The Ankylosing Spondylitis-associated HLA-B*2705 presents a B*0702-restricted EBV epitope and sustains the clonal amplification of cytotoxic T cells in patients

HLA-B*27 is strongly associated with an inflammatory autoimmune disorder, the Ankylosing Spondylitis (AS) and plays a protective role in viral infections. The two aspects might be linked. In this work, we compared in B*2705/B*07 positive patients with AS, the CD8+ T cell responses to two immunodominant EBV-derived epitopes restricted for either the HLA-B*27 (pEBNA3C) or the HLA-B*07 (pEBNA3A). We have unexpectedly found that the HLA-B*07-restricted EBNA3A peptide is presented by both the B*0702 and the B*2705 but not by the non AS-associated B*2709, that differs from the AS-associated B*2705 for a single amino acid in the peptide-binding groove (His116Asp). We then analysed 38 B*2705-positive/B*07-negative (31 AS-patients and 7 healthy donors) and 8 B*2709-positive/B*07-negative subjects. EBNA3A-specific CD8+ T lymphocytes were present in 55.3% of the HLA-B*2705 but in none of the B*2709 donors (p=0.0049). TCR β-chain analysis identified common TCRBV and TCRBJ gene segments and shared CDR3β sequences in pEBNA3A-responsive CTLs of B*2705 carriers, suggesting the existence of a shared TCR repertoire for recognition of the uncanonical B*2705/pEBNA3A complex. These data highlight the plasticity of the AS-associated HLA-B*2705, which presents peptides with suboptimal binding motifs, possibly contributing both to its enhanced capacity to protect against pathogens and to predispose to autoimmunity.