Distinct T-cell proliferative responses to 13762A rat mammary adenocarcinoma and derived clones

Immunotherapy of the rat 13762SC mammary adenocarcinoma by vaccinia virus augmentation of tumor immunity

We studied whether vaccinia virus (VV) functioned as an immunogenic carrier in augmenting anti-tumor immunity in rats bearing a syngeneic metastatic tumor. The primary tumor was induced by injecting 10(6) 13762SC mammary adenocarcinoma cells subcutaneously into the right hind footpad of Fischer 344 rats. A concomitant anti-tumor response is induced by the tumor as demonstrated by the inhibited growth of a second tumor challenge given in the contralateral footpad 3-15 days later. Attempts were made to increase the concomitant immunity by injecting tumor-bearing animals intramuscularly with irradiated, VV-infected or uninfected 13762SC cells without adjuvant. Provided the immunotherapy was done within 5 days of the tumor challenge, administration of 10(6)-10(7) irradiated, VV-infected 13762SC cells resulted in significantly slower tumor growth, or led to complete tumor regression, compared to control animals given no treatment. In contrast, tumor growth in animals given only VV or given irradiated, uninfected 13762SC cells, alone or mixed with VV, was the same as that in control animals. Kinetics of early primary tumor growth were predictive of a longer-term anti-tumor effect. Rechallenge of 13762SC tumor-cured animals with either the homologous or with a heterologous syngeneic mammary adenocarcinoma showed the animals to be specifically 13762SC tumor-resistant, since only rats challenged with the heterologous mammary adenocarcinoma developed progressive tumors. We interpret these results to mean that early immunotherapy with irradiated, VV-infected 13762SC cells enhances an on-going anti-tumor immune response sufficiently to cause rejection of the primary tumor and any metastases that have occurred. We also believe that later immunotherapy with irradiated, VV-infected cells has no effect due to tumor-induced immunosuppression becoming paramount.

In vitro proliferative responses of spleen lymphocytes from rats bearing progressive or regressive tumors induced by cell variants of a syngeneic colon carcinoma

From one colonic carcinoma chemically induced in the rat, 2 sublines of tumor cells have been cloned, one (PROb) inducing progressive tumors, the other (REGb) generating tumors that regress a few weeks after s.c. injection into syngeneic hosts. Our study was aimed at comparing cellular immunity between animals bearing PROb or REGb tumors. Spleen cells were first tested for in vitro proliferation in response to mitomycin-treated PROb or REGb cells. Only spleen cells from rats injected with REGb cells proliferated significantly when mixed with PROb or REGb cells. The proliferative response induced by REGb cells was considerably higher than the response to PROb cells. When spleen cells from rats bearing REGb tumors were cultured with a mixture of REGb and PROb cells at various PROb/REGb cell ratios, PROb cells significantly suppressed the strong proliferative response generated by the same number of REGb cells alone. REGb-immune spleen cells, after in vitro stimulation by PROb or REGb cells, were not cytotoxic for either cell variant. REGb-immune spleen cells did not differ in their content of T lymphocytes expressing CD4 or CD8 markers when they were stimulated by PROb or REGb cells in vitro, but REGb cells induced a larger number of activated lymphocytes expressing the IL-2 receptor. Our results indicate that, compared to REGb cells, PROb cells are poorer stimulators of proliferation of tumor-immune spleen cells, and that they are able to suppress the proliferative response induced by REGb cells.

Helper and suppressor functions of panned populations of immune peritoneal T cells with reactivity to the rat mammary adenocarcinoma 13762A

The phenotype of glass-adherence-depleted tumor-immune peritoneal exudate lymphocytes (PEL) which generated anti-tumor reactivity against the rat mammary adenocarcinoma 13762A in vitro was examined by indirect panning. Monoclonal antibodies W3/25 and OX8, directed against the CD4 and CD8 differentiation antigens, respectively, were used to separate immune PEL into subsets of functionally different T cells. The panned populations of immune PEL were examined for anti-tumor reactivity in three different in vitro assays. Tumor-specific proliferation, tumor-specific induction of the helper lymphokine interleukin 2 (IL-2), and tumor-specific induction of an antiproliferative tumor-induced suppressor lymphokine (TISL) were determined. Panning experiments together with indirect immunofluorescence analysis of unpanned immune PEL indirectly indicated that a proportion of cells (15-20%) coexpressed CD4 and CD8 antigens. Strong tumor-specific proliferation and IL-2 and TISL production were generated from these double-positive cells, as determined by double-panning experiments. Significant tumor-specific proliferation and IL-2 production were produced also from CD4+CD8- cells, but TISL production was minimal, and could be accounted for by contaminating CD4+CD8+ cells. CD4-CD8+ cells produced negligible responses against the tumors as measured by these three assays, and no synergistic responses were demonstrated when CD4-CD8+ cells were incubated together with CD4+CD8- cells. These data demonstrated that CD4+CD8+ T cells exist in primed populations of rat peripheral lymphocytes, and that both helper and suppressor functions were generated from these double-positive cells.

T-cell responses at the host: tumour interface

The evidence considered here reinforces the conclusion that T-cell responses to tumours involve complex cellular interactions. An attempt to summarize some of these interactions is shown. This emphasizes that not only are the interactions between the effector cell populations complicated, but that the target cell surface is also subject to variation and modification as a result of the immune response. A feature that also emerges from these studies is that most cells apparently responding to or infiltrating a tumour do not necessarily participate in its destruction, and it is in this area that experimental tumour systems have particular value. This also perhaps explains the preoccupation of experimentalists with the identification of 'the' effector cell crucial to tumour rejection. However, there is heterogeneity between systems in terms of the type of rejection response induced, but a logical basis for this heterogeneity is not established. If experimental studies could define the nature of the immune response generated by a tumour in the context of the biological features of the tumour itself, this could lead to the prediction of the immunogenicity and potential for induction of a rejection response for that tumor. Clearly, experimental tumour systems do not provide an exact reflection of the situation with human tumours. However, they may provide systems that illuminate particular aspects of the human response, and give precedents to guide the interpretation of data derived from human systems. This form of assessment is still at an early stage, but developments in the experimental field should provide a framework for the development and exploitation of T-cell responses to tumours.