FDA finalises potency guidance for cell and gene therapies

FDA issued final guidance on 2 November 2026 telling makers of cell and gene therapies to prove every batch works before it reaches a patient. What changes.

The United States Food and Drug Administration (FDA) on 2 November 2026 issued final guidance, "Potency Assurance for Cellular and Gene Therapy Products", which tells manufacturers to test and verify, before a product reaches a patient, that each batch meets a defined standard for working as intended. It replaces the agency's 2011 potency guidance for these treatments. The rule is a guide, not a law, but it sets what the FDA expects to see in applications, and it follows years of comment from industry, including a 2024 response that said the draft was unclear. This story relies on the FDA's own announcement and the professional society's published response to the earlier draft.

What the FDA announced

According to the FDA's news release dated 2 November, the guidance recommends that makers adopt a "potency assurance strategy". Potency here means the ability of a product to do the thing it is meant to do in the body. For a cancer treatment made from a patient's own immune cells, for instance, potency means those cells can attack the cancer; for a gene therapy it means the delivered gene can produce the protein it should.

The guidance, the FDA says, applies to treatments for serious and often life-threatening conditions. Its recommendations are risk-based and cover development from early-stage trial applications (called INDs, for investigational new drugs) through marketing applications (BLAs, biologics licence applications) and verification after approval. Topics include controls for variation in raw materials, testing during manufacturing, and laboratory tests confirming that each batch is biologically active in a way that matches its intended effect. There are specific sections for products with short shelf lives, viral-vector gene therapies and therapies made for one patient.

Karim Mikhail, who directs the FDA's Center for Biologics Evaluation and Research, said patients who receive these therapies "are often battling serious or life-threatening conditions." The FDA says the guidance gives manufacturers a clearer, more predictable path that may support faster access to safe and effective therapies for patients with few options. It will hold a webinar for stakeholders on 10 December 2026.

What potency testing is, and why it is hard

A drug made from a chemical, like paracetamol, can be tested by measuring how much of the chemical is in a tablet. A living-cell or gene therapy is different. The product is a batch of living cells or viral particles, no two batches are exactly alike, and "how well it works" cannot be read off a single number. A potency assay is a laboratory test that tries to measure the activity of the product, for example how well cells kill target cells in a dish.

It is hard for several reasons. The test has to relate to what the therapy does in a patient, which may not be fully understood. Early in development, when the product is changing, a final test may not exist. And the test uses up product, which for a therapy made from a patient's own cells may be in short supply. The FDA's earlier 2011 guidance on potency tests is the document now replaced.

What industry said about the draft

The final text arrives after a draft that the American Society of Gene and Cell Therapy (ASGCT), a professional body, commented on in April 2024. ASGCT's published response said the draft "did not provide needed clarity and direction to sponsors." It made three requests. It asked for "phase-appropriate" expectations, noting that full potency assays may not be possible early in development because of assay complexity, variability, small sample sizes and limited understanding of how the product works. It recommended one robust laboratory assay linked to the main mechanism of action for releasing a batch, with other measures used for characterisation rather than pass-fail release tests. And it asked that the guidance fit with existing quality standards instead of adding a new layer.

ASGCT also raised concerns: potency assay problems can delay development and cause clinical holds, may lead to products being abandoned, and extra testing leaves less product for dosing patients. We have not compared the final text with the draft in this run, so we cannot say which of ASGCT's requests the FDA adopted. The FDA release describes the guidance as risk-based and mentions specific considerations for short-shelf-life and patient-specific products, which touches on some of the concerns, but that is not proof the requests were met.

What the guidance does not say

The announcement does not give numbers: it does not say how many assays a product needs, what the acceptance limits are or how many programmes may be affected. It does not say how the FDA will treat products already approved or in late trials, other than that the recommendations run from early-phase applications to after approval. And, being guidance, it sets out the agency's "current thinking" and is not binding; a company can propose another approach if it satisfies the law. We did not open the guidance document itself, so the detail of its sections is beyond what we can report.

Nothing in the sources links the guidance to a particular product, company or approval, and we are not suggesting any.

What it means for developers, patients and India

For developers, the message is to plan potency from the start: define what the product is meant to do, find a way to measure it early, and show that the measure is reliable by the time of a marketing application. That can add cost and time, which is the burden ASGCT warned about; or it can reduce late surprises when a regulator asks for a better test than the developer has. The FDA says the aim is predictability.

For patients, the benefit the FDA claims is confidence that each batch of a therapy does what it should. The cost, if any, would show in development timelines for the therapies, a point the sources leave open. Patients and families should not read the guidance as a change in any single treatment's availability.

For India, where cell and gene therapy makers, contract manufacturers and academic groups are growing, the United States rules matter because companies that want to sell or run trials there have to meet them. The sources we read do not discuss India, so this is our general observation. India's own regulator, the Central Drugs Standard Control Organisation, has its own rules, and we did not check them here.

Use the simulator to see how test material can eat into a batch. The numbers are examples because the guidance gives none: how many doses a batch makes and how much of it a potency test uses.

What to watch next

The FDA webinar on 10 December 2026 should explain how the agency expects the guidance to be applied. Watch for how reviewers use it in decisions on pending therapy applications, for any company statements on cost or timing, and for feedback from ASGCT and other groups on the final text compared with the draft. Any move by other regulators, including in Europe and India, to align with the approach would show whether it becomes a global norm.

Key takeaways

- The FDA issued final guidance on potency assurance for cell and gene therapy products on 2 November 2026, replacing its 2011 potency guidance. - It asks manufacturers to set a strategy and to verify, before a product reaches a patient, that each batch meets a defined standard for working as intended. - The recommendations are risk-based and run from early-phase trial applications through approval and after-market checks, with special sections for short-shelf-life, viral-vector and patient-specific products. - ASGCT's 2024 response to the draft asked for phase-appropriate expectations and a single main release assay; we did not check how far the final text met these. - The guidance is not binding law, and the announcement gives no numbers on assays, limits or affected products.

Sources

- [FDA: FDA provides clarity to support cell and gene therapy development and quality](https://www.fda.gov/news-events/press-announcements/fda-provides-clarity-support-cell-and-gene-therapy-development-and-quality) - [ASGCT: Society responds to FDA's Potency Assurance for Cellular and Gene Therapy Products](https://www.asgct.org/news-publications/asgct-news/society-responds-to-fdas-potency-assurance-for-cellular-and-gene-therapy-products)

Tags: FDA Gene therapy Cell therapy Drug regulation Biotech