Quantitative and qualitative assessment of circulating NY-ESO-1 specific CD4⁺ T cells in cancer-free individuals

The germ cell antigen NY-ESO-1 is characterized by its frequent expression in patients bearing cancers of various histological types, that positively correlates with stage of disease, together with its frequent spontaneous immunogenicity in patients with advanced cancer. Because of these features, NY-ESO-1 is presently viewed as a prototype antigen for the development of cancer vaccines aimed at preventing disease progression. To gain a global view of the CD4⁺ T cell repertoire available for NY-ESO-1 in individuals of different genetic background, in this study, we have addressed the presence, frequency, and fine specificity of CD4⁺ T cells reactive against NY-ESO-1-derived sequences among circulating lymphocytes from healthy donors. NY-ESO-1 specific CD4⁺ T cells were present among circulating lymphocytes at a frequency between 0.5 and 5 precursors per million CD4 ⁺ T cells. In the majority of the cases, the reactivity of NY-ESO-1 specific CD4⁺ T cells was directed towards immunodominant regions located in the carboxyl-terminal half of the protein. Interestingly, immunodominant regions were confined to parts of the NY-ESO-1 protein containing hotspot sequences with predicted high binding for multiple frequently expressed MHC class II molecules. In contrast, no reactivity was found against the amino-terminal part of the protein, which was concomitant with the paucity, in this region, of sequences with predicted high binding to MHC class II molecules.