Combined effect of interleukin 2 and cyclophosphamide in therapy of mice with transitional cell carcinoma.

We investigated the effect of combination therapy with interleukin 2 (IL-2) and cyclophosphamide (CPM) in C3H/HeN mice implanted with mouse bladder tumor cells (MBT2). MBT2-bearing mice were treated with a single intraperitoneal injection of 120 mg/kg CPM on day 10 and/or subcutaneous administration of 5 x 10(4) units IL-2/day from day 11 to day 20. As a result, the growth of tumor in mice treated with IL-2 alone was slightly suppressed. On the other hand, regression was observed in all mice treated with CPM alone, although regrowth of tumor was seen in all of them. However, when IL-2 was administered with CPM, regrowth of tumor was completely suppressed. An immunologic study was done that showed cytotoxicity against YAC-1 and P815 in the spleen cells was suppressed in mice treated with CPM alone, but that both recovered to control levels when IL-2 was administered with CPM. Cytotoxicity against MBT2 in the spleen cells was most elevated in mice treated with both IL-2 and CPM. These findings suggested that clinical evaluation of combination therapy with IL-2 and CPM may be worthwhile.