The US FDA has approved Tysabri (natalizumab), formerly referred to as Antegren, as treatment for relapsing forms of multiple sclerosis (MS) to reduce the frequency of clinical relapses. FDA granted Accelerated Approval for Tysabri following Priority Review based on one-year data from two phase III studies, the Affirm monotherapy trial and the Sentinel add-on trial with Avonex (Interferon beta-1a), Biogen Idec and Elan Corporation, plc jointly announced here.

Tysabri, the first humanized monoclonal antibody approved for the treatment of MS, inhibits adhesion molecules on the surface of immune cells. Research suggests Tysabri works by preventing immune cells from migrating from the bloodstream into the brain where they can cause inflammation and potentially damage nerve fibres and their insulation.

"Tysabri is a powerful and innovative therapy that offers new hope for hundreds of thousands of people living with MS," James C. Mullen, chief executive officer, Biogen Idec said adding, "We believe Tysabri will revolutionize the treatment of MS and become the leading choice for patients and physicians."

"I believe Tysabri will be an important therapeutic advance for patients with relapsing MS," said Richard Rudick, lead investigator of the SENTINEL trial and director, Mellen Centre for Multiple Sclerosis, Cleveland Clinic Foundation. "Patients who have discontinued therapy, are newly diagnosed with MS, or have persistent active disease despite being on a current therapy will benefit from Tysabri," he added.

AFFIRM and SENTINEL are two-year trials. Two-year results are anticipated beginning in the first half of 2005. Patients who complete these trials are eligible for enrolment in a long-term safety extension study.

"The MS community is pleased that the FDA approval of Tysabri provides an additional treatment option for people with relapsing forms of MS. There are many people living with MS who may benefit from this different treatment approach," said Stephen C. Reingold, vice president for research, the National MS Society.

Biogen Idec and Elan are collaborating equally on the development of Tysabri in MS, Crohn's disease (CD), and rheumatoid arthritis (RA).