Phorbol ester treatment induces terminal macrophage differentiation and down regulates CD10 (CALLA), CD20, and CD49D (VLA-4) expression on pre-B acute lymphoblastic leukemia cells

We have investigated the effects of phorbol 12-myristate 13-acetate (PMA) on purified pre-B acute lymphocytic leukemia (ALL) cells (> 99% CD10⁺, CD20⁺, CD34^-, CD38⁺, HLA-DR⁺, Tdt) isolated from a patient who had the unusual presentation of cholecystitis as the primary manifestation of her disease. Cytogenetic analysis of the lymphoblasts also demonstrated the t(14;18) translocation which is common in low grade Non-Hodgkin's lymphoma, but exceedingly rare in ALL. Isolated lymphoblasts obtained from the patient's peripheral blood demonstrated L-2 morphology, were non-adherent, and were myeloperoxidase, sudan black, and non-specific esterase negative. Following 3 days of treatment with 10 ng/ml of PMA, 50-70% of the cells became adherent to plastic and exhibited macrophage morphology. The phorbol ester induced morphologic changes were observed in > 90% of the cells by day 7, with no further changes through 10 days. The majority of these cells became non-specific esterase, myeloperoxidase, and sudan black positive following PMA treatment. Flow cytometric analysis showed that treatment with PMA down-regulated the cell surface expression of B-cell leukemia antigens CD10(CALLA) and CD20 as well as the adhesion molecule CD49d (VLA-4). Monocyte and neutrophil markers (CD11b, CD14, CD15) remained negative following PMA treatment. Fifteen to 20% of the PMA-induced macrophages phagocytized opsonized red blood cells as visualized by light microscopy. These results demonstrate for the first time that functionally mature macrophages can be generated in vitro from pre-B ALL cells after 7 days of treatment with the protein kinase C activator PMA. Moreover, protein kinase C (PKC) activation in pre-B ALL cells is a differentiation signal without any proliferative component.