Uncovering T cell antigens in sarcoidosis 2308956

Abstract Introduction Sarcoidosis is characterized by the accumulation of clonally expanded CD4+ T cells within affected tissues, strongly implicating antigen-specific immune responses in granulomatous inflammation. However, the identity of antigens recognized by pathogenic T cells remains unknown, limiting understanding of disease mechanisms and opportunities for targeted therapies. Here, we undertook a systematic approach to identify CD4+ T cell antigens in sarcoidosis, focusing on subjects expressing HLA-DRB1*11:01, a risk allele associated with disease susceptibility. Methods CD4+ T cells from the bronchoalveolar lavage of HLA-DR11 sarcoidosis and beryllium-sensitized control subjects were single-cell sorted and paired TRA/TRB sequences identified using 10x Genomics to define TCR repertoires for each subject. A set of five related TCRs exhibiting hallmarks of antigen-stimulation and derived from three sarcoidosis patients were expressed as T cell hybridomas. Their specificity was probed using an unbiased decapeptide positional-scanning library (PSL) to define amino acid preferences at each peptide position contributing to activation. Results Initial PSL screens revealed repeated glycine and isoleucine preferences at multiple peptide positions, suggesting stimulatory peptides enriched for these residues, but also possible register-shifting of peptides within the HLA-DR11 binding groove. Deconvolution steps using dual-defined peptide mixtures and a biased PSL fixing glycine at position p5 and isoleucine at p7 led to the discovery of mimotopes and naturally-occurring peptides that activated all T cell hybridomas. The most stimulatory peptide was a specific conserved epitope of non-histone chromosomal protein 6, expressed by a variety of fungi. Conclusion These findings of antigen recognition by DR11-restricted T cells highlight a potential role for fungal antigens in disease, consistent with prior findings in acute sarcoidosis. Ongoing studies aim to define the breadth and disease specificity of these responses. Funding Source R01HL136137 Topic Categories Immune Mechanisms of Human Disease (HUM)