Recovery of the capacity for cytotoxic T cell generation in cyclophosphamide-treated mice by the addition of LYT-1/2- helper cells.

Spleen cells from mice treated with cyclophosphamide (150 mg/kg) and cultured at suboptimal concentrations do not generate cytotoxic T lymphocytes to allogeneic tumor cells. The reduced response of spleen cells from cyclophosphamide-treated mice is not due to the elimination of cytotoxic T cell precursors because normal responses are obtained by the addition of Lyt-1+2- T helper cells to the culture system. These results indicate that helper cells, required for the development of cytotoxic T cell responses to tumor alloantigens, are eliminated by cyclophosphamide in the absence of evident toxicity to cytotoxic T cell precursors.