Effects of mouse interferon on human tumour xenografts in the nude mouse host.

Murine interferon (IFN) inhibited the growth of 3/3 human tumour xenografts growing in nude mice. This inhibition was independent of the sensitivity of the xenograft to human IFN. In contrast to human IFN, the murine IFN did not directly affect the human tumour cells in vitro as measured by levels of the IFN-induced enzyme 2-5A synthetase or elevation of HLA expression. In preliminary investigations into the role of the host in the murine IFN-mediated tumour inhibition, we found equal activities of this IFN in nude and in beige (NK-deficient) nude mice. Moreover, murine IFN did not elevate levels of NK-cell activity in either of these mouse strains. We conclude that murine IFN mediates this tumour inhibition via an effect on the tumour-bearing host that may or may not involve immune mechanisms.