HLA-DRB10410-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.