Cell‐mediated anti‐tumor immunity in oncorna virus‐induced tumors: Specific cytostasis of tumor cells by spleen and lymph‐node cells

The cytostatic effect of lymphoid cell (LC) suspensions from MSV‐induced tumorbearing mice has been tested in the “cytostasis assay” (CA) according to Chia and Festenstein (1973). The target cells (TC) were syngeneic lymphoma cells in suspension. Specific cytostasis was observed mainly at low LC/TC ratios while non‐specific effects could be detected when ratios higher than 25/1 were used. The serum of MSV‐tumor‐bearing mice can either inhibit or stimulate immune cytostasis. Non‐immune lymphoid cells can be armed by this kind of stimulating serum which suggests that an indirect mechanism, possibly antibody‐dependent, is involved in this cell‐mediated immune reaction. The kinetics of the immune response in CA have been studied by comparison with the kinetics of the immune response which can be detected in the chromium release test (CRT) with the same target cells. The cytostasis response in CA persists long after tumor rejection while the CRT activity decreases rapidly, confirming that CA and CRT would probably detect two different effects of the immune lymphoid cells on the same target cells. These results are briefly dicussed.