Antigenic specificities of the cell-mediated anti-tumor reactions in the MSV system studied by the secondary chromium release test.

The SCRT and the inhibition test have been used to determine the specificity of cell surfacr antigens reacting with anti-M-MSV cytolytic lymphocytes. The method provides very sensitive and specific results. Some discrepancies exist between the results of SCRT and those obtained by the in vitro inhibition by tumor cells of cell-mediated immune cytolysis. The main point is that allogeneic cells are stimulatory in SCRT, whereas they are not reactive in the inhibition test. Several hypotheses are discussed to explain these discrepancies. In all the experiments, a strong secondary stimulation of cytotoxic lymphocytes was obtained in vitro when FMRGi (+) cells were used as stimulators, whatever the nature and the histocompatibility antigens of these cells. This suggests that an antigen of the "FMRGi system" is regularly involved in the cell-mediated anti-MSV reaction. However, other antigenic specificities of different natures are probably also concerned due to the antigenic complexity of these tumors.