A bold shift aims to scale one-patient gene editing successes like “Baby KJ” into a repeatable regulatory model
FDA regulators Vinay Prasad, M.D., and Commissioner Marty Makary, M.D., have introduced a new approval pathway that could redefine how individualized gene-editing therapies reach the market, outlining the framework in a New England Journal of Medicine article that has sent shockwaves through the cell and gene therapy sector.
Called the “plausible mechanism pathway,” the program provides a structured route for highly personalized therapies to obtain marketing authorization based on biological plausibility and direct mechanistic evidence, rather than requiring large-scale randomized clinical trials that are impractical for ultra-rare, patient-specific diseases.
The initiative builds directly on the landmark case of “Baby KJ,” the first custom CRISPR-based therapy administered to a single infant with a lethal genetic disorder. For many experts, including members of Baby KJ’s treatment team, the new pathway marks the FDA’s acknowledgement that traditional drug development paradigms cannot support the future of personalized gene editing.
Kiran Musunuru, M.D., Ph.D., a co-founder of Verve Therapeutics and part of Baby KJ’s clinical team, described the article as “light on specifics,” but emphasized that its publication “opens the door for us to request meetings with the FDA to discuss how the pathway might affect development of our phenylketonuria and urea cycle disorder platforms.”
Rare diseases are the priority but not the limit
In the NEJM article, Prasad and Makary state that the pathway will prioritize rare, fatal, or severely disabling pediatric genetic diseases, but will also be accessible to developers working on common conditions with no existing treatment options. However, a strict requirement remains the disease must have a defined biological cause, allowing the therapy to target a “specific molecular or cellular abnormality.”
This principle is central to the Baby KJ precedent. The new born suffered from a severe form of carbamoyl-phosphate synthetase 1 (CPS1) deficiency, and the team at CHOP and the University of Pennsylvania created a custom CRISPR therapy precisely directed at the causative mutations.
To greenlight the investigational use, the FDA relied on well-characterized natural history data in untreated patients and mouse model evidence demonstrating successful editing in 42% of liver cells.
Approvals based on biological plausibility and early clinical signals
Prasad and Makary outline several core conditions for approval under the new pathway:
- A therapy must show evidence that editing or correction successfully hits the intended biological target.
- The FDA will accept nonanimal models, and in some cases, a single first-in-class patient may be sufficient if mechanistic data are strong.
- There must be an observed improvement in clinical outcomes sufficient to rule out regression to the mean.
- Patients may serve as their own control, reflecting the realities of ultra-rare disease treatment.
Once a sponsor demonstrates successful outcomes across several consecutive bespoke treatments, the FDA intends to move toward granting platform-level marketing authorization. This would allow the technology such as a CRISPR delivery system to be used for additional individualized treatments with streamlined review.
The agency may issue either accelerated approval or standard approval, depending on the evidence submitted, and will require post-marketing real-world evidence collection to confirm durability, safety, and absence of off-target edits.
The pathway is a direct response to the FDA’s realization that managing individualized therapies via compassionate-use, single-patient INDs is unsustainable and slows equitable access.
Musunuru and collaborator Rebecca Ahrens-Nicklas recently argued in The American Journal of Human Genetics that relying on one-off applications “would be a disservice to the rare disease community.” The new model is designed to shift focus from approving one drug at a time to approving the therapeutic platform itself, dramatically reducing the burden on future patients.
The Alliance for Regenerative Medicine welcomed the pathway, saying it modernizes U.S. regulatory strategy and helps maintain scientific competitiveness against rising innovation hubs like China. The group urged the FDA to issue formal guidance to ensure consistent implementation, calling for the Baby KJ story to become “commonplace rather than extraordinary.”