On August 20, 2026, the U.S. Food and Drug Administration's (FDA) Center for Biologics Evaluation and Research (CBER) published a landmark draft guidance for industry titled "Potency Assessment of Active Immunotherapy Products" (FR Doc. 2026-16960; 91 FR 53880–53881; Docket No. FDA-2026-D-8561).
The guidance establishes CBER's current thinking on designing, validating, and implementing potency test methods for active immunotherapy products (ACTIMPs). Public comments on the docket are open for a 90-day consultation period through November 18, 2026. The Federal Register notice lists Janet Goldberg, CBER, at 240-402-7911 as the contact.
For Chemistry, Manufacturing, and Controls (CMC) leads, analytical development heads, and regulatory executives developing personalized cancer vaccines, neoantigen peptides, mRNA constructs, and cell-based immunotherapies, the document resolves a critical operational tension:
For an individualized, patient-specific neoantigen product where every manufacturing batch contains a unique sequence of peptides or mRNA transcripts, must the sponsor develop and execute a living biological potency assay (bioassay) for every single patient lot in Phase 1 clinical trials—and is updating the in silico neoantigen prediction algorithm treated as an internal software edit or a reportable CMC change?
The direct regulatory answer is no, a per-lot biological bioassay is not mandatory in Phase 1 if sequence confirmation and pipeline justification are established. A bioinformatics-pipeline change that may alter predicted epitopes or potency-related CQAs is not an internal software ticket: the draft says additional studies may be needed and that such a change can affect safety and effectiveness and is subject to reporting. It does not, in this document, assign that change to a Prior Approval Supplement versus a CBE-30.
Under the August 2026 draft guidance, CBER introduces a pragmatic, risk-based potency framework tailored to individualized medicine. For personalized peptide- and protein-based ACTIMPs, Phase 1 potency may be inferred from sequence confirmation supported by scientific justification of the bioinformatics pipeline. In later-phase trials, if epitopes are manufactured using a qualified process and justified pipeline, physicochemical testing of potency-related Critical Quality Attributes (CQAs) may be sufficient for lot release without developing a unique biological bioassay for every patient lot.
However, because the in silico algorithm dictates the pharmaceutical identity and biological activity of the final product, any change to the bioinformatics pipeline that could alter epitope selection or potency-related CQAs is a reportable manufacturing change under 21 CFR 312.31 and 21 CFR 601.12.
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ CBER ACTIMP POTENCY DRAFT GUIDANCE: REGULATORY SNAPSHOT │
├─────────────────────────────────────┬────────────────────────────────────────────────────────┤
│ Parameter │ Published Regulatory Specification │
├─────────────────────────────────────┼────────────────────────────────────────────────────────┤
│ Guidance Title │ Potency Assessment of Active Immunotherapy Products │
│ Issuing Center │ Center for Biologics Evaluation and Research (CBER) │
│ Federal Register Notice │ FR Doc. 2026-16960; 91 FR 53880–53881 (August 20, 2026)│
│ Agency Docket Number │ Docket No. FDA-2026-D-8561 │
│ Public Comment Deadline │ November 18, 2026 (90-day comment period) │
│ Statutory Potency Definition │ 21 CFR § 600.3(s) & Section 351 of PHS Act │
│ Relationship to Prior Guidance │ Supplements (does not replace) Dec 2023 CGT Draft │
│ Legal Status under 21 CFR 10.115 │ Draft — Not for Implementation; Nonbinding GGP │
│ Core Personalized Flexibilities │ Phase 1 sequence inference; later physicochemical CQAs │
│ Pipeline Governance Standard │ Algorithmic changes are reportable CMC (312.31/601.12) │
└─────────────────────────────────────┴────────────────────────────────────────────────────────┘
Below, we dissect the scope boundaries of ACTIMPs, contrast the 2026 draft with the December 2023 Cell and Gene Therapy (CGT) potency assurance framework, analyze the phased lot-release criteria for individualized neoantigens, evaluate the regulatory governance of bioinformatics pipelines, and contextualize the guidance against an independent ClinicalTrials.gov census of matched interventional neoantigen records.
Defining ACTIMPs: What Is in Scope and What Is Explicitly Excluded
A central achievement of the August 2026 draft is establishing a precise regulatory definition for Active Immunotherapy Products (ACTIMPs) within biological product oversight.
What Constitutes an ACTIMP?
Under the guidance, an ACTIMP is defined as a biological product intended to treat a pre-existing disease or clinical condition by inducing, stimulating, or modulating immune effector cells (such as antigen-specific T cells, B cells, natural killer cells, or antigen-presenting cells).
The scope spans diverse structural modalities:
- Personalized Neoantigen Therapies: Synthetic peptides, recombinant proteins, individualized mRNA lipid nanoparticles (LNPs), and DNA plasmids encoding patient-specific tumor mutations.
- Shared Antigen Immunotherapies: Off-the-shelf therapeutic cancer vaccines targeting shared tumor-associated antigens (e.g., NY-ESO-1, MAGE-A3, WT1).
- Oncolytic Viral Therapies: Genetically modified replication-competent or attenuated viruses designed to lyse tumor cells and stimulate systemic anti-tumor immunity.
- Immune Cell Therapies: Autologous or allogeneic dendritic cell vaccines, tumor-infiltrating lymphocytes (TILs), and engineered T-cell receptor (TCR) cell therapies intended for active immune induction.
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ ACTIMP SCOPE BOUNDARIES: INCLUSIONS VS. EXCLUSIONS │
├──────────────────────────────────────┬───────────────────────────────────────────────────────┤
│ Product Category / Modality │ CBER Regulatory Scope Determination │
├──────────────────────────────────────┼───────────────────────────────────────────────────────┤
│ Personalized Peptide / mRNA Vaccines │ IN SCOPE (Personalized ACTIMP Section) │
│ Shared Tumor Antigen Cancer Vaccines │ IN SCOPE (Conventional ACTIMP Section) │
│ Oncolytic Viruses (Therapeutic) │ IN SCOPE (Vector / Oncolytic ACTIMP Section) │
│ Dendritic Cell / Antigen-Loaded Cells│ IN SCOPE (Cell-Based ACTIMP Section) │
├──────────────────────────────────────┼───────────────────────────────────────────────────────┤
│ Preventive Infectious-Disease Vaccine│ EXPLICITLY OUT OF SCOPE (Standard CBER Vaccine Rules) │
│ Bacteriophage Therapies │ EXPLICITLY OUT OF SCOPE │
│ Live Biotherapeutic Products (LBPs) │ EXPLICITLY OUT OF SCOPE (Covered by 2016 LBP Guidance)│
│ Fecal Microbiota for Transplantation │ EXPLICITLY OUT OF SCOPE (Covered by CBER FMT Rules) │
│ Allergenic Products / Extracts │ EXPLICITLY OUT OF SCOPE (21 CFR Part 680) │
└──────────────────────────────────────┴───────────────────────────────────────────────────────┘
The Explicit Scope Exclusions
To prevent regulatory conflation across biologics review divisions, CBER explicitly excluded five major biological product categories from the ACTIMP guidance:
- Preventive Vaccines for Infectious Diseases: Standard prophylactic vaccines (e.g., influenza, RSV, COVID-19, pneumococcal) remain governed by traditional CBER Office of Vaccines Research and Review (OVRR) standards.
- Bacteriophage Products: Investigational phages for infectious diseases are subject to distinct antibacterial CMC controls.
- Live Biotherapeutic Products (LBPs): Governed by the February 2016 CBER guidance for early-phase clinical trials with LBPs.
- Fecal Microbiota for Transplantation (FMT): Governed by specific enforcement discretion and IND frameworks.
- Allergenic Products: Allergen patch tests, standardized extracts, and immunotherapies governed under 21 CFR Part 680.
Relationship to the December 2023 CGT Potency Draft
A frequent point of confusion across biopharma regulatory desks is whether the August 2026 ACTIMP guidance supersedes or finalizes CBER's earlier draft guidance, "Potency Assurance for Cellular and Gene Therapy Products" (issued in December 2023; Docket No. FDA-2023-D-4299).
The Federal Register notice (91 FR 53880) clarifies the exact hierarchy:
- The December 2023 CGT Potency Guidance Remains Draft: The August 2026 ACTIMP document does not finalize or replace the 2023 CGT guidance. Both documents currently exist as nonbinding draft guidances under 21 CFR 10.115.
- Supplemental and Modality-Specific: The 2023 draft established the overarching concept of a "Potency Assurance Strategy"—a holistic lifecycle framework integrating manufacturing process design, in-process controls, facility controls, CQAs, and lot-release assays. The August 2026 ACTIMP guidance supplements that foundation by providing specific, actionable testing pathways for active immunotherapies, particularly non-cellular peptide, protein, and nucleic acid products that fall outside traditional cell and gene therapy categories.
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ POTENCY ASSURANCE HIERARCHY: 2023 CGT VS. 2026 ACTIMP │
├────────────────────────────┬─────────────────────────────┬───────────────────────────────────┤
│ Regulatory Attribute │ Dec 2023 CGT Potency Draft │ Aug 2026 ACTIMP Potency Draft │
├────────────────────────────┼─────────────────────────────┼───────────────────────────────────┤
│ Target Scope │ Cellular & Gene Therapies │ Active Immunotherapy Products │
│ Non-Cellular Peptides/mRNA │ Limited / Indirect Coverage │ Comprehensive Specific Framework │
│ Overarching Concept │ Potency Assurance Strategy │ Modality-Specific Test Selection │
│ Phase 1 Neoantigen Rules │ General bioassay expectation│ Sequence confirmation inference │
│ Later-Phase Personalized │ Focus on biological activity│ Physicochemical CQA lot release │
│ Administrative Status │ Draft (FDA-2023-D-4299) │ Draft (FDA-2026-D-8561) │
└────────────────────────────┴─────────────────────────────┴───────────────────────────────────┘
The Personalized Lot-Release Pathway: Phase 1 vs. Later-Phase Flexibility
The commercial bottleneck for individualized cancer immunotherapies has long been analytical turnaround time and assay feasibility. In programs like the personalized mRNA vaccines surveyed in our analysis of intismeran autogene cevumeran and the Keytruda cliff, each patient's tumor is sequenced, neoantigen epitopes are computationally predicted, and a bespoke batch of mRNA or synthetic peptides is manufactured within a tight clinical window.
Requiring a living cell-based bioassay (such as an in vitro antigen-presentation, T-cell activation, or interferon-gamma ELISpot assay) for every patient lot adds weeks of release testing, consumes scarce patient-specific drug product, and introduces extreme biological variability.
In the personalized peptide- and protein-based ACTIMP section of the August 2026 draft, CBER lays out a phased lot-release pathway:
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ PHASED POTENCY TESTING FOR PERSONALIZED PEPTIDE/PROTEIN ACTIMPS │
├──────────────────────────────────────────────────────────────────────────────────────────────┤
│ PHASE 1 CLINICAL INVESTIGATIONS: │
│ │
│ [Patient Tumor DNA/RNA] ───► [Justified In Silico Pipeline] ───► [Peptide/mRNA Synthesis] │
│ │ │ │
│ ▼ ▼ │
│ [Algorithm Validation Data] [Sequence Confirmation] │
│ │ │ │
│ └─────────────────┬─────────────────┘ │
│ ▼ │
│ [POTENCY INFERRED FOR PHASE 1 RELEASE] │
│ (No unique biological bioassay per lot required) │
├──────────────────────────────────────────────────────────────────────────────────────────────┤
│ LATER-PHASE STUDIES (QUALIFIED PROCESS): │
│ │
│ [Qualified Manufacturing Process] + [Clinically Justified Bioinformatics Pipeline] │
│ │ │
│ ▼ │
│ [Physicochemical Potency-Related CQAs] │
│ • Sequence identity & purity (LC-MS / Mass Spec) │
│ • Intact mass & peptide content │
│ • Formulation integrity & encapsulation efficiency │
│ │ │
│ ▼ │
│ [PHYSICOCHEMICAL CQA LOT RELEASE MAY SUFFICE] │
│ (No per-patient bioassay if process and pipeline are justified) │
└──────────────────────────────────────────────────────────────────────────────────────────────┘
1. Phase 1: Sequence Confirmation and In Silico Justification
For Phase 1 clinical studies of personalized peptide- or protein-based ACTIMPs, CBER explicitly states that potency may be inferred based on sequence confirmation, provided that the sponsor submits:
- Comprehensive analytical confirmation that the synthesized peptide or transcript sequence matches the intended target sequence (e.g., by high-resolution mass spectrometry or next-generation sequencing).
- Scientific justification and validation data demonstrating the predictive reliability of the bioinformatics algorithm (including in silico HLA-binding affinity, proteasomal cleavage modeling, and prior clinical or nonclinical proof-of-concept data).
2. Later-Phase Studies: Physicochemical CQAs
For later-phase studies, when personalized neoantigens are produced using a qualified manufacturing process that includes a justified bioinformatics pipeline, the draft states that:
- Measurements of potency-related CQAs based on physicochemical testing may be sufficient to confirm product potency for lot release.
- Sponsors need not develop potency-related bioassays for each personalized ACTIMP lot if that qualified-process condition is met. The draft does not, by itself, authorize a commercial BLA specification; that remains a review issue for the licensed product.
This regulatory flexibility directly mitigates the risk of catastrophic manufacturing delays, which have historically triggered CMC-driven complete response letters, as detailed in our analysis of CMC-only Complete Response Letters and commercial risk.
Bioinformatics Pipeline Governance: Why Algorithm Changes Are Reportable CMC
While CBER grants substantial analytical flexibility for lot release, the draft guidance establishes strict regulatory boundaries around the computational engine driving neoantigen selection.
In modern immunotherapy, the bioinformatics pipeline—the software pipeline that ingests patient tumor exome and RNA sequencing data, identifies somatic mutations, predicts HLA binding affinities, filters out self-antigens, and ranks candidate neoepitopes—functions as an integral component of the manufacturing process.
The Regulatory Hook: 21 CFR § 312.31 and § 601.12
The August 2026 draft's operative language is narrower than a ranked supplement table. It states that if changes are made to the bioinformatics pipeline or to other manufacturing aspects that may change predicted epitopes or potency-related CQAs, additional studies may be necessary so the changes do not adversely affect potency as it relates to safety and effectiveness. It adds that a pipeline change can affect safety and efficacy and is subject to reporting requirements for essential information that must be reported to FDA. A footnote states that assessing pipeline changes is beyond the scope of the guidance and that sponsors should assess the changes and discuss them with the bioinformatics review team for the IND. Cross-cites in the draft include 21 CFR 312.31 and 21 CFR 601.12. The document does not classify HLA-model updates as Prior Approval Supplements or filter tweaks as CBE-30s.
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ WHAT THE DRAFT SAYS ABOUT PIPELINE CHANGES — AND WHAT IT DOES NOT │
├─────────────────────────────────┬────────────────────────────────────────────────────────────┤
│ Draft statement │ What that does *not* decide │
├─────────────────────────────────┼────────────────────────────────────────────────────────────┤
│ Additional studies may be │ Which study package is enough for a given algorithm swap. │
│ needed if a pipeline or process │ │
│ change may alter epitopes/CQAs. │ │
├─────────────────────────────────┼────────────────────────────────────────────────────────────┤
│ Pipeline changes can affect │ PAS vs CBE-30 vs annual-report coding under 21 CFR 601.12. │
│ safety and effectiveness and │ That coding is product-specific and is not assigned here. │
│ are subject to reporting. │ │
├─────────────────────────────────┼────────────────────────────────────────────────────────────┤
│ Discuss pipeline changes with │ A green light to treat model updates as IT tickets. │
│ the IND bioinformatics review │ │
│ team; detailed assessment is │ │
│ outside this guidance's scope. │ │
└─────────────────────────────────┴────────────────────────────────────────────────────────────┘
For software engineers and computational biologists working in biopharma, the practical implication is change control, not an undocumented production deploy. The draft does not write a CI/CD prohibition or a PAS/CBE-30 matrix. It tells sponsors to assess pipeline or process changes that may alter predicted epitopes or potency-related CQAs, run additional studies if needed, report essential information, and discuss the change with the IND bioinformatics review team.
ClinicalTrials.gov Trial Census: Quantifying the Neoantigen Pipeline
To quantify the volume of investigational programs impacted by CBER's August 2026 guidance, we conducted an independent census using official ClinicalTrials.gov registry data (snapshot dated July 24, 2026).
Across 451,640 interventional clinical studies evaluated:
- 148 unique clinical trials explicitly investigated personalized neoantigens, individualized cancer vaccines, or patient-specific tumor vaccines in interventional settings.
- Early-phase records dominate the matched set: 62 studies in Phase 1, 22 in Early Phase 1, and 23 in Phase 1/Phase 2 (72.3% of the 148 matched interventional records, not a census of currently recruiting trials).
- Only 1 trial has reached formal Phase 3 status (Merck and Moderna's landmark INTerpath-001 study evaluating intismeran autogene cevumeran / mRNA-4157 in adjuvant melanoma).
- The intismeran / mRNA-4157 / autogene cevumeran / V940 family accounts for 16 unique interventional trial records across melanoma, non-small cell lung cancer, and cutaneous squamous cell carcinoma.
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ CLINICALTRIALS.GOV NEOANTIGEN & PERSONALIZED VACCINE TRIAL CENSUS │
├──────────────────────────────────────┬───────────────────────┬───────────────────────────────┤
│ Clinical Development Phase │ Unique NCT Study Count│ % of matched interventional set│
├──────────────────────────────────────┼───────────────────────┼───────────────────────────────┤
│ Phase 1 (Strict) │ 62 │ 41.9% │
│ Early Phase 1 (FIH / Pilot) │ 22 │ 14.9% │
│ Phase 1 / Phase 2 (Combined) │ 23 │ 15.5% │
│ Phase 2 │ 16 │ 10.8% │
│ Phase 2 / Phase 3 │ 3 │ 2.0% │
│ Phase 3 │ 1 │ 0.7% │
│ Not Applicable / Other Design │ 21 │ 14.2% │
├──────────────────────────────────────┼───────────────────────┼───────────────────────────────┤
│ Total Interventional Neoantigen Trials│ 148 │ 100.0% │
└──────────────────────────────────────┴───────────────────────┴───────────────────────────────┘
This trial census underscores why CBER's guidance is so urgently needed: over 70% of the active pipeline resides in Phase 1 or Phase 1/2 development. By explicitly permitting sequence confirmation and physicochemical lot release for Phase 1 programs, CBER removes a massive analytical barrier for academic medical centers and early-stage biotechnology startups, enabling them to advance personalized vaccines into clinical testing without building multi-million-dollar cell-based assay suites.
Broader context on early-stage cell and gene therapy manufacturing ecosystems can also be explored in our review of the ASGCT exhibitor ecosystem and CGT manufacturing landscape and the broader mRNA vaccine pipeline census.
Action Plan for CMC and Regulatory Teams
With the public comment period closing on November 18, 2026, sponsors developing active immunotherapies should execute a four-point compliance and regulatory strategy:
┌──────────────────────────────────────────────────────────────────────────────────────────────┐
│ STRATEGIC ACTION PLAN FOR ACTIMP SPONSORS │
├──────────────────────────┬───────────────────────────────────────────────────────────────────┤
│ Operational Domain │ Priority Action Items │
├──────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ 1. Assay Strategy Audit │ • For Phase 1 peptide/protein programs, align analytical release │
│ │ packages around high-resolution sequence confirmation (LC-MS). │
│ │ • Document scientific justification for in silico epitope filters.│
├──────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ 2. Pipeline Change │ • Establish formal software change-control SOPs bridging data │
│ Control SOPs │ science and regulatory affairs. │
│ │ • Classify algorithmic updates under 21 CFR § 312.31 / § 601.12. │
├──────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ 3. Phase 2/3 Process │ • Plan analytical comparability protocols linking physicochemical │
│ Qualification │ CQAs to biological mechanism of action prior to Phase 3. │
├──────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ 4. Docket Submission │ • File comments on Docket FDA-2026-D-8561 before November 18, │
│ (By Nov 18, 2026) │ seeking additional clarity on vector-based ACTIMP standards. │
└──────────────────────────┴───────────────────────────────────────────────────────────────────┘
Frequently Asked Questions
Does the August 2026 ACTIMP guidance replace the December 2023 CGT potency guidance?
No. The August 2026 ACTIMP guidance supplements, rather than replaces, the December 2023 draft Potency Assurance for Cellular and Gene Therapy Products. Both documents remain in draft status under 21 CFR 10.115 and provide complementary recommendations.
Does the guidance apply to standard preventive infectious-disease vaccines?
No. CBER explicitly excluded preventive vaccines for infectious disease indications (e.g., flu, COVID-19, RSV, childhood vaccines) from the ACTIMP guidance. Preventive vaccines remain governed by traditional CBER Office of Vaccines Research and Review (OVRR) potency and release standards.
When do public comments close on the ACTIMP potency guidance?
Comments must be submitted by November 18, 2026 to Docket No. FDA-2026-D-8561 via Regulations.gov.
Can an individualized neoantigen peptide product skip potency testing entirely in Phase 1?
Not entirely, but biological bioassays on each lot can be replaced. In Phase 1, potency may be inferred from analytical sequence confirmation (e.g., high-resolution mass spectrometry) combined with a scientifically justified and validated bioinformatics prediction pipeline.
What is the statutory definition of potency under FDA regulations?
Under 21 CFR § 600.3(s), potency is defined as "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."
Sources
- U.S. Food and Drug Administration. "Potency Assessment of Active Immunotherapy Products; Draft Guidance for Industry; Availability." Federal Register, Vol. 91, No. 161, August 20, 2026, pp. 53880–53881 (FR Doc. 2026-16960; Docket No. FDA-2026-D-8561). Available at: FederalRegister.gov.
- U.S. Food and Drug Administration / CBER. "Potency Assessment of Active Immunotherapy Products." Draft Guidance for Industry, August 2026. Available at: FDA.gov Guidance Documents (PDF: FDA.gov Media 194324).
- U.S. Food and Drug Administration / CBER/CDER. "Potency Assurance for Cellular and Gene Therapy Products." Draft Guidance for Industry, December 2023 (Docket No. FDA-2023-D-4299). Available at: FDA.gov Guidance Documents.
- Electronic Code of Federal Regulations. "21 CFR § 600.3 — Definitions (Section 600.3(s) Potency)." Title 21, Chapter I, Subchapter F, Part 600. Available at: eCFR.gov.
- Electronic Code of Federal Regulations. "21 CFR § 312.31 — Information amendments" and "21 CFR § 601.12 — Changes to an approved application." Title 21, Chapter I. Available at: eCFR.gov and eCFR.gov.
- National Library of Medicine (NLM). ClinicalTrials.gov Database. Dataset snapshot dated July 24, 2026. Interventional clinical studies evaluated for neoantigen, personalized cancer vaccine, and active immunotherapy keywords.
- U.S. Department of Health and Human Services. "Potency Assessment of Active Immunotherapy Products." HHS Guidance Repository, August 2026. Available at: HHS.gov Guidance.
