Combined effects of natural resistance and chemotherapy against a murine lymphoma in lethally-irradiated mice.

Lymphoma EL-4 of B6 origin was inoculated into lethally-irradiated syngeneic B6 or resistant BD2F1 hybrid recipients. Marked impairment of lymphoma cell proliferation (i.e. hybrid resistance, HR) occurred in the spleen but not in the liver or lung of BD2F1 hosts. Treatment with DTIC at the optimal dose of 80 mg/kg i.p. produced inhibitory effects in spleen, liver and lung of young BD2F1 mice, that were much greater than those observed in syngeneic B6 hosts. Increased anti-lymphoma effects for HR and DTIC chemotherapy were not detectable in the liver or lung of old BD2F1 mice or in the spleen, liver or lung of young hybrid recipients depressed for HR by pretreatment with cyclophosphamide. This is the first report on combined antileukemic effects of the host's anti-tumor natural resistance and chemotherapy.