NY-ESO-1-specific cytotoxic reactivity of CD4+ T cell clones. (a) The CD4+ T cell clones NW 1454-CD4-68 (triangles) and NW 1662-CD4-2 (squares) were tested against the allogenic HLA-DP4+ EBV-B cell line NW1539-EBV-B, either pulsed with NY-ESO-1 p157-170 or not (closed and open symbols, respectively) in a 4-h chromium release assay at E/T ratios of 90, 30, 10, and 1:1. (b) The CD4+ T cell clone NW 1454-CD4-68 was tested against the HLA-DP4+ NY-ESO-1-positive melanoma cell lines NW-MEL-38, NW-MEL 634, and NW-MEL-450, against the NY-ESO-1-negative melanoma cell line NW-MEL-8, and against the HLA-DP4-negative melanoma cell line SK-MEL-29 in a 4-h chromium release assay.