Induction of cytotoxicity from fresh splenocytes after in vivo administration of cyclophosphamide. Importance of long-term culture with high-dose recombinant interleukin-2.

Cyclophosphamide, combined with lymphokine-activated killer (LAK) cells and recombinant interleukin-2 (rIL-2), is known to mediate regression of tumors, but the effects of cyclophosphamide on the subsequent generation of LAK cells are unclear. It was the aim of the experiments in this paper to determine whether fresh splenocytes cultured with rIL-2 would maintain or regain their cytotoxicity in vitro after being exposed to the cytotoxic agent cyclophosphamide in vivo. Functional monitoring of splenocytes after in vitro incubation with rIL-2 was performed at various times through chromium-release assays, thymidine assays and cell-cycle analysis. Chromium-release assays determined that the cytotoxicity of cultured splenocytes returned to normal after 12 days of in vitro culture with rIL-2. The thymidine assays indicated a normal rate of uptake of thymidine after 7 days in culture, while the cell cycle was still abnormal by day 12 of culture. The growth and expansion of rIL-2-activated splenocytes after different times of in vitro culture indicated a return to normal compared to control animals after 7 days of continuous in vitro exposure to rIL-2. It is concluded that murine splenocytes can demonstrate cytotoxicity after exposure to cyclophosphamide, through prolonged continuous in vitro culture with rIL-2. Since cyclophosphamide did not jeopardize the production of splenocyte cytotoxic effectors generated with rIL-2, it appears to be a strong contender for use in chemoimmunotherapy protocols.