THERAPEUTIC EFFICACY OF REPEATED CYCLES OF LOCAL IL-2 INJECTIONS IN MICE CARRYING SLOWLY GROWING TUMOR GRAFTS

Local IL-2 administration prior to transplantation of murine sarcoma v irus (MSV Harvey)-induced tumour MSVT2 provided a model of slowly grow ing tumours suitable for long-iterm investigation of the therapeutic e fficacy of repeated IL-2 injection cycles. Challenge of mice with the dose of sarcoma cells, which was lethal for 20/20 untreated control re cipients, revealed that 8/20 IL-2-pretreated mice were protected by ti re local IL-2 treatment and survived indefinitely. Nine out of twenty IL-2-pretreated mice died during the same time period as the control m ice, i.e,, during 36 days, and 3/20 IL-2 pretreated mice were tumour-n egative until day 60, when incipient rumours arose. The three late tum ours were used as a model to investigate the therapeutic efficacy of t he new cycles of repeated local IL-2 administration. It was found that no resistance to IL-2 immunotherapy was induced by pretreatment of th e late tumours and that the tumours were repeatedly susceptible to loc al IL-2 treatment. Spleen cells of the tumour-bearing mice, which were not cytotoxic for MSVT2 tumour cells in vitro, could be made cytotoxi c by addition of exogenous IL-2.