Generation of novel pMHC epitopes for alloreactive and autoreactive T cells

Abstract

Generation of novel pMHC epitopes for alloreactive and autoreactive T cells.

Recognition of allogeneic donor transplantation antigens as “non-self” by recipient T cells drives transplant rejection. Alloreactive CD8+ T cells recognise epitopes composed of allogeneic MHC class I complexed with a range of endogenous self-peptides. Inflammatory mediators such as interferon gamma (IFN-γ) can increase expression of MHC class I and immunoproteasome subunits, expanding the peptide repertoire (immunopeptidome) presented by MHC class I. Sterile inflammation is a prevalent issue in transplantation, as observed in ischemia reperfusion injury (IRI) during solid organ transplantation and the response to recipient preconditioning for hematopoietic stem cell transplantation. In response to these inflammatory conditions, tissue-specific proteins can become post-translationally modified (PTM), sometimes altering protein processing and presentation pathways. These modifications can create novel self-antigens and further amplify allorecognition.

Having shown that peptides present at physiological steady state across a range of tissues were recognised by a subset of alloreactive T cells under conditions of inflammatory perturbation, we subsequently sought to expand our understanding of changes to the immunopeptidome during inflammation. We applied mass spectrometry to characterise the murine immunopeptidome in different inflammatory settings. These include renal IRI in C57BL/6 (H-2b) mice, reduced intensity conditioning (RIC) with chemotherapy and irradiation in BALB/c (H-2d) mice in a Graft-versus-Host Disease model, and heart graft rejection in fully allogeneic BALB/c to C57BL/6, and C57BL/6 to BALB/c models. The number of unique peptides (total and/or with predicted affinity <500nM), cumulative abundance, and frequency of common PTMs including phosphorylation, deamidation, cysteinylation, and acetylation were recorded for H-2Kb, H-2Db, H-2Kd or H-2Ld in target tissues.