Immunodominant CD4⁺ responses identified in a patient vaccinated with full-length NY-ESO-1 formulated with ISCOMATRIX adjuvant

There is increasing evidence showing the involvement of CD4⁺ T cells in initiating and maintaining antitumor immune responses. NY-ESO-1 is expressed by various tumors but not normal tissues except testis. We conducted a cancer clinical trial by using full-length NY-ESO-1 protein formulated with ISCOMATRIX adjuvant and injected into patients intramuscularly. Autologous dendritic cells pulsed with NY-ESO-1 ISCOMATRIX in combination with overlapping synthetic peptides were used to identify immunodominant T cells from a vaccinated patient. We show here the identification and characterization of two novel CD4⁺ T cell epitopes. T cells specific to these epitopes not only recognized autologous dendritic cells loaded with NY-ESO-1 but also NY-ESO-1-expressing tumor cell lines treated with IFN-γ. One of the two responses identified was greater than the previously identified immunodominant HLA-DP4-restricted response and correlated with NY-ESO-1-specific CD8 ⁺ T cell induction after vaccination. This T cell response was vaccinated in most patients who expressed HLA-DR2. This study has systematically surveyed patients vaccinated with full-length tumor antigen for a vaccinated CD4 helper T cell response.