SecProbe.io

May 8 , 2014

Via E -mail
Isaac E. Ciechanover, M.D.
Chief Executive Officer
Atara Biotherapeutics, Inc.
3260 Bayshore Boulevard
Brisbane, CA 94005

Re: Atara Biotherapeutics, Inc.
Draft Registration Statement on Form S -1
Confidentially Submitted April 10, 2014
  CIK No. 0001604464

Dear Dr. Ciechanover:

We have reviewed your 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.  I f 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.

General

1. We note that there are a number of additional exhibits that have yet  to be filed.  Please
provide these exhibits as promptly as possible.  Please note that we may have comments
on these materials once they are provided.

2. We note that you intend to request confidential treatment for portions of information
contained in your exhibits.  If you have not done so, please submit your application for
confidential treatment as soon as possible so that we may begin our review of your
request.  Any staff comments to your application will be sent separately from comments
to your draft registration statement.

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 2

 3. Please confirm that the graphics included in your registration statement are the only
graphics you will use in your prospe ctus.  If those are not the only graphics, please
provide any additional graphics prior to their use for our review.

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.   Similarly, please
suppleme ntally provide us with any research reports ab out you that are published or
distributed in reliance upon Section 2(a)(3) of the Securities Act of 1933 added by
Section 105(a) of the Jumpstart Our Business Startups Act by any broker or dealer that is
participating or will participate in your offering.

Prospectus Summary ,
Corporate Information, page 4

5. Please revise your disclosure in this section, in your risk factor on page 42 and on page
62 under the header “Emerging Growth Company S tatus”  to describe how and when a
company may lose such status.

6. We note your disclosure on page 63 which states that you are opting out of the extended
transition period for complying with new or revised accounting  standards pursuant to
Section 107(b) of the JOBS Act.  Please expand your di sclosure to  discuss your e lection
under Section 107(b) of the JOBS Act in this section as well.  Also, please expand your
disclosure in this section and on page 63 to include a st atement that the election is
irrevocable.

Risk Factors , page 10

7. Please add an appropriatel y titled risk factor discussing your ability to use your net
operating loss carryforwards.  In doing so, please quantify the amount of your net
operating loss carryforwards and provide similar  information to that  contained in the
section entitled “Income T axes” on page 60 of your registration statement.

Risks related to Our Intellectual Property
If we are unable to obtain and maintain sufficient intellectual property…, page 24

8. Please expand your risk f actor discussion to highlight the  current expect ed expiration date
for the patents underlying your most advanced product candidates, PINTA 745 and STM
434.

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 3

 Risks Related to the Commercialization of Our Product Candidates
If we and our third -party manufacturers fail to comply with environmental…, page 39

9. Please disclose here and elsewhere  in the risk factors where you address the company’s
liability risks and c orresponding insurance coverage  that you carry insurance coverage
with policy limits that are customary for similarly situated companies and adequate to
provide you with insurance c overage for foreseeable risks .

Special Note Regarding Forward -Looking Statements and Industry Data, page 48

10. Please note that it is not appropriate to state or imply that you do not have liability for the
statemen ts in your registration statement.  Your statement s on page 48 that you “have not
independently verified market and industry data from third -party sources ” and  that
“neither your research nor your market definitions have been verified by any independent
source” could imply that you are not taking liability for the statistical and other industry
and market data included in your registration statement.  In order to eliminate any
inference that you are not liable for all of the information in your registratio n statement,
please delete these statements or include a statement specifically acknowledging
responsibility for the accuracy of these statements  and potential  liability under the federal
securities laws .

Use of Pr oceeds, page 49

11. To the extent practicable, please disclose how far in the planned confirmatory Phase 2
and initial  Phase I clinical trial s of, respectively, PINTA 745 and STM 434, you estimate
the offering proceeds and existing cash resources will enable you to  reach.

Capitalization, page 52

12. Please tell us why the issuance of the 2,204,693 shares of Series B convertible preferred
stock in January 2014 and the subsequent con version into common stock immediately
prior to the closing of this offering is excluded from pro forma .

Management’s Discussion and Analysis of Financial Condition and Results of Operations
Critical Accounting Policies and Significant Judgments and Estim ates
Accrued Research and Development Expenses, page 58

13. Please revise your disclosure to clarify whether changes in estimates have been material
for each period presented, quantifying any material changes in estimate.

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 4

 Business , page 69

14. Where the following terms first appear in this section and the Prospectus Summary,
please  give the meaning and significance of such terms in plain language that may be
underst ood by a lay reader  not acquainted with the relevant industry or scientific field.

 statistical  significance ;
 murine surrogate;
 FDA breakthrough designation;
 upregulated;
 CKD;
 histological;  and
 ligand

15. Please specify the studies  to which you refer in the fifth paragraph on page 69 regarding
the beneficial properties demonstrated by PINTA 745.

Our Product Candidates, page 72

16. Please disclose, where applicable in your discussion of your product candidates in
devel opment, including PINTA 745 and STM 434, when INDs  were filed for the
commencement of clinical trials, the name of the trial sponsor and, with respect to
PINTA 745, whether any INDs remain open.  If an IND was not filed pertaining  to any of
your clinical t rials, please explain why the IND was not required.

Preclinical Studies, page 76

17. We note that your preclinical trials m ake reference to p -values in the charts provided and
results that were statistically significant.  Please explain what the term “p -value” refers to
and what it indicates about the statistical significance of res ults obtained from the trials.

PINTA 745 Phase 1 Clinical Studies – Safety and Tolerability, page 78

18. Please quantify what you mean by “decreased slightly” and “remained slightly lower”
when you state, “Of note, b ody fat decreased slightly in the 3.0 mg/kg group at the end of
the treatment period and remained slightly lower  than baseline four weeks after the
cessation of treatment.”

STM 434, a Targeted Therapy for Ovarian Cancer and Potentially other Solid Tumors
Preclinical Studies
TOV -21G Mouse Models (Clear Cell Ovarian Tumors), page 85

19. We note that in a subsequent preclinical study where  you evaluated STM 434/s in a
TOV -21G model used as both a single agent and in combination with the chemotherapy

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 5

 agent 5 -fluorouracil, results from these experiments showed a statistically significant
reduction i n tumor volume for the agent.  In addition t o the accompanying table , please
expand the narrative description of the study  to quantify the statistically significant
reduction in tumor volume .

Inhibin Knockout Mouse Model (Granulosa Cell Tumors), page 87

20. We note that that knockout model treated with STM 434/s showed a statistically
significant improvement in surv ival as compared to knockout mice treated with saline.
Please expand your disclosure to quantify the statistically sign ificant improvement in
survival and include p -values .

Pipeline, page 88

21. We note that you have five pipeline product candidates in the research stage, but that you
only provide a description of three of these programs.  Please expand your disclosure to
provide a description of your other two programs.

License Agreements, page  90

22. Please expand your disclosure to quantify the amount of shares of Series A -1 preferred
stock which you issued to Amgen  under all of your license agreements.  Also, please
disclose that each share of preferred stock will convert to one share of common stock
immediately prior to the completion  of this offering

23. Please quantify the amount of fees you have paid to Amgen to date for clinical supplies
under your lic ense agreement for PINTA 745 .

Intellectual Propert y
Patents, page 91

24. Please disclose the expected expiration dates for your U.S. patents separately from your
non-U.S. patents.

Employment Arrangements
Gad Soffer, page 111

25. Please clarify whether Mr. Soffer’s employment agreement e ntitles him to any
termination -based payments or benefits.

Lock -Up Agreements, page 129

26. Please confirm that the lock -up agreement will be filed as part of the underwriting
agreement.  If not, please file the form of lock -up agreement as an exhibit.

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 6

Notes to Combined Financial Statements
2. Summary of Significant Accounting Policies
Basis of Presentation, page F -7

27. Please provide us an analysis that supports presenting the financial statements on a
combined basis.   Please demonstrate how Atara, Nina, Pinta  and Santa Maria were under
common control or management and provide the ownership and management information
for each of the companies separately.   Clarify what management functions Atara
provided other than the payment of common expenses as disclosed in Note 1  and whether
Atara has provided or provides management functions to entities besides Nina, Pinta and
Santa Maria.

Stock -based compensation expense, page F -10

28. Please provide the disclosure regarding expected volatility required by ASC 718 -10-50-
2.f.2.ii.

29. We may have additional comments on your accounting for stock compensation or any
beneficial conversion features once you have disclosed an estimated offering price.
Please provide us with a quantitative and qualitative analysis explaining the dif ference
between the estimated offering price and the fair value of each equity issuance through
the date of effectiveness for the preceding twelve months .

9. Subsequent Events, page F -22

30. Please describe to us the acco unting you will ascribe to the R ecapi talization and provide
us an analysis to support that accounting  with reference to appropriate authoritative
literature .

31. Please tell us how earnings per share will  be calculated and presented in financial
statement periods that precede and include the rec apitalization  with reference to
appropriate authoritative literature .

32. Please explain how you calculated the number of share s of common stock after the
recapitalization of 1,693,687 since it does not appear to be calculated by using the
number of shares b efore the recapitalization of 16,443,185 exchanged on a nine -for-one
basis.

If you intend to respond to these comments with an amended draft registration statement,
please submit it and any associated correspondence in accordance with the guidance we pro vide
in the Division’s October 11, 2012 announcement on the SEC website at
http://www.sec.gov/divisions/corpfin/cfannouncements/drsfilingprocedures101512.htm.

Isaac E. Ciechanover, M.D.
Atara Biotherapeutics, Inc.
May 8 , 2014
Page 7

 Please keep in mind that we may publicly post filing review correspondence in
accordance with ou r December 1, 2011 policy
(http://www.sec.gov/divisions/corpfin/cfannouncements/edgarcorrespondence.htm).  If you
intend to use Rule 83 (17 CFR 200.83) to request confidential treatment of information in the
correspondence you submit on EDGAR, please prope rly mark that information in each of your
confidential submissions to us so we do not repeat or refer to that information in our comment
letters to you.

You may contact Vanessa Robertson at (202) 551 -3649  or James Rosenberg  at (202)
551-3679  if you have questions regarding comments on the financial statements and related
matters.  Please contact Johnny Gharib at (202) 551 -3170 , Daniel Greenspan at (202) 551 -3623
or me at (202) 551 -3715 with any other questions.

Sincerely,

 /s/ Daniel Greenspan for

Jeffrey P. Riedler
Assistant Director

cc: Via E -mail
 Jodie Bourdet , Esq.
 Cooley  LLP