Cell cycle progression of B-chronic lymphocytic leukemia cells induced to differentiate by TPA.

The cell cycle transition and differentiation-associated surface antigen expression was studied in a clone of B cell chronic lymphocytic leukemia (B-CLL) with phenotypic properties similar to those of resting B lymphocytes. Differentiation was induced with TPA (12-O-tetradecanoyl-phorbol-13-acetate) and defined and quantitated by morphological and functional markers. Changes in the cell cycle position were determined by flow cytometry of acridine orange-stained cells. The uninduced B-CLL cells represented a homogeneous population with the same cell cycle position (GO) as resting normal peripheral blood lymphocytes. After five days of TPA stimulation, 56% of the B-CLL cells were found in G1A, 9% in G1B, and 3% in the S + G2/M phase, of which 2% was accounted to proliferating T cells. The cell cycle transition of the differentiating B-CLL cells was also examined using cell cycle-associated surface antigens as markers. HLA-DR and CD23 antigens were present already on noninduced cells. The former had a high constant expression, while the amount of CD23 increased upon induction. The 4F2 antigen was absent on noninduced cells but present on 86% of the induced cells. HH1 (CD37) was expressed by the majority of the cells before TPA treatment and decreased to almost undetectable levels within 24 hours. Two antigens related to late stages of the cell cycle, the interleukin 2 (IL 2; CD25) and the transferrin receptor, were present on about 20% of the induced cells. Experiments with enriched T cells showed that T but not B cells incorporated 3H-thymidine. Taken together these results and previous work on the induction of the protooncogene c-myc and c-fos suggest that this B-CLL clone represents GO cells that undergo differentiation without concomitant proliferation when exposed to TPA.