Characterization and Specificity of Murine Anti-Tumor Cytotoxic Effector Cells within an Ascitic Tumor

The anti-tumor immune reactivity of cells which are contained within a progressively growing ascitic tumor has been analyzed by studying the cell-mediated response of DBA/2 mice to the syngeneic mastocytoma P815Y. Peritoneal cells (P.C.) which were harvested from these P815Y tumor-bearing hosts were fractionated by velocity sedimentation at unit gravity. Cell-mediated cytotoxicity (CMC) of fractionated and unfractionated cells was measured by a 4-hr51Cr-release assay. The cell separation procedure revealed significant levels of CMC to P815Y in P.C. populations at 8 to 16 days following i.p. inoculation of 1 × 103 viable P815Y cells. The tumor-bearer P.C. which mediated CMC against P815Y were generally confined to P.C. populations that sedimented between 2 and 6 mm/hr. The cytolytic activity against P815Y mediated by tumor-bearer P.C. was sensitive to treatment with an anti-Thy-1.2 preparation and complement, but not to treatment with anti-immunoglobulin serum and complement. CMC against P815Y by tumorbearer P.C. was not inhibited by the presence of heat-aggregated human γ-globulin. In addition, it was shown that the cytolytic activity of tumor-bearer P.C. against P815Y was not mediated by “natural” killer cells, since the cytolytic activity was not labile at 37°C in culture. These results indicate that T lymphocytes which are cytotoxic for tumor cells in vitro can be found within a growing ascitic tumor. Analysis of the specificity of DBA/2 anti-P815Y cytotoxic T lymphocytes (CTL) demonstrated that these effector cells could lyse three of four DBA/2 tumor lines and four of four C57BL/6 tumor lines which were tested. Cytolysis of two strain A tumors and Con A- and LPS-induced DBA/2 or C57BL/6 lymphoblasts was not observed. No correlation was found between the surface expression of the gp69/71 or p30 components of murine leukemia virus and the susceptibility of tumor cells to lysis by these CTL. These results indicate the T cell killing directed against shared antigenic determinants on P815Y and other tumor cells is not H-2 restricted and that gp69/71 and p30 are not the target specificities recognized by DBA/2 anti-P815Y CTL.