Characterization of cytotoxic effector cells in the mouse mammary tumor system.

Cell types involved in the immune response in vitro to MTV-induced BALB/cfC3H mammary tumors have been studied with techniques designed to inactivate or deplete different cytotoxic effector cells from spleen cells populations. The minimal activity of spleen cells from neonatally MTV-infected virgin BALB/cfC3H females is dependent upon the presence of T cells. Spleens from multiparous BALB/cfC3H females bearing small tumors are similar to those of tumor-free multiparous females. However, after the tumors grow to large size, the activity of the non-T cell population is no longer detectable. The cytotoxic activity of spleen cells from BALB/c females older than 14 weeks (supposedly not infected with MTV) is not dependent upon the presence of T cells. No activity is shown by spleen cells from BALB/c females younger than 14 weeks. Positive control spleen cells were obtained from C3H female mice who had been immunized to BALB/c histocompatibility antigens by a skin allograft; both a T cell and a non-T cell response were found.