Immunosensitivity and histocompatibility antigens in drug-altered leukemic cells

New antigenic properties of experimental lymphomas have been reported previously following in vivo treatment with antitumor agents. 5-(3,3-Dimethyl-1-triazeno)imidazole-4-carboxamide (DIC) induced new antigenic characteristics on L1210 and L5178Y lymphomas, that were previously investigated in studies in animals compatible with the original untreated parental tumors. Here the L1210/DIC and L5178Y/DIC susceptibility to the cytotoxic effects of allogeneic and xenogeneic lymphocytes and sera obtained from animals sensitized to DBA/2 histocompatibility antigens were studied. The original and the DIC tumors showed the same sensitivity to anti-DBA/2 cellular and humoral cytotoxicity. The immune response electied in allogeneic mice by the original and DIC sublines was evaluated by in vitro cell-mediated and humoral cytotoxic assay. Beyond the immune response to histocompatibility antigens, a specific, anti-DIC-antigen immunoreaction was not found. Inhibition assay of the cell-mediated cytotoxicity and absorption of the humoral cytotoxicity demonstrated that DIC-induced antigens are not reciprocally related in cell-surface concentration to the natural DBA/2 histocompatibility antigens associated with tumor cells of DIC lines. An experiment was conducted in which specific activity against the DIC-treated L5178Y/DIC cells was observed with anti-L5178Y/DIC rabbit immune serum absorbed with the parental L5178Y lymphoma. This finding provides additional support to previous studies indicating that treatment with DIC induced new antigens on the lymphoma cells.