[Immune manipulation of BCG administered before or after cyclophosphamide for chemo-immunotherapy of L1210 leukemia]

1. BCG (1 mg/mouse) administered i.v. on day 5 after chemotherapy by cyclophosphamide (CPM), given itself at the dose of 80 or 134 or 403 mg/kg one day after the inoculation of L 1210 leukaemia 10(3) cells, increases the effect of the non-optimal doses: i.e. 80 mg/kg, which is insufficient to cure mice, and 403 mg/kg, which is toxic. It does not change the effect of the optimal dose of CPM (134 mg/kg) which cures most of the mice. 2. BCG (1 mg/mouse i.v.) given on day 15 before CPM decreases the effect of the latter at the dose of 134 mg/kg. These results suggest that: a. BCG given after chemotherapy is not only able to eradicate the residual disease, but can decrease chemotherapy toxicity; b BCG given before an optimal dose of chemotherapy may decrease its antileukaemic effect, via the enhancement of the chemotherapy immunodepressive action, as demonstrated by skin graft experiments; this deterioration of the effect of chemotherapy by immunodepression was also suggested when the combination of CPM and antithymocyte serum was used.