Potency Assurance for Cellular and 
Gene Therapy Products
 
 
 
Draft Guidance for Industry 
 
 
 
 
This guidance document is for comment purposes only. 
 
 
 
 
 
 
Submit one set of either electronic or written comments on this draft guidance by the date 
provided in the Federal Register notice announcing the availability of the draft guidance.  
Submit electronic comments to https://www.regulations.gov.  Submit written comments to the 
Dockets Management Staff (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Rm. 
1061, Rockville, MD 20852.  You should identify all comments with the docket number listed in 
the notice of availability that publishes in the Federal Register. 
 
Additional copies of this guidance are available from the Office of Communication, Outreach 
and Development (OCOD), 10903 New Hampshire Ave., Bldg. 71, Rm. 3128, Silver Spring, 
MD 20993-0002, or by calling 1-800-835-4709 or 240-402-8010, or email ocod@fda.hhs.gov, or 
from the Internet at https://www.fda.gov/vaccines-blood-biologics/guidance-compliance-
regulatory-information-biologies/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 
December 2023  Contains Nonbinding Recommendations 
 
Draft  Not for Implementation 
 
Table of Contents 
 
 
I.  INTRODUCTION............................................................................................................. 1 
II.  BACKGROUND ............................................................................................................... 2 
III.  REGULATORY FRAMEWORK ................................................................................... 3 
A.  Licensed CGT Products ....................................................................................... 3 
B.  Investigational CGT Products ............................................................................. 3 
C.  Current Good Manufacturing Practice .............................................................. 5 
IV.  DEVELOPING A POTENCY ASSURANCE STRATEGY ......................................... 6 
A.  Quality Risk Management and Assurance of Potency ...................................... 6 
B.  Applying Prior Knowledge and Experience ....................................................... 7 
C.  Gaining Product and Process Understanding .................................................... 8 
D.  Risk Assessment .................................................................................................... 9 
E.  Design of the Manufacturing Process ............................................................... 10 
F.  Control Strategy .................................................................................................. 10 
G.  Progressive Implementation of a Potency Assurance Strategy ...................... 12 
H.  Requesting FDA Advice on a Potency Assurance Strategy ............................ 14 
V.  POTENCY ASSAYS AND ACCEPTANCE CRITERIA ........................................... 16 
A.  Uses of Potency Assays ....................................................................................... 16 
B.  Assay Selection and Design ................................................................................ 17 
1.  Desirable Characteristics of Potency Assays .................................................. 18 
2.  Approaches to Potency Assay Selection and Design ...................................... 19 
C.  Assay Control and Change Management ......................................................... 21 
1.  Suitability ........................................................................................................ 21 
2.  Reference Materials ........................................................................................ 22 
3.  Qualification and Validation ........................................................................... 23 
4.  Assay Changes and Transfers ......................................................................... 23 
D.  Acceptance Criteria ............................................................................................ 24 
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Potency Assurance for Cellular and Gene Therapy Products 
1 
2   
3   
Draft Guidance for Industry 
4 
5   
6  This draft guidance, when finalized, will represent the current thinking of the Food and Drug 
7  Administration (FDA or Agency) on this topic.  It does not establish any rights for any person 
8  and is not binding on FDA or the public.  You can use an alternative approach if it satisfies the 
9  requirements of the applicable statutes and regulations.  To discuss an alternative approach, 
10  contact the FDA staff responsible for this guidance as listed on the title page.  
11   
12   
13  I.  INTRODUCTION 
14   
15  This draft guidance provides recommendations for developing a science- and risk-based strategy 
16  to help assure the potency1 of a human cellular therapy2 or gene therapy3 (CGT) product.  A 
17  potency assurance strategy is a multifaceted approach that reduces risks4 to the potency of a 
18  product through manufacturing process design, manufacturing process control, material control, 
19  in-process testing, and potency lot release assays.5  The goal of a potency assurance strategy is to 
20  ensure that every lot of a product released will have the specific ability or capacity to achieve the 
21  intended therapeutic effect.  
22   
23  This draft guidance document, when finalized, will supersede the document entitled Guidance 
24  for Industry:  Potency Tests for Cellular and Gene Therapy Products, dated January 2011 
25  (January 2011 guidance).6  When finalized, this guidance will describe FDAs recommendations 
26  for potency assays for CGT products and for a comprehensive approach to potency assurance 
 
1 As defined in 21 CFR 600.3(s), the word potency is interpreted to mean the specific ability or capacity of the 
product, as indicated by appropriate laboratory tests or by adequately controlled clinical data obtained through the 
administration of the product in the manner intended, to effect a given result. 
2 For the purposes of this guidance, cellular therapy products include tissue-engineered medical products regulated 
under section 351 of the Public Health Service Act (PHS Act) (42 U.S.C. 262). 
3 Human gene therapy seeks to modify or manipulate the expression of a gene or to alter the biological properties of 
living cells for therapeutic use.  FDA generally considers human gene therapy products to include all products that 
mediate their effects by transcription or translation of transferred genetic material, or by specifically altering host 
(human) genetic sequences.  Some examples of gene therapy products include nucleic acids, genetically modified 
microorganisms (e.g., viruses, bacteria, fungi), engineered site-specific nucleases used for human genome editing, 
and ex vivo genetically modified human cells. 
4 Risks are factors that may adversely affect product quality, including product potency.  Sources of risk to the 
potency of a product include, but are not limited to, inadequately designed or poorly controlled manufacturing 
processes, variable materials, and undetected changes in the potency-related attributes of the product. 
5 For the purposes of this guidance document, the term assay is synonymous with the terms test and analytical 
procedure.  Many CGT products undergo release testing using multiple potency assays; the January 2011 guidance 
expresses this concept of multiple assays using the term assay matrix. 
6 See https://www.fda.gov/media/79856/download. 
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27  that is grounded in quality risk management.7  Potency assays remain an important part of 
28  assuring the potency of CGT products, but the comprehensive strategy described in this draft 
29  guidance document also includes complementary approaches to help assure potency.  
30   
31  In general, FDAs guidance documents, including this guidance, do not establish legally 
32  enforceable responsibilities.  Instead, guidances describe the FDAs current thinking on a topic 
33  and should be viewed only as recommendations, unless specific regulatory or statutory 
34  requirements are cited.  The use of the word should in FDAs guidances means that something is 
35  suggested or recommended, but not required. 
36   
37   
38  II.  BACKGROUND 
39   
40  The scope of this guidance document is limited to assuring the potency of CGT products that are 
41  regulated as biological products under section 351 of the Public Health Service Act (PHS Act) 
42  (42 U.S.C. 262).8, 9 
43   
44  This guidance document includes recommendations for helping to assure the potency of CGT 
45  products at all stages of the product lifecycle.  For investigational products, we describe how to 
46  progressively implement a strategy for potency assurance during product development, and we 
47  provide additional considerations for assuring the potency of products that are undergoing rapid 
48  clinical development.  For licensed products, we describe requirements for potency assurance, 
49  including testing required for lot release.  
50   
51  Developing assays that measure the potency of CGT products can be challenging.  In this 
52  guidance document, we emphasize that potency assays and their corresponding acceptance 
53  criteria should be designed to make meaningful contributions to potency assurance by reducing 
54  risks to product potency.  We provide illustrative examples of approaches to potency assay 
55  development that are grounded in quality risk management.  Due to the diversity of CGT 
56  products and the product-specific nature of potency assays, the recommendations in this 
57  guidance document regarding the selection and design of potency assays are necessarily general.  
58  FDA may issue additional guidance documents that provide further advice about potency assays 
59  for specific classes of CGT products.  
60   
61   
 
7 Quality risk management is a systematic process for the assessment, control, communication, and review of risks 
to the quality of the drug product across the product lifecycle.  See Guidance for Industry:  Q9(R1) Quality Risk 
Management; May 2023, https://www.fda.gov/media/167721/download. 
8 Cellular and gene therapy products meet the definition of biological product in section 351(i) of the PHS Act (42 
U.S.C. 262(i)) when such products are applicable to the prevention, treatment, or cure of a disease or condition of 
human beings (see Federal Register Notice:  Application of Current Statutory Authorities to Human Somatic Cell 
Therapy Products and Gene Therapy Products (58 FR 53248, October 14, 1993), 
https://www.fda.gov/media/76647/download). 
9 This guidance does not apply to vaccines for infectious disease indications, bacteriophage products, live 
biotherapeutic products, fecal microbiota for transplantation (FMT) products and allergenic products. 
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62  III.  REGULATORY FRAMEWORK 
63   
64  A.  Licensed CGT Products 
65   
66  To obtain a biologics license, a biologics license application (BLA) must contain data 
67  demonstrating that the product is safe, pure, and potent, and the continued safety, purity, 
68  and potency of the product must be assured.10  Additional potency-related requirements 
69  for licensed products are as follows: 
70   
71    Each lot of product must be tested for potency, and potency assays must be 
72  performed on a sample that is taken after completing all manufacturing steps that 
73  may affect potency.11  The Center for Biologics Evaluation and Research (CBER) 
74  may permit an alternative approach to the requirements for lot release testing for 
75  potency in Title 21 Code of Federal Regulations (CFR) 610.1 and 21 CFR 610.10, 
76  but only if you demonstrate that the alternative approach will provide assurance of 
77  potency that is equal to or greater than the assurance of potency that would be 
78  provided by following the requirements in 21 CFR 610.1 and 21 CFR 610.10.12 
79   
80    Before introducing a change to the manufacturing or testing of an approved 
81  biologic, you must assess the effects of the change, and you must demonstrate that 
82  the change does not adversely affect the potency of the product as it may relate to 
83  the safety or effectiveness of the product.13 
84   
85  B.  Investigational CGT Products 
86   
87  You should describe your strategy for potency assurance in your investigational new drug 
88  application (IND).  Your IND must contain sufficient chemistry, manufacturing and 
89  control information to assure the proper identification, quality, purity and strength14 of 
90  the investigational drug, although the amount of information needed will vary depending 
91  on the phase of the investigation.15  The amount of information that must be submitted to 
92  the IND will increase as you expand the scope of clinical investigations.16  Accordingly, 
93  the degree of potency assurance for a product should be appropriate for the phase of 
94  clinical investigations and should progressively increase during the course of clinical 
95  development, as described in more detail in section IV.G of this guidance. 
96   
 
10 See 42 U.S.C. 262(a)(2)(C)(i), 21 CFR 601.2(a), 21 CFR 601.2(d), and 21 CFR 601.20(c). 
11 See 21 CFR 610.1 and 21 CFR 610.10. 
12 See 21 CFR 610.9. 
13 See 21 CFR 601.12(a)(2). 
14 In this guidance document, the term strength is interpreted to include both the concentration and potency of a 
product. 
15 See 21 CFR 312.23(a)(7)(i). 
16 See 21 CFR 312.23(a)(7)(ii) - (iii). 
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97  During all phases of clinical investigation, your IND must contain sufficient data to 
98  support the stability of the drug substance (DS) and drug product (DP) during planned 
99  clinical investigations.17  Stability studies should include assessments of potency, as 
100  described in more detail in section V.A of this guidance. 
101   
102  FDA may place investigations on clinical hold at any phase if, among other reasons, 
103  subjects would be exposed to an unreasonable and significant risk of illness or injury or if 
104  FDA finds there is insufficient information to assess whether the risks to subjects are 
105  reasonable.18  FDA may place a study on clinical hold on such grounds if the potency of 
106  the product to be administered in an investigation is not adequately assured, or the 
107  information in the IND is not adequate to assure the potency of the product to be 
108  administered in the study.19  
109   
110  FDAs review of INDs for phase 2 and 3 investigations includes assessing the likelihood 
111  that the investigations will yield data capable of meeting statutory standards for 
112  marketing approval,20 and FDA may place a phase 2 or 3 investigation on clinical hold if 
113  the plan or protocol for the investigation is clearly deficient in design to meet its stated 
114  objectives.21  If the lots of product that the sponsor plans to administer in such an 
115  investigation are not consistently potent, then some lots may not have the capacity to 
116  achieve the intended therapeutic effect in subjects, and therefore the investigation may 
117  have reduced statistical power to detect an effect of the product.  In addition, an 
118  investigation conducted with product lots that have unknown or inadequately-controlled 
119  potency may be unable to provide information for ensuring the continued potency of the 
120  product after licensure22 because it may be unclear whether the potency of the licensed 
121  product will be similar to the potency of the lots that were administered in the 
122  investigation.  Therefore, if an IND does not provide adequate assurance of product 
123  potency, a phase 2 or 3 investigation that is intended to provide substantial evidence of 
124  effectiveness for a marketing application may be considered clearly deficient in design to 
125  meet its stated objectives and placed on clinical hold. 
126   
127     
 
17 See 21 CFR 312.23(a)(7)(ii) and 21 CFR 312.23(a)(7)(iv)(a) - (b). 
18 See 21 CFR 312.42(b)(1)(i),(iv) and 21 CFR 312.42(b)(2)(i). 
19 See 21 CFR 312.23(a)(7)(i), 21 CFR 312.42(b)(1)(iv), and 21 CFR 312.42(b)(2)(i). 
20 See 21 CFR 312.22(a). 
21 See 21 CFR 312.42(b)(2)(ii). 
22 See 21 CFR 601.2(d). 
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128  C.  Current Good Manufacturing Practice 
129   
130  The facilities and methods used for manufacturing CGT products must comply with 
131  current good manufacturing practice (CGMP),23 and many aspects of CGMP help to 
132  assure product potency.24  The following recommendations for compliance with CGMP 
133  can also contribute to potency assurance.  These recommendations are discussed in more 
134  detail in the sections of this guidance that follow: 
135   
136    The manufacturing process should be designed and qualified to assure potency of 
137  the product and uniformity of the product from lot to lot.  
138   
139    The materials used for manufacturing may affect the products potency.  Materials 
140  should meet suitable specifications before being used in the manufacturing 
141  process.  
142   
143    Containers, closures, and product-contact equipment should be evaluated for 
144  potential adverse effects on product potency. 
145   
146    Manufacturing process controls and in-process testing should be adequate to help 
147  assure potency of the product.  
148   
149    Potency assays used for lot release should be verified to be suitable for their 
150  intended purpose (able to measure potency with sufficient specificity, accuracy 
151  and/or precision over the reportable range of the assay).  Potency assay 
152  performance characteristics should be established under actual conditions of use 
153  and documented during assay qualification and validation.  
154   
155    Phase-appropriate assays and acceptance criteria for potency should be 
156  established, and lots that fail to meet acceptance criteria should be rejected.  
157   
158  To further facilitate compliance with CGMP, you should develop an effective 
159  pharmaceutical quality system.25  Your overall aim should be to establish a 
 
23 Manufacturing for investigational and licensed 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 (j)).  DP manufacturing must also comply with FDAs CGMP regulations for finished pharmaceuticals in 21 
CFR part 211, except that most phase I investigational drugs are exempt from the requirement to comply with part 
211.  See 21 CFR 210.2(c) and Guidance for Industry:  CGMP for Phase I Investigational Drugs; July 2008, 
https://www.fda.gov/media/70975/download.  
24 As defined in 21 CFR 210.3(b)(16), the term strength encompasses the term potency when the term strength is 
used in the CGMP regulations for finished pharmaceuticals in part 211. 
25 See Guidance for Industry:  Quality Systems Approach to Pharmaceutical CGMP Regulations; September 2006,  
https://www.fda.gov/media/71023/download and Guidance for Industry:  Q10 Pharmaceutical Quality System; April 
2009, https://www.fda.gov/media/71553/download. 
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160  manufacturing process that is in a state of control,26 which will help to assure that the 
161  product will consistently be potent. 
162   
163   
164  IV.  DEVELOPING A POTENCY ASSURANCE STRATEGY 
165   
166  A potency assurance strategy is a comprehensive approach to help ensure that every lot of a 
167  product will have the potency necessary to achieve the intended therapeutic effect.  The 
168  foundation of an effective potency assurance strategy is a manufacturing process that is designed 
169  to consistently produce a potent product.  Potency assurance strategies should also reduce risks 
170  to potency by controlling aspects of the manufacturing process that may affect potency, which 
171  should include controls on material quality, control or monitoring of manufacturing process 
172  parameters, and in-process testing.  Finally, potency assurance strategies should include lot 
173  release testing that confirms that potency-related quality attributes meet appropriate acceptance 
174  criteria.  Lot release testing for most CGT products should include at least one bioassay27 that 
175  measures a biological activity related to the intended therapeutic effect of the product, as 
176  described in more detail in section V of this guidance.  
177   
178  In this section, we provide recommendations for using quality risk management to develop and 
179  refine a potency assurance strategy.  Your potency assurance strategy should evolve during 
180  product development as you gain manufacturing experience and product knowledge. 
181   
182  A.  Quality Risk Management and Assurance of Potency 
183   
184  At all stages of the product lifecycle, you should use quality risk management to assess 
185  risks to product potency and to reduce those risks to acceptable levels.  We recommend 
186  that you consider the following concepts28 when designing a potency assurance strategy 
187  for your product: 
188   
189    Quality target product profile (QTPP).  A QTPP should include a summary of 
190  the potency-related characteristics of the product.  The QTPP should be developed 
191  based on your understanding of the products mechanism of action (MOA), the 
192  intended clinical indication, and the route of administration. 
193   
 
26 A state of control is a condition in which the set of controls consistently provide assurance of continued process 
performance and product quality.  See Guidance for Industry:  Q10 Pharmaceutical Quality System; April 2009, 
https://www.fda.gov/media/71553/download. 
27 The term bioassay generally means an assay that measures the effect of a test article on living cells, tissues, or 
animals.  For the purpose of this guidance document, when discussing products that are themselves composed of 
living cells or tissues, we use the term bioassay more broadly to also include assays that measure a biological 
activity of the living cells or tissues in the product itself.  Additionally, for the purpose of this guidance document, 
assays that are not bioassays are referred to as physicochemical assays. 
28 See Guidance for Industry:  Q8(R2) Pharmaceutical Development; November 2009, 
https://www.fda.gov/media/71535/download and Guidance for Industry:  Q9(R1) Quality Risk Management; May 
2023, https://www.fda.gov/media/167721/download.  
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194    Control strategy.  Manufacturing process controls and product quality controls 
195  play vital roles in potency assurance, as described in more detail in section IV.F 
196  of this guidance.  These controls include process parameters, in-process testing, 
197  material testing or examination, lot release tests, and associated acceptance 
198  criteria. 
199   
200    Critical quality attribute (CQA).  Potency-related CQAs are attributes of the 
201  product that are important for achieving the intended therapeutic effect.  You 
202  should identify the potency-related CQAs of your product to the extent needed to 
203  establish a phase-appropriate control strategy.  Your manufacturing process 
204  should consistently produce lots that have all CQAs within appropriate pre-
205  determined limits.  
206   
207    Critical process parameter (CPP).  CPPs are manufacturing process parameters 
208  that can influence CQAs.  You should identify CPPs that may affect potency-
209  related CQAs, and you should monitor or control these CPPs within appropriate 
210  pre-determined limits.  
211   
212    Risk assessment.  You should identify risks to potency-related CQAs, analyze 
213  the probability and severity of these risks, and evaluate their significance.  You 
214  should assess risks not only when initially designing the manufacturing process 
215  and control strategy, but also throughout the product lifecycle. 
216   
217    Risk reduction.  Any risks to potency-related CQAs that are unacceptably high 
218  should either be avoided or reduced to acceptable levels by appropriately 
219  designing the manufacturing process and control strategy. 
220   
221  B.  Applying Prior Knowledge and Experience 
222   
223  When designing a potency assurance strategy, we recommend that you utilize any 
224  relevant information that is available, including experience from manufacturing and 
225  testing a similar product, published information, and established scientific principles. 
226  Prior knowledge and experience with a specific product class can also help you to 
227  identify potency-related CQAs and assays to measure and control these CQAs. 
228   
229  Although prior knowledge and experience are valuable when initially designing a 
230  products potency assurance strategy, manufacturers should consider that differences 
231  between products (e.g., MOA and intended therapeutic effect), differences in 
232  manufacturing processes, or differences in starting materials may affect potency in 
233  unexpected ways.  For an autologous cell therapy product, for example, the level of the 
234  products potency may be altered when cellular starting materials have been affected by 
235  disease or treatment history.  Therefore, you should perform characterization studies and 
236  risk assessments for your specific product and manufacturing process rather than relying 
237  solely on prior knowledge and experience. 
238   
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239  C.  Gaining Product and Process Understanding 
240   
241  A thorough understanding of the product and the manufacturing process is important for 
242  developing an effective potency assurance strategy.  We recommend that you consider 
243  the following advice at all stages of product development: 
244   
245    Mechanism of action.  An understanding of a products MOA is important when 
246  identifying the products potency-related CQAs and when developing a potency 
247  assurance strategy.  If you do not fully understand your products MOA, you 
248  should continue to seek such understanding during development and then update 
249  the products potency-related CQAs and potency assurance strategy accordingly. 
250  In addition, CGT products often have multiple activities, and the specific 
251  activities that are most relevant to the therapeutic effect may depend on the 
252  targeted disease or condition.  You should therefore consider the intended clinical 
253  indication when determining which quality attributes are relevant to the MOA and 
254  critical for product potency.  
255   
256    Nonclinical studies.  Nonclinical studies conducted early in development may be 
257  useful for learning about your products MOA and for identifying connections 
258  between product attributes and the products potential effect on a disease or 
259  condition.  If available, information from nonclinical studies should be used to 
260  inform your initial potency assurance strategy, including selecting potency-related 
261  CQAs and identifying appropriate acceptance criteria. 
262    
263    Product characterization and identifying CQAs.  Product characterization 
264  refers to assessing a broad range of product attributes to understand the properties 
265  of the product more completely.  Starting from the earliest stages of product 
266  development, we recommend that you conduct product characterization studies to 
267  better understand your products MOA and to help identify product attributes that 
268  may be potency-related CQAs.  We also recommend that you use characterization 
269  data when assessing manufacturing changes.  Assays used in characterization 
270  studies do not necessarily need to be qualified, but they should be scientifically 
271  sound and fit for their intended purpose, be sufficiently precise to detect 
272  meaningful differences in product attributes, and provide results that are reliable. 
273   
274    Establishing a relationship between CQAs and potency.  Potency-related 
275  CQAs should ideally have a clear relationship to the products MOA, and this 
276  relationship should be supported by prior knowledge (such as peer-reviewed 
277  literature), product characterization studies, nonclinical studies, or clinical studies. 
278  For products that have MOAs that are not fully understood, evidence of a 
279  statistical relationship between a product attribute and nonclinical or clinical 
280  outcomes may suggest that the attribute is relevant to potency.  However, a 
281  statistical relationship alone cannot establish a mechanistic relationship between 
282  an attribute and potency.  If needed, you should perform additional experiments or 
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283  studies with the product to determine whether there is a mechanistic relationship 
284  between a candidate potency-related attribute and potency. 
285   
286    Impact of material quality on potency.  During manufacturing process 
287  development, you should determine whether the attributes of the materials used 
288  during manufacturing may affect the products potency-related CQAs.  This 
289  information is valuable for developing material specifications, for performing 
290  supplier qualification, and for managing supply chain risk. 
291   
292    Process characterization and identifying CPPs.  You should perform process 
293  characterization studies to identify CPPs in your manufacturing process that affect 
294  potency-related CQAs, and you should mitigate risks to product potency by 
295  monitoring or controlling these CPPs.  You may adjust CPPs as you gain an 
296  increased understanding of the product and the manufacturing process, but you 
297  should ensure that such changes to CPPs do not increase risks to product potency. 
298   
299  D.  Risk Assessment 
300   
301  As part of quality risk management, you should use formal risk assessment tools to assess 
302  risks to potency comprehensively.29  Risk assessments should start with identifying what 
303  might go wrong:  what are the factors that might adversely affect the potency of your 
304  product both during and after manufacturing?  The process of identifying risks to potency 
305  will be most effective when the products MOA and potency-related CQAs are well 
306  understood and the risks to potency-related CQAs can be determined with confidence. 
307  Your risk assessment should include not only factors that may affect potency at the time 
308  of lot release, but also factors that may affect potency after lot release, such as the 
309  container closure, delivery devices, conditions for drug storage, shipping or handling, and 
310  conditions for thawing or preparing the drug for administration. 
311   
312  Analyzing and evaluating risks to potency can be challenging if assays used to measure 
313  potency-related CQAs have not been qualified to determine whether they have adequate 
314  performance.  Using unqualified assays may decrease your ability to analyze risks to 
315  potency, due to a potential for inconsistent assay performance or uncertainty about the 
316  ability of the assay to detect clinically relevant changes in product potency. 
317   
318  Risks to potency should be reassessed as you increase your understanding of your 
319  product and manufacturing process.  Before implementing manufacturing changes 
 
29 Risk assessment is a process for identifying hazards (e.g., failure modes of a manufacturing process, sources of 
variability), followed by analyzing and evaluating the risk that these hazards might harm product quality.  See 
Guidance for Industry:  Q9(R1) Quality Risk Management; May 2023, 
https://www.fda.gov/media/167721/download. 
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320  (including changes to materials), you should assess the risks that the changes may pose to 
321  product potency.30  
322   
323  Following evaluation of risks, any risks to potency that are unacceptably high should be 
324  mitigated or avoided through the design of the manufacturing process and the control 
325  strategy, as discussed in the following sections of this guidance. 
326   
327  E.  Design of the Manufacturing Process 
328   
329  You should design your manufacturing process with the goal of consistently producing 
330  potent lots.  We recommend that you use prior knowledge and experience to help develop 
331  a manufacturing process that minimizes known or likely risks to potency.  Process 
332  development studies and process design do not need to be performed under CGMP 
333  conditions. 
334   
335  A major contributor to the variability of cellular products is the inherent variability of 
336  cellular starting materials, and manufacturers should assess the impact of such starting 
337  material variability on product potency.  For many cellular products, some degree of 
338  variability in potency-related CQAs is unavoidable.  When feasible, risks to potency 
339  caused by material variability should be mitigated by designing a manufacturing process 
340  with adaptive steps that compensate for variations in the material.31  
341   
342  F.  Control Strategy 
343   
344  Your control strategy should mitigate any unacceptable risks to product potency.  We 
345  recommend that your control strategy include the following elements, as applicable for 
346  the stage of the product lifecycle: 
347   
348    Control of materials.  If a link between a material attribute and product potency 
349  is known or suspected, this attribute should be controlled in the materials 
350  specification by examination of the suppliers test results and/or acceptance 
351  testing for each lot of the material.  For example, if a manufacturing process for a 
352  cellular product includes a growth factor, the potential influence of the growth 
353  factor on the potency of the DP should be assessed.  If necessary to reduce risks to 
354  product potency, the growth factors biological activity32 should be controlled in 
355  the material specification using a bioassay and an appropriate acceptance 
356  criterion. 
357   
 
30 When implementing a manufacturing change for a licensed product, an assessment of the effect of the change on 
potency is required before distributing the post-change product.  See 21 CFR 601.12(a)(2). 
31 See Guidance for Industry:  Q8(R2) Pharmaceutical Development; November 2009, 
https://www.fda.gov/media/71535/download. 
32 For materials, we use the terms biological activity and bioassay instead of the terms potency and potency assay. 
Potency is a property associated with DS and DP, but not materials.  
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358    Process parameters.  When determining the operating ranges for process 
359  parameters, you should assess whether variation in the parameter has the potential 
360  to affect product potency.  When manufacturing some cellular products, for 
361  example, a longer time in culture may decrease potency because of increased cell 
362  death or differentiation.  In such cases, the duration of the culturing step is a CPP 
363  that should be assigned a limit based on prior knowledge and/or data from process 
364  development studies, process characterization studies, or process performance 
365  qualification studies. 
366   
367    In-process testing.  In-process samples should be tested to monitor quality 
368  attributes that may influence or predict product potency.  For cellular products, for 
369  example, we recommend measuring viability, growth rate, and/or phenotype at 
370  relevant stages during manufacturing.  
371   
372    Lot release testing.  Potency release assays and their acceptance criteria are 
373  essential elements of a potency assurance strategy.  As described in more detail in 
374  section V.B of this guidance, risks to potency-related CQAs often cannot 
375  adequately be mitigated by other aspects of the control strategy or process design. 
376  For potency testing of licensed products, potency release assays must be 
377  performed using a sample collected after completion of all manufacturing steps 
378  that may affect potency.33  For example, if cryopreservation of a cellular product 
379  poses a high risk to the products potency, then this risk should be mitigated by 
380  performing the potency assay on a sample taken after cryopreservation.  For 
381  products such as tissue-engineered medical products that are not amenable to 
382  destructive sampling, we recommend that you conduct potency release testing on 
383  an additional unit of the lot that is manufactured in parallel for the specific 
384  purpose of providing a representative sample.  
385   
386    Continued process verification.  During manufacturing of a licensed product, 
387  you should routinely collect and analyze product and process data to verify that 
388  the manufacturing process remains in a state of control that assures potency.34 
389  These analyses may suggest potential opportunities to improve potency assurance 
390  through adjustments to the manufacturing process or control strategy.  In certain 
391  cases, potency assurance may also be improved by including additional testing as 
392  part of continued process verification.  For products that have an extremely short 
393  shelf life with insufficient time to complete a potency bioassay before lot release, 
394  it should be possible to perform lot release testing for potency using 
395  physicochemical assays.  In such cases, we recommend that you also initiate one 
396  or more potency bioassays immediately after manufacturing the DP and evaluate 
397  the results when they become available post-release.  For both investigational and 
 
33 See 21 CFR 610.1 and 21 CFR 610.10. 
34 See Guidance for Industry:  Process Validation:  General Principles and Practices; January 2011, 
https://www.fda.gov/media/71021/download. 
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398  licensed products, such post-release testing will help to verify that the 
399  manufacturing process is continuously capable of producing potent lots.  The 
400  appropriateness and frequency of such post-release testing should be based on a 
401  risk assessment. 
402   
403  If one aspect of the potency assurance strategy cannot adequately mitigate a risk to 
404  product potency, then you should mitigate the risk by strengthening other aspects of the 
405  potency assurance strategy.  For example, lot release testing may not be able to fully 
406  confirm potency if a products potency-related CQAs are poorly understood or difficult to 
407  quantitate, or if a product has an extremely short shelf life that does not allow enough 
408  time to perform a bioassay.  In these cases, other aspects of the potency assurance 
409  strategy (such as process design and process control) will take on increased importance 
410  and should therefore be more stringent and extensive.  
411   
412  G.  Progressive Implementation of a Potency Assurance Strategy 
413   
414  You should have a defined potency assurance strategy throughout all stages of the 
415  product lifecycle, but during the early stages of product development some aspects of 
416  your strategy may not be fully mature.  As you accumulate manufacturing experience and 
417  clinical data, you should progressively refine your risk assessments, manufacturing 
418  process, and control strategy, with the goals of maintaining product potency and 
419  strengthening potency assurance. 
420   
421  Before beginning clinical investigations, you should identify initial potency-related 
422  CQAs for your product, and you should perform a risk assessment and develop a strategy 
423  for reducing risks to these CQAs.  To document that the potency assurance strategy will 
424  ensure an adequate level of potency for conducting early-phase clinical investigations and 
425  to obtain feedback on your plans for strengthening potency assurance, you should include 
426  the following information about your potency assurance strategy in Module 3 of the 
427  Common Technical Document (CTD) of your initial IND submission, and you should 
428  summarize this information in Module 2 of the CTD submission: 
429   
430    Your products MOA and QTPP, a list of your products initial CQAs, and an 
431  explanation of how potency-related CQAs were identified. 
432   
433    A description and justification of your potency assurance strategy, including risk 
434  assessments for potency-related CQAs and an explanation of how your process 
435  design and control strategy reduce risks to these CQAs.  If your control strategy 
436  includes potency testing for lot release, you should provide a description of 
437  potency assays, assay performance characteristics, and justifications for 
438  acceptance criteria.  If your control strategy does not include potency testing for 
439  lot release, you should explain how other aspects of your process design and 
440  control strategy provide adequate potency assurance for a product in early-phase 
441  clinical investigations. 
442   
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443    General descriptions of your plans for additional product characterization, plans 
444  for potency assay development, and plans for further strengthening your potency 
445  assurance strategy during product development. 
446   
447  Throughout early-phase clinical investigations, you should reassess and refine your 
448  products QTPP, CQAs, CPPs, and potency assurance strategy.  By later stages of clinical 
449  development, you should have developed a comprehensive potency assurance strategy 
450  that includes potency assays with appropriate acceptance criteria.35 
451   
452  As discussed in section III.B of this guidance, FDA may place certain investigations on 
453  clinical hold if the potency of the product is not adequately assured.  Before beginning 
454  clinical investigations that involve significant risk or clinical investigations that are 
455  intended to provide substantial evidence of effectiveness to support a marketing 
456  application, the manufacturing process and the control strategy should provide phase-
457  appropriate assurance that each lot of the product will be potent.  Your control strategy 
458  for a product used in such investigations should include at least one physicochemical 
459  assay or bioassay that is performed on a suitable sample for lot release and that 
460  quantitates a potency-related CQA.  Your control strategy should include acceptance 
461  criteria that are appropriate for the phase of investigation and that will result in rejection 
462  of sub-potent lots.  Potency assays for products used in these types of clinical 
463  investigations should be qualified to demonstrate that the performance characteristics of 
464  the assays are fit for the intended purpose of the assay.  Additionally, you should have 
465  evidence that potency-related CQAs are stable during storage and during preparation of 
466  the product for administration.  
467   
468  Before submitting a BLA, you should use all available product quality data and clinical 
469  data to reassess and refine your potency assurance strategy.  Assays used for lot release 
470  and in-process testing must be validated.36  You should describe the potency assays and 
471  reference materials that will be used for the licensed product, and you should explain and 
472  justify the impact of any differences from the potency assays and reference materials that 
473  were used during the clinical investigations that provide the primary evidence of 
474  effectiveness. 
475   
476  The potency assurance strategy in a BLA should be designed using knowledge gathered 
477  throughout development.  For products in rapid clinical development programs, however, 
478  it can be challenging to gather this knowledge quickly.  If you anticipate a compressed 
479  development timeline, we recommend that you thoroughly characterize the product and 
480  manufacturing process to help you rapidly establish a well-controlled manufacturing 
481  process that consistently yields a potent product.  We also recommend that you develop, 
482  qualify, and implement potency assays before the initiation of clinical investigations. 
483  Implementing potency assays will allow you to confirm product potency and to collect 
 
35 Final acceptance criteria for the DS and DP are not expected until the end of clinical development.  See 21 CFR 
312.23(a)(7)(i). 
36 See 21 CFR 211.165(e) and 21 CFR 211.194(a)(2). 
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484  reliable potency data during even the earliest stages of clinical development.  To increase 
485  the likelihood that the potency assays you develop will be usable for release of a licensed 
486  product, we recommend developing multiple assays that measure known or potential 
487  potency-related CQAs.  We recommend that you evaluate the utility of these assays in 
488  parallel during early clinical investigations.  Assays that are redundant may be 
489  discontinued later in development, as described in section V.B.1 of this guidance. 
490   
491  H.  Requesting FDA Advice on a Potency Assurance Strategy 
492   
493  You should engage CBER early in development for feedback on your potency assurance 
494  strategy and your plans for developing potency assays.  You should provide a detailed 
495  assessment of the risks to the potency of your product and explain how your potency 
496  assurance strategy reduces each of the identified risks to levels that are acceptable for the 
497  products stage of clinical development.  We also recommend that you consult CBER 
498  before making major changes to your potency assurance strategy. 
499   
500  We recommend that you request feedback either by asking CBER specific questions 
501  during meetings or by submitting an amendment to your IND that provides relevant 
502  background information and asks questions.37  Your questions should be specific, rather 
503  than general or open-ended.  During a meeting, you should limit discussion to the 
504  questions that you asked in the briefing materials; CBER cannot provide substantive 
505  feedback on new data or questions that you did not include in the briefing materials.  
506   
507  When asking for feedback on a potency assay, you should: 
508   
509    Explain how the attribute measured by the assay is relevant to the products MOA 
510  and the desired therapeutic effect.  You should include supporting data, if 
511  available. 
512   
513    Provide a clear description of the assay (e.g., reagents, reference materials, 
514  number of replicates, controls, method of analysis) and justification for the assay 
515  design.  Assay descriptions should include sufficient detail to understand the 
516  assay, yet should be written concisely.  We do not recommend that you submit 
517  assay protocols in meeting packages, unless specifically requested to do so. 
518   
519    Provide a summary of any available information about the performance 
520  characteristics of the assay.  We recommend that you also provide an assay 
521  qualification or validation report, if available. 
522   
523    Describe any limitations of the potency assay and explain why the assay is 
524  suitable for its intended purpose, despite these limitations. 
525   
 
37 See 21 CFR 312.31(b)(3). 
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526   
527     
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528  V.  POTENCY ASSAYS AND ACCEPTANCE CRITERIA 
529 
 
530  A.  Uses of Potency Assays  
531   
532 
Assays measuring potency-related CQAs are critical for developing an effective potency 
533 
assurance strategy and should be used in several ways throughout the product lifecycle. 
534 
 
535    Lot release testing.  Although the potency of a product cannot adequately be 
536  assured through release testing alone, release testing should be a key component 
537  of your potency assurance strategy.  Meeting potency acceptance criteria at the 
538  time of lot release helps to confirm that the lot released will be acceptably potent. 
539  One or more potency assays are required for lot release of licensed biologics.38  
540   
541    Stability evaluation.  When feasible, we recommend that you identify potency-
542  related CQAs that are stability-indicating by using forced degradation studies, 
543  real-time studies, or prior knowledge and experience.  Stability studies should 
544  include assays that quantitate these stability-indicating CQAs, and you should 
545  evaluate potency data from product stored at the relevant long-term condition 
546  when establishing a shelf life for your product.  If justified, acceptance criteria for 
547  potency-related CQAs in stability studies may be different from acceptance 
548  criteria used for lot release, but stability acceptance criteria for potency should 
549  still reflect the range of potency that is needed to mediate the intended therapeutic 
550  effect. 
551   
552    In-use studies and delivery device compatibility studies.  You should perform 
553  studies to evaluate whether your products potency will remain acceptable during 
554  preparation of the product and during administration through delivery devices.  If 
555  you anticipate a variety of delivery devices or in-use conditions, these studies 
556  should encompass or bracket the entire range of delivery devices or conditions, 
557  including the anticipated worst-case conditions. 
558   
559    Comparability studies.  If you change a products manufacturing process, this 
560  change should be supported by risk assessments and studies that demonstrate that 
561  the change does not adversely affect the potency of the product.39, 40 
562  Manufacturing changes typically pose different risks to product quality than the 
563  risks encountered during routine manufacturing, and therefore you should assess 
564  the risk that manufacturing changes may affect potency-related attributes that are 
565  not evaluated by routine lot release tests.  Comparability studies should include 
 
38 See 21 CFR 610.10. 
39 See Draft Guidance Document:  Manufacturing Changes and Comparability for Human Cellular and Gene 
Therapy Products; July 2023, https://www.fda.gov/media/170198/download.  When final, this guidance will 
represent the FDAs current thinking on this topic. 
40 For a licensed product, such assessments and studies are required before distributing the post-change product.  See 
21 CFR 601.12(a)(2). 
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566  analyzing data from the potency assays that are used for lot release and, if 
567  necessary, performing additional characterization studies of potency-related 
568  attributes that are at risk from the manufacturing change. 
569   
570    Manufacturing process studies.  An understanding of how manufacturing steps 
571  affect product potency is crucial for designing a manufacturing process and 
572  control strategy that assure potency adequately.  We recommend that you use 
573  potency assays during process development studies, process characterization 
574  studies, process qualification studies, and continued process verification studies. 
575  Data from these studies should be used in risk assessments to identify steps in the 
576  manufacturing process that should be adjusted, monitored, or controlled to 
577  improve potency assurance.  
578   
579  B.  Assay Selection and Design 
580   
581  Because CGT products usually have multiple potency-related CQAs that cannot be 
582  controlled adequately without release testing, your potency assurance strategy should 
583  typically include multiple release assays, each of which quantitates a potency-related 
584  CQA that is at risk.  These assays may include physicochemical assays and/or bioassays. 
585  However, some potency-related CQAs that are related to a CGT products biological 
586  activity can only be measured effectively with a bioassay, and if so we recommend that 
587  your potency assurance strategy include at least one bioassay.  The central purpose of the 
588  bioassay should be to quantitate a potency-related CQA that is at risk, and it is not 
589  essential for the bioassay to mimic the products MOA.  Rather, your understanding of 
590  the MOA should help to drive selection of the products potency-related CQAs. 
591   
592  Some CGT products consist of multiple active ingredients.41, 42 For products that are 
593  subject to the requirements of 21 CFR part 211, there must be lot release testing to assess 
594  the strength of each active ingredient in the DP, which requires measuring the 
595  concentration or potency of each of the active ingredients.43  For some CGT products that 
596  consist of multiple active ingredients, one bioassay may be sufficient to assess the 
597  potency of all of the active ingredients together (i.e., additional bioassays would not be 
598  needed to address risks to potency-related CQAs).  In such cases, there should also be 
599  additional physicochemical assays to measure the concentration of each of the individual 
600  active ingredients. 
601   
 
41 See 21 CFR 210.3(b)(7). 
42 Note that a CGT product that includes cells of multiple types does not necessarily have multiple active 
ingredients.  For example, some CGT products consist of a complex mixture of different cell types, where the 
contribution of each cell type to the activity of the product as a whole is either unknown or is intertwined with the 
contribution of other cell types in the mixture.  In such cases, the activity of the product is based on the totality of 
the cells in the mixture, and therefore the mixture of cells would be considered to be a single active ingredient. 
43 See 21 CFR 210.3(b)(16) and 21 CFR 211.165(a). 
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602  We recommend using risk assessment and prior knowledge and experience to identify 
603  how assay design, reagents, and parameters affect assay performance, and we recommend 
604  that you mitigate any unacceptable risks to assay performance through the design of the 
605  assay and its control strategy.44 
606   
607  1.  Desirable Characteristics of Potency Assays 
608   
609    The assay should mitigate a risk to product potency.  Potency lot release 
610  assays reduce risk by detecting problems with potency-related CQAs, ideally 
611  leading to rejection of lots with unacceptable potency.  You should implement 
612  lot release assays for potency-related CQAs that are at risk.  If you 
613  demonstrate that other aspects of the process design or control strategy 
614  adequately ensure that a particular potency-related CQA will remain within 
615  acceptable limits, then a lot release assay for that CQA may not be needed.  
616  As noted in section V.D of this guidance, each lot release assay should have 
617  an appropriate quantitative acceptance criterion that mitigates risk to the 
618  potency-related CQA.  
619   
620    The assay should be precise.  Using an assay that has poor precision (high 
621  standard deviation, relative to the width of the acceptance criterion) increases 
622  the likelihood that a potent lot will be rejected or that a sub-potent lot will fail 
623  to be rejected.  Bioassays may have substantial variability that can be difficult 
624  to eliminate.  In such cases, we recommend that potency bioassays be 
625  designed to quantitate potency relative to a reference material, which will 
626  increase the precision of the reportable value for the bioassay.  If assay 
627  precision cannot be sufficiently improved by changing the design of the assay, 
628  then we recommend that you reduce the standard uncertainty of the 
629  measurement by routinely performing multiple independent assay runs for 
630  each sample and reporting the mean value.45  The number of runs should be 
631  pre-specified in the assay protocol. 
632   
633    The assay should be accurate.  An inaccurate assay will produce biased 
634  results that do not closely match expected values.  The assay should have 
635  adequate precision and accuracy across the reportable range of the assay.  
636   
637    The assay should be specific.  Specificity should be demonstrated by testing 
638  non-potent product samples during assay qualification.  When feasible, we 
639  recommend that specificity be evaluated using a very similar product (or an 
 
44 See Draft Guidance Document:  Q14 Analytical Procedure Development; August 2022, 
https://www.fda.gov/media/161202/download.  When final, this guidance will represent the FDAs current thinking 
on this topic. 
45 For a normally-distributed variable x with a standard deviation of s, if n independent measurements of x are 
s
acquired, then the standard uncertainty  of the mean value x can be estimated as  =  . 
x n
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640  altered version of the product) that does not possess the potency-related 
641  attribute that is detected by the assay.  In addition, specificity should be 
642  demonstrated by showing lack of interference from relevant product-related 
643  impurities and sample matrices. 
644   
645    The assay should be robust.  If not, assay results may be unreliable and there 
646  may be frequent invalid assay runs.  You should build robustness into the 
647  assay using a quality risk management approach by identifying the potential 
648  sources of assay unreliability and either eliminating them or mitigating their 
649  impact.  
650   
651    Minimize assay redundancy.  A potency assay that measures one quality 
652  attribute may mitigate risks to other related quality attributes.  For example: 
653   
654  -  The MOA for a CGT product often depends on a stepwise chain of 
655  biological activities that occur after administration.  The process 
656  design and the control strategy should provide assurance that each lot 
657  of the product can carry out these biological activities, but it may not 
658  be necessary to test each of the activities directly.  For example, if a 
659  later step in the chain of biological activities is completely dependent 
660  on the earlier steps, then a bioassay at the later step that adequately 
661  ensures the products biological activity at that step will typically be 
662  sufficient to also ensure the biological activities at the earlier steps.  
663   
664  -  Some active ingredients have multiple linked biological activities that 
665  each contribute to the efficacy of the product.  In such cases, we 
666  recommend that you evaluate whether a bioassay that adequately 
667  controls one of these biological activities might also mitigate risks to 
668  the other linked biological activities, potentially in conjunction with 
669  relevant physicochemical assays.  If so, a separate bioassay to measure 
670  each biological activity may not be necessary for assuring potency of 
671  the active ingredient. 
672   
673    Minimize the use of animals in potency assays.  We encourage replacement, 
674  reduction, or refinement of animal usage in assays.46  We recommend that you 
675  use in vitro bioassays instead of animal-based bioassays when it is possible to 
676  do so without compromising potency assurance. 
677   
678  2.  Approaches to Potency Assay Selection and Design 
679   
 
46 For further information about FDAs approach to alternative methods, see https://www.fda.gov/science-
research/about-science-research-fda/advancing-alternative-methods-fda. 
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680  Examples of recommended approaches to potency assay selection are listed 
681  below.  These examples are not intended to cover all situations, and we emphasize 
682  that alternative approaches may also be acceptable. 
683   
684    For a cellular product:  A potency assay should measure a product 
685  attribute that is relevant to the products intended therapeutic effect.  
686  However, identifying such attributes for cellular products can be 
687  challenging if the MOA is complex or poorly-defined.  We recommend 
688  that you use nonclinical data and published scientific studies when 
689  identifying candidate potency-related CQAs and that you assess a broad 
690  range of attributes early in development during product characterization 
691  studies.  Such data or studies may reveal certain protein expression 
692  patterns or other attributes that are associated with the products biological 
693  activity.  If a mechanistic relationship between an attribute and the 
694  products biological activity can be established, this attribute may be a 
695  potency-related CQA.  If risks to a potency-related CQA cannot be 
696  adequately mitigated through other aspects of your potency assurance 
697  strategy, then you should include an assay for this CQA as one of the 
698  potency assays in the products lot release specification. 
699   
700    For a product with an extremely short shelf life:  There may not be 
701  sufficient time to perform a bioassay before the release of a short-lived 
702  product, such as a non-cryopreserved cellular therapy product.  Therefore, 
703  in addition to one or more physicochemical potency assays that are 
704  performed on a sample of the DP for lot release, your strategy for assuring 
705  the potency of such a product should incorporate sufficient in-process 
706  testing for attributes that predict product potency. In addition, for 
707  investigational products with an extremely short shelf life, you should 
708  initiate one or more potency bioassays immediately after manufacturing 
709  the DP and evaluate the results when they become available post-release, 
710  with the goal of confirming product potency and manufacturing process 
711  reliability.  Post-release potency bioassays should also be part of potency 
712  assurance for licensed products that have an extremely short shelf life, if 
713  the bioassays add value to continued process verification and reduce risks 
714  to potency.47 
715   
716    For a viral gene therapy vector intended for direct administration:  
717  Even at the earliest stage of product development, release testing for a 
718  gene therapy vector that expresses a transgene should generally include a 
719  potency assay that quantitates transgene mRNA or protein in transduced 
720  cells.  During further development of the product, you should also 
 
47 If a released lot of a licensed product is discovered to have unacceptable potency after distribution, you must 
submit a biological product deviation report to CBER.  See 21 CFR 600.14(b). 
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721  comprehensively evaluate risks to the potency-related CQAs of the vector 
722  particles and risks to the vectors nucleic acids.  For example, risks to the 
723  vector particles might compromise their structural integrity or ability to 
724  deliver nucleic acids to cells.  Risks to the nucleic acids might 
725  compromise their length, sequence, or activity.  For any risks to potency-
726  related CQAs that are not adequately mitigated by your manufacturing 
727  process design or control strategy, you should reduce the remaining risks 
728  to acceptable levels by implementing additional potency assays with 
729  appropriate quantitative acceptance criteria.  
730   
731    For vector-transduced patient-specific cellular products:  When 
732  products are manufactured on demand for individual patients, the failure 
733  of a vector-transduced cellular DP lot to meet specifications may 
734  significantly delay patient treatment while another lot is manufactured.  To 
735  reduce the risk of manufacturing a sub-potent lot of cellular DP, you 
736  should demonstrate that each vector lot has adequate biological activity 
737  before it is used for manufacturing cellular DP. Therefore, your strategy 
738  for assuring potency of the cellular DP should include not only a potency 
739  assay and quantitative acceptance criterion for DP lot release, but also a 
740  bioassay and quantitative acceptance criterion for release of each vector 
741  lot. 
742   
743    For a tissue-engineered medical product:  The potency of tissue-
744  engineered medical products can depend on a wide range of physical, 
745  structural, and biological factors.  Therefore, we recommend collecting a 
746  comprehensive set of characterization data from cells, scaffolds, or both 
747  (as applicable), using non-destructive and destructive assays to 
748  characterize physical, biomolecular, biochemical, immunological, and 
749  other biological properties.  These characterization data may reveal 
750  biological, chemical, biomechanical, or physiological attributes that may 
751  be mechanistically related to the products biological activity and may 
752  predict the potency of the tissue-engineered medical product.  If such an 
753  attribute is a potency-related CQA and a risk assessment determines that 
754  other aspects of your potency assurance strategy cannot adequately 
755  mitigate risks to this CQA, then you should include an assay for this CQA 
756  as one of the potency assays in the products lot release specification.  
757   
758  C.  Assay Control and Change Management 
759   
760  1.  Suitability 
761   
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762  Potency assay protocols should include pre-defined acceptance criteria for sample 
763  suitability and system suitability.48  Sample and system suitability criteria should 
764  be established based on risk assessment of the assay, and these suitability criteria 
765  should be designed to detect when the assay fails to perform properly.  An assay 
766  run should be invalidated if suitability criteria are not met.  
767   
768  Typical sample suitability assessments for potency assays should include 
769  acceptance criteria for the sample response curve and limits on variability among 
770  sample replicates.  Typical system suitability tests should include verifying that 
771  reference materials, positive controls, and negative controls meet pre-defined 
772  acceptance criteria.  In addition to establishing these suitability acceptance 
773  criteria, we recommend that you use control chart analysis49 of control sample 
774  data to detect any adverse trends in potency assay performance over time, as part 
775  of lifecycle management of the assay.50 
776   
777  2.  Reference Materials 
778   
779  Many potency assays are bioassays that are calibrated relative to a reference 
780  material that has been assigned an arbitrary potency value (e.g., 100%). For CGT 
781  products, there may be no compendial standard or otherwise-recognized standard 
782  that is relevant to assessing the potency of your product.  In such cases, you 
783  should develop an in-house reference material.  It is often appropriate to designate 
784  a well-characterized lot of DP as a reference material.  
785   
786  You should establish a protocol for qualifying reference material lots, including 
787  replacement reference material lots.  We recommend that you thoroughly qualify 
788  reference material lots using both routine release assays and in-depth 
789  characterization studies.  Reference material lots should also be monitored to 
790  evaluate their stability.  Before exhausting the supply of your current lot of 
791  reference material, you should evaluate the potency of a replacement lot using 
792  multiple independent assays run against the current lot, and you should use these 
793  data and pre-specified statistical procedures to assign a potency value to the 
794  replacement reference material lot.  
795   
796  In addition to the reference material that is used as a calibrator in each assay run, 
797  we recommend that each assay run also include a separate control material for use 
798  as a system suitability test, unless risk assessment of the assay indicates that such 
 
48 See Draft Guidance Document:  Q14 Analytical Procedure Development; August 2022, 
https://www.fda.gov/media/161202/download.  When final, this guidance will represent the FDAs current thinking 
on this topic. 
49 See Guidance for Industry:  Q9(R1) Quality Risk Management; May 2023, 
https://www.fda.gov/media/167721/download. 
50 See Guidance for Industry:  Analytical Procedures and Methods Validation for Drugs and Biologics; July 2015, 
https://www.fda.gov/media/87801/download. 
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799  a system suitability test is not necessary to assure the proper performance of the 
800  assay.  Any new lot of control material should be qualified using multiple potency 
801  assay runs, and you should use the data from these runs to assign an expected 
802  potency range to the lot of control material for the system suitability test. 
803   
804  3.  Qualification and Validation 
805   
806  Assay qualification involves determining the assays performance characteristics 
807  (e.g., accuracy, precision, specificity, and sensitivity).  Qualifying a potency assay 
808  allows one to determine whether assay performance is adequate for the intended 
809  purpose of helping to assure product potency, or whether assay performance 
810  instead needs to be further optimized.  Potency assays should be qualified as soon 
811  as feasible, and no later than the initiation of clinical investigations that are 
812  intended to provide substantial evidence of safety and effectiveness for a 
813  marketing application.  
814   
815  DP release assays for a licensed product must be validated.51  Assay validation 
816  should confirm the performance characteristics of the fully-optimized assay by 
817  comparing assay performance during the validation study to appropriate pre-
818  specified acceptance criteria for accuracy, precision, specificity, and other 
819  relevant performance characteristics.52  If robustness was not thoroughly 
820  evaluated and documented during assay development or qualification (or if there 
821  were post-qualification changes to the assay that might make it less robust), then 
822  robustness should be evaluated during assay validation to confirm that you have 
823  adequate understanding and control of the conditions and parameters that affect 
824  assay performance. 
825   
826  Many potency assays are bioassays, and bioassays are susceptible to numerous 
827  difficult-to-control sources of variability, including variability among instruments, 
828  variability among analysts running the assay, and variability among the lots of 
829  cells or other biological reagents used in the bioassay.  We recommend that you 
830  identify potential sources of variability that pose risks to assay performance, and 
831  you should evaluate the effect of these sources of variability on performance 
832  characteristics such as precision and accuracy.  If unacceptable risks are 
833  identified, you should reduce these risks to acceptable levels by either changing 
834  the design of the assay or improving control of the assay, for example by 
835  including additional control materials. 
836   
837  4.  Assay Changes and Transfers 
838   
 
51 See 21 CFR 211.165(e) and 21 CFR 211.194(a)(2).   
52 See Guidance for Industry:  Analytical Procedures and Methods Validation for Drugs and Biologics; July 2015, 
https://www.fda.gov/media/87801/download and Q2(R1) Validation of Analytical Procedures:  Text and 
Methodology Guidance for Industry; September 2021, https://www.fda.gov/media/152208/download. 
23  Contains Nonbinding Recommendations 
 
Draft  Not for Implementation 
 
839  When replacing or changing a validated potency assay, you should validate any 
840  new assay or perform partial revalidation of any changed assay, with the goal of 
841  achieving at least the same degree of control of the potency-related attribute as 
842  with the original assay.  When transferring a potency assay to a new laboratory, 
843  you should perform a risk assessment and prospectively design an assay transfer 
844  study that has sufficient statistical power to evaluate assay reproducibility 
845  between the original and the new laboratories.53  We recommend using 
846  equivalence testing to evaluate whether results from the new potency assay or 
847  new laboratory are sufficiently similar to results from the original assay or 
848  original laboratory. 
849   
850  D.  Acceptance Criteria 
851   
852  Assays for potency-related CQAs should include quantitative acceptance criteria that 
853  contribute to potency assurance by mitigating risks to the potency-related CQAs.  You 
854  should use a quality risk management approach to determine initial acceptance criteria, 
855  and you should refine the acceptance criteria based on additional risk assessments as you 
856  gain manufacturing experience and product knowledge.  We do not recommend 
857  acceptance criteria of report or for information only for release assays, because such 
858  acceptance criteria do not add to potency assurance. 
859   
860  The acceptance criteria for a potency assay should include an appropriate quantitative 
861  lower limit to confirm that each lot has an adequate ability or capacity to mediate the 
862  intended therapeutic effect.  If your product has biological activities that pose potential 
863  safety risks (or if it is unclear whether a product with high potency will be safe), you 
864  should also use available manufacturing data, nonclinical studies, and/or clinical 
865  experience to set an appropriate quantitative upper limit to confirm that the potency of 
866  each lot will not be in a potentially unsafe range.  
867   
868  For cellular products that have high inherent variability, acceptance criteria for potency 
869  release assays may be relatively permissive in early development, if justified in your 
870  IND.  However, the acceptance criteria should ensure that lots will be rejected if their 
871  potency is outside of the expected range, as guided by available manufacturing data, 
872  nonclinical studies, and/or clinical experience. 
873   
874  For a licensed product, acceptance criteria for potency release assays should link product 
875  potency to evidence of clinical effectiveness from clinical investigations.  Specifically, 
876  the acceptance criteria should be designed to ensure that the potency of the lots 
877  distributed under the license will be consistent with the potency of the lots that were 
878  administered to subjects in the clinical investigations that provided the primary evidence 
879  of the products effectiveness. 
 
53 See Guidance for Industry:  Analytical Procedures and Methods Validation for Drugs and Biologics; July 2015, 
https://www.fda.gov/media/87801/download.  
24  Contains Nonbinding Recommendations 
 
Draft  Not for Implementation 
 
880   
881  As noted in section V.A of this guidance, potency assays have important uses beyond 
882  controlling potency for lot release, including assessing product stability, delivery device 
883  compatibility, and product comparability after a manufacturing change.  The acceptance 
884  criteria for these types of assessments should be selected using a quality risk management 
885  approach, and they may differ from acceptance criteria for lot release.  
25