Flow cytometric determination of apoptosis by ISEL in antigen defined subpopulations (patient No. 24, Table 1). Peripheral lymphocytes were incubated in vitro in the presence or absence of F-ara-A (3 μmol/L) or CyA (100 ng/mL). Apoptosis was evaluated after 72 hours in CD19⁺, CD3⁺, CD4⁺, and CD8⁺ lymphocytes. The number in the top right quadrant represents the percentage of apoptotic cells in the antigen-defined population. The numbers in parentheses represent the percentage of antigen-defined apoptotic cells within the total number of peripheral lymphocytes.