Generation of cytotoxic lymphocytes to syngeneic tumors by using co-stimulator (Interleukin 2): in vivo activity.

Spleen cells from DBA/2J mice bearing the syngeneic tumor mastocytoma P815, incubated with co-stimulator (Interleukin 2) and P815 in vitro, were effective in killing P815 cells in vivo. Within 24 hr of injection, 1 X 10(7) cytotoxic lymphocytes (CL) killed most of 1 X 10(6) P815 cells. The host response to the tumor 7 to 9 days after the initial tumor injection was also greatly enhanced in mice that had received CL. This effect was potentiated in sublethally irradiated mice. CL were effective in mice with large tumors, overcoming suppressive factors that might be present. Under certain conditions, a significant fraction of CL-treated mice survived the P815 tumor indefinitely. These included i.p. CL given 2 days after a large dose (1 X 10(6)) of i.p. P815. In addition, some mice given i.v. and intra-tumor CL survived small doses (1 X 10(4)) of subcutaneous P815 cells. Long-term surviving mice remained resistant to challenge with 1 X 10(6) tumor cells (which is 10(4) times the normally lethal dose) for at lest 1 yr. No detrimental effects were noted even after injection of 5 X 10(7) CL per mouse.