LSTRA and RBL-5 lymphomas induced by Moloney and Rauscher leukemia viruses, respectively, were used to determine whether antigenically altered tumors induced by 5-(3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide in vivo would retain their original antigenic properties and/or have new antigenic properties. The tumors became highly immunogenic in the syngeneic hosts after 4 to 8 transplant generations with drug treatment. Syngeneic mice could be protected against challenge with the parental tumor by presensitization with the drug-altered sublines while unrelated tumor lines were incapable of protecting them. The drugaltered subline of LSTRA was used for treatment of the LSTRA in conjunction with chemotherapy, and this immunochemotherapy produced significant increases in number of survivors and increases in median survival time compared to either treatment alone. Tolerance studies indicated that there are novel antigens and parental tumor antigens associated with the drug-treated sublines.

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