Induction of tumor-reactive cytotoxic T-lymphocytes using a peptide from NY-ESO-1 modified at the carboxy-terminus to enhance HLA-A2.1 binding affinity and stability in solution

NY-ESO-1 is an attractive candidate tumor antigen for the development of immunotherapies for a wide variety of cancers. It is expressed in multiple types of tumors, but its normal tissue distribution is predominantly limited to the testes and ovaries; furthermore, both humoral and cellular immune responses can be mounted against this protein. Three overlapping HLA-A2.1-restricted T-cell epitopes have been identified within NY-ESO-1. In this investigation, the authors evaluated the in vitro immunogenicity of these peptides. From 2 of 12 HLA-A2.1⁺ patients with metastatic melanoma, peptide-reactive cytotoxic T-lymphocytes were generated using either NY-ESO-1:157-167 or NY-ESO-l:157-165 but not NY-ESO-l:155-163. Because NY-ESO-1:157-165 is a 9 amino acid peptide completely contained within NY-ESO-1:157-167, it seemed likely that this peptide was the minimal determinant, and thus it was selected for continued study. An amino acid substitution of C to V was introduced into NY-ESO-1:157-165 at P9 to attempt to improve its immunogenicity by enhancing its binding affinity to HLA-A2.1 and increasing its stability in solution, because the C residue is readily oxidized, leading to dimerization of the peptide. From 5 of 20 HLA-A2.1⁺ patients with metastatic melanoma, NY-ESO-1:157-165(165V) stimulated cytotoxic T-lymphocytes in vitro, which recognized peptide-pulsed target cells and HLA-A2.1⁺ NY-ESO-1⁺ tumor cells, suggesting that this peptide may be clinically valuable for the treatment of patients with NY-ESO-1⁺ tumors.