Host reactivity against clonable tumor cells and the total tumor cell population, studied in a syngeneic murine lymphoma system.

The host anti-tumor reactivity against a syngeneic transplantable T lymphoma (WEHI-7) was studied. The experimental subjects were normal mice, mice with WEHI-7-injected growing tumors, and partially resistant mice, immunized with mitomycin-treated WEHI-7 lymphoma cells. The cellular reactivity against tumor cells in vitro, i.e. natural killer (NK) activity, activity against WEHI-7 cells, and antibody-dependent cellular cytotoxicity (ADCC) were all increased in tumor-bearing animals but were not detected in immunized mice. Reactivity against agar-clonable (colony-forming) tumor cells (approximately 40% of the total tumor population) decreased in the tumor-bearing animals in which tumor had not yet disseminated, and host spleen and peritoneal cells from late tumor-bearing animals with disseminated tumor cells actually enhanced clonable tumor cells in vitro. Specific antibody production against WEHI-7 tumor cells was detected neither in tumor-bearing, nor in partially resistant mice. However, tumor-bearing animals did respond with production of plaque-forming cells after immunization with sheep red blood cells (SRBC), although the response decreased with the increasing tumor burden. The response of spleen cells from tumor-bearing mice to mitogen stimulation showed that the B-cell compartment was unaffected by tumor growth, while the T-cell compartment showed a slight stimulation. The results confirm the heterogeneous nature of the WEHI-7 cell population by demonstrating different sensitivity of tumor cell sub-sets to host reactivity in vitro.