Host-mediated antitumor effect of interferon in nude mice transplanted with human tumor

Mouse interferon (MuIFN) strongly suppressed the growth of human nasopharynx carcinoma (KB) transplanted into nude mice when given by subcutaneous injection around the tumor, though KB cells were insensitive not only to the antiproliferative activity of MuIFN, but also to natural killer (NK) activity in vitro. Moreover, the antitumor effect of MuIFN was not influenced by treatment with anti-asialo GM1, which eliminates NK activity in vivo. These results indicate that NK activity is not essential to the antitumor effect of IFN mediated by the host. Subcutaneous injection of MuIFN was more efficacious than intraperitoneal injection, suggesting the existence of regional tumor resistance of the host induced by IFN. The sera of mice treated with MuIFN showed no inhibitory activity on the growth of KB cells in vitro, indicating that no antiproliferative agent secondarily induced by IFN treatment is present in the serum. There was no difference between control and MuIFN-treated group in terms of the histology of tumor tissues in nude mice. An undefined host-dependent antitumor mechanism distinct from the proposed immune modulatory effect of IFN might be present.