Mixed lymphocyte/tumor-cell interaction in a murine sarcoma virus (Moloney)-induced tumor system. Comparison between lymphoproliferation and lymphocyte cytotoxicity.

Studies of the MLTI were performed in a primary MSV-induced tumor system. Reactivity against mitomycin-C-treated RBL-5 cells could be detected during a limited period at about 14 days after virus injection. The degree of reactivity of MSV 14 spleen cells was quite variable; stimulation indices ranged from 2.2 to 9.4. Activity in the MLTI appeared to a great extent to be dependent on T-lymphocytes. A relatively broad spectrum of specificity was demonstrated in experiments using additional stimulating cells besides RBL-5. The kinetics of the MLTI correlated well with the kinetics of the primary cytotoxic response in the CRA against RBL-5 cells. However, positive results in the in vivo and in vitro secondary cytotoxicity assays could be detected between 21 and 100 days after MSV injection when the MLTI was negative. Transplantation resistance against challenge with RBL-5 tumor cells also persists for a long time after MSV inoculation. Our data therefore indicate that the MLTI, in contrast to the secondary cytotoxicity assays, does not correlate well with the status of in vivo immunity.