Protection against murine ascites tumours by lymphoid cell populations with T memory or cytotoxicity

It was possible to protect irradiated C3H mice against lethal doses of allogeneic ascitic tumor cells (RBL-3 or P-815 Y) by systemic administration of low doses of syngeneic sensitized lymphoid cells. Two types of cell populations were active at similar doses: (1) spleen cells harvested 2 months after a nonlethal inoculation of tumour cells, at which time no cytotoxic lymphocytes wer in vivo sensitization or in vitro sensitized spleen cells; sucll and dose dependent and target cell specific. The findings imply that T memory cells as well as cytotoxic cells are able to protect, although it was not possible to exclude the presence of memory lymphocytes in the cytotoxic cell population. Antiserum to cytotoxic T cells (CTL) was prepared in an attempt to distinguish memory and cytotoxic effector cells. The antiserum did not react with the majority of T cells in a normal spleen or thymus, but showed specificity for the CTL cell lineage. Antiserum treatment and complement abolished protection in all types of sensitized cell populations. Since memory and cytotoxic cells appeared to share differentiation antigens, we could not establish whether memory cells are precursors or products of cytotoxic cells.