (a “Company Registration
Shelf”); 
 (ii) during the period forty-five (45) days prior to the Company’s good faith estimate of the date of filing of a Company
Registration Shelf; or 
 (iii) if the Company has caused a Registration Statement to become effective during the prior twelve (12) month period
pursuant to (x) this Section 2.1, (y) Section 2.1(a) of the Investors’ Rights Agreement or (z) Section 2.1(b) of the Investors’ Rights Agreement (in
each case provided that the Investors had the opportunity to register all of their Registrable Securities). 
 (d) If the Company has a Company Registration
Shelf in place at any time in which the Investors make a demand pursuant to Section 2.1(a), the Company shall file with the Commission, as promptly as practicable, and in any event within fifteen (15) business days
after such demand, a “final” prospectus supplement to its Company Registration Shelf covering the resale of the Registrable Securities by the Investors (the “Prospectus”); provided, however, that (i) the
Company shall not be obligated to make any such filing until after the Demand Effective Date and (ii) the Company shall not be obligated to file more than one Prospectus pursuant to this Section 2.1(d) in any six month
period to add additional Registrable Securities to the Company Registration Shelf that were acquired by the Investors other than directly from the Company or in an underwritten public offering by the Company. The Prospectus shall include the
information required under Item 507 of Regulation S-K of the Securities Act, which information shall be provided by the Investors in accordance with Section 2.7. Notwithstanding the
foregoing, before filing the Prospectus, the Company shall furnish to the Investors a copy of the Prospectus and afford a single outside counsel (in addition to any inside counsel) of the Investors an opportunity to review and comment on the
Prospectus. 

  
 4 













 (e) Deferral and Suspension. At any time after being obligated pursuant to this Agreement or the
Investors’ Rights Agreement to file a Resale Registration Shelf or Prospectus, or after any such Resale Registration Shelf has become effective or such Prospectus has been filed with the Commission, the Company may defer the filing of or
suspend the use of any such Resale Registration Shelf or Prospectus, upon giving written notice of such action to the Investors with a certificate signed by the Chief Executive Officer of the Company stating that in the good faith judgment of the
Board, the filing or use of any such Resale Registration Shelf or Prospectus covering the Registrable Securities would be seriously detrimental to the Company or its stockholders at such time and that the Board concludes, as a result, that it is in
the best interests of the Company and its stockholders to defer the filing or suspend the use of such Resale Registration Shelf or Prospectus at such time. The Company shall have the right to defer the filing of or suspend the use of such Resale
Registration Shelf or Prospectus for a period of not more than one hundred twenty (120) days from the date the Company notifies the Investors of such deferral or suspension; provided that the Company shall not exercise the right
contained in this Section 2.1(e) more than once in any twelve month period. In the case of the suspension of use of any effective Resale Registration Shelf or Prospectus, the Investors, immediately upon receipt of notice
thereof from the Company, shall discontinue any offers or sales of Registrable Securities pursuant to such Resale Registration Shelf or Prospectus until advised in writing by the Company that the use of such Resale Registration Shelf or Prospectus
may be resumed. In the case of a deferred Prospectus or Resale Registration Shelf filing, the Company shall provide prompt written notice to the Investors of (i) the Company’s decision to file or seek effectiveness of the Prospectus or
Resale Registration Shelf, as the case may be, following such deferral and (ii) in the case of a Resale Registration Shelf, the effectiveness of such Resale Registration Shelf. In the case of either a suspension of use of, or deferred filing
of, any Resale Registration Shelf or Prospectus, the Company shall not, during the pendency of such suspension or deferral, be required to take any action hereunder (including any action pursuant to Section 2.2 hereof) with
respect to the registration or sale of any Registrable Securities pursuant to any such Resale Registration Shelf, Company Registration Shelf or Prospectus. 

(f) Piggy-Back Rights. The Company must provide the Investors with ten (10) days’ notice before filing any Resale Registration Shelf or
Prospectus pursuant to a request by the Other Investors pursuant to Section 2.1(a) of the Investors’ Rights Agreement, and, upon the Investors’ written request, include the Investors as one or more selling stockholders in such Resale
Registration Shelf or Prospectus. Section 2.3(a) of the Investors’ Rights Agreement notwithstanding, the securities of the Investors and the Other Investors will be excluded on a pro rata basis from such Registration Statement if any such
exclusion is deemed necessary in order to comply with any applicable laws or request from any Government Entity, Nasdaq or any applicable listing agency. 

(g) Other Securities. Subject to Section 2.2(e) below, any Resale Registration Shelf or Prospectus may include Other
Securities, and may include securities of the Company being sold for the account of the Company; provided (subject to Section 2.3(b) of the Investors’ Rights Agreement) such Other Securities are excluded first from such Registration
Statement in order to comply with any applicable laws or request from any Governmental Entity, Nasdaq or any applicable listing agency. No Other Securities may be included in an Underwritten Offering pursuant to Section 2.2
without the consent of the Investors, except as expressly set forth herein or required pursuant to the Investors’ Rights Agreement. 

  
 5 













 2.2. Sales and Underwritten Offerings of the Registrable Securities. 

(a) Notwithstanding any provision contained herein to the contrary, the Investors, collectively, shall and subject to the limitations set forth in this
Section 2.2, be permitted (i) one Underwritten Offering per calendar year, but no more than three Underwritten Offerings in total (provided that the Investors and the Other Investors are limited to an aggregate of two
Underwritten Offerings per calendar year), and (ii) no more than two Underwritten Offerings or Block Trades in any twelve month period, to effect the sale or distribution of Registrable Securities. 

(b) If the Investors intend to effect an Underwritten Offering or Block Trade pursuant to a Resale Registration Shelf or Company Registration Shelf to sell or
otherwise distribute Registrable Securities, they shall so advise the Company and provide as much notice to the Company as reasonably practicable (and, in either case, not less than fifteen (15) business days prior to the Investors’
request that the Company file a prospectus supplement to a Resale Registration Shelf or Company Registration Shelf). 
 (c) In connection with any offering
initiated by the Investors pursuant to this Section 2.2 involving an underwriting of shares of Registrable Securities, the Investors shall be entitled to select the underwriter or underwriters for such offering, subject to
the consent of the Company, such consent not to be unreasonably withheld, conditioned or delayed. 
 (d) In connection with any offering initiated by the
Investors pursuant to this Section 2.2 involving an Underwritten Offering of Registrable Securities, the Company shall not be required to include any of the Registrable Securities in such underwriting unless the Investors
(i) enter into an underwriting agreement in customary form with the underwriter or underwriters, (ii) accept customary terms in such underwriting agreement with regard to representations and warranties relating to ownership of the
Registrable Securities and authority and power to enter into such underwriting agreement and (iii) complete and execute all questionnaires, powers of attorney, custody agreements, indemnities and other documents as may be requested by such
underwriter or underwriters. Further, the Company shall not be required to include any of the Registrable Securities in an Underwritten Offering or Block Trade if (Y) the underwriting/sale agreement proposed by the underwriter or underwriters
contains representations, warranties or conditions that are not reasonable in light of the Company’s then-current business (for the avoidance of doubt, the limitation in this clause (Y) is not related to the Company’s then-current
disclosure, which may need to be updated prior to such offering) or (Z) the underwriter, underwriters or the Investors require the Company to participate in any marketing, roadshow or comparable activity that may be required to complete the
orderly sale of shares by the underwriter or underwriters. 
 (e) Subject to Section 2.2(f) below, the Company must provide the
Investors with not less than ten (10) business days’ notice before effecting an underwritten public offering pursuant to a request by the Other Investors pursuant to Section 2.1(b) of the Investors’ Rights Agreement, and, upon
the Investors’ written request, include the Registrable Securities requested by the Investors in such underwritten public offering. 

  
 6 













 (f) If the total amount of securities to be sold in any offering initiated by the Investors pursuant to this
Section 2.2 involving an underwriting of shares of Registrable Securities, or any underwritten public offering initiated by the Other Investors pursuant to their registration rights, exceeds the amount that the underwriters
determine in their sole discretion is compatible with the success of the offering, then the Company shall be required to include in the offering only that number of such securities, including Registrable Securities (subject in each case to the
cutback provisions set forth in this Section 2.2(e)), that the underwriters and the Company determine in their sole discretion shall not jeopardize the success of the offering. If the Underwritten Offering has been
requested pursuant to Section 2.2(a) of this Agreement or the Investors’ Rights Agreement, the number of shares that are entitled to be included in the registration and underwriting shall be allocated in the following
manner: (a) first, shares of Company equity securities that the Company desires to include in such registration (including any Other Securities) shall be excluded and (b) second, Registrable Securities requested to be
included in such registration by the Investors and the Other Investors shall be excluded, pro rata. For the avoidance of doubt, no other person besides the Investors shall be entitled to participate in any Block Trade. To facilitate the allocation
of shares in accordance with the above provisions, the Company or the underwriters may round down the number of shares allocated to any of the Investors or the Other Investors to the nearest 100 shares. 

2.3. Fees and Expenses. All Registration Expenses incurred in connection with registrations pursuant to this Agreement shall be borne by the Company.
All Selling Expenses relating to securities registered on behalf of the Investors shall be borne by the Investors. 
 2.4. Registration Procedures.
In the case of each registration of Registrable Securities effected by the Company pursuant to Section 2.1 hereof (including, for the avoidance of doubt, Section 2.1(f)), the Company shall keep the
Investors advised as to the initiation of each such registration and as to the status thereof. The Company shall use its reasonable best efforts, within the limits set forth in this Section 2.4, to: 

(a) prepare and file with the Commission such amendments and supplements to such Registration Statement and the prospectuses used in connection with such
Registration Statement as may be necessary to keep such Registration Statement effective and current and comply with the provisions of the Securities Act with respect to the disposition of all securities covered by such Registration Statement; 

(b) furnish to the Investors such numbers of copies of a prospectus, including preliminary prospectuses, in conformity with the requirements of the Securities
Act, and such other documents as the Investors may reasonably request in order to facilitate the disposition of Registrable Securities; 
 (c) use its
reasonable best efforts to register and qualify the Registrable Securities covered by such Registration Statement under such other securities or blue sky laws of such jurisdictions in the United States as shall be reasonably requested by the
Investors, provided that the Company shall not be required in connection therewith or as a condition thereto to qualify to do business or to file a general consent to service of process in any such states or jurisdictions; 

  
 7 













 (d) in the event of any Underwritten Offering or Block Trade, and subject to
Section 2.2(d), enter into and perform its obligations under an underwriting agreement or Block Trade sale agreement, in usual and customary form (including any “lock-ups”
on behalf of the Company and its directors and officers), with the managing underwriter of such offering and take such other usual and customary action as the Investors may reasonably request in order to facilitate the disposition of such
Registrable Securities; 
 (e) notify the Investors at any time when a prospectus relating to a Registration Statement covering any Registrable Securities
is required to be delivered under the Securities Act of the happening of any event as a result of which the prospectus included 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 the light of the circumstances then existing. The Company shall use its reasonable best efforts to amend or supplement such prospectus in order
to cause such prospectus not to include any 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 the light of the circumstances then
existing; 
 (f) provide a transfer agent and registrar for all Registrable Securities registered pursuant to such Registration Statement and, if required,
a CUSIP number for all such Registrable Securities, in each case not later than the effective date of such registration; 
 (g) if requested by an Investor,
use reasonable best efforts to cause the Company’s transfer agent to remove any restrictive legend from any Registrable Securities, within two business days following such request; 

(h) cause to be furnished, at the request of the Investors, on the date that Registrable Securities are delivered to underwriters for sale in connection with
any Underwritten Offering or Block Trade, (i) an opinion, dated such date, of the counsel representing the Company for the purposes of such registration, in form and substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, and (ii) a letter or letters from the independent certified public accountants of the Company, in form and substance as is customarily given by independent certified public accountants to underwriters in
an underwritten public offering, addressed to the underwriters; and 
 (i) cause all such Registrable Securities included in a Registration Statement
pursuant to this Agreement to be listed on each securities exchange or other securities trading markets on which Common Stock is then listed. 
 2.5. The
Investors’ Obligations. 
 (a) Discontinuance of Distribution. The Investors agree that, upon receipt of any notice from the Company of the
occurrence of any event of the kind described in Section 2.4(e) hereof, the Investors shall immediately discontinue disposition of Registrable Securities pursuant to any Registration Statement covering such Registrable Securities until
the Investors’ receipt of the copies of the supplemented or amended prospectus contemplated by Section 2.4(e) hereof or receipt of notice that no supplement or amendment is required and that the Investors’ disposition of the
Registrable Securities may be resumed. The Company may provide appropriate stop orders to enforce the provisions of this Section 2.5(a). 

  
 8 













 (b) Compliance with Prospectus Delivery Requirements. The Investors covenant and agree that they
shall comply with the prospectus delivery requirements of the Securities Act as applicable to them or an exemption therefrom in connection with sales of Registrable Securities pursuant to any Registration Statement filed by the Company pursuant to
this Agreement. 
 2.6. Indemnification. 
 (a) To the
extent permitted by law, the Company shall indemnify the Investors, and, as applicable, their officers, directors, and constituent partners, legal counsel for each Investor and each Person controlling the Investors, with respect to which
registration, related qualification, or related compliance of Registrable Securities has been effected pursuant to this Agreement, and each underwriter, if any, and each Person who controls any underwriter within the meaning of the Securities Act
against all claims, losses, damages, or liabilities (or actions in respect thereof) to the extent such claims, losses, damages, or liabilities arise out of or are based upon (i) any untrue statement (or alleged untrue statement) of a material
fact contained in any prospectus or other document (including any related Registration Statement) incident to any such registration, qualification, or compliance, or (ii) any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein not misleading, or (iii) any violation or alleged violation by the Company of the Securities Act, the Exchange Act, any state securities law, or any rule or regulation
promulgated under the Securities Act, the Exchange Act or any state securities law applicable to the Company and relating to action or inaction required of the Company in connection with any such registration, qualification, or compliance; and the
Company shall pay as incurred to the Investors, each such underwriter, and each Person who controls the Investors or underwriter, any reasonable and documented
out-of-pocket legal expenses and any other expenses reasonably incurred in connection with investigating or defending any such claim, loss, damage, liability, or action;
provided, however, that the indemnity contained in this Section 2.6(a) shall not apply to amounts paid in settlement of any such claim, loss, damage, liability, or action if settlement is effected without the
consent of the Company (which consent shall not unreasonably be withheld); and provided, further, that the Company shall not be liable in any such case to the extent that any such claim, loss, damage, liability, or expense arises out of or is based
upon any violation by such Investor of the obligations set forth in Section 2.5 hereof or any untrue statement or omission contained in such prospectus or other document based upon written information furnished to the
Company by the Investors, such underwriter, or such controlling Person and stated to be for use therein or any bad faith or willful misconduct of the Investor. 

(b) To the extent permitted by law, each Investor (severally and not jointly) shall, if Registrable Securities held by such Investor are included for sale in
the registration and related qualification and compliance effected pursuant to this Agreement, indemnify the Company, each of its directors, each officer of the Company who signs the applicable Registration Statement, each legal counsel and each
underwriter of the Company’s securities covered by such a Registration Statement, each Person who controls the Company or such underwriter within the meaning of the Securities Act against all claims, losses, damages, and liabilities (or actions
in respect thereof) arising out of or based upon (i) any untrue statement (or alleged untrue 

  
 9 













 
statement) of a material fact contained in any such Registration Statement, or related document, or (ii) any omission (or alleged omission) to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, or (iii) any violation or alleged violation by such Investor of Section 2.5 hereof, the Securities Act, the Exchange Act, any state securities
law, or any rule or regulation promulgated under the Securities Act, the Exchange Act or any state securities law applicable to such Investor and relating to action or inaction required of such Investor in connection with any such registration and
related qualification and compliance, and shall pay as incurred to such persons, any reasonable and documented out-of-pocket legal expenses and any other expenses
reasonably incurred in connection with investigating or defending any such claim, loss, damage, liability, or action, in each case only to the extent that such untrue statement (or alleged untrue statement) or omission (or alleged omission) is made
in (and such violation pertains to) such Registration Statement or related document in reliance upon and in conformity with written information furnished to the Company by such Investor and stated to be specifically for use therein; provided,
however, that the indemnity contained in this Section 2.6(b) shall not apply to amounts paid in settlement of any such claim, loss, damage, liability, or action if settlement is effected without the consent of such
Investor (which consent shall not unreasonably be withheld); provided, further, that the Investor shall not be liable in any such case to the extent that any such claim, loss, damage, liability or expense arises out of or is based upon any bad faith
willful misconduct or gross negligence of the Company; and provided, further, that such Investors’ liability under this Section 2.6(b) (when combined with any amounts such Investor is liable for under
Section 2.6(d)) shall not exceed such Investors’ net proceeds from the offering of securities made in connection with such registration. 

(c) Promptly after receipt by an indemnified party under this Section 2.6 of notice of the commencement of any action, such
indemnified party shall, if a claim in respect thereof is to be made against an indemnifying party under this Section 2.6, notify the indemnifying party in writing of the commencement thereof and generally summarize such
action. The indemnifying party shall have the right to participate in and to assume the defense of such claim at its own expense; provided, however, that the indemnifying party shall be entitled to select counsel for the defense of
such claim with the approval of any parties entitled to indemnification, which approval shall not be unreasonably withheld; provided further, however, that if either party reasonably determines that there may be a conflict between the position of
the Company and the Investors in conducting the defense of such action, suit, or proceeding by reason of recognized claims for indemnity under this Section 2.6, then counsel for such party shall be entitled to conduct the
defense to the extent reasonably determined by such counsel to be necessary to protect the interest of such party. The failure to notify an indemnifying party promptly of the commencement of any such action, if prejudicial to the ability of the
indemnifying party to defend such action, shall relieve such indemnifying party, to the extent so prejudiced, of any liability to the indemnified party under this Section 2.6, but the omission so to notify the indemnifying
party shall not relieve such party of any liability that such party may have to any indemnified party otherwise than under this Section 2.6. 

(d) If the indemnification provided for in this Section 2.6 is held by a court of competent jurisdiction to be unavailable to an
indemnified party with respect to any loss, liability, claim, damage, or expense referred to therein, then the indemnifying party, in lieu of indemnifying such indemnified party hereunder, shall contribute to the amount paid or payable by such
indemnified 

  
 10 













 
party as a result of such loss, liability, claim, damage, or expense in such proportion as is appropriate to reflect the relative fault of the indemnifying party on the one hand and of the
indemnified party on the other in connection with the statements or omissions that resulted in such loss, liability, claim, damage, or expense as well as any other relevant equitable considerations. The relative fault of the indemnifying party and
of the indemnified party shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission to state a material fact relates to information supplied by the indemnifying party or
by the indemnified party and the parties’ relative intent, knowledge, access to information, and opportunity to correct or prevent such statement or omission. In no event, however, shall (i) any amount due for contribution hereunder be in
excess of the amount that would otherwise be due under Section 2.6(a) or Section 2.6(b), as applicable, based on the limitations of such provisions and (ii) a Person found by a court of
competent jurisdiction to be liable for fraudulent misrepresentation (within the meaning of the Securities Act), bad faith or willful misconduct be entitled to contribution from a Person who was not also found by a court of competent jurisdiction to
be liable for such fraudulent misrepresentation (within the meaning of the Securities Act), bad faith or willful misconduct. 
 (e) Notwithstanding the
foregoing, to the extent that the provisions on indemnification and contribution contained in the underwriting agreement entered into in connection with an Underwritten Offering, or the Block Trade sale agreement, are in conflict with the foregoing
provisions, the provisions in the underwriting agreement or Block Trade sale agreement shall control; provided, however, that the failure of the underwriting agreement to provide for or address a matter provided for or addressed by the
foregoing provisions shall not be a conflict between the underwriting agreement or the Block Trade sale agreement and the foregoing provisions. 
 (f) The
obligations of the Company and the Investors under this Section 2.6 shall survive the completion of any offering of Registrable Securities in a Registration Statement under this Agreement or otherwise. 

2.7. Information. The Investors shall furnish to the Company such information regarding the Investors and the distribution proposed by the Investors as
the Company may reasonably request and as shall be reasonably required in connection with any registration referred to in this Agreement. The Investors agree to, as promptly as practicable (and in any event prior to any sales made pursuant to a
prospectus), furnish to the Company all information required to be disclosed in order to make the information previously furnished to the Company by the Investors not misleading. The Investors agree to keep confidential the receipt of any notice
received pursuant to Section 2.4(e) and the contents thereof, except as required pursuant to applicable law. Notwithstanding anything to the contrary herein, the Company shall be under no obligation to name the Investors in any
Registration Statement or include such Investors’ Registrable Securities or Other Securities if the Investors have not provided the information required by this Section 2.7 with respect to the Investors as a selling
securityholder in such Registration Statement or any related prospectus. 

  
 11 













 2.8. Rule 144 Requirements. With a view to making available to the Investors the benefits of Rule 144
and any other rule or regulation of the Commission that may at any time permit the Investors to sell Registrable Securities to the public without registration, the Company agrees to use its reasonable best efforts to: 

(a) make and keep public information available, as those terms are understood and defined in Rule 144 at all times after the date hereof; 

(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; 

(c) prior to the filing of the Registration Statement or any amendment thereto (whether pre-effective or post-effective), and prior to the filing of any prospectus or prospectus supplement related thereto, to provide the Investors with copies of all of the pages thereof (if any) that reference the Investors; and 

(d) furnish to any Investor, so long as the Investor owns any Registrable Securities, forthwith upon request (i) a written statement by the Company that
it has complied with the reporting requirements of Rule 144, (ii) a copy of the most recent annual or quarterly report of the Company and such other reports and documents so filed by the Company, and (iii) such other information as may be
reasonably requested by an Investor in availing itself of any rule or regulation of the Commission which permits an Investor to sell any such securities without registration. 

2.9. Limitations on Subsequent Registration Rights. From and after the date of this Agreement, the Company shall not, without prior written consent of
the Investors, (Y) enter into any agreement with any holder or prospective holder of any securities of the Company which would provide to such holder rights with respect to the registration of such securities under the Securities Act or the
Exchange Act that would conflict with or adversely affect any of the rights provided to the Investors in this Section 2, or (Z) amend the Investors’ Rights Agreement in any manner that would conflict with or adversely affect any of
the rights provided to the Investors in this Section 2; it being understood and agreed that any subsequent agreement of the Company with any holder or prospective holder of any securities of the Company of the same class (or convertible into or
exchange for securities of the same class) as the Registrable Securities granting such Person rights under this Section 2 equivalent to the rights of the Investors under this Section 2 will not be prohibited by the terms of this
Section 2.9. 
 2.10. Termination of Status as Registrable Securities. The Registrable Securities shall cease to be Registrable Securities upon
the earliest to occur of the following events: (i) such Registrable Securities have been sold pursuant to an effective Registration Statement; (ii) such Registrable Securities have been sold by the Investors pursuant to Rule 144 (or other
similar rule), (iii) such Registrable Securities may be resold by the Investor holding such Registrable Securities without limitations as to volume or manner of sale pursuant to Rule 144; or (iv) ten (10) years after the date of this Agreement.


  
 12 













 Section 3. 

Miscellaneous 
 3.1. Amendment. No
amendment, alteration or modification of any of the provisions of this Agreement shall be binding unless made in writing and signed by each of the Company and the Investors. 

3.2. Injunctive Relief. It is hereby agreed and acknowledged that it shall be impossible to measure in money the damages that would be suffered if the
parties fail to comply with any of the obligations herein imposed on them and that in the event of any such failure, an aggrieved Person shall be irreparably damaged and shall not have an adequate remedy at law. Any such Person shall, therefore, be
entitled (in addition to any other remedy to which it may be entitled in law or in equity) to injunctive relief, including, without limitation, specific performance, to enforce such obligations, and if any action should be brought in equity to
enforce any of the provisions of this Agreement, none of the parties hereto shall raise the defense that there is an adequate remedy at law. 
 3.3.
Notices. All notices required or permitted under this Agreement must be in writing and sent to the address or facsimile number identified below. Notices must be given: (a) by personal delivery, with receipt acknowledged; (b) by
electronic mail followed by hard copy delivered by the methods under clause (c) or (d); (c) by prepaid certified or registered mail, return receipt requested; or (d) by prepaid reputable overnight delivery service. Notices
shall be effective upon receipt. Either party may change its notice address by providing the other party written notice of such change. Notices shall be delivered as follows: 
  

			
	If to the Investors:	  	 Baker Brothers Investments
 860 Washington St.,
3rd Floor
 New York, NY 10014
 Attention: Scott Lessing,
President
 Email: bbi_officialnotices@bbinvestments.com

		
	with a copy (which copy shall not constitute notice) to:	  	 Wilmer Cutler Pickering Hale and Dorr LLP
 60
State Street
 Boston, MA 02109
 Attention: Jason Kropp

Email: Jason.Kropp@wilmerhale.com

		
	If to the Company:	  	 TScan Therapeutics, Inc.
 830 Winter St.

Waltham, MA 02451
 Attention: Chief Executive Officer

Email:


		
	with a copy to:	  	 Gunderson Dettmer Stough Villeneuve Franklin & Hachigian, LLP

One Marina Park Drive
 Suite 900

Boston, MA 02210
 Attention: Timothy H. Ehrlich

Email: tehrlich@gunder.com



  
 13 













 3.4. Governing Law; Jurisdiction; Venue; Jury Trial. 

(a) This Agreement shall be governed by, and construed in accordance with, the law of the State of New York without giving effect to any choice or conflict of
law provision or rule (whether of the State of New York or any other jurisdiction) that would cause the application of the laws of any jurisdiction other than the State of New York. 

(b) Each of the Company and the Investors irrevocably and unconditionally submits, for itself and its property, to the nonexclusive jurisdiction of the courts
of the State of New York sitting in the Borough of Manhattan, New York and of the United States District Court of the Southern District of New York, and any appellate court from any thereof, in any action or proceeding arising out of or relating to
this Agreement and the transactions contemplated herein, or for recognition or enforcement of any judgment, and each of the Company and the Investors irrevocably and unconditionally agrees that all claims in respect of any such action or proceeding
may be heard and determined in such New York state court or, to the fullest extent permitted by applicable law, in such federal court. Each of the Company and the Investors hereto agrees that a final judgment in any such action or proceeding shall
be conclusive and may be enforced in other jurisdictions by suit on the judgment or in any other manner provided by law. 
 (c) Each of the Company and the
Investors irrevocably and unconditionally waives, to the fullest extent permitted by applicable law, any objection that it may now or hereafter have to the laying of venue of any action or proceeding arising out of or relating to this Agreement and
the transactions contemplated herein in any court referred to in Section 3.4(b) hereof. Each of the Company and the Investors hereby irrevocably waives, to the fullest extent permitted by applicable law, the defense of an
inconvenient forum to the maintenance of such action or proceeding in any such court. 
 (d) EACH OF THE COMPANY AND THE INVESTORS HEREBY IRREVOCABLY
WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY RIGHT IT MAY HAVE TO A TRIAL BY JURY IN ANY LEGAL PROCEEDING DIRECTLY OR INDIRECTLY ARISING OUT OF OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY (WHETHER BASED ON
CONTRACT, TORT OR ANY OTHER THEORY). EACH OF THE COMPANY AND THE INVESTORS (A) CERTIFIES THAT NO REPRESENTATIVE, AGENT OR ATTORNEY OF ANY OTHER PERSON HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SUCH OTHER PERSON WOULD NOT, IN THE EVENT OF
LITIGATION, SEEK TO ENFORCE THE FOREGOING WAIVER AND (B) ACKNOWLEDGES THAT EACH OF THE COMPANY AND THE INVESTORS HAS BEEN INDUCED TO ENTER INTO THIS AGREEMENT BY, AMONG OTHER THINGS, THE MUTUAL WAIVERS AND CERTIFICATIONS IN THIS SECTION. 

  
 14 













 3.5. Successors, Assigns and Transferees. Any and all rights, duties and obligations hereunder shall
not be assigned, transferred, delegated or sublicensed by any party hereto without the prior written consent of the other party; provided, however, that the Investors shall be entitled to transfer Registrable Securities to one or more
of their affiliates and, solely in connection therewith, may assign their rights hereunder in respect of such transferred Registrable Securities, in each case, so long as such Investor is not relieved of any liability or obligations hereunder,
without the prior consent of the Company. Any transfer or assignment made other than as provided in the first sentence of this Section 3.5 shall be null and void. Subject to the foregoing and except as otherwise provided
herein, the provisions of this Agreement shall inure to the benefit of, and be binding upon, the successors, permitted assigns, heirs, executors and administrators of the parties hereto. The Company shall not consummate any recapitalization, merger,
consolidation, reorganization or other similar transaction whereby stockholders of the Company receive (either directly, through an exchange, via dividend from the Company or otherwise) equity (the “Other Equity”) in any other
entity (the “Other Entity”) with respect to Registrable Securities hereunder, unless prior to the consummation thereof, the Other Entity assumes, by written instrument, the obligations under this Agreement with respect to such Other
Equity as if such Other Equity were Registrable Securities hereunder. 
 3.6. Entire Agreement. This Agreement, together with any exhibits hereto,
constitute the entire agreement between the parties relating to the subject matter hereof and all previous agreements or arrangements between the parties, written or oral, relating to the subject matter hereof are superseded. 

3.7. Waiver. No failure on the part of either party hereto to exercise any power, right, privilege or remedy under this Agreement, and no delay on the
part of either party hereto in exercising any power, right, privilege or remedy under this Agreement, shall operate as a waiver thereof; and no single or partial exercise of any such power, right, privilege or remedy shall preclude any other or
further exercise thereof or of any other power, right, privilege or remedy. 
 3.8. Severability. If any part of this Agreement is declared invalid
or unenforceable by any court of competent jurisdiction, such declaration shall not affect the remainder of the Agreement and the invalidated provision shall be revised in a manner that shall render such provision valid while preserving the
parties’ original intent to the maximum extent possible. 
 3.9. Titles and Subtitles. The titles and subtitles used in this Agreement are used
for convenience only and are not to be considered in construing or interpreting this Agreement. All references in this Agreement to sections, paragraphs and exhibits shall, unless otherwise provided, refer to sections and paragraphs hereof and
exhibits attached hereto. References to any section in the Investors’ Rights Agreement shall be deemed to refer to the equivalent section in the event of any amendment thereto. 

3.10. Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be enforceable against the parties that execute
such counterparts (including by facsimile or other electronic means), and all of which together shall constitute one instrument. 
 3.11. Term and
Termination. The Investors’ rights to demand the registration of the Registrable Securities under this Agreement, as well as the Company’s obligations under Section 2.1 hereof, shall terminate automatically
once all Registrable Securities cease to be Registrable Securities pursuant to the terms of Section 2.10 of this Agreement. 

[Remainder of Page Intentionally Left Blank; Signature Page Follows] 

  
 15 













 IN WITNESS WHEREOF, the parties hereto have executed this Registration Rights Agreement effective as of the
day, month and year first above written. 
  

			
	COMPANY:
	
	TSCAN THERAPEUTICS, INC.
		
	By:	 	/s/ David Southwell
		 	Name: David Southwell
		 	Title: Chief Executive Officer



  
 [Signature Page to
Registration Rights Agreement] 













 IN WITNESS WHEREOF, the parties hereto have executed this Registration Rights Agreement effective as of the
day, month and year first above written. 
  

			
	INVESTORS:
	
	667, L.P.
	By:	 	BAKER BROS. ADVISORS LP, management company and investment adviser to 667, L.P., pursuant to authority granted to it by Baker Biotech Capital, L.P., general partner to 667, L.P., and not as the general partner
		
	By:	 	/s/ Scott L. Lessing
		 	 Scott L. Lessing
 President



  

			
	BAKER BROTHERS LIFE SCIENCES, L.P.
	By:	 	BAKER BROS. ADVISORS LP, management company and investment adviser to BAKER BROTHERS LIFE SCIENCES, L.P., pursuant to authority granted to it by Baker Brothers Life Sciences Capital, L.P., general partner to BAKER BROTHERS LIFE
SCIENCES, L.P., and not as the general partner
		
	By:	 	/s/ Scott L. Lessing
		 	 Scott L. Lessing
 President




  
 [Signature Page to
Registration Rights Agreement] 













 Schedule A 

The Investors 
 667, L.P. 

BAKER BROTHERS LIFE SCIENCES, L.P. 
 To the above Investors: 

Baker Brothers Investments 
 860 Washington Street 

New York, NY 10014 
 Attn: Scott Lessing 

Email: slessing@BBInvestments.com 
 With a copy (which shall not
constitute notice) to: 
 Wilmer Cutler Pickering Hale and Dorr LLP 

60 State Street 
 Boston, MA 02109 

Attention: Jason Kropp 
 Email: Jason.Kropp@wilmerhale.com