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We have previously shown that 12 days of high‐dose calcineurin inhibition induced tolerance in MHCinbred miniature swine receiving MHC‐mismatched lung, kidney, or co‐transplanted heart/kidney allografts. However, if lung grafts were procured from donation after brain death (DBD), and transplanted alone, they were rejected within 19‐45 days. Here, we investigated whether donor brain death with or without allograft ischemia would also prevent tolerance induction in kidney or heart/kidney recipients. Four kidney recipients treated with 12 days of calcineurin inhibition received organs from donors rendered brain dead for 4 hours. Six heart/kidney recipients also treated with calcineurin inhibition received organs from donors rendered brain dead for 4 hours, 8 hours, or 4 hours with 4 additional hours of cold storage. In contrast to lung allograft recipients, all isolated kidney or heart/kidney recipients that received organs from DBD donors achieved long‐term survival (>100 days) without histologic evidence of rejection. Proinflammatory cytokine gene expression was upregulated in lungs and hearts, but not kidney allografts, after brain death. These data suggest that the deleterious effects of brain death and ischemia on tolerance induction are organ‐specific, which has implications for the application of tolerance to clinical transplantation. Donor brain death prevents tolerance induction in lung, but not isolated kidney or heart plus kidney, allograft recipients, suggesting that the deleterious effects of brain death on tolerance induction are organ specific.

Since the first attempt of pig‐to‐primate liver xenotransplantation (LXT) in 1968, survival has been limited. We evaluated a model utilizing α‐1,3‐galactosyltransferase knockout donors, continuous posttransplant infusion of human prothrombin concentrate complex, and immunosuppression including anti–thymocyte globulin, FK‐506, methylprednisone, and costimulation blockade (belatacept, n = 3 or anti‐CD40 mAb, n = 1) to extend survival. Baboon 1 remained well until postoperative day (POD) 25, when euthanasia was required because of cholestasis and plantar ulcers. Baboon 2 was euthanized following a seizure on POD 5, despite normal liver function tests (LFTs) and no apparent pathology. Baboon 3 demonstrated initial stable liver function but was euthanized on POD 8 because of worsening LFTs. Pathology revealed C4d positivity, extensive hemorrhagic necrosis, and a focal cytomegalovirus inclusion. Baboon 4 was clinically well with stable LFTs until POD29, when euthanasia was again necessitated by plantar ulcerations and rising LFTs. Final pathology was C4d negative and without evidence of rejection, inflammation, or thrombotic microangiopathy. Thus, nearly 1‐mo rejection‐free survival has been achieved following LXTin two of four consecutive recipients, demonstrating that the porcine liver can support life in primates for several weeks and has encouraging potential for clinical application as a bridge to allotransplantation for patients with acute‐on‐chronic or fulminant hepatic failure. The addition of costimulation blockade, in conjunction with exogenous coagulation factors, prolongs survival following pig‐to‐primate liver xenotransplantation, achieving the longest survivals reported to date.

The emergence of skin‐containing vascularized composite allografts (VCAs) has provided impetus to understand factors affecting rejection and tolerance of skin. VCAtolerance can be established in miniature swine across haploidentical MHCbarriers using mixed chimerism. Because the deceased donor pool for VCAs does not permit MHCantigen matching, clinical VCAs are transplanted across varying MHCdisparities. We investigated whether sharing of MHCclass I or IIantigens between donors and recipients influences VCAskin tolerance. Miniature swine were conditioned nonmyeloablatively and received hematopoietic stem cell transplants and VCAs across MHCclass I (n = 3) or class II(n = 3) barriers. In vitroimmune responsiveness was assessed, and VCAskin‐resident leukocytes were characterized by flow cytometry. Stable mixed chimerism was established in all animals. MHCclass II–mismatched chimeras were tolerant of VCAs. MHCclass I–mismatched animals, however, rejected VCAskin, characterized by infiltration of recipient‐type CD8+lymphocytes. Systemic donor‐specific nonresponsiveness was maintained, including after VCArejection. This study shows that MHCantigen matching influences VCAskin rejection and suggests that local regulation of immune tolerance is critical in long‐term acceptance of all VCAcomponents. These results help elucidate novel mechanisms underlying skin tolerance and identify clinically relevant VCAtolerance strategies. The specificity of MHC antigen matching between donors and recipients determines skin tolerance in vascularized composite allografts in a mixed chimerism‐based miniature swine model.

In our studies of life‐supporting α‐1,3‐galactocyltransferase knockout (GalT‐KO)pig‐to‐baboon kidneys, we found that some recipients developed increased serum creatinine with growth of the grafts, without histological or immunological evidence of rejection. We hypothesized that the rapid growth of orthotopic pig grafts in smaller baboon recipients may have led to deterioration of organ function. To test this hypothesis for both kidneys and lungs, we assessed whether the growth of outbred (Yorkshire) organ transplants in miniature swine was regulated by intrinsic (graft) or extrinsic (host environment) factors. Yorkshire kidneys exhibited persistent growth in miniature swine, reaching 3.7 times their initial volume over 3 mo versus 1.2 times for miniature swine kidneys over the same time period. Similar rapid early growth of lung allografts was observed and, in this case, led to organ dysfunction. For xenograft kidneys, a review of our results suggests that there is a threshold for kidney graft volume of 25 cm3/kg of recipient body weight at which cortical ischemia is induced in transplanted GalT‐KOkidneys in baboons. These results suggest that intrinsic factors are responsible, at least in part, for growth of donor organs and that this property should be taken into consideration for growth‐curve–mismatched transplants, especially for life‐supporting organs transplanted into a limited recipient space. Factors intrinsic to transplanted organs play a role in subsequent growth of those organs, suggesting that this property should be considered for growth‐curve mismatched transplants, especially when transplanting life‐supporting organs into limited recipient space.