Antigenic Changes of L1210 Leukemia in Mice Treated with 5-(3,3-Dimethy 1-1-triazeno )imidazole-4-carboxamidel

Strong antigenic changes were induced in two LI 210 leukemia lines (L1210 Cr and L1210 Ha) after several passages in CDF, and BDF, mice treated with 5-(3,3-dimethyl-l-triazeno)imidazole-4-carboxamide (DIG). The leukemic cells of both lines originally compatible with DBA/2 and related hybrid hosts elicited a pronounced allograft reaction in the same animals. The LI 210 Cr line was sensitive to the antitumor activity of DIG while L1210 Ha was not. Since no specific relationship could be found between the origin of drug resistance and the appearance of antigenic changes, any hypothesis based on selection of spontaneous mutants by DIG would appear to be excluded. In addition the possibility that DIG might play a direct role as a hapten on tumor cells was ruled out. DIG was found to exert a strong inhibition of the allograft reaction. However, the origin of antigenic lines could not be attributed to the immunosuppressive activity of DIG. It would appear that DIG acts in some way on tumor cells, changing their antigenic properties and preventing the immunoselection of the transformed cells by the host. It was suggested that DIG could activate a latent virus of LI 210 leukemic cells or induce somatic mutation at the level of histocompatibility antigens.