A CELL-SURFACE ANTIGEN (BAL) DEFINED BY A MOUSE MONOCLONAL-ANTIBODY INDUCING APOPTOSIS IN A HUMAN LYMPHOCYTIC-LEUKEMIA CELL-LINE

The lack of apoptosis or programmed cell death in human tumor cells ha s been suggested to be one factor allowing uncontrolled growth of neop lasms. We have developed a mouse monoclonal antibody (MAb) that induce s programmed cell death in a human acute leukemia cell line (KM-3) of the pre B-cell type. Stable, antibody-producing hybridomas were produc ed by fusing mouse myeloma cells to spleen cells from mice immunized w ith viable KM-3 cells. Incubation of KM-3 cells with the MAb (designat ed anti-BAL) resulted in growth inhibition and subsequent cell death w ithin 2-3 days. Anti-BAL required cross-linking with a rabbit anti-mou se antibody to induce DNA fragmentation typical of apoptosis. Immunobl otting experiments with anti-BAL identified a 37-kDa protein, apparent ly different from any previously described apoptosis-related surface a ntigen. Strongest expression of the antigen was generally found on cel ls of lymphoid or myeloid origin. However, several other cell types su ch as fibroblasts and endothelial cells were also stained by anti-BAL in flow cytometry but less intensively. Despite the apparent presence of this cell surface-bound 37-kDa antigen on several normal and malign ant cell lines expressing a more immature phenotype.