Co-transplantation of Vascularized Thymic Graft with Kidney in Pig-to-Nonhuman Primates for the Induction of Tolerance Across Xenogeneic Barriers

Abstract

Using advanced gene editing technologies, xenotransplantation from multi-transgenic alpha-1,3galacto-syltransferase knockout pigs has demonstrated marked prolongation of renal xenograft survival, ranging from days to greater than several months for life-supporting kidneys and >2 years in a heterotopic non-life-supporting cardiac xenograft model. However, continuous administration of multiple immunosuppressive drugs continues to be required, and attempts to taper immunosuppression have been unsuccessful. These data are consistent with previous reports indicating that the human-anti-porcine T cell response is similar or stronger than that across allogeneic barriers. Due to the strength of both the innate and adaptive immune responses in xenotransplantation, the level of continuous immunosuppression needed to control these responses and prolong xenograft survival has been associated with prohibitive morbidity and mortality. These facts provide compelling rationale to pursue a clinically applicable strategy for the induction of tolerance. Mixed chimerism and thymic tissue transplantation have both achieved xenogeneic tolerance in pig-to-mouse models, and both have recently been extended to pig-to-baboon models. Although these strategies are promising in small animal models, neither direct intravenous injection of porcine bone marrow cells nor direct fetal thymic tissue transplantation into recipients was able to achieve >2 days chimerism following BM Tx or the engraftment of thymic tissues across xenogeneic barriers in pig-to-nonhuman primate models. Several innovative procedures have been largely developed by Kazuhiko Yamada to overcome these failures. These include vascularized thymic transplantation, combined with either thymokidney (TK) or vascularized thymic lobe (VTL) transplantation. Utilizing the strategy of transplanting vascularized thymic grafts with kidney from the same GalT-KO donor without further gene modification, we have achieved longer than 6 months survival of life-supporting kidneys in a baboon. Notably, the recipient became

Antibody reactivity with new antigens revealed in multi‐transgenic triple knockout pigs may cause early loss of pig kidneys in baboons

“…Complement‐dependent cytotoxicity of baboon sera against porcine PBMC was measured using a modification of the technique in which detection of lysed cells was performed using the fluorescent viability stain 7‐actinoaminomycin D (7‐AAD, Sigma) in place of trypan blue. Analysis of cells stained with 7‐AAD was performed on 2 × 10 5 cells per sample using a FCM (FACS CANTO II, BD Biosciences) 20,21 …”

Xenotransplantation: Current Challenges and Emerging Solutions

“…Currently, donor thymic transplantation is the most effective method of achieving tolerance in xenotransplantation 34 . Studies have demonstrated prolonged swine-to-baboon renal graft survival times of more than 6 months after GKO swine kidney and thymus transplantation 35 , 36 . In humans, Montgomery et al 6 transplanted GKO swine thymus and kidney into two brain-dead patients; however, the follow-up period was too short for the thymus to assert its effects.…”

Expression of human CD47 in pig glomeruli prevents proteinuria and prolongs graft survival following pig‐to‐baboon xenotransplantation

“…All recipients of K+VT grafts were thymectomized 1 week before XTx. Simultaneous K+VT XTx were performed as previously reported 7,14,26,28 . Host thymectomy was performed prior to Tx 14 .…”

“…Simultaneous K+VT XTx were performed as previously reported. 7,14,26,28 Host thymectomy was performed prior to Tx. 14 Central venous lines were placed for drug administration and blood sampling 1 week prior to Tx.…”