Diminution of Cyclophosphamide-induced Suppression of Antitumor Immunity by an Immunomodulator PS-K and Combined Therapeutic Effects of PS-K and Cyclophosphamide on Transplanted Tumor in Rats1

An immunomodulator PS-K was shown to diminish the cyclophosphamide (CY)-induced suppression of specific antitumor transplantation resistance in WKA rats immunized with X-irradiated KMT-17 tumor cells when PS-K was given before treat ment of CY. In the immunochemotherapy of transplanted KMT17 tumor in WKA rats by a combination of CY and PS-K, an enhanced therapeutic effect was also observed when PS-K was given before treatment of CY, with different doses of CY and at different days of CY treatment. However, when PS-K was given just after treatment of CY, the therapeutic effect was rather diminished in comparison with the group having CY treatment alone. By means of the Winn assay, spleen cells obtained from KMT-17-bearing rats (TBR) treated with PS-K followed by CY inhibited the admixed tumor cells more strongly than did spleen cells obtained from TBR treated with CY alone. Recovery of thymus weight from the damage caused by CY was accelerated in TBR treated with PS-K followed by CY and was delayed in TBR treated with CY followed by PS-K. These observations suggest that diminution of CY-induced ¡mmunosuppression by PS-K possibly results in an enhanced thera peutic effect in WKA rats treated with PS-K followed by CY.