Dissecting cytotoxic T cell responses towards the NY-ESO-1 protein by peptide/MHC-specific antibody fragments

NY-ESO-1 is a germ cell antigen aberrantly expressed by different tumor types that elicits strong humoral and cellular immune responses, representing one of the most promising candidates for vaccination of cancer patients. A detailed analysis of CD8⁺ T cells generated in vaccine trials using NY-ESO-1 derived peptides (157-165 and 157-167) revealed that the dominant immune response was directed against a cryptic epitope (159-167) diverting the immune response from tumor recognition. Only CTL reactivity to the NY-ESO-1_157-165 peptide appeared to be capable of lysing NY-ESO-1/HLA-A0201-expressing tumor cells. To study the process of NY-ESO-1 peptide presentation by tumor cells in more detail we generated a high-affinity (K_D=60 nM) antibody fragment that specifically recognizes the NY-ESO-1_157-165 peptide/HLA-A0201 complex. Peptide variants such as the NY-ESO-1_157-167 peptide or the cryptic NY-ESO-1_159-167 peptide were not recognized. The antibody fragment blocked in a dose-dependent fashion the recognition of NY-ESO-1/HLA-A2-positive tumor cells by NY-ESO-1_157-165 peptide-specific CD8⁺ T cells. This antibody fragment is a novel reagent that binds with TCR-like specificity to the NY-ESO-1_157-165/HLA-A2 complex thus distinguishing between CTL responses against immunological meaningful or cryptic NY-ESO-1-derived peptides. It may therefore become a useful monitoring tool for the development of NY-ESO-1-based cancer vaccines.