Determinants of alloreactive T cell fate and function

Abstract

Expression of donor MHC class I in recipient hepatocytes using adeno-associated viral (AAV) vectors induces tolerance to subsequent skin grafts bearing the same mismatched MHC, even in the presence of pre-existing immune memory against the donor strain. The mechanisms underpinning tolerance induction are incompletely understood.

We are profiling the T cell receptor (TCR) repertoire of CD8 T cells responding to allogeneic epitopes to deepen our understanding of the molecular basis of alloreactivity. Leukocytes from the tolerant liver or rejecting skin graft site were isolated and examined. In this single MHC-mismatched model, B10.BR (H-2Kb) recipients were primed with a H-2Kd-bearing skin graft and the alloreactive cells collected at multiple timepoints after tolerance induction.

The TCR repertoire for each pMHC specificity have clear TRAV and TRBV preferential usage. Through probability and repertoire measurements, the influence of the recruiting allogeneic MHC in shaping the repertoire becomes clear. A solved pMHC:TCR crystal structure elucidated key binding patterns of a key TCR metaclonotype. The alloresponse in the tolerant skin graft site was mediated by CD4+ T regs, and CD8+ cytotoxic cells in the rejecting site. The liver CD8+ T cell leukocyte population evolved from highly reactive cycling cells and settled towards a resident innate-like phenotype which had gene expression patterns very similar to exhausted cells from other studies such as in chronic viral infection.

The work presented here is redefines the alloreactive TCRs at the repertoire level, giving new insights into the fundamental basis of alloreactivity. It expands the current understanding of the cellular and molecular mechanisms of tolerance and rejection in a transplantation setting.