Antibody lysis of human hematopoietic cells in the absence of complement and effector cells

The incubation of K-562 leukemia cells with specific goat immunoglobulin resulted in gradual cytolysis in the absence of complement and effector cells. Optimal lysis (100%), reached in 3-4 days, occurred when the concentration of the antibody in the culture medium was about 20 micrograms/ml containing an initial inoculum of 15,000 cells. A lower concentration (10 micrograms/15,000 cells/ml) led to partial cytolysis; the surviving cells, cultured in fresh medium, were still vulnerable to antibody lysis (30 micrograms/ml), thus indicating the lack of an apparent resistant cell population. The amount of free antibody in the culture medium diminished rapidly and very little or none was detectable after 2-3 hours of incubation with K-562 cells. The immune gamma-globulin also inhibited colony formation of K-562 cells in soft agar. The immune gamma-globulin, absorbed extensively with normal blood cells, to pluripotent K-562 cells, cross-reacted with several human malignant hematopoietic cell lines tested. These cells included T-lymphoblasts (JM and MOLT-4), promyelocytes (HL-60), Burkitt's lymphoma cells (RAJI), myeloblasts (KG-1 and KG-1a), and multiple myeloma cells (K-737). The absorption of the immune gamma-globulin with an equal number of cells from each of the cell lines assayed diminished but did not completely remove the antibody responsible for cytolysis of K-562 target cells. Thus, the K-562 leukemia blasts appear to possess common and specific antigens that may be only partially expressed on other committed leukemia cell lines studied. For this reason, the cytolytic activity of the immune gamma-globulin could only be removed by absorption with K-562 cells possessing a complete array of antigens solely present on pluripotential hematopoietic cells.