Serological study for in vitro use of monoclonal antibody for autologous bone marrow transplantation in null cell-type acute lymphocytic leukemia.

In connection with autologous bone marrow transplantation (BMT) in null cell-type acute lymphocytic leukemia (Null-ALL) patients, the optimal conditions for in vitro elimination of leukemia cells from transplanted bone marrow cells with monoclonal antibodies (MoAb) plus rabbit complement (C) were investigated. Three monoclonal antibodies, NL-1, NL-22 and HL-47, which were produced in our laboratories and shown to react predominantly to Null-ALL cells, were used. In most cases, 10 micrograms/ml of MoAb and 50% of C were required for optimal killing of leukemia cells. Combined use of MoAbs and multiple treatments were studied, but generally no significant increase in the cytotoxicity to the target leukemia cells was observed as compared with a single treatment with the most effective single MoAb. Selection of C was very important, because some lots had lower C activity from the beginning or after incubation with normal bone marrow mononuclear cells. Nonspecific cytotoxicity to human hematopoietic cells was also observed in some lots of C. Under the optimal conditions thus defined, the three MoAbs did not inhibit the growth of granulocyte-macrophage colony-forming units (CFU-GM) or three other types of hematopoietic stem cells. Modulation of the antigens was also examined, and NL-1 antigen showed mild modulation, whereas NL-22 and HL-47 antigen did not. The results obtained indicated that these three MoAbs may be useful for eliminating Null-ALL cells in vitro from bone marrow in autologous BMT.