NY-ESO-1–specific CD4⁺ T cell precursors are present not only in patients with NY-ESO-1 antibody but also in patients without NY-ESO-1 antibody. CD4⁺ T cells and CD4⁺CD25^- T cells were isolated from PBMCs as described in “Study design” and were cultured with APCs pulsed with indicated NY-ESO-1 peptides. Fifteen to 20 days later, NY-ESO-1–specific Th1 cell induction was analyzed by ELISPOT assay. These experiments were performed independently at least twice with similar results. Data are expressed as means +SD.