Assistant Research Professor University of Colorado Anschutz Aurora, Colorado, United States
Disclosure(s):
Michael Falta, PHD: No financial relationships to disclose
Introduction/Rationale: 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.
