Interpatient variation in BCL-2 oncoprotein expression levels of primary leukemic cells from children with newly diagnosed childhood ALL. In two independent experiments depicted in (A)] and (B), which yielded virtually identical results, BCL-2 and actin expression levels of leukemic cells from 11 patients were compared by Western blot analysis using the ECL chemiluminiscence detection system, as described in Materials and Methods. In (A), the BCL-2 levels ranged from 14 U/blast (pt. no. 3, BCL-2/actin ratio = 0.10) to 160 U/blast (pt. no. 2, BCL-2/actin ratio = 1.13). In (B), duplicate samples from the same patients were subjected to an independent Western blot analysis. Consistent with the initial results shown in (A), the BCL-2 levels ranged from 14 U/blast in pt. no. 3 (BCL-2/actin ratio = 0.15) to 173 U/blast in pt. no. 2 (BCL-2/actin ratio = 1.15). NALM-6 cell lysates were included in each experiment as an internal standard to assign a unit value to the BCL-2 expression levels of primary leukemic cells. Arrow indicates the position of the 27 kD BCL-2 protein.