XIAP down-regulation restores apoptotic capability of grzB in HL cells. L1309 B cells, Jurkat T cells, or HL cells L428, L428-scr-shRNA, L428-XIAP-shRNA, L540, L540-scr-shRNA, L540-XIAP-shRNA (all 10⁶) were left untreated or treated with adenovirus (moi of 100), isolated human grzB (600 ng), or adenovirus (moi of 100) plus isolated human grzB (600 ng). (A) Cell death was determined after 4 hours. (B) After 2 hours, cytosolic extracts were isolated and caspase-3 activity was measured using DEVD-AFC as substrate. Cell death was assessed after 4 hours.