Identification of a sperm protein 17 CTL epitope restricted by HLA-A1

Sperm protein 17 (Sp17) is a novel cancer-testis antigen. We previously reported the successful generation of Sp17-specific HLA-A1-restricted cytotoxic T-lymphocytes (CTLs) from the peripheral blood of a healthy donor using a recombinant Sp17 protein. These CTLs were able to kill not only target cells pulsed with the recombinant protein but also fresh Sp17⁺ tumor cells. In the present study, we have identified a nonapeptide sequence within the Sp17 protein that is predicted to have a high binding affinity for the HLA-A1 molecules. We generated the synthetic nonapeptide and successfully propagated a peptide-specific CTL line. We confirmed that peptide Sp17_103-111 (ILDSSEEDK) contains an Sp17 CTL epitope restricted by HLA-A1 and identified amino acid residues 104, 107, 109 and 110 as crucial for the CTL lysis. Our findings therefore provide the tool for the characterization of CD8 T-cell function in vivo and generation of epitope-specific treatment strategies.