Human interferon inhibits the growth of established human breast tumours in the nude mouse.

In this paper we describe a model system for looking at the effects of human interferon, IFN, on an established human tumour. Highly purified human IFN derived from lymphoblastoid cells (HuIFN alpha-Namalwa) strongly inhibited the growth of a human breast cancer growing as a xenograft in nude mice. The effect was dose-dependent, required daily treatment for an optimal effect and was time-dependent, little inhibition being seen before 2 weeks of therapy. With the doses used, however, neither tumour regression nor disappearance were seen and on morphological examination, treated tumours appeared as miniatures of control tumours. The inhibition of the tumour by HuIFN alpha-Namalwa appeared to be due to a direct effect on the human cells as this IFN had little effect on the mouse immune system in vitro as measured by NK cells activity. Also HuIFN therapy had no effect on levels of an interferon induced enzyme, 2-5A synthetase, in the mouse spleen cells but stimulated this enzyme in the human tumour.