Amino acid sequences of tryptic and chymotryptic peptides from human lymphoblastoid interferon (IFN-alpha) have been determined. The results show that IFN-alpha consists of a family of proteins with at least five different, but homologous, primary structures. There appears to be little, if any, glycosylation of the major components of IFN-alpha.

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SUMMARYHighly purified interferon-~ (IFN-~) prepared from a human lymphoblastoid line (Namalwa) was analysed by gel filtration and polyacrylamide gel electrophoresis (PAGE). Gel filtration separated the IFN-~ into two peaks (A and B). All the components of peak A were retained by a monoclonal antibody (NK2) column, but some of those from peak B were not retained. The IFN that was not bound was active on mouse cells and could be resolved into two major bands by PAGE. The bound fraction (about 759/0 of the interferon protein) was purified by means of the monoclonal antibody column, although complete purification of crude interferon was not achieved in one passage.

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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.

During 1949 we isolated three red crystalline antipernicious anaemia factors from Streptomyce8 griseus fermentation liquors. The first of these was vitamin B12 itself, originally isolated by Rickes, Brink, Koniuszy, Wood & Folkers (1948) and a little later in these laboratories (Lester Smith & Parker, 1948). The next was vitamin Bl2b, the second factor we obtained from liver; it was later crystallized by Pierce, Page, Stokstad & Jukes (1949). The third was vitamin B120, which has been referred to under

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