NY-ESO-1 p157-170-specific CD4+ T cell reactivity is restricted by HLA-DP4. The CD4+ T cell clone NW 1662-CD4-12 was tested against a panel of HLA-DP4-positive and HLA-DP4-negative allogeneic EBV-B cell lines pulsed with NY-ESO-1 p157-170 (black bars) in ELISPOT assays. NY-ESO-1 p157-170-specific reactivity was documented against peptide-pulsed HLA-DP4+ EBV-B cells only. The white bars represent the background reactivity against EBV-B cells alone.