I have watched seven exosome programs in the last five years choose the 361 HCT/P route thinking it would save them time and money. Five of those programs are now on FDA hold. One has a warning letter. One pivoted to 351(a) BLA and is the only program of the seven still moving forward. The pattern is so consistent it has stopped being interesting to me.
What the distinction is
A 361 HCT/P product is regulated under Section 361 of the Public Health Service Act and 21 CFR Part 1271. To qualify, four criteria must all be met. The cells or tissue must be minimally manipulated. The product must be intended for homologous use only. The product cannot be combined with another article. And the product must not have a systemic effect unless used in autologous or first-or-second-degree relative settings.
Miss any one of those four, the product becomes 351. 351 means BLA. BLA means CMC documentation, clinical trials, and the long road.
Why exosomes consistently fail the test
The agency disagrees with 361 arguments for exosomes on the manipulation step almost every time. Ultracentrifugation, density-gradient separation, cell-culture conditioning all count as more than minimal manipulation.
The agency disagrees on homologous use almost every time. Exosomes from mesenchymal stem cells treating joint pain is not the original biological function the source cells perform.
The agency disagrees on systemic effect almost every time. Allogeneic exosomes administered intravenously have systemic effects in non-autologous patients.
The practical reality
The 351(a) BLA path requires an IND supported by CMC documentation that demonstrates control over identity, strength, quality, purity, and potency. GMP manufacturing of the parent cell line. Characterized donor sources. Validated isolation and purification. Defined potency assays.
From IND to BLA approval, count on five to eight years and 50 to 200 million dollars in development cost.
That is the honest math. Anyone selling shorter timelines for cell-derived therapeutics is selling around the agency, not with it.
The advice
For pre-IND programs: accept the 351 pathway. Build the CMC documentation. Engage CBER through pre-IND or INTERACT meetings.
For operating under 361 claim: do an honest audit against the four criteria. If any fails, plan the transition.
For investors: ask the pathway question and the supporting documentation question. If the answer is "we are 361" and the founder cannot explain why all four criteria are met, walk.
Source: Section 351 of the Public Health Service Act.