W136 - Overcoming Obstacles to Porcine Thymic Transplantation for Xenograft Tolerance of Human T Cells

vrushali agashe – Columbia University; Benjamin Vermette – Columbia University; Farshid Fathi – Columbia University; Haowei Li – Columbia University; Tara Talaie – Columbia University; Robert Winchester – Columbia University; Megan Sykes – Columbia University

Abstract Text: Xenotransplantation could alleviate the inadequate supply of organs for transplantation. However, toxic immunosuppression is required to prevent xenograft rejection. Instead, we aim to induce xenograft tolerance by transplanting porcine thymic tissue. In human immune system (HIS) mice, human T cells develop in porcine thymus grafts and demonstrate specific tolerance of the donor pig. However, these mice also demonstrated reduced HLA-restricted immune responses and T cell homeostasis. We compared selection of human thymocytes in NSG mice receiving human CD34+ Hematopoietic Stem Cells (HSCs) with either autologous human fetal thymus (HU/HU mice) or SLA-inbred (SLAhh) miniature swine thymus (SW/HU mice). The proportion of CD4/CD8 double positive (DP) thymocytes undergoing positive selection, as measured by the expression of CD69, was significantly reduced in SW/HU thymus compared to HU/HU thymus. TCR diversity was reduced in CD69+ DP and SP thymocyte populations of SW/HU vs HU/HU mice. TCRβ CDR3 hydrophobicity reflects affinity for self-peptide/MHC and positive selection (CD69- to CD69+ DP) was associated with increased hydrophobicity in SW/HU and HU/HU thymocytes. A decrease or no change in hydrophobicity occurred in the CD69+ DP to CD4SP transition in HU/HU mice but hydrophobicity increased during this progression in SW/HU mice, suggesting altered negative selection. CDR3 hydrophobicity among thymic Tregs in HU/HU mice was increased compared to non-Treg CD4 SP cells, indicating appropriate diversion of strongly self-reactive thymocytes, whereas SW/HU thymocytes showed no hydrophobicity change during this transition. We currently aim to normalize thymic selection in the swine thymus by introducing stem cell-derived human thymic epithelial cells.