Development of a 24-h Preservation Protocol of Forearm Vascularized Composite Allotransplants in Nonhuman Primates Using Subnormothermic Machine Perfusion.

Background: Subnormothermic machine perfusion shows promise as a viable alternative to static cold storage for prolonged preservation of vascularized composite allografts. To date, most studies have been conducted in nonprimate models, and we report its first utilization in a cynomolgus forearm preclinical model for 24-h preservation. Methods: Forearms were procured from nonhuman primates weighing between 5 and 8 kg. Two perfusion protocols were implemented. In group 1 (n = 6), limbs were perfused with 1.5 L of recirculating Steen; the perfusate flow was adjusted to maintain stable vascular pressures. In group 2 (n = 6), limbs were perfused with a Steen+ solution, doubling the albumin concentration, with a full-volume exchange at mid-perfusion under a stable low-flow regimen. Dynamic and metabolic parameters, histological analysis, and response to neurostimulation were assessed. Results: After 24 h of continuous perfusion, mean weight gain was 24.8 ± 5.5% in group 1 and 8.0 ± 4.7% in group 2. Perfusion and metabolic parameters indicated the onset of a compartment syndrome in group 1 with an increase in resistance, lactate, and potassium production at mid-perfusion. In group 2, dynamic and metabolic parameters remained stable for 24 h, and histological analysis showed well-preserved tissues. Finally, in group 2, limbs exhibited muscular contraction recovery quantified at 2.4/5 ± 0.89 after 24 h compared with 0/5 after 3 h of ischemia or after perfusion in group 1. Conclusions: Successful 24-h perfusion and muscle contractility restoration demonstrate promising outcomes for vascularized composite allograft preservation and reconditioning.