03O Identification of Class I HLA genetic predispositions and prediction of autoantigenic epitopes in dermatomyositis patients of Indian origin

The discovery of dermatomyositis (DM)-specific autoantibodies has led to a more refined categorization of DM patients into homogenous subgroups. While previous studies have demonstrated the association of Human Leucocyte Antigen (HLA) alleles with DM-specific autoantibodies, the specific epitopes involved in these associations remain unexplored. We aimed to genotype Class-I MHC alleles and to examine specific HLA genetic variants associated with DM patients and to finally predict autoantigenic epitopes. HLA-A, HLA-B, and HLA-C alleles were directly genotyped in Indian cohort of 71 DM patients and 114 ethnically matched controls by next generation sequencing, sequence-specific primer PCR assay, or multiplex assay using the blood genomic DNA. Allele frequency analysis and amino acid alignments were performed using the Genentech/MiDAS bioinformatics package. T-cell epitope prediction was performed using Immune Epitope Database and Tools (IEDB). HLA-A*33:03 allele (Pa= 0.010, OR= 12.024 [3.652 – 54.452]) was more frequently detected in DM-specific autoantibody positive patients (12.26%) than healthy controls (1.32%). Out of all the DM-specific autoantibodies, this Class-I HLA allele showed significant positive association with Mi-2 autoantibody (Pa= 0.006, OR= 15.136 [4.150 – 72.444]) only, which retained its significance after the stepwise conditioning analysis as well. Its association with rest of the autoantibody positive (anti-MDA5 (n=9), anti-NXP2 (n=8), and anti-TIF1g (n=5)) subgroups did not reach statistical significance. Based on Class-I MHC binding, processing, and immunogenicity prediction scores, 15 out of 7,614 peptides of 8 to 11 amino acid residues were predicted to be epitope of Mi-2 autoantigen. High-resolution HLA sequencing more precisely characterised the allele associated with Mi2 autoantibody. Prediction of Mi-2 autoantigenic epitopes presents promising candidates for experimental validation which could pave the way for peptide immunotherapy in Mi2-positive DM subgroup in future.