Immune responses to weakly immunogenic murine-leukemia-virus-induced tumors. VII. Kinetic studies on various parameters of effects induced with suppressor cells.

YAC, a Moloney-virus-induced tumor of A mice, caused an inhibition of specific immunologic responses in A and C57BL/6 mice, which was mediated by suppressor cells. In contrast, YAC-1, the in vitro-carried tumor derived from cultivated YAC cells, stimulated the appearance of antitumor reactive cells in A mice. Splenocytes from YAC-1-injected mice generated anti-YAC cytotoxic cells after six days of culture. The suppressor cells from YAC-injected mice efficiently inhibited the cytotoxic responses of the cultivated reactive cells (YAC-1-primed cells) when added at the start of the culture, but not when added at later times. Suppressor cells appeared in A mice three days after injecion of YAC cells and persisted in the animals for at least 50 days. YAC-1-primed cells, derived from A mice 1, 3, 9 and 20 days after injection of YAC-1 cells, were sensitive to the suppressor cells.