Abstract Text: CD4+ T cells play a fundamental role in orchestrating various aspects of immune responses and tissue homeostasis by recognizing a plethora of self and foreign antigens. However, our inability to unbiasedly associate various peptide HLA-II complexes with their cognate TCR has significantly hampered our understanding of CD4+ function and its role in the etiology of human disease. Therefore, we have recently developed TScan-II, a platform for unbiasedly discovering CD4+ antigens using genome-scale human and virome libraries. This platform simultaneously incorporates the endogenous HLA-II antigen processing machinery in APC cells and the endogenous T cell signaling in T cells for antigen discovery. We illustrate the adaptability of the TScan-II for multiplexed HLA and TCR screens by leveraging the platform for de novo antigen discovery of clonally expanded CD4+ T cells in the salivary gland(SG) of Sjögren's disease(SjD) patients. We identified self-antigens expressed on multiple HLA alleles that can readily activate their cognate TCRs. Furthermore, through spatial transcriptomics and single-cell sequencing of SG biopsies, we observed that the identified antigens are expressed within cells in the SG cells capable of processing and presenting HLA-II antigens. Collectively these observations implicate CD4+ in SjD pathogenesis.
