Active immunotherapy of friend virus-induced erythroleukemia and its spontaneous regression

Summary We have tested the effects of specific and nonspecific immunostimulation on the spontaneous regression and recurrence of erythroleukemia induced by a strain of the Friend murine leukemia virus complex, RFV. Subcutaneous inoculation of mice with UV-irradiated allogeneic leukemic spleen cells (LSC) protected against subsequent virus challenge. RFV-leukemic mice injected with LSC into subcutaneous BCG-primed sites had a significantly increased incidence of leukemia regression. When leukemic mice received BCG or LSC alone or normal allogeneic spleen cells (NSC) in place of LSC the incidence of regression was not different from that recorded in untreated controls. A single treatment of recently regressed mice with LSC given into BCG-primed sites prolonged the disease-free period, while LSC alone, BCG alone, or NSC had no such effect. Our data support an immunological basis for spontaneous regression of erythroleukemia and for maintenance of the regressed state. This system provides a model for testing the efficacy of immunotherapeutic protocols for maintenance of leukemia remission and tumor dormancy.