FDA drafts route for gene therapies to add new mutations on lab data alone

The US Food and Drug Administration published draft guidance on Tuesday 27 October that would let a developer of a personalised gene therapy win approval for one mutation through a largely conventional route and then add further mutations in the same gene on laboratory data rather than a fresh clinical study¹².

What the guidance proposes

The draft is aimed at therapies built to correct different mutations in a single disease-causing gene, where each mutation is often so rare that a standard trial is impractical or impossible¹. The first approval would rest on a more traditional evidence package. The original application would then set out what the FDA calls an "individualized feature space", the parameters within which later versions for other mutations could be cleared using lab data¹.

The proposal extends the plausible mechanism framework the FDA set out in draft guidance on 23 February, which covers genome editing and RNA-based approaches such as antisense oligonucleotides that target the root cause of a rare disease³. That framework asked sponsors to identify the underlying biological cause, show the therapy reaches its target, and allowed well-characterised natural history data as an external control where adequate³. At the time Robert F. Kennedy Jr., head of the Department of Health and Human Services, said a disease with 100 distinct mutations in one gene "will no longer require 100 clinical trials"³.

Rare disease advocates welcomed the October draft. Paul Scribner of the PKD Foundation described the draft as a signal from the agency that the area matters².

What it means for the market

The commercial problem the FDA is addressing is that individual treatments needing their own clinical studies are not profitable for most drugmakers¹. TD Cowen analyst Joseph Thome described the result as plug and play optionality for developers and said in a client note that the draft could be especially relevant to products in development at Prime Medicine, whose shares rose 15% early on Wednesday¹. Beam Therapeutics shares rose 8%, and its chief executive John Evans wrote that the approach fits the science behind base editing, the company's core technology¹.

The draft sits within a wider push on rare disease. The FDA held a meeting on Wednesday afternoon at its White Oak campus on its Rare Disease Framework Initiative, which aims to set standards condition by condition¹. The Centers for Medicare and Medicaid Services is also looking to widen a programme giving Medicaid patients access to cell and gene therapies, which began with sickle cell disease¹. Evans welcomed that plan, having asked whether one-time prices would hold back gene-editing medicines or whether payers would work to secure access¹.

For developers, the proposal would concentrate the cost of a full clinical study on the first product, with later variants for the same gene supported by laboratory data within parameters set in the original application¹. How narrowly the FDA will set those parameters in practice is not yet clear.

Caveats

This is draft guidance, and TD Cowen's view of its relevance to Prime depends on it being enacted¹. When the February framework was released, a senior FDA official said the agency was not lowering its evidence standards and that approvals under it would face a high bar³. In the same period the agency had turned down gene therapies from uniQure and Regenxbio for rare diseases, including over the use of a natural history control arm³. Under the February framework the FDA said it would keep collecting data after approval and could withdraw a product if follow-up showed it was less safe or effective than thought³.