Cytokine secretion by leukemia reactive T-cell clones. T-cell clones, 2.4.1 and 2.4.8, were stimulated with the indicated irradiated stimulator cells or with PMA/ionomycin for 72 hours. The release of IFN-γ and IL-4 in the culture medium was assessed by cytokine-specific sandwich ELISA and expressed as the mean of the triplicate cultures.