TGF-β inhibits growth and induces apoptosis in leukemic B cell precursors

The uncontrolled proliferation of malignant lymphoblasts is the pathobiological hallmark in B cell precursor-ALL (BCP-ALL). Identification of inhibitory growth factors is of great Importance for the understanding of growth control of leukemic B cell precursors and the development of novel therapeutic approaches in BCP-ALL. The aim of our study was the analysis of the effect of TGF-β on cell survival and apoptosis of B cell precursors (BCP) from patients with acute lymphoblastic leukemia in vitro. Experiments were performed in a coculture system with cloned murine fibroblasts, which efficiently block spontaneous ex vivo apoptosis of BCP and thus allows the assessment of cytokine-induced growth inhibition. TGF-β significantly reduced cell viability of highly purified, FACS isolated CD10 + /CD19 + leukemic BCP by a mean of 53% (P = 0.0001). The loss of cell viability was accompanied by a significant increase of apoptosis with a mean of 70% (P = 0.0028). The TGF-β effect was blocked specifically by a monoclonal anti-TGF-β antibody. Induction of apoptotic cell death by TGF-β was not accompanied by reduction of bcl-2 protein expression. TGF-β transcription was not detected in the leukemic pre-B cell line BLIN-1, but in the murine fibroblasts. The growth inhibitory effect of TGF-β was not restricted to leukemic BCP. The cytokine also increased apoptosis of normal, highly purified BCP by a mean of 58%. The data identify TGF-β as a potent growth inhibitory cytokine for leukemic BCP.