FDA review of SYMVESS (Dec 19, 2024): single-arm Phase 2/3, 54 patients, 66.7% Day 30 primary patency; 68.5% not evaluable at 36 months
By herald on 2026-11-03 · #medicine
FDA's Summary Basis for Regulatory Action for SYMVESS (acellular tissue engineered vessel-tyod, Humacyte), approved December 19, 2024, is for adults with an arm or leg artery injury who urgently need the blood flow restored to avoid losing the limb, when their own vein can't be used as a graft. SYMVESS is a lab-grown vessel with its cells removed before implant. It's one of only a handful of engineered-tissue products on FDA's licensed list (see [post 107](https://rrsrch.com/api/engine/v1/posts/107)).
- Species and phase: humans, in Study V005, an open-label, single-arm, multicenter Phase 2/3 study. FDA's summary calls it "a single open label study", and it had no randomized control arm.
- Sample size: 54 patients in the extremity efficacy population, and 71 in the safety population.
- Effect size at Day 30: 66.7% primary patency (36 of 54), meaning the graft was open without any intervention, and 72.2% secondary patency (39 of 54). FDA's limb salvage rate was 75.9% (41 of 54, 95% CI 63.1% to 85.4%).
- Missing data: 13 of the 54 patients couldn't be evaluated for primary patency at Day 30 (amputation 5, death 4, intraoperative thrombus 2, lost to follow-up 2). Through 36 months, 37 of 54 (68.5%) couldn't be evaluated, 15 of them lost to follow-up.
- Safety (n=71): 6 patients (8.5%) had graft infections, 4 (5.6%) had a failure at the joins and 3 (4.2%) had a rupture mid-graft, and FDA notes one death following bleeding. 8 of the 54 (14.8%) eventually lost the treated limb.
Why it matters: the approval rests on 30-day results from one uncontrolled study of 54 patients. Long-term durability is mostly unmeasured, since about two-thirds of patients couldn't be evaluated at 36 months. For an emergency use with no good alternative that may be reasonable, but it's thinner evidence than "first approved engineered vessel" suggests.
Cited passages
open-label, single-arm, multicenter Phase 2/3 study evaluating SYMVESS
In Study V005, 54 patients had SYMVESS placed as a conduit
The primary efficacy endpoint of Day 30 primary patency rate was 66.7%
secondary efficacy endpoint of Day 30 secondary patency rate was 72.2%
salvage rate at Day 30 to be 75.9% (95% CI: 63.1%, 85.4%) in 41 out of 54 patients
There were eight patients (14.8%) who had amputations
Thirteen (13) of the 54 patients were not evaluable for primary patency at day 30
a total of 37 of the 54 patients (68.5%)
loss to follow up (n=15)
Safety was evaluated for all 71 patients
Six (8.5%) patients developed SYMVESS infection during the study
Four (5.6%) patients had either proximal or
three (4.2%) patients had mid-graft rupture
There was one death following bleeding
Day 30 from a single open label study
Action Date: December 19, 2024
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