Biogen Idec and Elan Corporation, plc announced that they expect to submit to the US Food and Drug Administration (FDA) an application for approval of Antegren (natalizumab) as a treatment for multiple sclerosis (MS). The companies expect to submit the filing mid-year 2004. The decision to file a Biologics License Application (BLA) was made after discussions with the FDA of one-year data from the two ongoing two-year Phase III trials in MS. The companies are committed to completing the two-year trials. To protect the integrity of the trials, the companies are not disclosing the one-year data at this time.

Biogen Idec and Elan are collaborating equally on the development of natalizumab for MS, Crohn's disease, and rheumatoid arthritis. About the Antegren MS Clinical Trials The AFFIRM (natalizumab safety and efficacy in relapsing-remitting MS) trial is a two-year, randomized, multi-center, placebo-controlled, double-blind study of approximately 900 patients, evaluating the ability of natalizumab to slow the progression of disability in MS and reduce the rate of clinical relapses. The Sentinel (safety and efficacy of natalizumab in combination with Avonex (Interferon beta-1a)) trial is a two-year, randomized, multi-center, placebo-controlled, double-blind study of approximately 1,200 patients with relapsing-remitting MS, evaluating the effect of the combination of natalizumab and Avonex compared to treatment with Avonex alone in slowing the progression of disability and reducing the rate of clinical relapses. Both studies have protocols that included a one-year analysis of the data.

The primary endpoints for both Phase III two-year trials in MS are based on the Expanded Disability Status Scale (EDSS) and relapse rates. The pre-specified primary endpoint of the one-year analysis was relapse rates.

About Antegren (natalizumab) Natalizumab, a humanized monoclonal antibody, is the first alpha-4 antagonist in the new SAM (selective adhesion molecule) inhibitor class. The drug was designed to selectively inhibit immune cells from leaving the bloodstream and to prevent these cells from migrating into chronically inflamed tissue as occurs in a variety of inflammatory diseases. To date, approximately 2,800 patients have received natalizumab in clinical studies. In previous clinical trials, the following adverse events occurred more commonly with natalizumab when compared to placebo: headache, nausea, abdominal pain, infection, urinary tract infection, pharyngitis and rash. Serious adverse events have included infrequent hypersensitivity-like reactions.