W155 - Evidence for Human Thymopoiesis in a Porcine Thymus Graft and T Cell Tolerance to the Source Pig in a Living Human Recipient of a Porcine Galsafe™ Thymokidney Xenotransplant

Abstract Text:

Introduction: Porcine thymic transplantation tolerizes xenogeneic recipients to the porcine source animal in animal models (1,2). A 54-year-old woman with complex comorbidities received a composite thymokidney transplant from a GGTA knockout pig (GalSafe™), achieving initial renal function before graft failure for non-immunological reasons on POD47.

Methods:
Serial PBMC samples were analyzed by spectral FCM, and mixed lymphocyte reactions (MLRs) were performed on purified T cells to assess tolerance. Thymocytes were isolated from the thymic portion of the graft explant and analyzed using spectral FCM.

Results:
T cell levels in peripheral blood declined to 10/µl post-induction therapy and recovered to a peak of 342/µl by POD28. By POD21, 64% of the recovering CD4 T cells displayed a CD45RA+CCR7+ "naïve" phenotype and expressed CD31, consistent with recent thymic emigrants (RTEs). Pre-transplant CD4 T cells included < 10% RTEs. Cells from the POD47 thymic graft contained human CD45+ leukocytes (0.85%), including double-positive (CD4+CD8+), single-positive, and double-negative thymocytes. The double-negative cells expressed markers such as CD5, CD7, CD1a, and CD34, consistent with human T cell progenitors in the porcine thymus. MLR results demonstrated progressive hyporesponsiveness toward the source pig with preserved responses to third-party pig and allogeneic human cells, achieving full source-specific unresponsiveness by POD47 and POD86.

Conclusion:
These findings suggest that a porcine thymus in a GGTA kncockout thymokidney graft supported human thymopoiesis and the development of T cells tolerant to the source pig. Thymic transplantation is a promising approach to achieving T cell tolerance in xenotransplant recipients.