Swine Xenografts Share Few Predicted Indirectly Recognisable SLA-Derived Epitopes With HLA-Derived Epitopes From Human Kidney Grafts

Abstract

Swine-derived kidneys are a promising alternative organ source for transplantation, but compatibility in the major histocompatibility complex remains an immunological barrier. Furthermore, in repeat transplantations, CD4+ memory T cells can lead to a more rapid immune response against repeated exposure to the same antigens. Several studies have shown that HLA and SLA proteins share overlapping B cell epitopes due to structural or electrostatic similarities, but the role of overlapping T cell epitopes has not been fully explored. This study aims to computationally analyse the potential risk of memory T cell activation in subsequent human-after-swine and swine-after-human transplantation by evaluating shared T cell epitopes between the two graft sources. We show that while HLA and SLA demonstrate striking structural similarities, their linear protein sequences are very distinct, which translates to disparate HLA- and SLA-derived peptidomes and T cell epitopes. By applying the PIRCHE-II Tmem analysis to a simulated panel of recipients receiving repeat transplantations from a human kidney and from a swine xenograft, we observed a median of 1 shared T cell epitope in the cross-species context, compared to a median of 17 shared between two human-derived kidneys. This suggests that a swine xenograft exposes a low risk of T cell memory against a later human donor, and that xenotransplantation may provide an opportunity to receive a graft for highly HLA-sensitised recipients.