Phorbol ester-induced differentiation of human T-lymphoblastic cell line HPB-ALL

12-O-Tetradecanoylphorbol-13-acetate (TPA), a potent tumor promoter, induced phenotypic differentiation in the human thymic acute lymphocytic leukemia cell line, HPB-ALL. Within 30 min of seeding in the presence of TPA, the cells formed a smooth round shape. After a 7-day exposure to TPA, most of the cells became smaller and reminiscent of large or atypical lymphocytes. Electron microscopic analysis evidenced morphological differentiation in TPA-treated HPB-ALL cells. Thymic antigens stained with monoclonal antibody OKT6 were dramatically reduced while Leu2a-positive cells were increased in the TPA-treated HPB-ALL cells. However, OKT3-positive cells did not appear in these TPA-treated cells for up to 7 days. Upon TPA-induced phenotypic differentiation, the growth rate of cells was significantly inhibited, their ability to incorporate DNA and RNA via 3H-labeled precursors was reduced, their ability to bind sheep red blood cell rosettes was significantly increased, and the proportion of terminal deoxynucleotidyl transferase-positive cells was decreased.