How the FDA reviews cell and gene therapies

A growing share of the catalysts in our tracker are for cell and gene therapies: treatments that deliver a gene, edit one, or use living cells as the medicine. They follow the same broad path as any other product, ending in a PDUFA date, but several parts of that path are different, and those differences explain a lot of the delays and extensions you'll see in their rows.

A different centre and a different application

Cell and gene therapies are biologics, so they're filed as a Biologics License Application rather than an NDA (NDA vs BLA explains the split). They're reviewed by the FDA's Center for Biologics Evaluation and Research (CBER), in its Office of Therapeutic Products, not by the drug centre that reviews most small molecules and antibodies. If an advisory committee is called, it's usually the Cellular, Tissue, and Gene Therapies Advisory Committee.

The review clock is the same: a standard or priority review goal from the filing date. But the work inside that clock is weighted differently.

Manufacturing is a bigger part of the review

For a small-molecule drug, the hard question is usually "does it work?". For a cell or gene therapy, "can it be made consistently?" is often just as hard. The product may be a viral vector grown in cells, or a patient's own cells modified and returned to them, and small changes in the process can change the product.

That shows up in the review in a few ways:

Potency assays. The company has to show a reliable test that the product does what it should, batch after batch. Disagreements over potency testing are a recurring theme in these reviews.
Facility inspections. The FDA inspects the manufacturing sites, which are often specialist contract manufacturers. Problems found there can delay or block approval even when the clinical data are fine.
Process changes. If the company changed its manufacturing between the trials and the commercial process, it has to show the products are comparable.

Late in a review, the FDA may ask for more manufacturing information. A large submission of that kind can be classed as a major amendment, which extends the PDUFA date by three months.

From the tracker

Capricor's deramiocel, a cell therapy for Duchenne muscular dystrophy cardiomyopathy, had its PDUFA date extended from 22 August to 22 November 2026 after the FDA classified a BLA amendment as a major submission (8-K exhibit). See the Capricor page.

Expedited pathways are common

Many of these therapies target serious, rare diseases, so they often carry one or more of the expedited designations. Cell and some gene therapies can receive RMAT (Regenerative Medicine Advanced Therapy) designation, which works like Breakthrough Therapy designation. Accelerated approval on a biomarker, such as the amount of a missing protein a gene therapy produces, is also used.

From the tracker

Lexeo guides to a "potential BLA submission under accelerated approval pathway in first half of 2028" for its Friedreich ataxia cardiomyopathy gene therapy (8-K exhibit). See the Lexeo page.

Long-term follow-up

A gene therapy is often given once and meant to last for years, so the FDA wants to know what happens over years. Its 2020 guidance on long-term follow-up recommends monitoring patients for up to 15 years for products that integrate into the genome or edit it, and up to five years for others, such as most AAV-based therapies. Those studies continue after approval as post-marketing requirements.

The range of products in the tracker

"Cell and gene therapy" covers very different technologies, and the tracker includes many of them:

Viral gene therapy: a virus engineered to deliver a working gene. Ultragenyx's UX111 for Sanfilippo syndrome type A was approved in September 2026 (Ultragenyx page).
In vivo gene editing: editing genes inside the body. Intellia's lonvo-z for hereditary angioedema has a PDUFA date of 10 March 2027, and the tracker's note records that it would be among the first in vivo CRISPR therapies to reach an FDA decision (Intellia page).
Non-viral and oncolytic approaches: enGene's non-viral gene therapy and Candel's adenovirus-delivered therapy, both heading for BLAs (enGene, Candel).
Cell therapies: living cells as the medicine, such as Capricor's deramiocel and Cartesian's mRNA-engineered CAR-T Descartes-08, which guides to a BLA in mid-2027 (Cartesian page).

What to watch in these filings

Mentions of manufacturing, CMC, potency or inspection near a PDUFA date. These are the most common sources of delay.
Major amendment extensions, which often follow late manufacturing questions.
Whether an approval is accelerated or traditional, and what confirmatory evidence is required.
Durability data: how long the effect lasts in the longest-treated patients.

More guides

What a PDUFA date is, and why the FDA doesn't publish themThe PDUFA target action date is the FDA's own deadline for deciding on a drug application. Here is where it comes from, how it moves, and why you only hear about it from the company.
What happens at an FDA advisory committee meetingWho sits on an FDA advisory committee, how the day runs, what the vote means and doesn't mean, and where to find the documents beforehand.
What a Complete Response Letter means, and what usually followsA Complete Response Letter is the FDA's "not yet" on a drug application. What it contains, the company's options, how resubmission clocks work, and how to read the announcement.
How to read a Phase 3 topline readoutEndpoints, p-values, effect sizes, safety tables and the phrase "met its primary endpoint": a practical guide to reading the press release a company puts out when pivotal trial results land.
Clinical trial phases explained: Phase 1 to Phase 4What each phase of clinical development is for, roughly how big the trials are, what the in-between labels like 1b, 2a and 2/3 mean, and what a readout at each stage can and can't tell you.
NDA vs BLA: the two kinds of US drug applicationWhy some products are filed as a New Drug Application and others as a Biologics License Application, who reviews each, what supplements and rolling submissions are, and why the difference matters after approval.
Fast Track, Breakthrough, Priority Review and Accelerated Approval explainedThe FDA's expedited programmes are often lumped together, but they do different things at different stages. What each one is, what it changes about the timeline, and what it doesn't promise.
How to verify a catalyst date yourself on SEC EDGARA step-by-step walkthrough of the method behind this site: finding the filing that announced a PDUFA date or readout window, reading it properly, and spotting the traps that catalyst calendars fall into.
8-K vs 6-K vs press release: where catalyst dates are disclosedWhy almost every row on this site links to an 8-K exhibit, what the 6-K is for, when a press release has no filing behind it, and how the item numbers and "furnished vs filed" affect what you're reading.
Why catalyst windows like "H2 2026" are vague, and how they narrowMost biotech catalysts don't have a date, only a window the company guided to. Why that is, what the common phrases mean, how windows tighten or slip, and how this site handles them.
Orphan drug designation explainedWhat orphan designation is, the 200,000-patient threshold, the seven years of exclusivity and other incentives it brings, and what it doesn't change about an FDA review.
What happens after an FDA approvalAn approval is more than a yes. What's in the approval letter and the label, what boxed warnings, REMS and post-marketing requirements mean, and why a drug isn't always on sale the next day.
Glossary of FDA and biotech catalyst termsPlain-English definitions of the regulatory, clinical and SEC-filing terms used across the tracker and the guides, from AdComm to Type A meeting.