Immunological response in cynomolgus macaques to porcine α‐1,3 galactosyltransferase knockout viable skin xenotransplants—A pre‐clinical study

Abstract

Background: Allogeneic skin recovered from human deceased donors (HDD) has been a mainstay interim treatment for severe burns, but unfortunately risk of infectious disease and availability limitations exist. Genetically engineered ɑ-1,3 galactosyltransferase knockout (GalT-KO) porcine source animals for viable skin xenotransplants may provide a promising clinical alternative. Methods: Four cynomolgus macaque recipients received full-thickness surgical wounds to model the defects arising from excision of full-thickness burn injury and were treated with biologically active skin xenotransplants derived from GalT-KO, Designated Pathogen Free (DPF) miniature swine. Evaluations were conducted for safety, tolerability, and recipient immunological response. Results: All skin xenotransplants demonstrated prolonged survival, vascularity, and persistent dermal adhesion until the study endpoint at post-operative day 30. No adverse outcomes were observed during the study. Varying levels of epidermolysis coincided with histologic detection of CD4+ and CD8+ T cells, and other cellular infiltrates in the epidermis. Recipient sera IgM and IgG demonstrated significant antibody immune response to non-α-1,3-galactose porcine xenoantigens. Separately, specific wound healing mediators were quantified. Neither porcine cell migration nor PERV were detected in circulation or any visceral organs. Conclusions: These results provide a detailed analysis of vital skin xenotransplants utilizing a non-human primate model to predict the anticipated immunological response of human patients. The lack of adverse rejection even in the presence of elevated Ig indicates this is a prospective therapeutic option. The findings reported here directly supported regulatory clearance for a first-in-man, Phase I xenotransplantation clinical trial.

Large‐gap peripheral nerve repair using xenogeneic transplants in rhesus macaques

“…Previous testing of skin xenotransplants had demonstrated that porcine cells were detectable at the graft site but as found here, this did not extend to the peripheral circulation [70], which did not appear to be the case for this study. Given the lack of detection here and the immunological responses shown, this supports the expectation that the porcine transplant is fully replaced and repopulated by the host cells.…”

“…Due to the large number of surgeries, ve sciatic nerve segments were transplanted fresh one to two days after donor harvesting while the remaining ve were cryopreserved and subsequently thawed for transplantation over two days the week following based on Holzer et. al., 2020 [70]. Cryopreservation of xenogeneic skin transplants has been shown to be safe and effective for up to seven years [75], demonstrating no signi cant or meaningful differences between fresh and frozen transplants.…”

Large-gap Peripheral Nerve Repair Using Xenogeneic Transplants in Primates

“…Lymphocytes in the surrounding tissue are indicative of a low level, long-term immune response consistent with porcine tissue clearance and nerve remodeling observed at the transplantation site [24]. detectable at the graft site [15]. In this study, qPCR for the porcine centromere was negative.…”

“…Due to the large number of surgeries, five sciatic nerve segments were transplanted fresh one to two days after donor harvesting while the remaining five were cryopreserved and subsequently thawed for transplantation over two days the week following based on Holzer et. al., 2020 [15].…”

Xenotransplantation literature update, November/December 2020

“…The advent of cutting‐edge tools and techniques to genetically engineer donor animals is a significant advantage and such technologies such as CRISPR has allowed researchers to produce the α1,3‐galactosyltransferase (GGTA1) gene knockout (GALKO) pig in order to mitigate hyperacute rejection in the xenotransplantation setting 23 . To investigate the potential for porcine xenograft skin replacement and to confirm the safety, tolerability, and recipient's immunological response from GALKO pigs Holzer et al 24 investigated the effectiveness of skin xenotransplants in a non‐human primate model (NHP). The cynomolgus macaque recipients received full‐thickness surgical wounds to model the defects arising from excision of full‐thickness burn injury and were subsequently treated with biologically active skin xenotransplants derived from GALKO pigs and monitored for 30 days.…”