SecProbe.io

CORRESP
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 CORRESP

 Cabaletta Bio, Inc.
 2929 Arch Street, Suite 600
 Philadelphia, Pennsylvania 19104 August 13,
2025 Via EDGAR Transmission Securities and
Exchange Commission Division of Corporation Finance 100 F
Street, N.E. Washington, D.C. 20549 Attention: Joshua
Gorsky

 Re:
 Cabaletta Bio, Inc.: Registration Statement on Form S-3 filed
August 7, 2025 (File No. 333-289339)
 Ladies and Gentlemen: Pursuant to Rule 461 under the
Securities Act of 1933, as amended (the “ Act ”), Cabaletta Bio, Inc. (the “ Company ”) hereby requests that the effective date of the above-referenced registration statement (the “ Registration
Statement ”) be accelerated to August 15, 2025, at 4:01 pm Eastern Time, or as soon thereafter as practicable, unless we or our outside counsel, Goodwin Procter LLP, request by telephone that such Registration Statement be declared
effective at some other time. In making this acceleration request, the Company acknowledges that it is aware of its responsibilities under the Act. If
you have any questions regarding this request, please contact Finnbarr Murphy, Esq. of Goodwin Procter LLP at (212) 459-7257.

 Sincerely,

 CABALETTA BIO, INC.

 /s/ Steven Nichtberger, M.D.

 Steven Nichtberger, M.D. President and Chief
Executive Officer

 cc:
 Michael Gerard, Esq., Cabaletta Bio, Inc.
 Mitchell S. Bloom, Esq., Goodwin Procter LLP
 Finnbarr Murphy, Esq., Goodwin Procter LLP

<DOCUMENT>
<TYPE>TEXT-EXTRACT
<SEQUENCE>2
<FILENAME>filename2.txt
<TEXT>
 August 13, 2025

Steven Nichtberger
President and Chief Executive Officer
Cabaletta Bio, Inc.
2929 Arch Street, Suite 600
Philadelphia, PA 19104

 Re: Cabaletta Bio, Inc.
 Registration Statement on Form S-3
 Filed August 7, 2025
 File No. 333-289339
Dear Steven Nichtberger:

 This is to advise you that we have not reviewed and will not review your
registration
statement.

 Please refer to Rules 460 and 461 regarding requests for acceleration.
We remind you
that the company and its management are responsible for the accuracy and
adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action
by the staff.

 Please contact Joshua Gorsky at 202-551-7836 with any questions.

 Sincerely,

 Division of
Corporation Finance
 Office of Life
Sciences
cc: Kristen McCarthy, Esq.
</TEXT>
</DOCUMENT>

CORRESP
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CORRESP

 Cabaletta Bio, Inc.

2929 Arch Street, Suite 600

Philadelphia, Pennsylvania 19104

 April 24,
2023

 Via EDGAR Transmission

 Securities and
Exchange Commission

 Division of Corporation Finance

 100 F
Street, N.E.

 Washington, D.C. 20549

 Attention: Alan R.
Campbell

Re:

Cabaletta Bio, Inc.: Registration Statement on Form S-3 filed March 16, 2023

(File No. 333-270599)

 Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Act of 1933, as amended (the “Act”), Cabaletta Bio, Inc. (the
“Company”) hereby requests that the effective date of the above-referenced registration statement (the “Registration Statement”) be accelerated to April 26, 2023, at 4:01 pm Eastern Time, or as soon thereafter
as practicable, unless we or our outside counsel, Goodwin Procter LLP, request by telephone that such Registration Statement be declared effective at some other time. In making this acceleration request, the Company acknowledges that it is aware of
its responsibilities under the Act.

 If you have any questions regarding this request, please contact Gabriela Morales-Rivera, Esq. of
Goodwin Procter LLP at (617) 570-1329.

Sincerely,

CABALETTA BIO, INC.

/s/ Steven Nichtberger, M.D.

 Steven Nichtberger, M.D.

 President and Chief
Executive Officer

 cc: Michael Gerard, Esq., Cabaletta Bio, Inc.

      Mitchell S. Bloom, Esq., Goodwin Procter LLP

      Michael Minahan, Esq., Goodwin Procter
LLP

       Gabriela
Morales-Rivera, Esq., Goodwin Procter LLP

United States securities and exchange commission logo
March 22, 2023
Steven Nichtberger
President and Chief Executive Officer
Cabaletta Bio, Inc.
2929 Arch Street, Suite 600
Philadelphia, Pennsylvania 19104
Re:Cabaletta Bio, Inc.
Registration Statement on Form S-3
Filed March 16, 2023
File No. 333-270599
Dear Steven Nichtberger:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Alan Campbell at 202-551-4224 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences
cc:       Gabriela Morales-Rivera, Esq.

CORRESP
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CORRESP

 Cabaletta Bio, Inc.

2929 Arch Street, Suite 600

Philadelphia, Pennsylvania 19104

November 16, 2020

 Via EDGAR Transmission

Securities and Exchange Commission

 Division of Corporation
Finance

 100 F Street, N.E.

 Washington, D.C. 20549

        Re:

Cabaletta Bio, Inc.: Registration Statement on Form S-3 filed November 10, 2020

(File No. 333-250006)

 Ladies and Gentlemen:

Pursuant to Rule 461 under the Securities Act of 1933, as amended (the “Act”), Cabaletta Bio, Inc. (the
“Company”) hereby requests that the effective date of the above-referenced registration statement (the “Registration Statement”) be accelerated to November 18, 2020, at 4:01 pm Eastern Time, or as soon
thereafter as practicable, unless we or our outside counsel, Goodwin Procter LLP, request by telephone that such Registration Statement be declared effective at some other time. In making this acceleration request, the Company acknowledges that it
is aware of its responsibilities under the Act.

 If you have any questions regarding this request, please contact Gabriela Morales-Rivera,
Esq. of Goodwin Procter LLP at (617) 570-1329.

Sincerely,

CABALETTA BIO, INC.

/s/ Steven Nichtberger, M.D.

 Steven Nichtberger, M.D.

 President and Chief
Executive Officer

cc:
 J. Brian Stalter, Esq., Cabaletta Bio, Inc.

Mitchell S. Bloom, Esq., Goodwin Procter LLP

Michael Minahan, Esq., Goodwin Procter LLP

Gabriela Morales-Rivera, Esq., Goodwin Procter LLP

United States securities and exchange commission logo
November 16, 2020
Steven Nichtberger
President and Chief Executive Officer
Cabaletta Bio, Inc.
2929 Arch Street, Suite 600
Philadelphia, Pennsylvania 19104
Re:Cabaletta Bio, Inc.
Registration Statement on Form S-3
Filed November 10, 2020
File No. 333-250006
Dear Mr. Nichtberger:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rules 460 and 461 regarding requests for acceleration.  We remind you
that the company and its management are responsible for the accuracy and adequacy of their
disclosures, notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Alan Campbell at 202-551-4224 with any questions.
Sincerely,
Division of Corporation Finance
Office of Life Sciences

CORRESP
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CORRESP

 October 22, 2019

VIA EDGAR

 United States Securities and Exchange
Commission

 Division of Corporation Finance

 Mail Stop 4561

 100 F Street, N.E.

 Washington, D.C. 20549

Re:
 Cabaletta Bio, Inc.

Registration Statement on Form S-1 (File
No. 333-234017) (the “Registration Statement”)

 Ladies and Gentleman:

In connection with the above-referenced Registration Statement, and pursuant to Rule 461 under the Securities Act of 1933, as amended (the “Act”),
we hereby join in the request of Cabaletta Bio, Inc. that the effective date of the Registration Statement be accelerated so that it will be declared effective at 4:00 p.m. Eastern Time on October 24, 2019, or as soon thereafter as practicable.

 Pursuant to Rule 460 under the Act, please be advised that we and the other prospective underwriters have distributed approximately 2,080 copies of the
preliminary prospectus dated October 16, 2019 (the “Preliminary Prospectus”) through the date hereof to underwriters, dealers, institutions and others.

In connection with the Preliminary Prospectus distribution for the above-referenced issue, we hereby confirm that we are, and the other prospective
underwriters have confirmed that they are, complying with the 48-hour requirement as promulgated by Rule 15c2-8 under the Securities Exchange Act of 1934, as amended.

 [Remainder of page intentionally left blank]

 Very truly yours,

MORGAN STANLEY & CO. LLC

 COWEN AND COMPANY, LLC

EVERCORE GROUP, L.L.C.

 As Representatives of the several
Underwriters

 MORGAN STANLEY & CO. LLC.

By:

/s/ Kalli Dircks

 Name: Kalli Dircks

 Title: Executive
Director

COWEN AND COMPANY LLC

By:

/s/ Bill Follis

 Name: Bill Follis

 Title: Managing
Director

EVERCORE GROUP, L.L.C.

By:

/s/ Maren Winnick

 Name: Maren Winnick

 Title: Senior Managing
Director

 [Signature Page to Request for
Acceleration of Effectiveness]

CORRESP
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CORRESP

 VIA EDGAR

October 22, 2019

 United States Securities and Exchange
Commission

 Division of Corporation Finance

 Mail Stop 4561

 100 F Street, N.E.

 Washington, D.C. 20549

Attention: Julia Griffith

 Dietrich King

Re:
 Cabaletta Bio, Inc.

Acceleration Request for Registration Statement on Form S-1

File No. 333-234017

Dear Ms. Griffith and Mr. King,

Pursuant to Rule 461 under the Securities Act of 1933, as amended (the “Act”), Cabaletta Bio, Inc. (the
“Company”) hereby requests that the effective date of the above-referenced registration statement (the “Registration Statement”) be accelerated to October 24, 2019, at 4:00 p.m., Eastern Time, or as soon
thereafter as practicable, unless we or our outside counsel, Goodwin Procter LLP, request by telephone that such Registration Statement be declared effective at some other time. In making this acceleration request, the Company acknowledges that it
is aware of its responsibilities under the Act.

 Once the Registration Statement is effective, please orally confirm the event with our
counsel, Goodwin Procter LLP by calling Barbara Bispham at (212) 459-7252. We also respectfully request that a copy of the written order from the Securities and Exchange Commission (the
“Commission”) verifying the effective time and date of the Registration Statement be sent to our counsel, Goodwin Procter LLP, Attention: Barbara Bispham, by facsimile to (646) 219-7880.

 If you have any questions regarding this request, please contact Barbara Bispham of Goodwin
Procter LLP at (212) 459-7252.

 Sincerely,

 CABALETTA BIO, INC.

/s/ Steven Nichtberger

 Steven Nichtberger

 President and Chief Executive Officer

cc:
 Steven Nichtberger, Cabaletta Bio, Inc.

Anup Marda, Cabaletta Bio, Inc.

Mitchell S. Bloom, Goodwin Procter LLP

Michael Minahan, Goodwin Procter LLP

Barbara Bispham, Goodwin Procter LLP

[Signature Page to Acceleration Request]

CORRESP
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CORRESP

 Goodwin Procter LLP

 100 Northern Avenue

Boston, MA 02210

 goodwinlaw.com

+1 617 570 1000

 FOIA CONFIDENTIAL TREATMENT REQUEST

The entity requesting confidential treatment is:

 Cabaletta Bio,
Inc.

 2929 Arch Street, Suite 600

 Philadelphia, Pennsylvania
19104

 Attn: Steven Nichtberger, Chief Executive Officer

Telephone: (267) 759-3100

CERTAIN PORTIONS OF THIS LETTER AS FILED VIA EDGAR HAVE BEEN OMITTED AND FILED SEPARATELY WITH THE
COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS. OMITTED INFORMATION HAS BEEN REPLACED IN THIS LETTER AS FILED VIA EDGAR WITH A PLACEHOLDER IDENTIFIED BY THE MARK “[***].”

October 11, 2019

 VIA COURIER AND EDGAR

United States Securities and Exchange Commission

 Division of
Corporation Finance

 Office of Healthcare and Insurance

 100
F Street, N.E.

 Washington, D.C. 20549

 Attention: Keira
Nakada; Lisa Vanjoske

Re:
 Cabaletta Bio, Inc.

 Draft Registration Statement on Form S-1

 File No. 333-234017

 CIK No. 0001759138

Rule 83 Confidential Treatment Request by Cabaletta Bio, Inc.

Dear Ms. Nakada and Ms. Vanjoske:

 On
behalf of Cabaletta Bio, Inc. (the “Company”), in response to comments from the staff (the “Staff”) of the Securities and Exchange Commission (the “Commission”) set forth in the letter dated
August 28, 2019 (the “Original Comment Letter”) from the Staff to Steven Nichtberger, the Company’s Chief Executive Officer, relating to the Company’s Registration Statement on Form
S-1,

 1

 Ms. Nakada

Ms. Vanjoske

 Securities and Exchange Commission

October 11, 2019

  Page
 2

 originally confidentially submitted
to the Commission on August 2, 2019, resubmitted to the Commission on September 6, 2019, resubmitted to the Commission on September 20, 2019, and subsequently publicly filed by the Company with the Commission on September 30,
2019 (File No. 333-234017) (the “Registration Statement”), we submit this supplemental letter to further address comment 12 of the Original Comment Letter. This supplemental letter
revises and replaces the letter previously submitted on October 9, 2019.

 The Company respectfully requests that the bracketed
information contained in this letter be treated as confidential information pursuant to Rule 83 promulgated by the Commission, 17 C.F.R. §200.8, and that the Commission provide timely notice to Anup Marda, Chief Financial Officer, Cabaletta
Bio, Inc., 2929 Arch Street, Suite 600, Philadelphia, Pennsylvania, 19104 before it permits any disclosure of the bracketed information in this letter.

For the convenience of the Staff, we have recited the prior comment from the Staff in italicized type and have followed the comment with the
Company’s response.

 Critical Accounting Policies and Significant Judgments and Estimates–Stock Based-Compensation, page 103

12. Once you have an estimated offering price or range, please explain to us the reasons for any differences between the recent valuations of your common
stock leading up to the initial public offering and the estimated offering price. This information will help facilitate our review of your accounting for equity issuances including stock compensation and beneficial conversion features.

The Company advises the Staff that the approach taken by the Company in determining the fair value of its common stock was to obtain
third-party valuations on specific dates, including as of (a) October 10, 2018, (b) as of January 2, 2019, (c) as of February 11, 2019, and (d) as of August 2, 2019, which third-party valuations were used for awards
issued near or after these dates where the Company’s equity valuation did not materially change. This information is set forth on pages 103 and 104 of the preliminary prospectus included in the Registration Statement and included in the table
below, with all such information presented before giving effect to a reverse stock split to be implemented prior to the Company’s proposed initial public offering (“IPO”).

 Grant Date

 Type of Award

Number of
Shares
Subject to
Awards
Granted

Per share
Exercise
Price or
Purchase
Price

Fair Value of
Common
Stock Used
for Financial
Reporting
Purposes

 October 2018

 Options

1,367,023

$
0.67

1.60

 November 2018

 Options

90,000

$
0.67

1.60

 January 2019

 Options

208,922

$
2.82

3.45

 February 2019

 Options

97,331

$
4.20

4.20

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Nakada

Ms. Vanjoske

 Securities and Exchange Commission

October 11, 2019

  Page
 3

 Grant Date

 Type of Award

Number
of Shares
Subject
to
Awards
Granted

Per share
Exercise
Price or
Purchase
Price

Fair Value of
Common
Stock Used
for Financial
Reporting
Purposes

 March 2019

 Options

193,141

$
4.20

4.20

 May 2019

 Options

200,565

$
4.20

4.20

 June 2019

 Options

278,563

$
4.20

4.20

 August 2019

 Options

465,694

$
6.36

6.36

 September 2019

 Options

37,856

$
6.36

6.36

 These third-party valuations were performed in accordance with the guidance outlined in the American Institute
of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation, and were prepared using either an option pricing method (“OPM”) or a
hybrid method, both of which used market approaches to estimate our enterprise value. The OPM treats common stock and preferred stock as call options on the total equity value of a company, with exercise prices based on the value thresholds at which
the allocation among the various holders of a company’s securities changes. Under this method, the common stock has value only if the funds available for distribution to stockholders exceeded the value of the preferred stock liquidation
preferences at the time of the liquidity event, such as a strategic sale or a merger. A discount for lack of marketability of the common stock is then applied to arrive at an indication of value for the common stock. The hybrid method is a
probability-weighted scenario analysis, where the equity value in one or more scenarios is allocated using an OPM. The hybrid method is a scenario-based methodology that estimates the fair value of common stock based upon an analysis of future
values for the company, assuming various outcomes.

 October 10, 2018 Valuation

The fair value of the Company’s common stock was determined to be $1.60 per share at October 10, 2018. For purposes of measuring
compensation for accounting purposes with respect to awards in October and November 2018, the Company performed a retrospective common stock valuation as of October 28, 2018 with the assistance of an independent third-party valuation
specialist. This valuation utilized an OPM back-solve for inferring and allocating the equity value predicated on the sale of the Company’s Series A Preferred Stock. This method was selected as the Company’s management concluded that its
sale of Series A Preferred Stock on October 10, 2018 was an arm’s-length transaction. Furthermore, as of the valuation date, the Company was at an early stage of development with only two full-time
employees with no further milestones occurring through November 2018, and future liquidity events were difficult to forecast. Application of the OPM back-solve method involves making assumptions for the expected time to liquidity, volatility and
risk-free rate and then solving for the value of equity such that value for the most recent financing equals the amount paid. The valuation assumed a 71% volatility rate and a 1.3-year weighted-average
estimated term and applied a discount for lack of marketability of 35% due to the Company being privately held.

 January 2, 2019 Valuation

 The fair value of the Company’s common stock of $3.45 per share at January 2, 2019 for purposes of measuring compensation
for accounting purposes was determined in a retrospective

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Nakada

Ms. Vanjoske

 Securities and Exchange Commission

October 11, 2019

  Page
 4

 common stock valuation as of
January 2, 2019, with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid back-solve method considering two scenarios in a scenario framework and using the OPM to allocate value in one of the scenarios.
The scenarios included: a trade-sale scenario predicated on the Company’s arm’s-length Series B Preferred Stock capital raise that closed on January 2, 2019, and an IPO scenario also based on
the Series B Preferred Stock transaction. Under the hybrid method, the per share value calculated under the two scenarios are weighted based on expected exit outcomes and the quality of the information specific to each allocation methodology to
arrive at a final estimated fair value per share value of the common stock before a discount for lack of marketability is applied. The valuation (i) assigned a 90% probability of a trade-sale scenario, assuming a 75% volatility rate and a 1.6-year weighted-average estimated term and applying a discount for lack of marketability of 30% due to the Company being privately held, and (ii) assigned a 10% probability to the scenario of an IPO, assuming
a 0.8-year estimated term and applying a discount for lack of marketability of 15%. The valuation combined the value estimates of the Company’s common stock from each of the scenarios and rounded to the
nearest cent. The increase in the fair value of the Company’s common stock between October 10, 2018 and January 2, 2019 was largely driven by the closing of the Company’s arms-length Series B Preferred Stock transaction, which
strengthened the Company’s financial position, and its hiring of a key employee with industry-specific experience to support the Company’s planned and continuing preclinical activities.

February 11, 2019 Valuation

 The
fair value of the Company’s common stock of $4.20 per share at February 11, 2019 was determined by the Company’s board of directors with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid
back-solve method considering two scenarios in a scenario-based framework and using the OPM to allocate value in one of the scenarios. The scenarios included: a trade-sale scenario predicated on the purchase price of the Company’s Series B
Preferred Stock and an IPO scenario with reference to the purchase price of the Company’s Series B Preferred Stock. Under the hybrid method, the per share value calculated under the two scenarios are weighted based on expected exit outcomes and
the quality of the information specific to each allocation methodology to arrive at a final estimated fair value per share of the common stock before a discount for lack of marketability is applied. For the February 11, 2019 valuation, the
Company: (i) assigned a 65% probability of a trade-sale scenario, assuming a 76% volatility rate and a 1.6-year weighted-average estimated term and applying a discount for lack of marketability of 30%,
and (ii) assigned a 35% probability to the scenario of an IPO, assuming a 0.7-year estimated term and 30% discount rate and applying a discount for lack of marketability of 15%. The valuation combined the
value estimates of the Company’s common stock from each of the scenarios and rounded to the nearest cent. The increase in the fair value of the Company’s common stock between January 2, 2019 and February 11, 2019 was largely due
to the Company: having identified its lead underwriting banks for a potential IPO; and having held an organizational meeting for the IPO at the end of January 2019. The Company utilized the February 11, 2019 valuation for the grant of awards
through June 2019 as its primary focus during this period was the development of its preclinical-stage product candidates.

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Nakada

Ms. Vanjoske

 Securities and Exchange Commission

October 11, 2019

  Page
 5

 During this period, the Company
determined that additional confirmatory preclinical studies were warranted to advance its preclinical program prior to seeking additional financing in the public markets. As a result, the Company temporarily postponed further work on its potential
IPO until July 2019. If the Company had instead applied a weighting of 100% to the short-term IPO scenario, the fair value of the Company’s common stock in the February 2019 valuation would have been $[***] per share (before giving effect to
any discount for lack of marketability or time value of money).

 August 2, 2019 Valuation

The fair value of the Company’s common stock of $6.36 per share at August 2, 2019 was determined by the Company’s board of
directors with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid framework estimate the common stock value. The valuation utilized two scenarios, which included IPO and
non-IPO scenarios that were probability-weighted based on their expected likelihoods of occurring. The valuation (i) assigned a 50% probability of a trade-sale scenario, allocating the equity value in an
OPM assuming an 82% volatility rate and a 1.4-year weighted-average estimated term and applying a discount for lack of marketability of 25.1%, (ii) assigned a 25% probability to the scenario of an IPO with a
term of 0.29 years, applying a discount for lack of marketability of 5% and (iii) assigned a 25% probability to the scenario of an IPO with a term of 0.54 years, applying a discount for lack of marketability of 7.5%. The valuation combined the
value estimates of the Company’s common stock from each of the scenarios. The weighting of the three scenarios reflects the Company’s initial confidential submission of its Registration Statement on August 2, 2019, the uncertainty
related to both the potential filing and acceptance of the investigational new drug application (“IND”) for its lead product candidate, DSG3-CAART, as well as market conditions. During this period, the Company conducted the
additional confirmatory preclinical studies described above. Upon completion of those studies in July, the Company determined to proceed with the confidential submission of its Registration Statement. If the Company had instead applied a weighting
of 100% to the short-term IPO scenario, the fair value of the Company’s common stock in the August 2019 valuation would have been $[***] per share (before giving effect to any discount for lack of marketability or time value of money).

Comparison of Most Recent Valuation and the Preliminary Price Range

The Company advises the Staff that after taking into consideration guidance and market data from its underwriters in the IPO, the Company
expects the proposed price range for the common stock to be between $[***] to $[***] per share (the “Preliminary Price Range”), before giving effect to a reverse stock split to be implemented prior to the Company’s proposed
IPO. The Preliminary Price Range is based on a number of factors, including the prevailing market conditions and estimates of the Company’s business potential, the general condition of the securities market, the recent market prices of, and the
demand for, publicly-traded common stock of generally comparable companies and preliminary discussions with the underwriters for this offering regarding potential valuations of the Company. The actual bona fide price range to be included in a
subsequent

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Nakada

Ms. Vanjoske

 Securities and Exchange Commission

October 11, 2019

  Page
 6

 amendment to the Registration
Statement has not yet been determined and remains subject to adjustment based on factors outside of the Company’s control. However, the Company believes that the actual bona fide price range will be within the Preliminary Price Range. In
addition, the actual price range to be included in such amendment will comply with the Staff

CORRESP
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filename1.htm

CORRESP

 Goodwin Procter LLP

 100 Northern
Avenue
Boston, MA 02210

 goodwinlaw.com

 +1 617 570
1000

 FOIA CONFIDENTIAL TREATMENT REQUEST

The entity requesting confidential treatment is:

 Cabaletta Bio,
Inc.

 2929 Arch Street, Suite 600

 Philadelphia, Pennsylvania
19104

 Attn: Steven Nichtberger, Chief Executive Officer

Telephone: (267) 759-3100

CERTAIN PORTIONS OF THIS LETTER AS FILED VIA EDGAR HAVE BEEN OMITTED AND FILED SEPARATELY WITH THE COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED
WITH RESPECT TO THE OMITTED PORTIONS. OMITTED INFORMATION HAS BEEN REPLACED IN THIS LETTER AS FILED VIA EDGAR WITH A PLACEHOLDER IDENTIFIED BY THE MARK “[***].”

 October 9, 2019

 VIA
FEDERAL EXPRESS AND EDGAR

 United States Securities and Exchange Commission

Division of Corporation Finance

 Office of Healthcare and
Insurance

 100 F Street, N.E.

 Washington, D.C. 20549

Attention: Julia Griffith; Dietrich King

Re:
         Cabaletta Bio, Inc.

        Draft Registration Statement on Form S-1

        File No. 333-234017

        CIK No. 0001759138

Rule 83 Confidential Treatment Request by Cabaletta Bio, Inc.

Dear Ms. Griffith and Mr. King:

 On
behalf of Cabaletta Bio, Inc. (the “Company”), in response to comments from the staff (the “Staff”) of the Securities and Exchange Commission (the “Commission”) set forth in the letter dated
August 28, 2019 (the “Original Comment Letter”) from the Staff to Steven Nichtberger, the Company’s Chief Executive Officer, relating to the Company’s Registration Statement on Form
S-1, originally confidentially submitted to the Commission on August 2, 2019, resubmitted to the Commission on September 6, 2019, resubmitted to the Commission on September 20, 2019, and
subsequently publicly filed by the Company with the Commission on September 30, 2019 (File No. 333-234017) (the “Registration Statement”), we submit this supplemental letter to
further address comment 12 of the Original Comment Letter.

 1

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

October 9, 2019

 Page 2

 The Company respectfully requests that the bracketed information contained in this letter
be treated as confidential information pursuant to Rule 83 promulgated by the Commission, 17 C.F.R. §200.8, and that the Commission provide timely notice to Anup Marda, Chief Financial Officer, Cabaletta Bio, Inc., 2929 Arch Street, Suite 600,
Philadelphia, Pennsylvania, 19104 before it permits any disclosure of the bracketed information in this letter.

 For the convenience
of the Staff, we have recited the prior comment from the Staff in italicized type and have followed the comment with the Company’s response.

Critical Accounting Policies and Significant Judgments and Estimates–Stock Based-Compensation, page 103

12. Once you have an estimated offering price or range, please explain to us the reasons for any differences between the recent valuations of your common
stock leading up to the initial public offering and the estimated offering price. This information will help facilitate our review of your accounting for equity issuances including stock compensation and beneficial conversion features.

The Company advises the Staff that the approach taken by the Company in determining the fair value of its common stock was to obtain
third-party valuations on specific dates, including as of (a) October 10, 2018, (b) as of January 2, 2019, (c) as of February 11, 2019, and (d) as of August 2, 2019, which third-party valuations were used for awards
issued near or after these dates where the Company’s equity valuation did not materially change. This information is set forth on pages 103 and 104 of the preliminary prospectus included in the Registration Statement and included in the table
below, with all such information presented before giving effect to a reverse stock split to be implemented prior to the Company’s proposed initial public offering (“IPO”).

 Grant Date

Type of Award

Number of
Shares
Subject to
Awards
Granted

Per share
Exercise
Price
or Purchase Price

Fair Value of
Common Stock
Used for Financial
Reporting Purposes

 October 2018

Options

1,367,023

$
0.67

1.60

 November 2018

Options

90,000

$
0.67

1.60

 January 2019

Options

208,922

$
2.82

3.45

 February 2019

Options

97,331

$
4.20

4.20

 March 2019

Options

193,141

$
4.20

4.20

 May 2019

Options

200,565

$
4.20

4.20

 June 2019

Options

278,563

$
4.20

4.20

 August 2019

Options

465,694

$
6.36

6.36

 September 2019

Options

37,856

$
6.36

6.36

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

October 9, 2019

 Page 3

 These third-party valuations were performed in accordance with the guidance outlined in the
American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation, and were prepared using either an option pricing method
(“OPM”) or a hybrid method, both of which used market approaches to estimate our enterprise value. The OPM treats common stock and preferred stock as call options on the total equity value of a company, with exercise prices based on
the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, the common stock has value only if the funds available for distribution to stockholders exceeded the value of the
preferred stock liquidation preferences at the time of the liquidity event, such as a strategic sale or a merger. A discount for lack of marketability of the common stock is then applied to arrive at an indication of value for the common stock. The
hybrid method is a probability-weighted scenario analysis, where the equity value in one or more scenarios is allocated using an OPM. The hybrid method is a scenario-based methodology that estimates the fair value of common stock based upon an
analysis of future values for the company, assuming various outcomes.

 October 10, 2018 Valuation

The fair value of the Company’s common stock was determined to be $1.60 per share at October 10, 2018. For purposes of measuring
compensation for accounting purposes with respect to awards in October and November 2018, the Company performed a retrospective common stock valuation as of October 28, 2018 with the assistance of an independent third-party valuation
specialist. This valuation utilized an OPM back-solve for inferring and allocating the equity value predicated on the sale of the Company’s Series A Preferred Stock. This method was selected as the Company’s management concluded that its
sale of Series A Preferred Stock on October 10, 2018 was an arm’s-length transaction. Furthermore, as of the valuation date, the Company was at an early stage of development with only two full-time
employees with no further milestones occurring through November 2018, and future liquidity events were difficult to forecast. Application of the OPM back-solve method involves making assumptions for the expected time to liquidity, volatility and
risk-free rate and then solving for the value of equity such that value for the most recent financing equals the amount paid. The valuation assumed a 71% volatility rate and a 1.3-year weighted-average
estimated term and applied a discount for lack of marketability of 35% due to the Company being privately held.

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

October 9, 2019

 Page 4

 January 2, 2019 Valuation

The fair value of the Company’s common stock of $3.45 per share at January 2, 2019 for purposes of measuring compensation for
accounting purposes was determined in a retrospective common stock valuation as of January 2, 2019, with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid back-solve method considering two scenarios
in a scenario framework and using the OPM to allocate value in one of the scenarios. The scenarios included: a trade-sale scenario predicated on the Company’s arm’s-length Series B Preferred Stock
capital raise that closed on January 2, 2019, and an IPO scenario also based on the Series B Preferred Stock transaction. Under the hybrid method, the per share value calculated under the two scenarios are weighted based on expected exit
outcomes and the quality of the information specific to each allocation methodology to arrive at a final estimated fair value per share value of the common stock before a discount for lack of marketability is applied. The valuation (i) assigned
a 90% probability of a trade-sale scenario, assuming a 75% volatility rate and a 1.6-year weighted-average estimated term and applying a discount for lack of marketability of 30% due to the Company being
privately held, and (ii) assigned a 10% probability to the scenario of an IPO, assuming a 0.8-year estimated term and applying a discount for lack of marketability of 15%. The valuation combined the value
estimates of the Company’s common stock from each of the scenarios and rounded to the nearest cent. The increase in the fair value of the Company’s common stock between October 10, 2018 and January 2, 2019 was largely driven by
the closing of the Company’s arms-length Series B Preferred Stock transaction, which strengthened the Company’s financial position, and its hiring of a key employee with industry-specific experience to support the Company’s planned
and continuing preclinical activities.

 February 11, 2019 Valuation

The fair value of the Company’s common stock of $4.20 per share at February 11, 2019 was determined by the Company’s board of
directors with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid back-solve method considering two scenarios in a scenario-based framework and using the OPM to allocate value in one of the scenarios. The
scenarios included: a trade-sale scenario predicated on the purchase price of the Company’s Series B Preferred Stock and an IPO scenario with reference to the purchase price of the Company’s Series B Preferred Stock. Under the hybrid
method, the per share value calculated under the two scenarios are weighted based on expected exit outcomes and the quality of the information specific to each allocation methodology to arrive at a final estimated fair value per share of the common
stock before a discount for lack of marketability is applied. For the February 11, 2019 valuation, the Company: (i) assigned a 65% probability of a trade-sale scenario, assuming a 76% volatility rate and a
1.6-year weighted-average estimated term and applying a discount for lack of marketability of 30%, and (ii) assigned a 35% probability to the scenario of an IPO, assuming a
0.7-year estimated term and 30% discount rate and applying a discount for lack of marketability of 15%. The valuation combined the value estimates of the Company’s common stock from each of the scenarios
and rounded to the nearest cent. The increase in the fair value of the Company’s common stock between January 2, 2019 and February 11, 2019 was largely due to the Company: having identified its lead underwriting banks for a potential
IPO; and having held an organizational meeting for the IPO at the end of January 2019. The Company utilized the February 11, 2019 valuation for the grant of awards through June 2019 as its primary focus during this period was the development of
its preclinical-stage product candidates. During this period, the Company determined that additional confirmatory preclinical studies were warranted to advance its preclinical program prior to seeking additional financing in the public markets. As a
result, the Company temporarily postponed further work on its potential IPO until July 2019.

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

October 9, 2019

 Page 5

 August 2, 2019 Valuation

The fair value of the Company’s common stock of $6.36 per share at August 2, 2019 was determined by the Company’s board of
directors with the assistance of an independent third-party valuation firm. This valuation utilized a hybrid framework estimate the common stock value. The valuation utilized two scenarios, which included IPO and
non-IPO scenarios that were probability-weighted based on their expected likelihoods of occurring. The valuation (i) assigned a 50% probability of a trade-sale scenario, allocating the equity value in an
OPM assuming an 82% volatility rate and a 1.4-year weighted-average estimated term and applying a discount for lack of marketability of 25.1%, (ii) assigned a 25% probability to the scenario of an IPO with a
term of 0.29 years, applying a discount for lack of marketability of 5% and (iii) assigned a 25% probability to the scenario of an IPO with a term of 0.54 years, applying a discount for lack of marketability of 7.5%. The valuation combined the
value estimates of the Company’s common stock from each of the scenarios. The weighting of the three scenarios reflects the Company’s initial confidential submission of its Registration Statement on August 2, 2019, the uncertainty
related to both the potential filing and acceptance of the investigational new drug application (“IND”) for its lead product candidate, DSG3-CAART, as well as market conditions. If the Company had instead applied a weighting of 100%
to the short-term IPO scenario, the fair value of the Company’s common stock in the August 2019 valuation would have been $[***] per share (before giving effect to any discount for lack of marketability or time value of money).

Comparison of Most Recent Valuation and the Preliminary Price Range

The Company advises the Staff that after taking into consideration guidance and market data from its underwriters in the IPO, the Company
expects the proposed price range for the common stock to be between $[***] to $[***] per share (the “Preliminary Price Range”), before giving effect to a reverse stock split to be implemented prior to the Company’s proposed
IPO. The Preliminary Price Range is based on a number of factors, including the prevailing market conditions and estimates of the Company’s business potential, the general condition of the securities market, the recent market prices of, and the
demand for, publicly-traded common stock of generally comparable companies and preliminary discussions with the underwriters for this offering regarding potential valuations of the Company. The actual bona fide price range to be included in a
subsequent amendment to the Registration Statement has not yet been determined and remains subject to adjustment based on factors outside of the Company’s control. However, the Company believes that the actual bona fide price range will
be within the Preliminary Price Range. In addition, the actual price range to be included in such amendment will comply with the Staff’s interpretation regarding the parameters of a bona fide price range.

 FOIA CONFIDENTIAL
TREATMENT REQUESTED BY CABALETTA BIO, INC.

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

October 9, 2019

 Page 6

 With respect to the Preliminary Price Range, the Company notes that, as is typical in IPOs,
the estimated price range for its offering was not derived using a formal determination of fair value but was determined based upon discussions between the Company and the underwriters. Among the factors considered in setting the Preliminary Price
Range were prevailing market conditions, estimates of the Company’s business potential, progress in its clinical and pre-clinical development efforts and developments in its business, the general
condition of the securities market and the market prices of, and demand for, publicly-traded common stock of generally comparable companies.

In addition, the Company believes the increase in value reflected betw

CORRESP
1
filename1.htm

CORRESP

 Goodwin Procter LLP

100 Northern Avenue

 Boston, MA 02210

 goodwinlaw.com

+1 617 570 1000

 September 30,
2019

 Ms. Julia Griffith

Mr. Dietrich King

 Office of Healthcare and Insurance

Division of Corporation Finance

 Securities and Exchange
Commission

 100 F Street, N.E.

 Washington, D.C. 20549

Re:

Cabaletta Bio, Inc.

Draft Registration Statement on Form S-1

Submitted August 2, 2019

CIK No. 0001759138

 Dear Ms. Griffith and Mr. King:

This letter is submitted on behalf of Cabaletta Bio, Inc. (the “Company”) in response to comments of the staff of the
Division of Corporation Finance (the “Staff”) of the U.S. Securities and Exchange Commission (the “Commission”) with respect to the Company’s Draft Registration Statement on Form
S-1, originally confidentially submitted on August 2, 2019 (the “Original Draft Registration Statement”), as set forth in the Staff’s letter dated August 28, 2019
to Steven Nichtberger, the Company’s Chief Executive Officer (the “Original DRS Comment Letter”). The Company subsequently confidentially submitted Amendment No. 1 to the Draft Registration Statement on
September 6, 2019 and Amendment No. 2 to the Draft Registration Statement on September 20, 2019 (“Amendment No. 2”). Concurrently with the submission of this letter to the Staff, the Company is
filing its Registration Statement on Form S-1 (the “Registration Statement”), which includes changes to reflect responses to the Staff’s comments and other updates.

For reference purposes, the text of the comments to which this letter responds has been reproduced and italicized herein, with responses below
each numbered comment. Unless otherwise indicated, page references in the descriptions of the Staff’s comments refer to the Original Draft Registration Statement, and page references in the responses refer to the Registration Statement. All
capitalized terms used and not otherwise defined herein shall have the meanings set forth in the Registration Statement.

 The responses
provided herein are based upon information provided to Goodwin Procter LLP by the Company. In addition to submitting this letter via EDGAR, we are sending via Federal Express four (4) copies of each of this letter and the Registration Statement
(marked to show changes from Amendment No. 2).

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

September 30, 2019

  Page
 2

 Draft Registration Statement on Form S-1 filed August 2, 2019

 Risk Factors, page 12

8.
 Please refer to the Risk Factor on page 36 which states that you expect to grow the size of your
organization by expanding your employee base. Please explain, here and in the Use of Proceeds section on page 84, what portion of the proceeds of this offering you plan to spend on this endeavor, how long you expect that application of proceeds to
last, or what additional source of funds you expect to use in growing your employee base.

 RESPONSE: The
Company’s respectfully acknowledges the Staff’s comment and has revised the disclosure on pages 35 and 82 of the Registration Statement to explain that it expects to spend a portion of the proceeds of this offering on this endeavor and
that the Company expects the application of proceeds to last until at least the first quarter of 2022. The Company further advises the Staff that the timing and extent of future increases in the Company’s headcount depends in part on a number
of factors, the impact of which are not reasonably certain at this time, including, without limitation, the timing and progress of the Company’s preclinical and clinical development activities and the extent to which the Company engages
third-parties to assist in such activities.

 Use of Proceeds, page 84

10.
 Please revise to clarify whether you believe the net proceeds will be sufficient to complete the Phase 1
clinical trials for your four product candidates, and if not, how far into those trials you expect the proceeds to last.

RESPONSE: The Company’s respectfully acknowledges the Staff’s comment and has revised the disclosure on page 82 of the
Registration Statement to clarify that the Company believes the net proceeds will be sufficient for the advancement of DSG3-CAART, the Company’s lead product candidate, through completion of Phase A Dose Escalation of the Company’s planned
Phase 1 clinical trial. The Company respectfully advises the Staff that the Company’s other product candidates are too early in their respective stages of development to forecast the funding and progression of each individual candidate and has
revised the disclosure on page 82 of the Registration Statement to clarify that the net proceeds will go towards general discovery and preclinical advancement of the Company’s other product candidates. The Company further advises the Staff that
it has revised the disclosure on page 15 of the Registration Statement to clarify that the Company expects to require significant additional financing to complete its Phase 1 clinical trial for DSG3-CAART and any future clinical trials for its other
product candidates.

 * * * * *

 Ms. Griffith

Mr. King

 Securities and Exchange Commission

September 30, 2019

  Page
 3

 Should you have any further comments or questions with regard to the foregoing, please
contact the undersigned at (617) 570-1021.

 Sincerely,

/s/ Michael J. Minahan

 Michael J. Minahan, Esq.

Enclosures:

 cc:

 Steven Nichtberger, Cabaletta Bio, Inc.

 Anup Marda, Cabaletta Bio, Inc.

 Mitchell S. Bloom, Goodwin Procter LLP

 Patrick O’Brien, Ropes & Gray LLP

 Benjamin Kozik, Ropes & Gray LLP

September 17, 2019
Steven Nichtberger
Chief Executive Officer and President
Cabaletta Bio, Inc.
2929 Arch Street, Suite 600
Philadelphia, PA 19104
Re:Cabaletta Bio, Inc.
Amendment No. 1 to
Draft Registration Statement on Form S-1
Submitted August 2, 2019
CIK No. 0001759138
Dear Mr. Nichtberger:
            We have reviewed your amended draft registration statement and have the following
comments.  In some of our comments, we may ask you to provide us with information so we
may better understand your disclosure.
            Please respond to this letter by providing the requested information and either submitting
an amended draft registration statement or publicly filing your registration statement on
EDGAR.  If you do not believe our comments apply to your facts and circumstances or do not
believe an amendment is appropriate, please tell us why in your response.
            After reviewing the information you provide in response to these comments and your
amended draft registration statement or filed registration statement, we may have additional
comments.
Amended Draft Registration Statement on Form S-1
Financial Statements
Statements of Operations, page F-4
1.With regard to your response to comment 13, please:
•tell us why you believe it is appropriate to weight the period of April 3, 2017 to
August 22, 2017 at 51% when there were no shares outstanding to share in the loss,
•reconcile the issuance of 4,183,250 common shares on August 22, 2017 shown in your
response letter dated September 6, 2019 to the 5,000,000 common shares shown as
issued in 2017 on page F-5 of the draft registration statement and explain why the
computation is not based on the 5,000,000 shares,

 FirstName LastNameSteven Nichtberger
 Comapany NameCabaletta Bio, Inc.
 September 17, 2019 Page 2
 FirstName LastName
Steven Nichtberger
Cabaletta Bio, Inc.
September 17, 2019
Page 2
•provide us your computation of the 204,187 shares and 3,156 shares that vest in some
quarters as shown in your response letter dated September 6, 2019, and
•tell us where the vesting of the 3,130,874 shares is shown in your calculation in your
response.
Notes to the Financial Statements
6. Commitments and Contingencies
The Regents of the University of California, page F-15
2.Refer to your response to comment 15.  Please disclose the amount of obligation you are
committed to fund or disclose that such amount is not material as we believe this is a
significant term of the agreement that should be disclosed.
            You may contact Keira Nakada at 202-551-3267 or Lisa Vanjoske at 202-551-3614 if
you have questions regarding comments on the financial statements and related matters.  Please
contact Julie Griffith at 202-551-3267 or Dietrich King at 202-551-8071 with any other
questions.
Sincerely,
Division of Corporation Finance
Office of Healthcare & Insurance

August 28, 2019
Steven Nichtberger
Chief Executive Officer and President
Cabaletta Bio, Inc.
2929 Arch Street, Suite 600
Philadelphia, PA 19104
Re:Cabaletta Bio, Inc.
Draft Registration Statement on Form S-1
Submitted August 2, 2019
CIK No. 0001759138
Dear Mr. Nichtberger:
            We have reviewed your registration statement and have the following comments.  In
some of our comments, we may ask you to provide us with information so we may better
understand your disclosure.
            Please respond to this letter by amending your registration statement and providing the
requested information.  If you do not believe our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.
            After reviewing any amendment to your registration statement and the information you
provide in response to these comments, we may have additional comments.
Draft Registration Statement on Form S-1
Prospectus Summary, page 1
1.Please revise the disclosure in the first paragraph of the Overview to clarify what you
mean by "IND-ready."
Pipeline, page 2
2.We note your disclosure regarding "in vivo  evidence of efficacy and safety in an animal
model..." We also note other examples of statements regarding safety and efficacy on
pages 3, 117, 119, and 124.  Since none of your product candidates has received FDA
approval, please revise your disclosure regarding safety and efficacy in the summary and
throughout your prospectus to clarify this point.

 FirstName LastNameSteven Nichtberger
 Comapany NameCabaletta Bio, Inc.
 August 28, 2019 Page 2
 FirstName LastNameSteven Nichtberger
Cabaletta Bio, Inc.
August 28, 2019
Page 2
3.We note your statement on page 13 that you are early in your development efforts and
have not initiated clinical trials for any product candidates.  Please expand the table on
page 2 to include more information about the progress of the company's pre-clinical trials,
 and to clarify in the table that no products are past the phase of IND enabling studies. In
addition, please include columns for Phase 1, 2 and 3 testing that are equally prominent
with the pre-clinical columns, and clarify that these columns refer to clinical testing. In
this regard, our concern is that potential investors see a balanced graphical presentation of
where you are in the drug development process, and that the table adequately depict, if
true, that you have not yet filed an IND application for any product.  Please make
conforming changes in the Business section as well.
Implications of Being an Emerging Growth Company, page 7
4.Please supplementally provide us with copies of all written communications, as defined in
Rule 405 under the Securities Act, that you, or anyone authorized to do so on your behalf,
present to potential investors in reliance on Section 5(d) of the Securities Act, whether or
not they retain copies of the communications.
Risk Factors, page 12
5.We note that there are references to foreign regulators and foreign markets throughout the
Risk Factors and other sections of your prospectus. Please revise to explain what non-U.S.
markets, if any, you plan to enter, and what steps you have taken to attain the necessary
regulatory approvals.
6.Please provide us with a basis for your statement on page 21 that although clinical trials
for cell-based therapies have historically included "a lymphodepleting chemotherapeutic
regime to condition the patient prior to infusion [with CAR T-cell based therapies]," and
that such infusions have resulted in neurotoxicity and other serious side effects,  you
believe that  the use of CAR T cell therapies without preconditioning will avoid
neurotoxicity or other side effects.  We note your statement that "Based on evidence from
other CAR T cell clinical trials demonstrating clinical activity without prior conditioning
and the levels of certain cytokines that promote T cell expansion in the patients we are
treating relative to cancer patients, as well as data from engineered T cell therapy in the
setting of HIV without conditioning, we believe that CAAR T cell therapy may be
functional in our autoimmune target patient populations without preconditioning
regimens. Based on preclinical studies where DSG3-CAART is combined with
stimulatory DSG3 antibodies, we observed these antibodies generate a modest level of
cytokine activity that is an order of magnitude less than what was observed when DSG3-
CAART engaged with target B cells. We believe this data indicates the presence of
soluble DSG3 antibodies could stimulate DSG3-CAART expansion and potentially
facilitate engraftment. This information coupled with the risks associated with certain
lymphodepleting regimens used for preconditioning, we believe exposing autoimmune
patients to these regimens without data to support the benefit is difficult to justify."  Please

 FirstName LastNameSteven Nichtberger
 Comapany NameCabaletta Bio, Inc.
 August 28, 2019 Page 3
 FirstName LastNameSteven Nichtberger
Cabaletta Bio, Inc.
August 28, 2019
Page 3
expand your disclosure to include references to the specific studies on which you base
your beliefs, and clarify the reasons for your belief that preconditioning is not necessary
for your product candidate.
7.We note your disclosure on page 80 and on page 184 that your exclusive forum provision
does not apply to actions arising under the Securities Act or the Exchange Act. Please also
ensure that the exclusive forum provision in the bylaws (as effective on the closing of the
offering) states this clearly, or tell us how you will inform investors in future filings that
the provision does not apply to any actions arising under the Securities Act or Exchange
Act.
8.Please refer to the Risk Factor on page 36 which states that you expect to grow the size of
your organization by expanding your employee base.  Please explain, here and in the Use
of Proceeds section on page 84, what portion of the proceeds of this offering you plan to
spend on this endeavor, how long you expect that application of proceeds to last, or what
additional source of funds you expect to use in growing your employee base.
9.Please revise your risk factor disclosure to address more specifically the fact that 88.7% of
the company will be held by the current stockholders following the offering, and detail
more clearly the dilutive impact on investors in this offering that the conversion of
outstanding convertible notes, convertible preferred stock, and the exercise of outstanding
stock options would have, or tell us why you believe this is not a material risk.
Use of Proceeds, page 84
10.Please revise to clarify whether you believe the net proceeds will be sufficient to complete
the Phase 1 clinical trials for your four product candidates, and if not, how far into those
trials you expect the proceeds to last.
Management’s Discussion and Analysis of Financial Condition and Results of Operations
Components of Operating Results
Research and Development, page 95
11.Please quantify the research and development expenses by types of costs incurred for each
of the periods presented.
Critical Accounting Policies and Significant Judgements and Estimates
Stock-Based Compensation, page 103
12.Once you have an estimated offering price or range, please explain to us the reasons for
any differences between the recent valuations of your common stock leading up to the
initial public offering and the estimated offering price. This information will help facilitate
our review of your accounting for equity issuances including stock compensation and
beneficial conversion features.
Financial Statements

 FirstName LastNameSteven Nichtberger
 Comapany NameCabaletta Bio, Inc.
 August 28, 2019 Page 4
 FirstName LastNameSteven Nichtberger
Cabaletta Bio, Inc.
August 28, 2019
Page 4
Statements of Operations, page F-4
13.Please provide us your computation of weighted-average number of shares used in
computing net loss per share for all periods presented.  Also, tell us your consideration of
disclosing in the financial statements how you determined weighted-average number of
shares used in computing net loss per share.
Notes to the Financial Statements
6. Commitments and Contingencies
Operating Lease Agreement, page F-14
14.Please tell us how you recognize rental expense for leases in which the rent varies from
year to year.
The Regents of the University of California, page F-15
15.Please quantify the obligation you are committed to fund.  If no such amount is defined in
the contract, disclose the estimate of such obligations and whether there is a limit to such
obligations.
General
16.Please provide us mockups of any pages that include any additional pictures or graphics to
be presented, including any accompanying captions. Please keep in mind, in scheduling
your printing and distribution of the preliminary prospectus, that we may have comments
after our review of these materials.
            We remind you that the company and its management are responsible for the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action or absence of
action by the staff.
            Refer to Rules 460 and 461 regarding requests for acceleration.  Please allow adequate
time for us to review any amendment prior to the requested effective date of the registration
statement.
            You may contact Keira Nakada at 202-551-3659 or Lisa Vanjoske at 202-551-3614 if
you have questions regarding comments on the financial statements and related matters.  Please
contact Julia Griffith at 202-551-3267 or Dietrich King at 202-551-8071 with any other
questions.
Sincerely,
Division of Corporation Finance

 FirstName LastNameSteven Nichtberger
 Comapany NameCabaletta Bio, Inc.
 August 28, 2019 Page 5
 FirstName LastName
Steven Nichtberger
Cabaletta Bio, Inc.
August 28, 2019
Page 5
Office of Healthcare & Insurance