Granzyme B enzyme activity data. (▪) Cord blood (n = 8) and (□) BM (n = 4) mononuclear cell preparations were incubated in IL-2 (500 U/mL). After 3 days, the cells were washed and lysed and the resulting cell extracts were incubated with a substrate for granzyme B. Freshly isolated cord blood mononuclear cell extracts (n = 8) were also analyzed. Enzyme activity was followed colorimetrically at 405 nm and is expressed as a change in OD + 1 SD with time. Readings were taken after 3 days of incubation at 37°C. The Mann Whitney statistical test was used to compare data. *P< .02.