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CORRESP
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CORRESP

 Divakar Gupta

 +1 212 479 6474

dgupta@cooley.com

VIA EDGAR

 *FOIA Confidential Treatment Request*

Confidential Treatment Requested by Turnstone Biologics Corp.

in connection with its Registration Statement on Form S-1 (File
No. 333-272600)

 June 21, 2023

U.S. Securities and Exchange Commission

 Division of Corporation
Finance

 Office of Life Sciences

 100 F Street, N.E.

Washington, D.C. 20549

Attn:
 Lauren Sprague Hamill

Joshua Gorsky

 Christine Torney

 Mary Mast

Re:
 Turnstone Biologics Corp.

Registration Statement on Form S-1

June 12, 2023

 File No. 333-272600

 Ladies and Gentlemen:

On behalf of Turnstone Biologics Corp. (the “Company”), in response to comments from the staff (the
“Staff”) of the U.S. Securities and Exchange Commission (the “Commission”) received by letter dated June 9, 2023 (the “Comment Letter”), relating to the Company’s
draft Registration Statement on Form S-1 confidentially submitted to the Commission on May 15, 2023 (the “DRS”), and which was subsequently updated by the Company with a
Registration Statement on Form S-1 filed with the Commission on June 12, 2023 (the “Registration Statement”), we are submitting this supplemental letter to further address Comment
No. 19 of the Comment Letter. For the convenience of the Staff, we have incorporated the text of Comment No. 19 into this letter.

Due to the commercially sensitive nature of information contained in this letter, this submission is accompanied by the Company’s request
for confidential treatment for selected portions of this letter. The Company has filed a separate letter with the Office of Freedom of Information and Privacy Act Operations in connection with the confidential treatment request pursuant to Rule 83
of the Commission’s Rules on Information and Requests (17 C.F.R. § 200.83).

 Cooley LLP    55 Hudson
Yards    New York, NY    10001

 T:+1 212 479 6000    f:+1 212 479
6275    cooley.com

 U.S. Securities and Exchange Commission

June 21, 2023

 Page Two

 Staff Comment

Management’s Discussion and Analysis of Financial Condition and Results of Operations Critical Accounting Policies and Estimates

Determination of the Fair Value of Common Stock, page 109

19.
 Once you have an estimated offering price or range, please explain to us how you determined the fair value of
the awards underlying your incentive units and the reasons for any differences between the recent valuations of your units leading up to the IPO and the estimated offering price. This information will help facilitate our review of your accounting
for equity issuances including stock compensation. Please discuss with the staff how to submit your response.

 Response:

Preliminary Price Range

 The
Company advises the Staff that the Company currently expects a price range of approximately $[***] to $[***] per share (the “Preliminary Price Range”) for the initial public offering
(“IPO”) of the Company’s common stock, par value $0.001 per share (the “Common Stock”), which Preliminary Price Range does not reflect the impact of a 1-for-[***] reverse stock split of the Common Stock that the Company anticipates may be effected prior to the effectiveness of the Registration Statement (the “Reverse Stock Split”).
The share and per share numbers in this letter are presented on a pre-Reverse Stock Split basis.

The Preliminary Price Range is based in part upon the Company’s prospects, prospects for the biotechnology industry generally, the
general condition of the securities markets and the recent market prices of, and the demand for, publicly traded shares of generally comparable companies in the biotechnology industry, as well as input received from BofA Securities, Inc., SVB
Securities LLC and Piper Sandler & Co., the representatives of the several underwriters for the Company’s IPO (the “Representatives”). The Company notes that, as is typical in IPOs, the Preliminary Price Range
for the Company’s IPO was not derived using a formal determination of fair value or single valuation methodology, but was determined by discussions among the Company and the Representatives based on a variety of considerations and
methodologies, including the assessment of the aforementioned factors.

 The Company will include a narrower bona fide price range of the
Common Stock, as adjusted for the Reverse Stock Split, in an amendment to the Registration Statement that will be filed prior to the commencement of the Company’s road show. However, the parameters of the bona fide price range will be subject
to then-current market conditions, continuing discussions with the Representatives and material business developments impacting the Company, and due to the volatility in the securities markets, in particular the volatility experienced in the market
by recent IPO issuers, there is a possibility that the bona fide price range for the IPO may fall outside of the Preliminary Price Range. In any event, the Company confirms to the Staff that the bona fide price range will comply with Item 501(b)(3)
of Regulation S-K and C&DI 134.04.

 FOIA Confidential
Treatment Requested by Turnstone Biologics Corp.

 Cooley LLP    55 Hudson Yards    New York, NY
10001

 T:+1 212 479 6000    f:+1 212 479 6275    cooley.com

 U.S. Securities and Exchange Commission

June 21, 2023

 Page Three

 Common Stock Valuation Methodologies

As there has been no public market for the Common Stock to date, the estimated fair value of its Common Stock for purposes of granting equity
awards has been determined by the Company’s board of directors (the “Board”), as of the date of each option grant, with input from management, considering the Company’s (i) most recent arm’s length sales
of its convertible preferred stock, (ii) and the most recent third-party valuation of its Common Stock, as well as the Board’s assessment of additional objective and subjective factors that the Board believed were relevant and which may
have changed from the date of the most recent third-party valuation through the date of the grant. The Board considered various objective and subjective factors to determine the estimated fair value of the Common Stock as of each grant date,
including:

•

 the prices of the Company’s convertible preferred stock sold to outside investors in arm’s length
transactions and the rights, preferences, and privileges of the Company’s convertible preferred stock as compared to those of the Common Stock, including liquidation and redemption preferences of the Company’s convertible preferred stock;

•

 the progress of the Company’s research and development programs, including the status and results of
preclinical studies and clinical trials for the Company’s product candidates and progress of the Company’s development and manufacturing processes;

•

 the Company’s stage of development and business strategy, and material risks related to the Company’s
business;

•

 the hiring of key personnel and management;

•

 external market conditions affecting the biotechnology industry, and trends within the biotechnology industry;

•

 the Company’s financial position, including cash on hand, and historical and forecasted performance and
results of operations;

•

 the lack of an active public market for the Common Stock and the Company’s convertible preferred stock;

•

 the likelihood of achieving a liquidity event for the holders of Common Stock, such as an IPO, or a sale of the
Company, given prevailing market conditions;

•

 the achievement of enterprise milestones, including entering into collaboration and license agreements;

•

 the analysis of IPOs and the market performance of similar companies in the biotechnology industry; and

•

 the economy in general.

 FOIA Confidential
Treatment Requested by Turnstone Biologics Corp.

 Cooley LLP    55 Hudson Yards    New York, NY
10001

 T:+1 212 479 6000    f:+1 212 479 6275    cooley.com

 U.S. Securities and Exchange Commission

June 21, 2023

 Page Four

 The third-party valuations of the Common Stock that the Board considered in making its
determinations were prepared in accordance with the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation (the
“Practice Aid”), which prescribes several valuation approaches for determining the value of an enterprise, such as the cost, market and income approaches, and various methodologies for allocating the value of an enterprise to
its capital structure and specifically its common stock.

 In accordance with the Practice Aid, the Company considered the following
methods for allocating the enterprise value across its classes and series of capital stock to determine the estimated fair value of the Common Stock at each valuation date.

•

 Option Pricing Method (“OPM”). The OPM estimates the value of the
Common Stock using the various inputs in the Black-Scholes option pricing model. The OPM treats the rights of the holders of Common Stock as equivalent to that of call options on any value of the enterprise above certain break points of value
based upon the liquidation preferences of the holders of the Company’s convertible preferred stock, as well as their rights to participation, and the stock prices of the outstanding options. Thus, the value of the Common Stock can be determined
by estimating the value of its portion of each of these call option rights. Under this method, the Common Stock has value only if the funds available for distribution to stockholders exceed the value of the liquidation preference at the time of a
liquidity event, such as a merger or sale.

•

 Probability-Weighted Expected Return Method (“PWERM”). The PWERM is a
scenario-based analysis that estimates the value per share based on the probability-weighted present value of expected future investment returns, considering each of the possible outcomes considered by the Company, as well as the economic and
control rights of each share class.

•

 Hybrid Method (“Hybrid Method”). The Hybrid Method is a weighted-average
method that combines both OPM and PWERM. Weighting allocations are assigned to the OPM and PWERM methods factoring in possible future liquidity events.

In order for the Board to determine the estimated fair value of the Common Stock, as the Company had obtained better visibility into the
timing of a potential IPO, but still considered the uncertainty around the Company’s value should an IPO not occur, the Hybrid Method was utilized for the independent third-party valuations of the Common Stock as of April 29, 2022 (the
“April 29, 2022 Valuation”) and as of March 31, 2023 (the “March 31, 2023 Valuation” and together with the April 29, 2022
Valuation, the “Valuations”), each as discussed below. The Hybrid Method is commonly used in these situations and is consistent with guidance from the Practice Aid. In the Company’s case, the Hybrid Method incorporated
two scenarios: (1) the sale scenario where the allocation of total equity value was performed using the OPM, and (2) the IPO scenario, where all outstanding shares of the Company’s convertible preferred stock were assumed to be
mandatorily converted into shares of Common Stock. In addition, given the Common Stock represents a non-marketable equity interest in a private enterprise, an adjustment to the preliminary value estimates had
to be made in each sale and IPO scenarios to account for the lack of liquidity that a stockholder experiences. This adjustment is commonly referred to as a discount for lack of marketability (“DLOM”).

 FOIA Confidential
Treatment Requested by Turnstone Biologics Corp.

 Cooley LLP    55 Hudson Yards    New York, NY
10001

 T:+1 212 479 6000    f:+1 212 479 6275    cooley.com

 U.S. Securities and Exchange Commission

June 21, 2023

 Page Five

 At each grant date, the Board evaluated any recent events and their potential impact on the
estimated fair value per share of the Common Stock. For grants of awards made on dates for which there was no contemporaneous independent third-party valuation, the Board determined the estimated fair value of the Common Stock on the date of grant
taking into consideration the most recent valuation report as well as other pertinent information available to it at the time of the grant.

 Common
Stock Valuations and Stock Option Grants

 The Company granted the following stock option awards since June 1, 2022:

 Date of Grant

Numbers of
Shares Subject to
Stock Options
Granted

Exercise Price Per
Share of Common
Stock

Estimated Fair
Value Per Share of
Common Stock at
Grant Date

 June 30, 2022

[
***]

$
[
***]

$
[
***]

 September 7, 2022

[
***]

$
[
***]

$
[
***]

 December 14, 2022

[
***]

$
[
***]

$
[
***]

 March 2, 2023

[
***]

$
[
***]

$
[
***]

 May 31, 2023

[
***]

$
[
***]

$
[
***]

 Except as described below under “Common Stock Valuation and Stock Issuance”, there were no other
equity incentive awards granted by the Company since June 1, 2022.

 April 29, 2022 Valuation – June 30, 2022, September 7,
2022, December 14, 2022 and March 2, 2023 Stock Option Grants

 From June 1, 2022 to March 2, 2023, the Company
granted stock options to purchase a total of [***] shares of Common Stock at an exercise price of $[***] per share. The Board determined the estimated fair value of the Common Stock at the time of each of the grants to be $[***] per share based on a
number of factors, including the April 29, 2022 Valuation.

 For the April 29, 2022 Valuation, the Company estimated the fair
value of the Common Stock by using the Hybrid Method, with the sale scenario using the OPM being weighted at [***]% and the IPO scenario using the OPM being weighted at [***]%.

The total equity values in the sale and IPO scenarios were estimated using the Subject Company Transaction Method of the Market Approach, and
specifically the backsolve method (the “Backsolve Method”) as of June 29, 2021, the date of the closing of the Series D preferred stock financing (the “Financing Date”), discussed below, and then
rolled forward to the valuation date for the April 29, 2022 Valuation to account for the changes in the market and values for comparable biotechnology companies between the Financing Date and the valuation date for the April 29, 2022
Valuation. In addition, the total equity values for each scenario were then adjusted for the changes in the Investigational New Drug (“IND”) probability between the Financing Date and the date of the April 29, 2022 Valuation.

For purposes of the April 29, 2022 Valuation, the Hybrid Method reflected the Company’s issuance and sale of 29,285,356 shares of
the Company’s Series D convertible preferred stock on the Financing Date (the “Series D Preferred Stock Financing”). Shares of the Company’s Series D convertible preferred stock were issued and sold at
a purchase price of $2.73174 per share. In determining the implied total equity value under the Backsolve Method, the Company used an estimated volatility of [***]% and an estimated time to liquidity of [***] years in the sale scenario and
volatility of [***]% and an estimated time to liquidity of [***] years in the IPO scenario, based on management’s best estimates of a liquidity event at such time.

 FOIA Confidential
Treatment Requested by Turnstone Biologics Corp.

 Cooley LLP    55 Hudson Yards    New York, NY
10001

 T:+1 212 479 6000    f:+1 212 479 6275    cooley.com

 U.S. Securities and Exchange Commission

June 21, 2023

 Page Six

 In the IPO scenario of the Hybrid Method, the Company’s total equity value as of the
valuation date for the April 29, 2022 Valuation was allocated to the Company’s equity securities within an OPM framework on an as-if-converted basis while also
considering the optionality of the Company’s stock options, assuming an IPO event would occur in [***] 2022. The Company believes that the nature of the scenarios used in the Hybrid Method and the scenario