Tumor metastases and cell-mediated immunity in a model system in DBA/2 mice. VII. Interaction of metastasizing and nonmetastasizing tumors with normal tissue in vitro.

Three mouse tumors known to metastasize in vivo and 3 nonmetastasizing mouse tumors that grow only locally in vivo were examined for their ability to adhere to and invade normal syngeneic lung organ cultures in vitro. All 3 metastasizing tumors adhered to and invaded the normal lung cultures. In contrast, tumors that grow only locally in vivo neither adhered to nor invaded the normal lung tissue. The described system is ideally suited to correlate the in vivo invasiveness of a given tumor with its potential to metastasize in vivo and to study in vitro how to influence the interaction of metastasizing tumor cells with normal tissue.

Demonstration of tumor-associated immunity with a leukocyte adherence inhibition (LAI) assay.

A modification of the leukocyte adherence inhibition (LAI) assay of Halliday was used to search for immune reactions against tumor-associated antigens of mouse tumors as well as against embryonic antigens in such neoplasms. Soluble antigen extracts were prepared from transplanted (BALB/c) methylcholanthrene-induced sarcomas and carcinomas, from normal BALB/c embryos taken at 14-18 days' gestation and from kidneys and livers of adult BALB/c mice. Peritoneal cells (PC) from mice immunized against syngeneic tumors gave leukocyte adherence inhibition more commonly when exposed to antigens prepared from the same tumor than did PC from normal (untreated) mice or from mice immunized against a different tumor. However, different tumor antigen preparations varied vastly in their ability to give specific adherence inhibition; some preparations consistently gave a high tumor-specific inhibition, while others did not. This may explain why the degree of reactivity observed was low and its tumor specificity not absolute when data obtained with all different antigen extracts were pooled. PC from multiparous mice gave adherence inhibition when exposed to antigenic extracts from syngenic mouse embryos or from tumors, as compared to PC from virgin mice exposed to the same extracts. Furthermore, PC from tumor-immunized mice reacted more commonly against antigen extracts from mouse embryos than did peritoneal cells from normal untreated mice. Adherence inhibition was not observed when PC from tumor-immunized or multiparous mice were exposed to antigen extracts from adult syngeneic livers or kidneys.

Tumor metastases and cell-mediated immunity in a model system in DBA/2 mice. IV. Antigenic differences between a metastasizing variant and the parental tumor line revealed by cytotoxic T lymphocytes.

The syngeneic cytotoxic T-cell response against a metastasizing murine lymphoma variant was investigated and compared with the response against the non-metastasizing parental tumor line Eb. Anti-tumor cytotoxicity was not detectable in a 4-h 51Cr release assay in spleens taken directly from tumor-bearing animals (primary CMC). After restimulation in vitro (secondary CMC) however, high anti-tumor cytotoxic activity was detected. This activity was mediated by immune T lymphocytes as shown by its sensitivity to treatment with anti-Thy 1.2 serum and complement. Ten cells of the metastasizing tumor ESb, inoculated subcutaneously, were sufficient to raise a local tumor and metastases and to induce cytotoxic T memory cells in the spleens. In contrast, about 104 cells were required to raise a local tumor and to induce splenic cytotoxic T memory cells, when the parental tumor Eb was tested. The specificity studies of the anti-tumor cytotoxic activity demonstrated that cytotoxic T cells could distinguish unrelated, chemically induced syngeneic tumors and also recognize antigenic differences between the parental tumor Eb and its variant ESb. Eb and ESb tumor cells were recognized as carrying distinct antigens at the responder cell level, the stimulator cell level and the target cell level. The in vivo significance of these findings is discussed.