Frequently Asked Questions — Developing Potential Cellular and Gene Therapy Products: Guidance for Industry

Administrative guidance, not enacted legislation. This captured publisher edition preserves the listed document and attachments; later developments are not independently consolidated.

Frequently Asked Questions —
Developing Potential Cellular and
Gene Therapy Products
Guidance for Industry
Additional copies of this guidance are available from the Office of Communication, Outreach
and Development (OCOD), Center for Biologics Evaluation and Research, Food and Drug
Administration or by calling 1-800-835-4709 or 240-402-8010, or email
industry.biologics@fda.hhs.gov, or from the Internet at https://www.fda.gov/vaccines-blood-
biologics/guidance-compliance-regulatory-information-biologics/biologics-guidances.
For questions on the content of this guidance, contact OCOD at the phone numbers or email
address listed above.
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Biologics Evaluation and Research
August 2026

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Table of Contents
I. 	INTRODUCTION............................................................................................................. 1
II. 	BACKGROUND ............................................................................................................... 1
III. 	SUBMISSIONS AND FDA REVIEW ............................................................................. 2
A. 	IND Submission and Quality ............................................................................... 2
Q1. 	What should sponsors know about electronic submission of an Investigational
New Drug application? ..................................................................................... 2
Q2. 	What is important for inclusion in an original IND submission? ..................... 4
Q3. 	What regulatory forms are included in original INDs and IND amendments? 8
Q4. 	What is the general process for evaluating original INDs for CGT
investigational products? .................................................................................. 9
Q5. 	What should sponsors know about submission tracking numbers for
applications submitted through the Electronic Submission Gateway? ........... 10
B. 	Meeting Types ..................................................................................................... 11
Q6. 	What are the differences between INTERACT and pre-IND meetings? ........ 11
Q7. 	How should sponsors prepare briefing packages for and request INTERACT
and pre-IND meetings? ................................................................................... 12
Q8. 	What is a Type D meeting and how do sponsors request one? ....................... 14
Q9. 	Does FDA recommend a pre-BLA meeting, and what should be included in
the briefing package if sponsors choose to request one? ................................ 15
C. 	IND Amendments................................................................................................ 16
Q10. 	What is FDA’s timeline for feedback on new or revised information submitted
to an active IND? ............................................................................................ 16
D. 	Expedited Programs ........................................................................................... 17
Q11. 	When does rolling review begin for qualifying BLAs and what is the timing of
module submission? ........................................................................................ 17
IV. 	PRODUCT DEVELOPMENT CONSIDERATIONS ................................................. 18
A. 	Donor Eligibility .................................................................................................. 18
Q12. 	What are some differences between autologous and allogeneic donor
eligibility considerations? ............................................................................... 18
B. 	Product Characterization ................................................................................... 19
Q13. 	What is the difference between product characterization testing and release
testing? ............................................................................................................ 19
C. 	Critical Quality Attributes ................................................................................. 21
Q14. 	What information should be submitted regarding critical quality attributes?. 21
D. 	Analytical Methods ............................................................................................. 22
Q15. 	How should analytical methods be shown to be fit for purpose for first-in-
human trials? ................................................................................................... 22
E. 	Process Characterization/Validation ................................................................ 23
Q16. 	At what scale should process characterization and validation be executed? .. 23
Q17. 	How many process performance qualification lots are recommended for
process validation? .......................................................................................... 23

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F. 	Manufacturing Changes ..................................................................................... 23
Q18. 	How should manufacturers evaluate comparability of pre- and post-change
products? ......................................................................................................... 23
G. 	Stability ................................................................................................................ 24
Q19. 	What stability information is needed to support first-in-human studies? ....... 24
H. 	Preparing for BLA .............................................................................................. 24
Q20. 	What CMC issues should sponsors consider as they prepare to submit a BLA?
......................................................................................................................... 24
V. 	CONDUCTING NONCLINICAL STUDIES ............................................................... 25
A. 	Selection of Animal Models/Species .................................................................. 25
Q21. 	What are FDA’s recommendations regarding adequate animal species
selection for certain nonclinical studies of cell and gene therapy products? .. 25
Q22. 	Does FDA have specific recommendations regarding selection of an animal
model for pharmacology studies for assessing the activity of CGT products?26
Q23. 	What approach should be taken if there is no available animal model of
disease in which the investigational product can be evaluated? ..................... 26
Q24. 	Can alternative test methods or new approach methodologies be used in place
of animal studies even if animal models exist? .............................................. 27
B. 	Product Selection for Nonclinical Studies......................................................... 27
Q25. 	What are important aspects to be considered when evaluating the similarity of
human and analogous animal CGT products? ................................................ 27
C. 	Tumorigenicity .................................................................................................... 28
Q26. 	What is the FDA’s recommendation regarding tumorigenicity studies before
the first use of CGT products in human subjects? .......................................... 28
D. 	Proof-of-Concept Studies ................................................................................... 28
Q27. 	Why are proof-of-concept data important for CGT products? Can FDA
provide details on how much and what type of proof-of-concept data are
appropriate prior to conducting a clinical trial? .............................................. 28
E. 	Toxicity................................................................................................................. 29
Q28. 	Can sponsors submit INDs without conducting nonclinical toxicology studies
for certain products? ....................................................................................... 29
Q29. 	For a single-dose administration investigational product, what are the
considerations for the duration of the pivotal toxicology study? .................... 29
F. 	Design of Cell Distribution/Biodistribution Studies ........................................ 30
Q30. 	Does FDA recommend certain testing methods for cell distribution or vector
biodistribution studies? ................................................................................... 30
G. 	Dose Levels .......................................................................................................... 31
Q31. 	What are the recommended methods for dose level extrapolation from animals
to humans? ...................................................................................................... 31
VI. 	CONDUCTING HUMAN TRIALS .............................................................................. 31
A. 	Trial Design ......................................................................................................... 31
Q32. 	What is important for sponsors to consider when designing clinical trials for
CGTs? ............................................................................................................. 31

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Q33. 	How many trials are required to demonstrate substantial evidence of
effectiveness of a CGT product, with the ultimate goal being FDA licensure?
......................................................................................................................... 33
B. 	Selecting Endpoints............................................................................................. 34
Q34. 	What should sponsors consider when using a surrogate endpoint as a primary
outcome measure for a later phase clinical trial intended to support approval
of a CGT product? .......................................................................................... 34
C. 	Safety Data ........................................................................................................... 35
Q35. 	What should sponsors consider for short- and long-term safety monitoring in
trials of investigational CGT products? .......................................................... 35
Q36. 	When investigating gene therapies in Phase 1 trials, should only safety be
tested, or should efficacy endpoints also be incorporated?............................. 37
VII. 	REFERENCES................................................................................................................ 38

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Frequently Asked Questions — Developing Potential Cellular and
Gene Therapy Products1
Guidance for Industry
This represents the current thinking of the Food and Drug Administration (FDA or Agency) on
this topic. It does not establish any rights for any person and is not binding on FDA or the
public. You can use an alternative approach if it satisfies the requirements of the applicable
statutes and regulations. To discuss an alternative approach, contact the FDA staff responsible
for this guidance as listed on the title page.
I. 	INTRODUCTION
This guidance is intended to provide industry with answers to frequently asked questions (FAQs)
and commonly faced issues that arise during the development of cellular and gene therapy (CGT)
products and is intended to help facilitate the development of safe, effective, and high-quality
CGT products. The FAQs represent common questions directed to the Agency and span
multiple disciplines, including regulatory review, chemistry, manufacturing, and controls
(CMC), pharmacology/toxicology (PT), clinical, and clinical pharmacology.
In general, FDA’s guidance documents, including this guidance, do not establish legally
enforceable responsibilities. Instead, guidances describe the FDA’s current thinking on a topic
and should be viewed only as recommendations, unless specific regulatory or statutory
requirements are cited. The use of the word should in FDA’s guidances means that something is
suggested or recommended, but not required.
II. 	BACKGROUND
On September 30, 2022, the FDA User Fee Reauthorization Act of 2022 was signed into law.
The Act includes the sixth reauthorization of the Prescription Drug User Fee Act (PDUFA),
PDUFA VII: Fiscal Years 2023 – 2027 FDA,2 which provides FDA with resources to help
maintain a predictable and efficient review process for human drug and biological products.
This guidance was created as part of FDA’s response to the PDUFA VII commitment to increase
efficiency in the development of CGT products. CGT-related research and development in the
United States continues to grow at a fast rate, with a number of products already approved and
many more advancing in clinical development. This guidance is intended to support the
1 This guidance has been prepared by the Office of Therapeutic Products in the Center for Biologics Evaluation and
Research at the Food and Drug Administration.
2 See www.fda.gov/industry/prescription-drug-user-fee-amendments/pdufa-vii-fiscal-years-2023-2027.

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development of CGT products by providing a repository of common questions posed to the
Office of Therapeutic Products (OTP) in the Center for Biologics Evaluation and Research
(CBER) by sponsors and other key stakeholders. To develop this guidance, the Agency
compiled FAQs received from a variety of sources, including FDA interactions with sponsors in
development programs, questions received following public presentations by FDA staff,
questions received from public stakeholders via CBER’s Industry.Biologics@fda.hhs.gov email
address, and OTP’s virtual events series. For example, OTP hosted a series of virtual town hall
meetings in a question-and-answer format to engage with product development stakeholders and
discuss topics related to OTP-regulated products with the goal of providing regulatory
information to advance drug development.3 As such, the guidance covers relevant, current, and
timely topics related to the development of CGT products. FDA may update this guidance in the
future to include additional FAQs as appropriate. Sponsors are encouraged to visit the Cellular
& Gene Therapy Guidances webpage on the FDA website for a full list of finalized as well as
draft guidances relevant to the development of CGT products.4
III. 	SUBMISSIONS AND FDA REVIEW5
A. 	IND Submission and Quality
Q1. 	What should sponsors know about electronic submission of an
Investigational New Drug application?
Sponsors of Investigational New Drug applications (IND), other than
noncommercial INDs, are generally required to submit an IND through FDA’s
Electronic Submission Gateway (ESG) in electronic common technical document
(eCTD) format, whereas the eCTD format is optional for sponsors of
noncommercial INDs (also commonly referred to as research INDs).6 FDA’s
document titled “Instructions for Filling Out Form FDA 1571” discusses when
“Research” versus “Commercial” should be selected, which correlates to when
eCTD requirements apply for an IND application.7
A commercial IND is generally one for which the sponsor (usually a corporate
entity) intends to commercialize the product by eventually submitting a marketing
3 FDA town hall meetings can be found at https://www.fda.gov/news-events/otp-events-meetings-and-workshops.
4 A list of relevant guidances can be found at https://www.fda.gov/vaccines-blood-biologics/biologics-
guidances/cellular-gene-therapy-guidances.
5 For additional information, see Interactions with Office of Therapeutic Products | FDA.
6 See section 745A of the FD&C Act and FDA Guidance, Providing Regulatory Submissions in Electronic Format –
Certain Human Pharmaceutical Product Applications and Related Submissions Using the eCTD Specifications
(Feb. 2020) (“Submissions in Electronic Format Guidance”) at 2. Section 745A(a)(2) of the FD&C Act allows FDA
to establish exemptions from the electronic submission requirements; FDA has established limited exemptions,
including for submissions to noncommercial INDs. https://www.fda.gov/media/156718/download?attachment.
7 See FDA, Instructions for Filling out Form 1571available at https://www.fda.gov/media/77596/download. The
instructions describe how certain INDs, including expanded access INDs and protocols, should be marked as
“Research” and are exempt from eCTD requirements.

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application. In this case, the sponsor should select “Commercial IND” on FDA
Form 1571 Field 7B. FDA may also designate an IND as commercial if it is clear
that the sponsor intends for the product to be commercialized at a later date.
In comparison, a noncommercial IND is an IND for a product that is not intended
for commercial distribution and includes research and investigator-sponsored
INDs.8 The sponsor of a noncommercial IND may generally be an individual
investigator, academic institution, or non-profit entity. The studies proposed in
these INDs are generally for research, and may result in publications in peer-
reviewed journals.
One difference between the submission of a commercial versus a noncommercial
IND is that commercial INDs must be submitted consistent with the eCTD
requirements under section 745A(a)(2) of the FD&C Act, whereas
noncommercial INDs are encouraged but not required to be submitted in eCTD
format.9 However, when a sponsor of a research IND submits either a Phase 2 or
Phase 3 clinical protocol, the sponsor should select “Commercial” or otherwise
submit a justification, along with a protocol, explaining why their Phase 2 or
Phase 3 protocol is still solely for research. If the Phase 2 or Phase 3 IND is not
considered to be a noncommercial IND, eCTD requirements would apply.10
FDA recommends that noncommercial IND sponsors submit their applications in
common technical document (CTD) format previously described in FDA’s
guidance entitled “M4 Organization of the Common Technical Document for the
Registration of Pharmaceuticals for Human Use: Guidance for Industry,” October
2017, [Ref. 1] if they cannot submit their application in eCTD format. In the
CTD format, each module should be submitted as a separate PDF file, named
after the CTD module name or number, with a dedicated table of contents with
hyperlinks to content as noted in FDA’s guidance entitled “Providing Regulatory
Submissions in Electronic Format — Certain Human Pharmaceutical Product
Applications and Related Submissions Using the eCTD Specifications: Guidance
for Industry,” February 2020 [Ref. 2] (hereinafter referred to as “Submissions in
Electronic Format Guidance”). Also see “SOPP 8110: Submission of Regulatory
Applications – Exempt from eCTD Requirements,” [Ref. 3].
8 See Submissions in Electronic Format Guidance, at 2.
9 See section 745A(a)(2) of the FD&C Act and Submissions in Electronic Format Guidance, at 2.
10 See section 745A(a)(2) of the FD&C Act and Submissions in Electronic Format Guidance, at 2.

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Q2. 	What must be included in an original IND submission?11
In addition to the required12 Form FDA 1571,13 a cover letter should be included.
The cover letter can be addressed to OTP without a specific name. The letter
should identify in bold font that the submission is an original IND application and
should provide a brief explanation of the study, product name (company monikers
(e.g., PMN 201, BS648, S103A26) are discouraged), brief product description,
and mode of action. The title of the protocol and the proposed indication should
also be included. We highly encourage sponsors to include a list of all authorized
contacts for the IND if individuals other than authorized representatives (those
identified in Form FDA 1571) are allowed to communicate with the FDA
regarding the IND. If an INitial Targeted Engagement for Regulatory Advice on
CBER/CDER ProducTs (INTERACT) and/or a pre-IND meeting was held prior
to IND submission, then that/those meeting(s) should be referenced in the cover
letter.
For INDs cross-referencing other INDs or information submitted in other
applications, sponsors must include a Letter of Authorization (LOA) from the
sponsor of the cross-referenced IND or file (e.g., Master File (MF)) in the IND
submission.14 This gives FDA permission to review the relevant information for
the new IND. In the LOA, sponsors or MF holders allowing cross-reference must
describe the incorporated material by name; reference number (e.g., IND, MF, or
other number (e.g., Biologics License Application (BLA)); and location and
nature of the information authorized for cross reference.15 The LOA should also
include information such as the name of sponsor being authorized; reference
number incorporating the information; and name or description of the product
using the supportive information, when available. The LOA should also be
submitted as an amendment to the originating IND or MF.
Please note that both active and inactive files may be cross-referenced, but
sponsors must always cross-reference the original source of information.16 This
means that if a sponsor chooses to cross-reference an IND where the information
being referenced is located in another submission, the sponsor must include LOAs
11 See 21 CFR 312.23. See also SOPP 8217: Administrative Processing and Review Management Procedures for
Investigational New Drug Applications, available at https://www.fda.gov/media/156718/download?attachment, at 5.
12 See FDA guidance, Frequently Asked Questions – Statement of Investigator (Form FDA 1572), question 6:
"Although the sponsor is required to collect the 1572 from the investigator, FDA does not require the form to be
submitted to the agency. Many sponsors submit the 1572 to FDA, however, because it collects, in one place,
information about the investigators that must be submitted to FDA under 21 CFR 312.23(a)(6)(iii)(b)."
13 See 21 CFR 312.23(a)(1) (stating that “A reference to information submitted to the agency by a person other than
the sponsor is required to contain a written statement that authorizes the reference and that is signed by the person
who submitted the information.”)
14 See 21 CFR 312.23(b).
15 See 21 CFR 312.23(b).
16 See 21 CFR 312.23(b).

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from both the cross-referenced IND and the IND or MF containing the original
source of information.17
Other information required in IND submissions18 includes: a general
investigational plan; Investigator’s Brochure (IB) for sponsors other than sponsor-
investigators; investigational drug labeling; and environmental assessment or a
claim of categorical exclusion.19 If applicable, IND submissions should also
include cross-reference to previously submitted information from the same
sponsor and previous correspondence (e.g., relevant pre-IND or INTERACT
meeting correspondences).
Please also note that the IND submission must be in the English language.20 Per
21 CFR 312.23(c), a sponsor must submit an accurate and complete English
translation of each part of the IND that is not in English. The sponsor must also
submit a copy of each original literature publication for which an English
translation is submitted.21
For additional considerations related to information to include in original IND
submissions, refer to Submissions in Electronic Format Guidance [Ref. 2] and
INDs by Sponsor-Investigators Guidance [Ref. 4].
CMC
Please include detailed, complete information on drug substance (DS) and drug
product (DP) manufacture and testing in Module 3 of the IND, as referenced in
FDA’s guidance entitled “M4Q: The CTD — Quality: Guidance for Industry,”
August 2001 [Ref. 6]. The amount and type of CMC information required to
support the clinical study outlined in the IND may vary depending on the phase of
the study.22 Instructions on how to receive, handle, prepare, and administer the
investigational product at the clinical site (e.g. Pharmacy Manual, Instructions for
Use, Investigator's Brochure) should be provided in Module 5 and hyperlinked to
the quality section in Module 2 of the IND.
For additional information on CMC information in INDs for CGTs, refer to
FDA’s guidances “Chemistry, Manufacturing, and Control (CMC) Information
for Human Gene Therapy Investigational New Drug Applications (INDs):
Guidance for Industry,” January 2020 [Ref. 7] (hereinafter referred to as “CMC
GT INDs Guidance”) and “Content and Review of Chemistry, Manufacturing,
and Control (CMC) Information for Human Somatic Cell Therapy Investigational
17 See 21 CFR 312.23(b).
18 See 21 CFR 312.23. See also SOPP 8217: Administrative Processing and Review Management Procedures for
Investigational New Drug Applications, available at https://www.fda.gov/media/156718/download?attachment at 5.
19 21 CFR 312.23.
20 See 21 CFR 312.23(c).
21 See 21 CFR 312.23(c).
22 See also 21 CFR 312.23(a)(7).

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New Drug Applications (INDs): Guidance for Industry,” April 2008 (hereinafter
referred to as “CMC CT INDs Guidance”) [Ref. 8]. Additional product-specific
resources for CGT CMC are located on the CGT guidances website.23
Pharmacology/Toxicology
Please include PT information in Module 4, and summaries in Modules 2.4 and
2.6, as applicable. PT studies of the CGT product involving laboratory animals or
in vitro studies must provide a scientific basis to ensure reasonable safety of the
product in the proposed clinical investigation.24 The kind, duration, and scope of
animal and other tests required varies with the duration and nature of the proposed
clinical investigations.25 Animal studies in a relevant animal species and model
of disease/injury should mimic the proposed clinical trial design as closely as
possible, including route of administration (ROA). Studies should be performed
using the final clinical product, to the extent feasible, or you should provide a
comparison of the final clinical product to the product used in the nonclinical
studies. For each nonclinical toxicology study subject to Good Laboratory
Practice (GLP) regulations, a statement that the study was conducted in
compliance with GLP must be submitted; otherwise, if the study was not
conducted in compliance with GLP, a brief statement of the reason for
noncompliance must be submitted.26 If technical limitations do not allow for GLP
compliance, it is acceptable to perform the study as a non-GLP study with Quality
Assurance (QA) oversight, following GLP practices, to the extent feasible. The
QA unit/personnel must be independent of the personnel responsible for
conducting the study to ensure quality and integrity of the data. 27
Data from nonclinical studies should support all elements of the clinical study
design. Rationale and supporting information for each animal model, test system,
and calculation for dose-level extrapolation from animal to human should be
submitted. For applicable nonclinical studies initiated after March 15, 2023,
standardized datasets in the Standard for the Exchange of Nonclinical Data
(SEND) format are required as discussed in FDA’s guidance “Study Data
Technical Conformance Guide [Ref. 9].”
Nonclinical data should be submitted to support starting dose level, dose regimen,
and ROA. Additionally, information should be provided on nonclinical product
lots, animal model/species selection, rationale for nonclinical study designs, and
safety and activity information.
23 https://www.fda.gov/vaccines-blood-biologics/biologics-guidances/cellular-gene-therapy-guidances.
24 See 21 CFR 312.23(a)(8).
25 See 21 CFR 312.23(a)(8).
26 See 21 CFR 312.23(a)(8)(iii).
27 See 21 CFR 58.35

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An IB must be included in the IND if the sponsor is not a sponsor-investigator.28
The IB must include a brief description of the DS and formulation, as well as the
following information:29
(1) A summary of the PT effects of the product in animals and humans, if
known
(2) A summary of pharmacokinetics and biological disposition, and/or
pharmacodynamics in animals and humans, where applicable
(3) A summary of information relating to safety and effectiveness in humans
obtained from prior studies.
For additional information regarding PT for CGT products, refer to FDA’s
guidance “Preclinical Assessment of Investigational Cellular and Gene Therapy
Products: Guidance for Industry,” November 2013 (hereinafter referred to as
“Preclinical Assessment CGT Guidance”) [Ref. 10].
Clinical
Please include clinical information in Module 5. Sponsors must provide a brief
summary of previous human experience with the investigational product,
including referencing prior clinical investigations and marketing history outside
the United States, if relevant.30 A complete protocol for each planned study must
be submitted and must include:31
(1) Study objectives and design
(2) Appropriate inclusion/exclusion criteria
(3) Product administration and dosing plan
(4) Observations and measurements made to fulfill the objectives of the study
(5) Monitoring plan
For Phase 2 and Phase 3 protocols, the study design should be adequate to
evaluate both safety and efficacy.
The protocol submission should also include a statistical analyses plan. The
requirements regarding the content of the protocol submission will depend on the
stage of product development.32
28 See 21 CFR 312.23(a)(5); 21 CFR 312.55.
29 See 21 CFR 312.23(a)(5).
30 See 21 CFR 312.23(a)(3)(ii).
31 See 21 CFR 312.23(a)(6).
32 See 21 CFR 312.23(a)(6)(i)-(ii).

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Q3. 	What regulatory forms are included in original INDs and IND
amendments?33
Form FDA 1571 is required for a sponsor submitting an IND submission.34 This
form contains a sponsor’s commitment to conduct the investigation in accordance
with all applicable regulatory requirements and must be signed by the sponsor or
authorized representative.35 Please note that for sponsors who do not reside or
have a place of business within in the United States, the IND is required to
contain an additional signature from an attorney, agent, or authorized official who
resides or maintains a place of business in the U.S.36 Form 1571 also provides an
overview of the contents of the submission and is used by CBER’s document
control center staff and regulatory project managers (RPMs) to route submissions
to the appropriate office and review team.
Please include administrative documents, such as Form FDA 1571, as well as
cover letters, reviewer guides, cross-reference authorization letters, claims of
categorical exclusion, and labeling information, in Module 1 of the CTD
submissions. The cover letter for the sponsor’s submission should include a brief
explanation of the submission and its contents. When amendments are submitted
to the IND for manufacturing changes, the cover letter should clearly describe the
purpose of the amendment and highlight proposed changes. For IND
amendments containing numerous or significant changes (e.g., manufacturing
process, assays for critical quality attributes (CQAs), new manufacturing site, or
manufacturer, etc.), the Agency recommends that the sponsor include a
“Reviewer’s Guide,” as described in FDA’s eCTD Technical Conformance
Guide: Technical Specifications Document,37 or a document with all changes
tracked, and that the sponsor allows sufficient lead time (e.g., 30 days) for FDA
review before release of a new lot of clinical trial material as discussed in the
CMC GT INDs Guidance [Ref. 7]. A signed copy of Form FDA 3674,38 which
contains a certification that the sponsor has complied with the requirements
related to clinical trial registration under section 402(j) of the Public Health
Service Act (PHS Act), to the extent applicable, must be submitted and contain
the appropriate National Clinical Trial control numbers.39
33 See FDA Information Sheet Guidance for Sponsors, Clinical Investigators, and IRBs: Frequently Asked Questions
– Statement of Investigator (Form FDA 1572) May 2010, for additional information regarding Form 1572, at 11.
34 See 21 CFR 312.23(a)(1).
35 See 21 CFR 312.23(a)(1).
36 See 21 CFR 312.23(a)(1)(ix).
37 eCTD Technical Conformance Guide: Technical Specifications Document, December 2019.
https://www.fda.gov/media/93818/download.
38 Title VIII of the Food and Drug Administration Amendments Act of 2007 (FDAAA). See also Form FDA 3674,
available at https://www.fda.gov/media/134964/download, and FDA guidance, Form FDA 3674 – Certifications To
Accompany Drug, Biological Product, and Device Applications/Submissions (June 2017), available at
https://www.fda.gov/regulatory-information/search-fda-guidance-documents/form-fda-3674-certifications-
accompany-drug-biological-product-and-device-applicationssubmissions.
39 Section 402(j)(5)(B) of the PHS Act.

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Q4. 	What is the general process for evaluating original INDs for CGT
investigational products?40
Stage 1 of the 30-day IND review process begins when FDA receives the IND.
The document control center processes the submission and sends a submission
notice to OTP who then confirms the submission is in the correct office. An RPM
is then assigned to the IND and performs an administrative review to ensure the
submission appears to be complete. The RPM then verifies that the sponsor’s
authorized representative has a secure email and emails an acknowledgement
letter to the authorized representative.41
IND review Stage 2 includes assigning reviewers from each discipline, including
CMC, PT, and clinical. Additional experts are assigned as needed (e.g.,
biostatistics, bioinformatics, clinical outcome assessment). This stage is also
known as the IND interactive review period and includes safety reviews
conducted by discipline reviewers. Consults are requested as needed, which can
be internal (within CBER) or external to CBER (e.g., Center for Drug Evaluation
and Research (CDER), Center for Devices and Radiological Health (CDRH),
etc.). If the review team or a specific discipline identifies missing information or
requires clarification of any information in the IND, the RPM emails information
requests to the sponsor and may also request informal meetings.
In Stage 3, INDs are generally determined as safe to proceed or placed on clinical
hold. Internal meetings may be held to discuss these decisions, and discipline
supervisors review and concur on the IND decision. The RPM then notifies the
authorized contact whether the IND is deemed safe to proceed or FDA places an
IND on clinical hold by issuing an order to the sponsor via phone call, voicemail,
or email. An IND goes into effect 30 calendar days after FDA receives the IND,
unless FDA notifies the sponsor that the trials described in the IND are subject to
a clinical hold, or on earlier notification by FDA that the trials may proceed.42
If an IND is placed on clinical hold43, the RPM informs the sponsor via phone
call, voicemail, or email. After this notification, the review team provides
specific comments for the clinical hold letter, which will explain the basis for the
hold44, such as the specific deficiencies causing the IND to be placed on clinical
40 Further information can be found in the webcast “Original IND Applications — Behind the Scenes,”
https://fda.yorkcast.com/webcast/Play/0fb4cbfbbcaa4746917bdc836b2372cd1D. See also SOPP 8217:
Administrative Processing and Review Management Procedures for Investigational New Drug Applications,
available at https://www.fda.gov/media/156718/download?attachment.
41 For a description of how CBER uses email for regulatory communications, see SOPP 8119: Use of Email for
Regulatory Communications, available at https://www.fda.gov/media/108992/download
42 21 CFR 312.40(b).
43 21 CFR 312.42. See also SOPP 8201: Administrative Processing of Clinical Holds for Investigational New Drug
Applications, available at https://www.fda.gov/media/88774/download.
44 21 CFR 312.42(d).

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hold and what actions the sponsor needs to take to remove the hold. The
comments are sent for supervisory review and concurrence, with internal
meetings held as necessary. The RPM sends a letter to the authorized
representative within 30 days of the hold decision date.45
On the other hand, if an IND is safe to proceed, the RPM typically sends an email
communicating that information, which can be used by sponsors as official
correspondence that might be needed by other entities, such as Institutional
Review Boards (IRBs). Non-hold comments are sent in a separate
communication. CBER does not send letters to sponsors when INDs are allowed
to proceed.
Q5. 	What should sponsors know about submission tracking numbers for
applications submitted through the Electronic Submission Gateway?
Sponsors of applications subject to the electronic submission requirements of
section 745A(a) of the FD&C Act must submit their applications in eCTD format,
in the electronic format required under the statute.46 Most submissions are sent
electronically through FDA’s ESG, which is an Agency-wide solution for
accepting electronic regulatory submissions. The FDA ESG enables the secure
submission of premarket and postmarket regulatory information for review and is
the central transmission point for sending information electronically to the FDA.
A tracking number is pre-assigned by CBER prior to receiving an eCTD-
submitted original submission (e.g., IND or BLA) to automate receipt and
processing of the submission. The tracking number is included within the
electronic submission’s XML backbone and on FDA’s fillable-PDF version of
Form FDA 356h or Form FDA 1571 for electronic BLAs and electronic IND
submissions. When requested, CBER will issue the tracking number to a
sponsor/applicant no earlier than 8 weeks in advance of the target receipt date for
the electronic submission. When a sponsor/applicant requests a pre-submission
(PS) number for an INTERACT or pre-IND meeting, or for a Type D meeting
with no associated IND, CBER’s Regulatory Information Branch (RIB) within the
Division of Informatics, Office of Regulatory Operations, should provide the
number within 2 business days of the request.
Sponsor/applicant requests for preassigned numbers should be made by email to
cberrib@fda.hhs.gov. The request should include the sponsor/applicant name and
address; primary point of contact name and phone number; the biological product
name (company monikers (e.g., PMN 201, BS648, S103A26 are discouraged))
and indication; and the anticipated submission date.
45 21 CFR 312.42(d).
46 See section 745A(a) of the FD&C Act and the Submissions in Electronic Format Guidance.

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Sponsors should include the tracking number on:
(1) The cover page of the submission
(2) The XML backbone for a submission in the eCTD format
(3) The PDF Form FDA 356h or Form FDA 1571
(4) All future correspondence and submissions
Please note that in CBER, PS numbers (for a pre-IND meeting) and IND numbers
(for an IND submission) are separate. Sponsors who are preparing their IND
submission should not reuse their PS number but should request an IND number
by contacting the RIB at cberrib@fda.hhs.gov. More information about PS
numbers can be found in FDA’s “SOPP 8117: Issuing Tracking Numbers in
Advance of Electronic Submissions in eCTD Format,” (hereinafter referred to as
“SOPP 8117”) [Ref. 12].
B. 	Meeting Types47
Q6. 	What are the differences between INTERACT and pre-IND
meetings?
INTERACT is a meeting at a specific time early in product development. This
meeting type is intended for novel products and development programs that
present unique challenges in early development. The appropriate timing for an
INTERACT meeting generally should be when a sponsor has identified the
investigational product to be evaluated in a clinical study and conducted some
preliminary preclinical proof-of-concept (POC) studies with the intended
investigational product but has not yet designed and conducted definitive
nonclinical studies.
Considerations for whether the status of product development is premature or too
advanced for an INTERACT meeting for CGTs are discussed on FDA’s
webpage.48 For additional details on a development program’s qualification for
INTERACT, how to request an INTERACT meeting, and where to send the
meeting request, see FDA’s “SOPP 8101: Regulatory Meetings with Sponsors
and Applicants for Drugs and Biological Products,” (hereinafter referred to as
“SOPP 8101”) [Ref. 13].49 Additionally, sponsors may email meeting requests to
cberdcc_emailsub@fda.hhs.gov, with OTPRPMS@fda.hhs.gov in the cc line for
Regulatory Management Staff awareness.
The primary purpose of a pre-IND meeting is for sponsors to receive feedback on
their product development program before submitting an IND. A pre-IND
meeting is an opportunity to obtain feedback on the design of nonclinical studies,
the design of the initial clinical study, and product manufacturing and quality
47 For additional information see Interactions with Office of Therapeutic Products | FDA.
48 See https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/otp-interact-meeting.
49 See https://www.fda.gov/media/84040/download.

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controls needed to initiate human studies. The meeting may also provide an
opportunity to discuss the plans for studying the product in pediatric populations,
strategize the target product profile, identify the design and results of any natural
history studies, and discuss the best approach for presentation and formatting of
data in the IND, among other possible relevant topics.
Examples of when a pre-IND meeting would be appropriate include when:
(1) The sponsor has defined the manufacturing process to be used for the
clinical studies and has developed assays and preliminary lot-release
criteria
(2) The sponsor has completed POC and possibly some preliminary
nonclinical safety/toxicology studies and desires to move to the definitive
toxicology studies
(3) The sponsor’s questions involve IND-enabling CMC, PT, and/or clinical
trial design issues
For additional information on meeting types and procedures, refer to FDA’s draft
guidance “Formal Meetings Between the FDA and Sponsors or Applicants of
PDUFA Products: Draft Guidance for Industry,” September 2023 (hereinafter
referred to as “PDUFA Formal Meetings Draft Guidance”) [Ref. 14].50
Q7. 	How should sponsors prepare briefing packages for and request
INTERACT and pre-IND meetings?
INTERACT
INTERACT meeting requests and briefing packages should be submitted through
FDA’s ESG or by email to cberdcc_emailsub@fda.hhs.gov.
OTP does not send an acknowledgement email or letter following receipt of the
request. If the meeting request is granted, OTP intends to send confirmation of
the meeting within 21 days and schedule the meeting within 75 days of FDA
receipt of the request. INTERACT meetings are typically scheduled as
teleconferences. Similarly, OTP intends to communicate meeting denials within
21 days with a rationale for denial.
INTERACT briefing packages should be submitted with the meeting request and
not exceed 50 pages in length (excluding appendices). The package should
include the summary information pertinent to the product, relevant questions the
sponsor needs advice on,51 and sufficient background for the questions included
50 When final, this guidance will represent FDA’s current thinking on this topic. See
https://www.fda.gov/media/172311/download.
51 For more information regarding CMC, pharmacology/toxicology, and clinical information in an INTERACT
briefing package, see https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/otp-interact-
meeting.

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in the package. The package should contain a high-level description of the
manufacturing process, characterization, and proposed lot release for CMC. For
the nonclinical section, sponsors should include detailed summaries of animal
studies conducted with the investigational product and discussions on any
additional planned POC studies, including protocol outlines for the intended
patient population. Clinical sections should include a description of the proposed
indication, target patient population, available treatments, summary of natural
history data, and a brief outline of the first-in-human (FIH) study protocol.
Additional information about an INTERACT meeting can be found in SOPP 8101
[Ref. 13].52
A pre-assigned PS number is not required for an INTERACT meeting request. If
you do not have a pre-assigned PS number, one will be automatically assigned to
you upon submission of your INTERACT meeting request. Additional
information on requesting a PS number or submission tracking numbers for
electronic INDs can be found in SOPP 8117 [Ref. 12].
Pre-IND
Pre-IND meeting requests and briefing packages should be submitted through
FDA’s ESG or by email to cberdcc_emailsub@fda.hhs.gov.53, 54 The meeting
request should include a list of specific meeting objectives and draft questions
grouped by disciplines (e.g., CMC, PT, etc.).
OTP does not send an acknowledgement email or letter following receipt of the
pre-IND meeting request. If the meeting request is granted, the RPM intends to
send confirmation of the meeting within 21 days and schedule the meeting within
60 days of FDA receipt of the request. Similarly, meeting denials are also
communicated within 21 days with a rationale for denial.
Please note pre-IND meeting requests should not be submitted under an IND
number. All pre-IND meeting requests should be submitted under a PS number.
Sponsors who want a pre-assigned PS number should contact the RIB at
cberrib@fda.hhs.gov. Additional information on requesting a PS number or
submission tracking numbers for electronic INDs can be found in SOPP 8117
[Ref. 12].
Pre-IND briefing packages should be submitted no later than 30 days before the
scheduled date of the pre-IND meeting or written response only. Pre-IND
briefing packages are typically 50 to 100 pages in length (excluding appendices)
52 See https://www.fda.gov/media/84040/download.
53 Cited email addresses are current as of publication of this draft guidance. Please see FDA website below for up-
to-date information.
54 For additional ways to submit to CBER, please see https://www.fda.gov/about-fda/center-biologics-evaluation-
and-research-cber/regulatory-submissions-electronic-and-paper-format-cber-regulated-products.

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and should include a maximum of 10 targeted questions (inclusive of sub-
questions) that directly address concerns about the product development
programs.55 A cover letter should be included in the briefing package with the
inclusion of the assigned PS number.
For additional information on meeting types and procedures, refer to the PDUFA
Formal Meetings Draft Guidance [Ref. 14].
Q8. 	What is a Type D meeting and how do sponsors request one?
A Type D meeting is a meeting focused on a narrow set of issues (limited to no
more than two focused topics) and should not require input from more than three
disciplines or divisions. Type D meetings should be requested at critical junctures
of development where decisions regarding critical questions for the development
program are needed.
Consistent with the PDUFA Formal Meetings Draft Guidance [Ref. 14], examples
of when a Type D meeting would be appropriate include:
(1) A follow-up question that raises a new issue after a formal meeting (i.e.,
more than just a clarifying question about an FDA response from a prior
meeting)
(2) A narrow issue on which the sponsor is seeking Agency input with only a
few (e.g., three to five total) associated questions
(3) A general question about an innovative development approach that does
not require extensive, detailed advice
Type D meeting requests and accompanying briefing packages should be
submitted through FDA’s ESG or by email to cberdcc_emailsub@fda.hhs.gov. If
the meeting request is granted, OTP intends to send confirmation of the meeting
within 14 days and schedule the meeting within 50 days of FDA receipt of the
request.
In the briefing package, sponsors should include summary information pertinent
to the product or issue, with an adequate background section for the questions
posed in the package, and a list of questions (limited to no more than three to five
questions including sub-questions regarding the one to two focused topics).
Type D meetings may be converted to Type B or C meetings if the scope of the
meeting is broad or includes complex questions or issues that require input from
more than three disciplines or divisions. FDA will inform the sponsor that the
Agency will be converting the Type D meeting to the appropriate meeting type,
55 For additional information, please see the webpage “Interactions with Office of Therapeutic Products” at
https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/interactions-office-therapeutic-
products.

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and the sponsor can withdraw their initial request or accept the FDA’s meeting
conversion without submitting a new request.
Q9. 	Does FDA recommend a pre-BLA meeting, and what should be
included in the briefing package if sponsors choose to request one?
In an effort to mitigate review delays, the Agency strongly recommends sponsors
schedule a pre-BLA meeting with their review team in OTP to help ensure all
information, data, and analyses necessary to support review are included in the
BLA submission. FDA has found that delays associated with the initial review of
a marketing application may be reduced by exchange of information about a
proposed marketing application.56 The primary purpose of this kind of exchange
is to uncover any major unresolved problems; identify those studies that the
sponsor is relying on as adequate and well-controlled to establish the product’s
effectiveness; identify the status of ongoing or needed studies to assess pediatric
safety and effectiveness; acquaint FDA reviewers with the general information to
be submitted in the marketing application (topline study results and technical
information should be included in the pre-BLA briefing document); discuss
appropriate methods for statistical analysis of the data; discuss the best approach
for presenting and formatting data in the marketing application; and discuss
inspection and facility related information.57, 58
Only one 60-minute pre-BLA meeting will typically be granted for a specific
product or indication planned for the submission of an original marketing
application. Pre-BLA meetings should be multi-disciplinary; discipline-specific
CMC or clinical pre-BLA meetings will generally not be granted.
Meeting Request
The sponsor should submit the meeting request as an amendment to the existing
IND. The meeting request should include a list of the specific objectives of the
meeting and a list of questions grouped by discipline. The meeting request should
include adequate information for the FDA to assess the potential utility of the
meeting and to identify FDA staff necessary to discuss proposed agenda items.
The meeting request should be submitted at least 4 months before the anticipated
BLA submission. Upon receipt of the request, OTP will determine if the request
is appropriate for a pre-BLA meeting (i.e., if the sponsor is ready for a pre-BLA
meeting) as described in more detail in the PDUFA Formal Meetings Draft
Guidance [Ref. 14]. If the meeting request is granted, the RPM intends to send
confirmation of the meeting within 21 days and schedule the meeting within 60
56 21 CFR 312.47(b)(2).
57 See 21 CFR 312.47(b)(2).
58 Also see https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/otp-pre-bla-meetings (for
more information about pre-BLA meetings).

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days of FDA receipt of the request. Confirmation will include meeting date, time,
and briefing package due date. If the meeting is denied, a rationale for the denial
will be provided.
Briefing Package
Sponsors should submit briefing packages at least 30 days before the scheduled
meeting. Based on experience, to facilitate a productive meeting, we recommend
that no more than 10 questions or sub-questions are included in the briefing
package. It is important to provide background information sufficient to support
the questions in the package.
OTP will not commit to reviewing packages greater than 250 pages or answering
questions that require review of large volumes of material. The briefing package
contents should include all elements detailed in the PDUFA Formal Meetings
Draft Guidance [Ref. 14].
C. 	IND Amendments
Q10. 	What is FDA’s timeline for feedback on new or revised information
submitted to an active IND?
Sponsors submit amendments to alert FDA about changes to their development
program on a regular basis. The CMC information in an IND describes a
sponsor’s commitment to perform manufacturing and testing of the
investigational product as stated in the IND or in a cross-referenced IND or MF.
If a manufacturing change could affect product quality, the Agency considers the
manufacturing change essential information that must be submitted in an
information amendment to the IND (21 CFR 312.31(a)(1)). The sponsor should
submit such amendments for FDA review prior to use of the changed product in
clinical investigations. Please also see the answer to question 3.
A new or revised clinical protocol may be implemented provided the sponsor has
submitted the change to FDA for its review, and the change has been approved by
the IRB responsible for review and approval of the study.59 The sponsor may
comply with these two conditions in any order.60 With a few exceptions61,
amendments with new or revised protocols submitted to an active IND do not
have a review clock associated with them; provided the requirements in 21 CFR
312.30 are met, sponsors can implement the protocols without waiting for FDA to
finish its review.62
59 21 CFR 312.30(a)-(b).
60 21 CFR 312.30(a)-(b).
61 See e.g., 21 CFR 312.305(d)(2) regarding expanded access protocols.
62 For details, please see 21 CFR 312.30.

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If the sponsor desires FDA to comment on the submission, including before the
sponsor initiates the protocol or implements a manufacturing change, a request for
such comment should be made in the cover letter with the specific questions the
sponsor wishes FDA to address. The cover letter should also indicate when the
sponsor intends to initiate the new protocol or implement a change. Although
OTP strives to provide prompt feedback, the ability to provide input within a
specific timeframe may depend on several factors, including complexity of the
requested feedback and/or competing priorities. Therefore, sponsors should
ensure that if such feedback is desired, that they submit the new or revised
information well in advance of when they plan to implement the change, such as a
protocol or manufacturing change. More detailed information regarding
communication timing can be found in Best Practices for Communication
Between IND Sponsors and FDA During Drug Development Guidance [Ref. 15].
D. 	Expedited Programs
Refer to Expedited Programs for Serious Conditions – Drugs and Biologics; Guidance for
Industry [Ref. 16] and Expedited Programs for Regenerative Medicine Therapies for
Serious Conditions; Guidance for Industry [Ref. 17] for additional details.
Q11. 	When does rolling review begin for qualifying BLAs and what is the
timing of module submission?
Rolling review means that FDA may consider reviewing portions of a BLA before
the sponsor submits the complete BLA.
A drug may receive rolling review if it has Fast Track, Breakthrough Therapy, or
Regenerative Medicine Advanced Therapy (RMAT) designation and if certain
criteria are met; however, FDA must still agree to rolling review. Sponsors obtain
preliminary Agency agreement on the proposal at the pre-BLA meeting or earlier
(e.g., end-of-phase 2 meeting). A request to submit portions of an application
ordinarily should be included in the information package for the pre-BLA
meeting. Sponsors should also submit an amendment to their IND describing the
proposed submission schedule, including dates each complete module would be
submitted. After reviewing the amendment, FDA will indicate its decision on
rolling review.
If FDA agrees with a rolling review, FDA will generally accept only complete
modules for Modules 3, 4, and 5. FDA may also generally accept select sections
of Modules 1 and 2 given their content and relationship to the other modules. For
example, a sponsor might initially submit the complete Module 5 along with the
related portions of Modules 1 and 2, then submit the complete Module 4 along
with the related portions of Modules 1 and 2, and finally submit the complete
Module 3 along with the remaining portions of Modules 1 and 2. If FDA agrees
to a rolling review, no more than 12 months should elapse from the first
submission of BLA content to the final submission to complete the BLA.

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FDA’s review clock starts once the final module is received and the applicant
informs the Agency that a complete BLA or NDA was submitted.63
IV. 	PRODUCT DEVELOPMENT CONSIDERATIONS
Product development issues are addressed in the sections below. More detailed information on
CMC for CGT products can be found in the CMC GT INDs Guidance [Ref. 7] and the CMC CT
INDs Guidance [Ref. 8].
A. 	Donor Eligibility
Q12. 	What are some differences between autologous and allogeneic donor
eligibility considerations?
A donor eligibility determination under 21 CFR § 1271.50 and donor screening or
testing under 21 CFR §§ 1271.75, 1271.80, and 1271.85 are not required for cells
and tissues used in the manufacture of autologous products.64 However, the
manufacturer must include the applicable required labeling on the product.65 For
example, for products intended for autologous use, the manufacturer must
prominently label the product with the statement “FOR AUTOLOGOUS USE
ONLY.”66 As another example, unless all otherwise applicable donor screening
and testing under 21 CFR §§ 1271.75, 1271.80, and 1271.85 are performed, the
manufacturer must prominently label the product with the statement, “NOT
EVALUATED FOR INFECTIOUS SUBSTANCES”.67, 68 Additionally, FDA
recommends that the manufacturer include a minimum of two unique identifiers
(e.g., donor identification number (DIN), product tracking number, etc.) for
autologous therapies to minimize potential for mix-ups.
For allogeneic donor material, manufacturers are required to determine whether a
donor is eligible based upon the results of donor screening and testing in
accordance with 21 CFR §§ 1271.75, 1271.80, and 1271.85.69 A responsible
person must determine and document the eligibility of a cell or tissue donor.70
63 Section 506(d)(2) of the FD&C Act provides that any time period for review of human drug applications shall not
apply until the date on which the application is complete. See also Expedited Programs Drug and Biologics
Guidance.
64 21 CFR 1271.90(a).
65 21 CFR 1271.90(c).
66 21 CFR 1271.90(c)(1).
67 21 CFR 1271.90(c)(2).
68 For more information on prominence in labelling, see Product Name Placement, Size, and Prominence in
Promotional Labeling and Advertisements; Guidance for Industry, December 2017, available at
https://www.fda.gov/media/87202/download.
69 21 CFR 1271.50(a).
70 21 CFR 1271.50(a).

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Note that screening and testing are two different components. Screening entails
reviewing relevant medical records for risk factors for, and clinical evidence of,
relevant communicable disease agents and diseases, and communicable disease
risks associated with xenotransplantation.71 Relevant medical records refers to a
collection of documents that includes: (1) a current donor medical history
interview; (2) a current report of the physical assessment of a cadaveric donor or
the physical examination of a living donor; and (3) other available records listed
in 21 CFR 1271.3(s).72 Testing is performed on a specimen from the donor,
typically blood. Testing must be performed using FDA-licensed, approved, or
cleared test kits according to the manufacturer’s instructions for use73 and must be
performed in a Clinical Laboratory Improvement Amendments-certified
laboratory or equivalent as determined by the Centers for Medicare and Medicaid
Services.74 The donor specimen must be collected for testing at the time of
recovery of cells or tissue from the donor or up to 7 days before or after, except
for donors of peripheral blood stem/progenitor cells or bone marrow, in which
case the specimen for testing may be collected up to 30 days before recovery.75
For more details, refer to FDA’s guidance “Eligibility Determination for Donors
of Human Cells, Tissues, and Cellular and Tissue-Based Products (HCT/Ps):
Guidance for Industry,” August 2007 [Ref. 18].
B. 	Product Characterization
Q13. 	What is the difference between product characterization testing and
release testing?
Characterization testing provides information about the product, whereas release
testing demonstrates that the product is of acceptable quality (safety, identity,
purity, and potency). Release tests are part of the product specification, which
establishes the set of criteria that a drug product must meet to be considered
acceptable for its intended use.76 A specification should include a list of all
release tests, references to analytical procedures, and appropriate acceptance
criteria (AC), which are numerical limits, ranges, or other criteria for the tests
described [Refs. 7, 19]. Prior to initiating a pivotal study, intended to provide
primary evidence of effectiveness of the drug, release tests must be qualified, tests
must have predefined AC, and tests must comply with current good
manufacturing practice (CGMP).77 Release tests must be validated prior to BLA
71 21 CFR 1271.75(a).
72 21 CFR 1271.3(s).
73 21 CFR 1271.80(c).
74 21 CFR 1271.55(b)(1)(i) and (ii), 21 CFR 1271.80(c)
75 21 CFR 1271.80(b).
76 21 CFR 211.165
77 21 CFR §§ 210.2, 211.165.

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submission.78 In contrast, characterization tests do not need to be qualified, have
AC, or comply with the CGMP requirements for testing and release for
distribution.
Release test results should be reported on the product certificate of analysis
(COA), whereas characterization test results are not reported on a COA. Both
release tests and key characterization assay results should be recorded and
submitted to an IND application or BLA at relevant places in Module 3 of the
CTD at the appropriate phase of development.
The Agency recommends characterization testing of both the DS and the DP.
Information gained from characterization testing is valuable for multiple
purposes, including identifying CQAs,79 guiding analytical assay development,
and evaluating product comparability following manufacturing changes.
The appropriate characterization tests depend on the unique features of the
product type. For example, characterization testing of a cell-based product may
include extended assessment of cell surface phenotypic markers, such as those
associated with immune-cell activation, differentiation, and exhaustion. For
adeno-associated viral vectors, examples of characterization testing may include
orthogonal measures of activity, vector genome size analysis, and detection of
capsid amino acid modifications by mass spectrometry. For tissue-engineered
medical products, examples may include biomechanical testing to assess the
ability of a vascular graft to tolerate repeat access without leaking, permeability
testing to assess the characteristics of a skin graft, or cellular distribution
throughout a cell scaffold construct.
Some tests are necessary to confirm safety of the product prior to release but are
not performed on the final product; such samples should be acquired at the
necessary and appropriate manufacturing steps. For example, tests for
mycoplasma and adventitious agents should be performed on cell culture harvest
material prior to further processing. Tests for sterility, endotoxin, and identity
should be performed on formulated product in the final labeled container to
ensure that microbial contamination and product mix-ups (such as those that may
occur during final DP manufacturing steps) do not occur.
78 21 CFR 211.165(e).
79 For purposes of this guidance, a critical quality attribute is defined as a physical, chemical, biological, or
microbiological property or characteristic that should be within an appropriate limit, range, or distribution to ensure
the desired product quality. See guidance for industry Q8(R2) Pharmaceutical Development (November 2009)
available at https://www.fda.gov/media/71535/download.

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C. 	Critical Quality Attributes
Q14. 	What information should be submitted regarding critical quality
attributes?
In the IND, sponsors should describe the quality attributes relevant to the
performance of the product, including attributes of the DS, DP, intermediates, and
excipients. Sponsors should consider including information related to but not
limited to assessments of attributes important to product quality, CQA
determination, and justification of specifications based on available data. These
quality attributes include physicochemical or biological properties of the product,
such as strength used to establish dosing units, genotypic or phenotypic variation,
biological activity or potency, and/or immunological activity. CQAs are a subset
of quality attributes. It can be crucial to establish CQAs for a product as early as
possible, particularly when sponsors plan to make manufacturing changes during
product development, because well-established CQAs are generally necessary for
assessing analytical comparability between different versions of a product [Ref.
22].
Given the complex nature of CGT products, assuring a product’s potency can be
one of the more challenging aspects of development. To help manufacturers meet
potency requirements for INDs and BLAs, FDA has provided recommendations
to manufacturers in its draft guidance, “Potency Assurance for Cellular and Gene
Therapy Products: Draft Guidance for Industry,” December 2023 [Ref. 20].80
FDA acknowledges that understanding and defining product characteristics that
are relevant to the clinical performance of the investigational product may be
challenging during early stages of product development, when product quality
may not be sufficiently understood. Therefore, FDA recommends that sponsors
evaluate a number of product characteristics during early clinical development to
help identify and understand CQAs.
For more details, refer to FDA’s guidance “Q8(R2) Pharmaceutical Development:
Guidance for Industry,” November 2009 [Ref. 21] and draft guidance
“Manufacturing Changes and Comparability for Human Cellular and Gene
Therapy Products: Draft Guidance for Industry,” July 2023 (hereinafter referred
to as “Manufacturing Changes CGT Draft Guidance”) [Ref. 22].81
In traditional product development, CQAs of the product are evaluated during
each phase of clinical development, and characterization data from many DP lots
may be correlated to clinical outcomes. For rare diseases, some aspects of the
development programs, such as limited population size and fewer lots
80 When final, this guidance will represent FDA’s current thinking on this topic.
81 When final, this guidance will represent FDA’s current thinking on this topic.

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manufactured, may make it challenging to follow traditional product development
strategies. For specific guidance on product development approaches for rare
diseases, refer to FDA’s guidance entitled “Human Gene Therapy for Rare
Diseases: Guidance for Industry,” January 2020 (hereinafter referred to as “GT
for Rare Diseases Guidance”) [Ref. 23].
D. 	Analytical Methods
Q15. 	How should analytical methods be shown to be fit for purpose for
first-in-human trials?
For FIH studies, the IND should contain a description of each non-compendial
analytical method used to assess quality of the product (DP, DS, and
components), with an evaluation of assay performance characteristics (i.e.,
accuracy, precision, sensitivity, and specificity) to justify that the method is fit for
purpose (i.e., at a stage of development that is phase-appropriate). More
information can be found in FDA’s guidance “Analytical Procedures and Methods
Validation for Drugs and Biologics,” July 2015 (hereinafter referred to as
“Analytical Procedures and Methods Guidance”) [Ref. 24].
Tests performed to assure product safety, including microbial testing, should
demonstrate adequate performance including but not limited to suitability under
actual conditions of use and an absence of interference from the product, even for
the initial IND submission. Notably, to assure safety of gene therapy (GT)
products, the sponsor should qualify the assay(s) used to determine dose (e.g.,
vector genome titer by quantitative polymerase chain reaction (qPCR),
transducing units, plaque forming units, transduced cells) prior to initiating
clinical studies. In a sponsor’s IND submission, a detailed description should be
provided of the qualification protocol (e.g., samples; standards; positive/negative
controls; reference lots; and controls evaluated, such as operators, reagents,
equipment, dates) and data supporting the accuracy, precision, sensitivity, and
specificity of the analytical method.
Many tests for DS/DP release are compendial, and their assay performance
characteristics have already been established. However, for methods to be
considered compendial, they should be found in the United States
Pharmacopeia/National Formulary (USP/NF) compendia. If the sponsor plans to
reference other compendia to support fitness of a method, the sponsor should
include detailed information about how the methods are performed and whether
they have the same performance characteristics as the corresponding USP
methods.
For more information on establishing AC during product development, please see
the CMC GT INDs Guidance [Ref. 7]. While interim AC are acceptable for

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Phase 2 and 3 studies, proposed commercial AC should be in place at the time of
BLA submission.82
E. 	Process Characterization/Validation
Q16. 	At what scale should process characterization and validation be
executed?
The validation of a commercial manufacturing process should be supported by
data from commercial-scale batches. Although use of a scaled down model is not
appropriate for process performance qualification (PPQ), scaled-down models can
be used at the process design and characterization stages to evaluate process
variability, determine appropriate process parameters, and supportive studies such
as viral or impurity clearance.83 Sponsors should demonstrate the validity of the
scaled-down process, and the scaled-down version should represent the intended
commercial manufacturing process as closely as possible.
Q17. 	How many process performance qualification lots are recommended
for process validation?
There is no fixed number of lots recommended for PPQ. In general, a greater
understanding and knowledge of the product and manufacturing process can
reduce the number of PPQ lots that should be sufficient to qualify the
performance of the manufacturing process. The number of PPQ lots should be
informed by a risk assessment and should be sufficient to demonstrate that
consecutive runs of the manufacturing process perform as expected and
consistently yield a product that meets AC.
For more details, refer to FDA’s guidance entitled “Process Validation: General
Principles and Practices: Guidance for Industry,” January 2011 (hereinafter
referred to as “Process Validation Guidance”) [Ref. 25] and "Chemistry,
Manufacturing, and Controls Flexibilities for Developing Human Cellular and
Gene Therapy Products for a Biologics License Application,” May 2026 [Ref.
39].
F. 	Manufacturing Changes
Q18. 	How should manufacturers evaluate comparability of pre- and
post-change products?
When evaluating comparability of pre- and post-change products, consider the
recommendations in FDA’s Manufacturing Changes CGT Draft Guidance [Ref.
82 See 21 CFR 312.23(a)(7)(i).
83 Q11 Development and Manufacture of Drug Substances; Guidance for Industry, November 2012, available at
https://www.fda.gov/media/80909/download

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22]. The Agency recommends that sponsors submit a meeting request to their
IND to discuss significant manufacturing changes and effect on comparability,
particularly when such manufacturing changes would be implemented during later
stages of product development.
G. 	Stability
Q19. 	What stability information is needed to support first-in-human
studies?
Demonstrating product stability is needed at all stages of product development.84
Sponsors should be able to show that the product is within acceptable quality
limits for the duration of its planned usage within a clinical study85; however, an
incremental approach may be appropriate for setting AC to support stability. For
example, data to support stability of the product for Phase 1 studies can be based
on data from nonclinical lots, engineering lots, or highly similar product lots that
have been stored in the same manner as the clinical material (e.g., the same
formulation, concentration, storage temperature, and container), when sufficiently
justified. For topics like shipping stability, in-use stability, device compatibility,
and additional stability considerations, please see CMC GT INDs Guidance [Ref.
7].
H. 	Preparing for BLA
Q20. 	What CMC issues should sponsors consider as they prepare to submit
a BLA?
Specific CMC concerns are guided by the stage of product development.
Nonclinical and CMC safety testing data must be provided prior to initiation of
Phase 1 studies, along with basic product and process characterization data.86
Product development activities may be implemented incrementally but should
progress along with clinical development. For analytical methods, the Agency
recommends that sponsors evaluate assay performance throughout product
development. When preparing the BLA submission, the manufacturing process
and all analytical methods performed to support product quality must be
validated87 and comply with the regulations in 21 CFR 610.
Manufacturing for investigational and approved drugs (including biological
products) must comply with CGMP, as required by section 501(a)(2)(B) of the
Federal Food, Drug, and Cosmetic Act (FD&C Act) (21 U.S.C. 351(a)(2)(B) and
84 For purposes of this guidance, “stability” in this context is described in 21 CFR 312.23. See also 21 CFR
211.166.
85 21 CFR 312.23(a)(7)(iv)(b)
86 21 CFR 312.23(a)(7)-(8).
87 See 21 CFR 211.165.

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21 U.S.C. 351(j)) at all stages of clinical investigation. For example, DP
manufacturing must comply with FDA’s CGMP regulations for finished
pharmaceuticals in 21 CFR part 211, except that most Phase 1 investigational
drugs are exempt from the requirement to comply with part 211. See 21 CFR
210.2(c) and FDA’s guidance “CGMP for Phase 1 Investigational Drugs:
Guidance for Industry,” July 2008 [Ref. 26].
Additionally, CMC development (including process and analytical method
controls and compliance with CGMP, as outlined in 21 CFR 210 and 211) should
evolve concurrently with clinical development. A BLA must contain, among
other information, data which demonstrate that the product meets requirements of
safety, purity and potency, a full description of manufacturing methods and data
establishing stability of the product through the data period.88 Process
characterization and validation studies that must be conducted to meet CGMP are
outlined in 21 CFR 211 Subpart F — Production and Process Controls.
For more details, see the CMC GT INDs Guidance [Ref. 7], the Process
Validation Guidance [Ref. 25], and the Analytical Procedures and Methods
Guidance [Ref. 24].
V. 	CONDUCTING NONCLINICAL STUDIES
I. 	Selection of Models
Q21. 	What are FDA’s recommendations regarding adequate animal species
selection for certain nonclinical studies of cell and gene therapy
products?
When selecting an animal species for nonclinical PT studies, key considerations
include whether the investigational CGT product is pharmacologically active in
the species, the technical feasibility of using the intended clinical delivery device
or procedure for product administration, comparability of the physiology and
anatomy between animals and humans for the ROA and target anatomic sites that
the product is intended to reach, and the sensitivity of the selected species to
potential toxicities for the product.
Specific considerations for cell therapy (CT) products include the ability of the
species/strain to support survival and engraftment of the CT product or
availability of an appropriate analogous89 animal product. Additional
considerations for GT products include the permissiveness or susceptibility of the
species to the vector, vector transduction profile, and the pharmacological
88 21 CFR 601.2(a).
89 For purposes of this guidance, analogous animal product refers to products modified to be compatible with the
animal species used for testing that are analogs of the ultimate clinical product in phenotype and biological activity.

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response to the vector and the expressed transgene. FDA supports the use of New
Approach Methodologies (NAMs) and the principles of the 3Rs (i.e., reduce,
refine, and replace animal use) to encourage the judicious use of animals in
nonclinical development programs.90 FDA encourages sponsors to consult with
us if they wish to use a non-animal testing method they believe is suitable,
adequate, validated, and feasible.
Q22. 	Does FDA have specific recommendations regarding selection of an
animal model for pharmacology studies for assessing the activity of
CGT products?
Sponsors should consider the biological relevance of a particular animal or
disease model to the target patient population. This may depend on the
characteristics of the product, the proposed clinical indication, and the feasibility
of using the intended clinical delivery device or procedure when selecting animal
models for pharmacology studies. The sponsor should provide scientific
justification in pre-IND and IND submissions for the animal model/species
selection. A comprehensive discussion, with supporting data, regarding the
biological relevancy of each animal model should be provided. This should
include, but is not limited to, the following:
(1) Progression of the disease phenotype or injury observed in each animal
model
(2) The lifespan of each model
(3) The similarities and differences between the animal model(s) and the
proposed patient population (e.g., pathophysiology, biochemistry,
functional changes, etc.)
(4) The timing of product administration relative to disease onset and
progression as it pertains to the proposed patient population, and
(5) A description of the relevant anatomy and physiology related to the
delivery method and target anatomic site(s) in animals versus humans
The selection of animal model(s) of disease should be science-based and allow
both sponsors and the FDA to evaluate the safety and bioactivity of the intended
clinical product.
Q23. 	What approach should be taken if there is no available animal model
of disease in which the investigational product can be evaluated?
When animal models of the target disease are not available or if the
investigational CGT product is incompatible with an animal model, the sponsor
should provide supporting data from other sources. Some examples include in
90 For additional information, see https://www.fda.gov/media/191986/download?attachment and
https://www.fda.gov/media/186092/download?attachment.

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vitro studies, in silico studies, in vivo studies using an analogous animal product,
and relevant nonclinical or clinical data from studies evaluating a related product
(products of the same or similar class) or indication.
The sponsor should integrate these data to establish adequate scientific
justification to support the proposed clinical trial. If there are no available animal
models of the target disease to evaluate activity and safety of the CGT product,
the pivotal safety studies are typically conducted in pharmacologically relevant
healthy animals to identify potential toxicities related to the CGT product or
administration procedure(s).
Q24. 	Can alternative test methods or new approach methodologies be used
in place of animal studies even if animal models exist?
The nonclinical program for any investigational product should be individualized
with respect to scope, complexity, and overall design. Proposals, with
justification for any potential alternative approaches (e.g., in vitro or in silico
testing), should be submitted during early communication meetings with FDA
(see section III.B of this guidance). FDA supports the use of NAMs, where
feasible, and is open to alternative methods that are backed by science and
produce scientifically valid data and will consider whether such an alternative
could be used in place of an animal test method within a particular context of use.
J. 	Product Selection for Nonclinical Studies
Q25. 	What are important aspects to be considered when evaluating the
similarity of human and analogous animal CGT products?
Evaluation of the intended clinical product in animals may not always be feasible.
This could be due to potential xenogeneic responses after administration of a
human-specific CGT product in animal models or differences in the homology of
a transgene product or target between humans and the animal species. Therefore,
depending on the type of product, the use of an analogous animal product may be
a suitable alternative in animal studies. The analogous animal product should be
representative of the intended clinical human product to the extent possible.
A sufficient comparison between the analogous animal product and the intended
clinical product should be provided in pre-IND and IND submissions. Depending
on the type of CT product, this comparison should include, but is not limited to,
the following characteristics: product identity, cell type(s), cell phenotype,
function, manufacturing (i.e., procedures, formulation, stability, potency), and
other CQAs. For GT products, additional considerations can include
vector/transgene sequence, target specificity, and/or transgene expression levels,
physical titer, and empty capsid content. For LNP based GT products, additional
considerations can include lipid identity and quality, final lipid formulation, cargo

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(e.g. mRNA), and manufacturing process. Whether data generated from the in
vitro and/or in vivo nonclinical evaluation of an analogous animal product would
be appropriate to serve as a comparison is considered on a case-by-case basis.
K. 	Tumorigenicity
Q26. 	What is the FDA’s recommendation regarding tumorigenicity studies
before the first use of CGT products in human subjects?
Evaluation of tumorigenic potential prior to administration of an investigational
CGT product in a FIH clinical trial depends on the type of investigational CGT
product. For example, the differentiation status of a CT product, the extent of ex
vivo cell manipulation, the potential for integration of genetic material into the
host genome, the expressed transgene in a GT product, and the in vivo
distribution and persistence profile should be considered when determining the
need for assessing tumorigenic potential of the CGT product. Tumorigenicity
studies are generally recommended for pluripotent stem cell-derived products,
which have the potential for aberrant cell proliferation, differentiation, and
teratoma formation. The sponsor can conduct tumorigenicity testing in either a
dedicated study or as a component of a nonclinical safety/toxicology study. The
animal species/strain for in vivo assessment of tumorigenicity should be
permissive to the engraftment and long-term survival of the investigational
product following administration via the planned clinical ROA.
The number of animals included in an in vivo tumorigenicity study should be
sufficient to collect all protocol-specified parameters and detect low-frequency
events. Thus, it is important to ensure that a robust number of animals are
followed to scheduled sacrifice to allow for meaningful data interpretation. Study
duration and selection of the appropriate sacrifice time points for tumorigenicity
studies should be based on the in vivo distribution and persistence profile of the
investigational CGT product. The sponsor should determine the cellular origin of
any detected tumors (i.e., whether they are derived from host or donor cells). It
should be noted that an analogous animal product would typically not be
appropriate for tumorigenicity testing. If the sponsor considers a Error! B
ookmark not defined.tumorigenicity study unnecessary, they should provide a
scientific justification with supporting data in their submission to OTP for review.
L. 	Error! Bookmark not defined.Proof-of-Concept Studies
Q27. 	Why are proof-of-concept data important for CGT products? Can
FDA provide details on how much and what type of proof-of-concept
data are appropriate prior to conducting a clinical trial?
POC studies are important to evaluate bioactivity, determine the feasibility of the
ROA, and provide a rationale for use of an investigational CGT product in the
target clinical population. POC studies often characterize the putative mechanism

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of action of the investigational CGT product and aid in determining a potentially
active dose level range and optimized dosing regimen for the initial clinical trial.
Once POC data have been obtained, it can be helpful for sponsors to discuss the
adequacy of these data and the details of the protocol(s) for planned pivotal
toxicology studies at a pre-IND meeting. If the POC data submitted are
inadequate to support the planned clinical studies, sponsors may be asked to
conduct additional POC studies. Additionally, data from POC studies can be used
to support a prospect of direct benefit prior to initiating a clinical study in children
that presents more than minimal risk.91 The sponsor should provide
pharmacology summaries and final study reports for each POC study in the IND
submission. The adequacy of the nonclinical data to support administration of the
investigational CGT product in the proposed clinical trial is determined based on
the review of the POC and safety data in the IND.
M. 	Toxicity
Q28. 	Can sponsors submit INDs without conducting nonclinical toxicology
studies for certain products?
An IND must contain adequate information about pharmacological and
toxicological studies of the drug involving laboratory animals or in vitro, on the
basis of which the sponsor has concluded that it is reasonably safe to conduct the
proposed clinical investigations.92 The design of nonclinical toxicology/safety
studies should be based on the product type, ROA, and intended clinical
indication. Toxicology/safety studies are important to characterize potential risks
for the administration of investigational CGT products in a proposed clinical trial.
For general guidance on safety and toxicology studies in CGTs, refer to
Preclinical Assessment CGT Guidance [Ref. 10]. If a sponsor believes adequate
information about toxicological risk of the drug can be provided without further
toxicology testing for a specific product, they should provide a discussion of the
available data (nonclinical or clinical) to support the safety profile of the
investigational product and their scientific rationale for why they believe further
toxicological assessment is unnecessary in their IND submission.
Q29. 	For a single-dose administration investigational product, what are the
considerations for the duration of the pivotal toxicology study?
The duration for a pivotal toxicology/safety study evaluating a single-dose
administration will vary based on the product characteristics and ROA for the
intended clinical population. The study duration may be informed by data
obtained from pilot safety and biodistribution (BD) studies. The pivotal
91 See 21 CFR Part 50 Subpart D, 21 CFR 50.52.
92 21 CFR 312.23(a)(8).

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toxicology/safety study should be of sufficient duration to evaluate potential acute
and long-term toxicities, as well as the potential for resolution or stabilization of
any findings. Multiple sacrifice time points following administration of an
investigational product should be included to comprehensively characterize
potential adverse findings. The sponsor should provide their rationale, with
supporting data to justify the dose levels, sacrifice timepoints, panel of
tissues/biofluids collected for clinical chemistry and pathology assessments, and
duration of their safety/toxicology studies.
N. 	Design of Cell Distribution/Biodistribution Studies
Q30. 	Does FDA recommend certain testing methods for cell distribution or
vector biodistribution studies?
For CT products, various methods have been used to assess in vivo cell
distribution, such as imaging modalities for detection of radioisotope-labeled
cells, genetically modified cells (e.g., expressing green fluorescent protein),
nanoparticle-labeled cells (e.g., iron-dextran nanoparticles), qPCR or droplet
digital PCR (ddPCR) analysis and immunohistochemistry to identify cells of
human origin or cells of a karyotype different than the host (e.g., sex). A
potential advantage of in vivo imaging techniques is that in many instances, the
same animal can be evaluated over time, thus decreasing variability and reducing
the number of animals used. Data should be provided to support the viability and
function of the CT product if the cells are modified to enable use of such imaging
techniques. Other detection methods may be considered if scientifically
supported.
For GT products, use of a quantitative and sensitive assay such as qPCR or
ddPCR for vectors or LC-MS/MS for LNP-based products is recommended to
analyze BD and persistence in various tissues/biofluids. For samples that are
determined to be positive for vector or LNP presence upon analysis, transgene
mRNA, cargo RNA and/or protein expression levels should also be measured
using an appropriate method. Determining levels of protein expression resulting
from transduction can inform on the safety and potential bioactivity of the
product. For details, refer to FDA’s guidances entitled “S12 Nonclinical
Biodistribution Considerations for Gene Therapy Products: Guidance for
Industry,” May 2023 [Ref. 27] and “Long-Term Follow-Up After Administration
of Human Gene Therapy Products: Guidance for Industry,” January 2020
(hereinafter referred to as “LTFU After GT Products Guidance”) [Ref. 28].

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O. 	Dose Levels
Q31. 	What are the recommended methods for dose level extrapolation from
animals to humans?
The proposed starting clinical dose level and dose escalation planned for an
investigational CGT product should be supported by data from nonclinical POC
and safety/toxicology studies. The methods for dose level extrapolation from
animals to humans should be based on, for example, body weight, volume of
target tissue/organ, organ mass, or surface area depending on the ROA and
product type. The proposed starting clinical dose level of an investigational CGT
is typically determined based on the bioactivity of the product from nonclinical
POC studies performed in an animal model of disease and should also be
supported by nonclinical safety studies. The dose level extrapolation and safety
margin should be determined for each animal species administered the intended
clinical product (or analogous product) in the POC and toxicology studies. When
technical limitations do not allow for the determination of a starting clinical dose
level from in vivo nonclinical studies, or there are appropriate alternatives to
animal studies, data from other sources (e.g., in vitro, NAMs) may be considered
with sufficient scientific support.
VI. 	CONDUCTING HUMAN TRIALS
A. 	Trial Design
Q32. 	What is important for sponsors to consider when designing clinical
trials for CGTs?
Licensure of biological products, including CGTs, requires a showing that the
products are “safe, pure, and potent.”93 Potency has long been interpreted to
include effectiveness.94 FDA has generally considered substantial evidence of
effectiveness to be necessary to support licensure of a biological product under
section 351 of the PHS Act.95 Substantial evidence may be satisfied by two
adequate and well-controlled clinical investigations to establish effectiveness, but
in some cases, FDA may consider data from one adequate and well-controlled
93 See section 351(a) of the Public Health Service Act (PHS Act) (42 U.S.C. 262).
94 21 CFR 600.3(s).
95 In 1972, FDA initiated a review of the safety and effectiveness of all previously licensed biologics. The Agency
stated then that proof of effectiveness would, with limited exceptions, consist of controlled clinical investigations as
defined in the provision for “adequate and well-controlled studies” for new drugs (21 CFR 314.126) (see former 21
CFR 601.25(d)(2) (2015) (revoked as no longer necessary, 81 FR 7445 (Feb. 12, 2016))). We note that, in section
123(f)) of the Food and Drug Modernization Act of 1997 (FDAMA), Congress also directed the agency to take
measures to “minimize differences in the review and approval” of products required to have approved BLAs under
section 351 of the PHS Act and products required to have approved NDAs under section 505(b)(1) of the FD&C
Act.

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clinical investigation and confirmatory evidence to constitute substantial
evidence.96 For additional guidance, refer to FDA’s draft guidance entitled
“Demonstrating Substantial Evidence of Effectiveness for Human Drug and
Biological Products: Guidance for Industry97,” June 2026 [Ref. 35].
A purpose of conducting clinical trials with an investigational product is to
distinguish the effect of the product on the target condition from other influences,
such as spontaneous change in the course of the disease, placebo effect, or biased
observation. When properly conducted, a clinical trial that includes appropriate
blinding and random assignment of subjects to either a treatment or a concurrent
control group, to optimally promote the similarity of compared groups, will
generally allow us to determine if the treatment effect is attributed to the
investigational product.
Some of the features of an adequate and well-controlled clinical study include a
valid comparison with a control to provide a quantitative assessment of drug
effect, a suitable method of assignment to treatment and control groups (e.g.,
randomization), and adequate measures to minimize bias (e.g., blinding of study
subjects and/or evaluators).98
There are generally five types of controls: (1) the placebo/sham concurrent
control; (2) the active concurrent control, or control therapy that involves an
accepted alternative treatment; (3) the dose-ranging concurrent control; (4) the no-
treatment concurrent control; and (5) the external or historical control.99 When
feasible and/or ethical, sponsors should first consider study designs using one of
the first three types of controls, each of which permits randomization and
blinding, making the study results largely free of bias and highly interpretable.
Sponsors should next consider the no-treatment control because although the
study subjects will know they are not receiving the treatment, they will be
otherwise selected and assessed according to the same protocol as those receiving
the investigational CGT product. In some cases, such as with rare diseases that
have a natural history that does not improve with other interventions, or
spontaneously, a well-conducted natural history study may serve as an acceptable
external or historical control. Blinding and randomization are feasible when a
placebo control, active concurrent control, or dose-ranging concurrent control is
used. Sponsors developing an investigational product for a rare disease should
consider designing their FIH study to be an adequate and well-controlled clinical
study so that the results of such a study may contribute to meeting the substantial
evidence standard for effectiveness to support a marketing application. For
further information on development of CGT products for rare diseases, refer to
the GT for Rare Diseases Guidance [Ref. 23].
96 See section 505(d) of the FD&C Act.
97 When final, this guidance will represent FDA’s current thinking on this topic.
98 See 21 CFR 314.126(b).
99 See 21 CFR 314.126(b)(2).

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For more details, refer to the following draft guidances: “Considerations for the
Design and Conduct of Externally Controlled Trials for Drug and Biological
Products: Draft Guidance for Industry,” February 2023 [Ref. 29] and “Rare
Diseases: Natural History Studies for Drug Development: Draft Guidance for
Industry,” March 2019 [Ref. 30].100 Additionally, see FDA’s guidance “Rare
Diseases: Considerations for the Development of Drugs and Biological Products:
Guidance for Industry,” December 2023 [Ref. 31] and “Considerations for the
Design of Early-Phase Clinical Trials of Cellular and Gene Therapy Products:
Guidance for Industry,” June 2015 (hereinafter referred to as “CGT Early-Phase
Trials Guidance”) [Ref. 32].
Q33. 	How many trials are required to demonstrate substantial evidence of
effectiveness of a CGT product, with the ultimate goal being FDA
licensure?
As noted above, substantial evidence of effectiveness may be satisfied by two
adequate and well-controlled clinical investigations but in some cases, FDA may
conclude that one adequate and well-controlled clinical study plus confirmatory
evidence is sufficient to establish effectiveness.101 Several factors may be
relevant to whether reliance on a single adequate and well-controlled clinical
study plus confirmatory evidence is appropriate. These factors may include the
persuasiveness of the single trial; the robustness of the confirmatory evidence; the
seriousness of the disease; the size of the patient population; and whether it is
ethical and practicable to conduct more than one adequate and well-controlled
clinical study. Additionally, poor execution can cause a trial of any design to be
inadequate or not well-controlled, and unable to support a finding of substantial
evidence of effectiveness.
For more details, refer to FDA’s guidances “Providing Clinical Evidence of
Effectiveness for Human Drug and Biological Products: Guidance for Industry,”
May 1998 [Ref. 33] and “Clinical Trial Endpoints for the Approval of Cancer
Drugs and Biologics: Guidance for Industry,” December 2018 [Ref. 34]
(hereinafter referred to as “Cancer Drugs Endpoints Guidance”). Further
information can be found in draft guidances “Demonstrating Substantial Evidence
of Effectiveness for Human Drug and Biological Products: Draft Guidance for
Industry,” June 2026 (hereinafter referred to as “Substantial Evidence of
Effectiveness Draft Guidance”) [Ref. 35] and “Demonstrating Substantial
Evidence of Effectiveness With One Adequate and Well-Controlled Clinical
Investigation and Confirmatory Evidence: Draft Guidance for Industry,”
September 2023 [Ref. 36].102
100 When final, these guidances will represent FDA’s current thinking on these topics.
101 See section 505(d).
102 When final, these guidances will represent FDA’s current thinking on these topics.

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B. 	Selecting Endpoints
Q34. 	What should sponsors consider when using a surrogate endpoint as a
primary outcome measure for a later phase clinical trial intended to
support approval of a CGT product?
For approval of a CGT, whether through traditional or accelerated approval, the
product must be “safe, pure, and potent,”103 and there must be substantial
evidence of effectiveness. As compared to accelerated approval, for traditional
approval, the Agency accepts clinical endpoints that directly reflect a meaningful
clinical benefit (i.e., how study participants feel or function, or how long they
survive) or validated surrogate endpoints (i.e., those that have been shown to
predict a specific clinical benefit). For accelerated approval, FDA accepts
evidence of a demonstrated effect on a surrogate endpoint that is reasonably likely
to predict a clinical benefit or on an intermediate clinical endpoint (a clinical
endpoint that can be measured earlier than irreversible morbidity or mortality, that
is reasonably likely to predict a clinical benefit).104 For products approved under
accelerated approval, FDA requires post-approval trials to verify the predicted
clinical benefit. The importance of the clinical outcome to patients and the
feasibility of showing a treatment effect in a trial of reasonable duration are
primary considerations for our evaluation of clinical outcomes.
Clinical Versus Surrogate Endpoints
A clinical benefit denotes a positive therapeutic effect that is clinically
meaningful in the context of a particular disease. A clinical endpoint directly
measures a therapeutic effect of a medical product and assesses how a patient
feels, functions or how long they survive. A surrogate endpoint is a marker, such
as a laboratory measure, physical sign, radiographic image or other measure that
is used in clinical trials as a substitute for a direct measure of how a patient feels,
functions, or survives.105 Surrogate endpoints are not direct measures of clinical
benefit; however, treatment effects on a surrogate endpoint may predict the
clinical benefit of a treatment. Depending on the strength of the evidence
supporting the ability of a measure to predict clinical benefit, a marker may be a
surrogate endpoint that is known to predict clinical benefit (i.e., a “validated”
surrogate endpoint) or could be a surrogate endpoint that is reasonably likely to
predict a drug’s intended clinical benefit.
103 See section 351(a) of the PHS Act.
104 See section 506(c)(1)(A) of the FD&C Act; see also the Expedited Program for Serious Conditions – Accelerated
Approval of Drugs and Biologics Draft Guidance [Ref. 40]. When final, this guidance will represent FDA’s current
thinking on this topic.
105 See, e.g. FDA-NIH Biomarker Working Group, BEST (Biomarkers, EndpointS, and other Tools) Resource,
Available at: https://www.ncbi.nlm.nih.gov/books/NBK326791/ (Co-published by FDA and the National Institutes
of Health ).

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Biomarker Surrogate Endpoints
Biomarkers are laboratory or imaging test results, or other clinical measures that
are indirect measures of physiological function, or physical signs that can tell us
something about the state of severity of a disease process and potentially about
the activity of an investigational product on the disease process. Biomarkers can
also be very useful for identifying toxicity, exploring pharmacodynamic effects,
and identifying the right dose.
The utility of a biomarker and the decision regarding how best to use them in
clinical studies depends on a number of factors including how well the biomarker
tracks the disease process; how likely it is that a pharmaceutical effect on the
biomarker would predict a clinically meaningful improvement in the way a
patient feels, functions, or survives; and the assay or imaging technique used to
measure the biomarker. Scientific data are needed to support the utility of a
biomarker.
Some factors considered when assessing whether a biomarker may have utility as
a surrogate endpoint are:
(1) To what extent the pathophysiology of the disease is well understood and
whether data suggest that the candidate surrogate is on the causal pathway
of progression to the clinical outcome(s) of interest
(2) The strength and consistency of the epidemiologic data supporting the
relationship between the biomarker and the clinical outcome(s) of interest
(3) Whether treatment effects on the biomarker have been shown to predict
treatment effects on the clinical outcome(s) of interest, ideally with
different types of interventions
C. 	Safety Data
Q35. 	What should sponsors consider for short- and long-term safety
monitoring in trials of investigational CGT products?
Short-Term Follow-up
Many CGT products are administered once. Close monitoring of subjects
immediately following product administration is critical to capture early safety
signals. This means that during and immediately following product
administration, there should be intensive safety monitoring with frequent
monitoring of vital signs, physical examinations, laboratory studies, radiologic
evaluations, and other relevant studies as warranted. During the subsequent
weeks and months, subjects should be monitored frequently for assessment of
emerging safety signals via clinical evaluation and ancillary testing.

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FIH studies of CGT products should generally employ a safety strategy of
staggered enrollment and treatment to limit the number of subjects exposed to
unknown but potentially significant risks. Staggered enrollment and treatment
incorporate a waiting period into the protocol for safety observation between
subsequent subjects and between dose cohorts to identify potential safety issues
before dosing the next subject. The staggering interval, either within a cohort or
between cohorts, is intended to be long enough to monitor for acute and subacute
adverse events prior to treating additional subjects at the same dose or prior to
increasing the dose in subsequent subjects. The choice of staggering interval
should consider the time course of acute and subacute adverse events that were
observed in animal studies and in any previous human experience with related
products.
Clinical studies of CGT products should have stopping rules which, if met, cause
temporary suspension of enrollment and dosing until the situation can be assessed.
Well-designed stopping rules allow sponsors to assess and address risks identified
as the trial proceeds and to assure that risks to subjects remain reasonable.106 The
protocol should include study stopping rules that specify the number of adverse
events, as well as the nature and/or the severity of those events, which would
trigger the temporary suspension of drug administration in the study, pending a
safety investigation. In addition, stopping rules should be independent of
attribution as the safety profile is unknown.
Long-Term Follow-Up
The appropriate duration of follow-up for CGT products depends on the results of
nonclinical studies, experience with related products, knowledge of the disease
process, and other scientific information.
FDA advises sponsors to observe subjects for delayed adverse events for as long
as 15 years following exposure to the investigational product, depending on the
type of product, in long-term follow-up trials. One of the main principles is that
GT products may be integrated into the genome or cause genome editing and
subjects receiving these therapies need to be monitored for the longer period
because of the potential higher risk of cancer or other off-target effects.
For more details, refer to the LTFU After GT Products Guidance [Ref. 28].
106 See, e.g. 21 CFR 312.56(d) (requiring a sponsor to discontinue an investigation if a sponsor determines that its
investigational drug presents an unreasonable and significant risk to subjects).

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Q36. 	When investigating CGT therapies in Phase 1 trials, should only
safety be tested, or should efficacy endpoints also be incorporated?
FDA advises sponsors to carefully design their early-phase studies in the context
of the overall development program’s objectives. While Phase 1 studies are
primarily geared toward evaluating safety, tolerability, and dose exploration, it is
important to explore POC, preliminary efficacy, and pharmacodynamic measures
to help inform the design of the later studies. It is important to follow all Phase 1
study subjects in long-term follow-up studies where clinical outcomes measures
should also be assessed. Clinical outcomes measured in these early treated
subjects may provide confirmatory evidence of effectiveness.
In particular, for rare diseases, a well-designed Phase 1 study designed to assess
both safety and efficacy utilizing clinically meaningful endpoints may potentially
serve as a pivotal study to support approval. For details, refer to the CGT Early-
Phase Trials Guidance [Ref. 32].

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VII. 	REFERENCES
1. 	M4 Organization of the Common Technical Document for the Registration of
Pharmaceuticals for Human Use; Guidance for Industry, October 2017, available at:
https://www.fda.gov/media/71551/download.
2. 	Providing Regulatory Submissions in Electronic Format — Certain Human
Pharmaceutical Product Applications and Related Submissions Using the eCTD
Specifications; Guidance for Industry, February 2020, available at:
https://www.fda.gov/media/135373/download.
3. 	SOPP 8110: Submission of Regulatory Applications -- Exempt from eCTD
Requirements; available at: 	https://www.fda.gov/media/89820/download?attachment.
4. 	Investigational New Drug Applications Prepared and Submitted by Sponsor-
Investigators; Draft Guidance for Industry, May 2015, available at:
https://www.fda.gov/media/92604/download.
5. 	SOPP 8217: Administrative Processing and Review Mnagement Procedures for
Investigational New Drug Applications (Version 6); available at:
https://www.fda.gov/media/156718/download?attachment.
6. 	M4Q: The CTD — Quality; Guidance for Industry, August 2001, available at:
https://www.fda.gov/media/71581/download.
7. 	Chemistry, Manufacturing, and Control (CMC) Information for Human Gene Therapy
Investigational New Drug Applications (INDs); Guidance for Industry, January 2020,
available at: https://www.fda.gov/media/113760/download.
8. 	Content and Review of Chemistry, Manufacturing, and Control (CMC) Information for
Human Somatic Cell Therapy Investigational New Drug Applications (INDs); Guidance
for Industry, April 2008, available at: https://www.fda.gov/media/73624/download.
9. 	Study Data Technical Conformance Guide, Technical Specifications Document, June
2026, available at: https://www.fda.gov/media/153632/download
10. 	Preclinical Assessment of Investigational Cellular and Gene Therapy Products; Guidance
for Industry, November 2013, available at: https://www.fda.gov/media/87564/download.
11. 	Information Sheet Guidance for Sponsors, Clinical Investigators, and IRBs, Frequently
Asked Questions Statement of Investigator (Form FDA 1572); Draft Guidance for
Industry, May 2021, available at: https://www.fda.gov/media/148810/download.

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12. 	SOPP 8117: Issuing Tracking Numbers in Advance of Electronic Submissions in eCTD
Format; available at: https://www.fda.gov/media/93416/download?attachment.
13. 	SOPP 8101.1: Regulatory Meetings with Sponsors and Applicants for Drugs and
Biological Products; available at:
https://www.fda.gov/media/84040/download?attachment.
14. 	Formal Meetings Between the FDA and Sponsors or Applicants of PDUFA Products;
Draft Guidance for Industry, September 2023, available at:
https://www.fda.gov/media/172311/download.
15. 	Best Practices for Communication Between IND Sponsor and FDA During Drug
Development; Guidance for Industry and Review Staff, December 2017, available at:
https://www.fda.gov/media/94850/download.
16. 	Expedited Programs for Serious Conditions – Drugs and Biologics; Guidance for
Industry, May 2014, available at: https://www.fda.gov/media/86377/download.
17. 	Expedited Programs for Regenerative Medicine Therapies for Serious Conditions;
Guidance for Industry, February 2019, available at:
https://www.fda.gov/media/120267/download.
18. 	Eligibility Determination for Donors of Human Cells, Tissues, and Cellular and Tissue-
Based Products (HCT/Ps); Guidance for Industry, August 2007, available at:
https://www.fda.gov/media/73072/download.
19. 	Q6B Specifications: Test Procedures and Acceptance Criteria for
Biotechnological/Biological Products; Guidance for Industry, August 1999, available at:
https://www.fda.gov/media/71510/download.
20. 	Potency Assurance for Cellular and Gene Therapy Products; Draft Guidance for Industry,
December 2023, available at: https://www.fda.gov/media/175132/download.
21. 	Q8(R2) Pharmaceutical Development; Guidance for Industry, November 2009, available
at: https://www.fda.gov/media/71535/download.
22. 	Manufacturing Changes and Comparability for Human Cellular and Gene Therapy
Products; Draft Guidance for Industry, July 2023, available at:
https://www.fda.gov/media/170198/download.
23. 	Human Gene Therapy for Rare Diseases; Guidance for Industry, January 2020, available
at: https://www.fda.gov/media/113807/download.

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24. 	Analytical Procedures and Methods Validation for Drugs and Biologics; Guidance for
Industry, July 2015, available at: https://www.fda.gov/media/87801/download.
25. 	Process Validation: General Principles and Practices; Guidance for Industry, January
2011, available at: https://www.fda.gov/media/71021/download.
26. 	CGMP for Phase 1 Investigational Drugs; Guidance for Industry, July 2008, available at:
https://www.fda.gov/media/70975/download.
27. 	S12 Nonclinical Biodistribution Considerations for Gene Therapy Products; Guidance for
Industry, May 2023, available at: https://www.fda.gov/media/167605/download.
28. 	Long Term Follow-Up After Administration of Human Gene Therapy Products;
Guidance for Industry, January 2020, available at:
https://www.fda.gov/media/113768/download.
29. 	Considerations for the Design and Conduct of Externally Controlled Trials for Drug and
Biological Products; Draft Guidance for Industry, February 2023, available at:
https://www.fda.gov/media/164960/download.
30. 	Rare Diseases: Natural History Studies for Drug Development; Draft Guidance for
Industry, March 2019, available at: https://www.fda.gov/media/122425/download.
31. 	Rare Diseases: Considerations for the Development of Drugs and Biological Products;
Guidance for Industry, December 2023, available at:
https://www.fda.gov/media/119757/download.
32. 	Considerations for the Design of Early-Phase Clinical Trials of Cellular and Gene
Therapy Products; Guidance for Industry, June 2015, available at:
https://www.fda.gov/media/106369/download.
33. 	Providing Clinical Evidence of Effectiveness for Human Drug and Biological Products;
Guidance for Industry, May 1998, available at:
https://www.fda.gov/media/71655/download.
34. 	Clinical Trial Endpoints for the Approval of Cancer Drugs and Biologics; Guidance for
Industry, December 2018, available at: https://www.fda.gov/media/71195/download.
35. 	Demonstrating Substantial Evidence of Effectiveness for Human Drug and Biological
Products; Draft Guidance for Industry, June 2026, available at:
https://www.fda.gov/media/133660/download.

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36. 	Demonstrating Substantial Evidence of Effectiveness With One Adequate and Well-
Controlled Clinical Investigation and Confirmatory Evidence; Draft Guidance for
Industry, September 2023, available at: https://www.fda.gov/media/172166/download.
37. 	Clinical Trial Considerations to Support Accelerated Approval of Oncology
Therapeutics; Draft Guidance for Industry, March 2023, available at:
https://www.fda.gov/media/166431/download.
38. 	Considerations for Discussion of a New Surrogate Endpoint(s) at a Type C PDUFA
Meeting Request; November 2018, available at:
https://www.fda.gov/media/115120/download.
39. 	Chemistry, Manufacturing, and Controls Flexibilities for Developing Human Cellular and
Gene Therapy Products for a Biologics License Application; Guidance for Industry, May
2026, available at: https://www.fda.gov/media/192321/download.
40. 	Expedited Program for Serious Conditions – Accelerated Approval of Drugs and
Biologics: Draft Guidance for Industry, December 2024, available at:
https://www.fda.gov/media/184120/download.