Zhanzak, Z.; Cina, D.; Zhang, X.; Hadley, A.; Kissick, H.; Larsen, C.

Donor-specific T cell responses, particularly against human leukocyte antigen (HLA)-DQ antigens, are critical in transplant immunology as they influence graft survival and rejection. This study investigated HLA-DQ-specific CD4 T cell responses in naive individuals using HLA-DQ monomers, representing common donor HLA-DQ antigens (DQ2.5, DQ5, DQ6, DQ8), as defined alloantigen sources to enrich and detect HLA-DQ-specific T cells. Using a repeated stimulation protocol with HLA-DQ monomers, we achieved an enrichment of HLA-DQ-specific CD4 T cells, evidenced by proliferation and activation marker upregulation. Additionally, in silico epitope prediction identified 15-mer HLA-DQ peptides capable of binding to self-HLA-DRB1 alleles. TCR sequencing demonstrated an enriched, oligoclonal repertoire of HLA-DQ-specific CD4 T cells post-stimulation, with specific TCR clonotypes expanding in response to HLA-DQ monomer stimulation. Together, our study presents an in vitro method for enriching HLA-DQ-specific CD4 T cells using HLA-DQ monomers as an alloantigen source, thereby improving the detection of alloreactive, donor-specific T cells in naive individuals with the potential to mediate immune responses, including graft rejection and donor-specific antibody (DSA) production.