Susceptibility to CTL-induced lysis of chronic-phase CML. A conventional 4-hour ⁵¹Cr release assay was performed by using the MNCs derived from the peripheral blood of a male patient with chronic-phase CML positive for HLA-A1 as target cell population. HLA-A1-restricted CTLs directed against the HY antigen were added at different E/T ratios. Data shown are as mean percentages of specific lysis induced ± SD (n = 3).