HLA Epitope Immunodominance and Concordant Residue Targeting Among Kidney Allograft Recipients with Antibody-Mediated Rejection 2254936

Abstract Introduction Late kidney transplant (KT) rejection is primarily caused by donor-specific antibodies (DSA) that recognize mismatched donor HLA. Yet, the structural features that render certain mismatched HLA alleles highly immunogenic remain poorly understood, limiting our ability to predict and prevent alloantibody formation. To dissect these structural determinants, we isolated HLA-A*01:01 (A1)-reactive B cells from the graft and peripheral blood of a KT recipient (N006) and generated 49 recombinant monoclonal antibodies (Abs). B cell receptor sequencing revealed 17 distinct clonal lineages, and high-resolution epitope mapping of three representative Abs (E07, L02, M07) from immunodominant lineages showed recognition of distinct epitopes near the A1 peptide-binding groove (PBG). We hypothesized that DSA from N006 and other A1-mismatched KT recipients target shared immunodominant epitopes and residues in A1. Methods To define DSA epitopes, we performed cross-inhibition assays using N006 Abs and sera from genetically distinct A1-sensitized KT recipients (n = 10). To identify A1 residues essential for DSA binding, we assessed serum and N006 Ab reactivity to wild-type and single-residue mutant A1 (n = 27) by flow cytometry. Results All N006 Abs recognized A1 epitopes overlapping with those of E07, L02, or M07. Competitive inhibition with E07 and L02, which target non-overlapping epitopes near the A1 PBG, strongly attenuated cohort serum DSA binding (mean MFI reduction: 89.6%). A restricted set of A1 residues governed most DSA interactions. Affinity-matured Abs showed markedly enhanced binding to A1 compared with their Unmutated Common Ancestors. Conclusion Our results reveal that DSA responses in A1-mismatched KT recipients converge on immunodominant epitopes near the A1 PBG through affinity maturation rather than germline encoding. These structural insights define shared determinants of HLA immunogenicity and may guide improved donor-recipient matching and organ allocation. Funding Source NIAID Immunologic Diseases and Basic Immunology T32 (5T32AI007051-47) Topic Categories Transplantation Immunology (TRAN)