Immune cytolysis of murine tumor cells mediated by xenogeneic “Immune” RNA

Using a quantitative assay for lymphocyte‐mediated cytotoxicity, it was shown that normal, non‐immune C3Hf/HeCr mouse spleen cells were converted to effector cells specifically cytotoxic to chemically induced C3H tumor cells by incubation in vitro with “immune” RNA extracted from the lymphoid organs of specifically immunized guineapigs. This response was specific for the tumor used to immunize the RNA donor. Cytotoxicity indices (CIs) at 0.30 to 0.54 were consistently obtained. Spleen cells incubated with RNA from guinea‐pigs immunized with a different tumor, or with normal C3H tissue, failed to lyse the target cells. These immune responses were abrogated when the “immune” RNA was treated with RNase prior to incubation with the spleen cells. However, pre‐treatment with DNase or pronase did not alter the activity of the “immune” RNA. “Immune” RNA to a second chemically induced C3H tumor mediated a cytotoxic response to that tumor (CI=0.45), but not to the first tumor. This clearly demonstrates that xenogeneic “immune” RNA mediates tumor‐specific immune cytolysis, in vitro.