188 Immunosuppressive Virus in a Murine Tumor

A variety of murine transplantable tumors have been found to be immunosuppressive. In the case of viral-induced neoplasms, immunosuppression could often be related to the effects of the corresponding oncogeneic type C virus (1-3). In the case of chemically induced or spontaneous neoplasms, the concept has been raised that tumor cells, or their metabolic soluble products, were immunosuppressive (4-6). In a previous study, 1 a subline of EL-4 lymphoma, EL-4(G-), was shown to have strong inhibitory effects on allogeneic mixed lymphocyte cultures (MLC) 2 in vitro. EL-4 is a chemically induced, thymus-derived transplantable tumor of C57BL mice (7, 8), which contains endogenous type C viruses (reference 9 and footnote 3), and is also contaminated by common murine viruses. In the present study, we report on our findings of common virus contamination of the EL-4(G-) subline maintained in our laboratory. We have accumulated evidence consistent with the hypothesis that the inhibitory activity of EL4(G-) ascites cells and the culture fluid was mediated by an infectious virus. At the present time, the best candidate for this activity is a variant of minute virus of mice (MVM).