The announcement by Immunex Corp. of a North American co-promotion agreement with Wyeth-Ayerst Laboratories for Enbrel, IMNX's tumor necrosis factor receptor to treat advanced rheumatoid arthritis, may be more significant for what it says about the future of IMNX than the potential $100 million the biotech company stands to earn from the deal.

In contrast to many biotech funny-money deals, this one has significant milestones that can be achieved fairly rapidly - made possible because Enbrel is a late-stage product. American Home Products (New York, N.Y.), which owns 54 percent of IMNX, will provide the biotech company with a $15 million signing fee, $20 million upon filing a BLA with the FDA, and $30 million upon FDA approval. Other milestone payments would be triggered by label expansion of Enbrel for patients with early-stage RA, and achievement of sales targets. IMNX is targeting its BLA submission for 1998.