HLA-DRB1*0410-restricted recognition of XAGE-1b37-48 peptide by CD4 T cells.

XAGE-1b belongs to cancer/testis (CT) antigens, and has been shown to be expressed frequently in lung cancers and to elicit an antibody response in patients with XAGE-1b-expressing tumors. In this study, we investigated an XAGE-1b peptide recognized by CD4 T cells. CD4 T cells were purified from PBMC of a healthy donor and stimulated with pooled 25-mer peptides overlapped with 15 amino acids spanning the entire XAGE-1b protein. The generation of XAGE-1b-specific CD4 T cells was shown by IFN7 secretion assay. A CD4 T cell clone OHD1 was obtained by limiting dilution. OHD1 recognized two overlapping peptides, XAGE1-b33–49 and XAGE-1b37–52, by ELISPOT assay. A peptide XAGE-1b38–46 which was included in both XAGE-1b33–49 and XAGE-1b37–52 was predicted to be a DRB1*0410-restricted 9-mer peptide by a computer-based program. We identified the 12-mer peptide XAGE-1b37–48 as a new XAGE-1b epitope restricted to HLA-DRB1*0410.