Life-Supporting Pig Thymus Plus Kidney Transplantation Leads To Generation Of New Baboon T-Cells And Swine-Specific Hyporesponsiveness

Introduction: We have achieved greater than 6-month survivals in baboons that received vascularized thymus plus kidney xenotransplants (VT+KTx). We assessed the thymic function and recipient immune responses >4 months post-transplant. Methods: Six baboon recipients that survived >4 months after VT+KTx were studied. All animals underwent thymectomy and bilateral nephrectomy prior to Tx. Two received anti-CD154 mAb-based (129 and 193 days survivals) and the other four received anti-CD40 mAb-based immunosuppression (126, 154, 174 and 187 survivals). Three of the animals received grafts from GalTKO donors, without other transgenes, and three received grafts from hCD47+GalTKO pigs Tg for additional human complement +/- coagulation regulatory proteins. In vitro T cell responses as well as anti-donor antibodies were assessed using recipient PBMCs and kidney grafts. Graft cell infiltrates were examined with anti-CD3 and anti-FoxP3 Abs. Newly developed baboon T cells in peripheral blood were determined using anti-human CD3/CD4/CD31/CD45RA mAbs. Results: All animals had stable renal function for the first 4 months. Some exhibited eventual increased serum creatinine (Cre) due to organ growth. No grafts showed signs of acute or chronic rejection histologically. All animals showed pig-specific hyporesponsiveness at all time points tested, including the day of euthanasia. Only one baboon, which was euthanized at POD187 due to SVC syndrome associated with MMF toxicity, developed anti-donor IgG after POD60 (PODs 90, 120 and 187), with no rise in Cre (0.6-0.9mg/dL) and no histologic evidence of rejection (Figure), suggesting accommodation. The remaining five did not develop anti-pig Abs. One kidney displayed cell infiltrates around vessels without tubulitis or endothelialitis (biopsy at POD144) that were FoxP3+, consistent with Treg-rich organized lymphoid structures (TOLs). Three baboons (174, 187 and 193 day survivors), all of whose native thymi had been removed prior to VT+K Tx, showed peripheral naïve recipient T cells, which gradually increased after POD60 post-VT+KTx, suggesting recipient thymopoiesis in the donor pig thymus. Conclusion: Life-supporting porcine VT+KTx in thymectomized baboon recipients led to new host T cell development and specific hyporesponsiveness to pig antigens, accompanied by development of FoxP3+ TOLs in the donor kidneys, without evidence of acute rejection.