DRUG-MEDIATED CHANGES IN THE SUSCEPTIBILITY OF HUMAN LYMPHOBLASTOID B-CELLS TO NK-MEDIATED CYTOLYSIS - STUDIES WITH A TRIAZENE COMPOUND

Previous studies have shown that treatment of leukemia-bearing mice with triazene compounds results in a profound alteration of the immunological properties of leukemic cells. These cells become highly immunogenic and susceptible to natural immunity (NI). Moreover, in a pilot clinical study, dacarbazine was found to suppress bone marrow blasts in patients with acute non-lymphoblastic leukemias. The cytotoxic mechanism involved could be of biochemical and immunological origin as well. Therefore experiments were carried out to test whether triazenes could influence the susceptibility of blast cells to human NI effector lymphocytes (represented, at least in part, by NK cells). The results obtained with target Epstein-Barr virus (EBV)-immortalized B cells and effector cells of different donors, showed that: (a) multiple in vitro treatments of lymphoblastoid cells with methyl-triazene-benzoic acid (MTBA, a triazene compound active in vitro), gave origin to lines that were more resistant than the parental lines to the antitumor effects of MTBA; (b) MTBA-treated lines were more susceptible (37.5% of cases), or less susceptible (31.2% of cases) to NI than parental cells. Effector lymphocytes of various donors recognized different changes in susceptibility to natural killer (NK)-mediated lysis; (c) treatment of parental or MTBA-treated lines with interferon-beta reduced target cell susceptibility to NK-mediated cytolysis, but increased NK activity and lymphoblast chemosensitivity to MTBA.