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Disappointing Results Announced from Clinical Trial of Tysabri (Natalizumab) in Secondary-Progressive MS

October 21, 2015

• A phase III clinical trial of Tysabri® (natalizumab, Biogen) compared with placebo in 889 people with secondary-progressive MS did not meet its primary endpoint, meaning that Tysabri was not shown to slow progression using a combined measure of disability.
• These results are reported in an October 21 press release from Biogen. Details of these results will be presented at a future medical meeting.

Background: Tysabri is a laboratory-produced monoclonal antibody that is approved for people with relapsing forms of MS to delay the accumulation of physical disability and reduce the frequency of clinical exacerbations. It is designed to hamper movement of potentially damaging immune cells from the bloodstream into the brain and spinal cord.

This clinical trial, sponsored by Biogen, involved people with secondary-progressive MS who had not experienced relapses in the two years before enrolling in the study. Of about 85 percent of people who are initially diagnosed with relapsing-remitting MS, many will eventually transition to secondary-progressive MS, which means that after a period of time in which they experience relapses and remissions, the disease will begin to progress more steadily, with or without relapses. Although many of the MS disease-modifying therapies are approved for “relapsing forms” of MS, which includes people with secondary-progressive MS who experience relapses, there are few options for those with progressive forms of MS in the absence of relapses.

The Study:  A total of 889 participants with secondary-progressive MS were recruited in 15 countries worldwide, and were randomly assigned to receive either natalizumab 300 mg or placebo, infused into the vein every four weeks, for a total of 96 weeks. Most of the participants had EDSS disability scores of 6 to 6.5, meaning they required a walking aid. The primary endpoint established for the trial was to determine whether Tysabri could slow the accumulation of disability, as determined by a “composite” measure. This measure combined results from the EDSS scale of disability, the 9-hole Peg Test of upper extremity function, and the Timed 25-Foot Walk test of mobility and leg function.

According to the press release, the study did not meet its primary endpoint of slowing progression measured by the composite measure of disability, results from the 9-Hole Peg Test suggested that Tysabri slowed the loss of function in the arms and hands. Details of these results will be presented at a future medical meeting.

Next Steps: “These results are very disappointing, but further analysis may provide important insights for future trials,” says Dr. Bruce Bebo, Executive Vice President, Research, at the National MS Society. “This reinforces our resolve to find solutions for people with all forms of progressive MS.”

Read more about secondary-progressive MS.
Read more about ongoing research in progressive forms of MS.

Tysabri is a registered trademark of Biogen.

About Multiple Sclerosis

Multiple sclerosis is an unpredictable disease of the central nervous system. Currently there is no cure. Symptoms vary from person to person and may include disabling fatigue, mobility challenges, cognitive changes, and vision issues. An estimated 1 million people live with MS in the United States. Early diagnosis and treatment are critical to minimize disability. Significant progress is being made to achieve a world free of MS.

About the National Multiple Sclerosis Society

The National MS Society, founded in 1946, is the global leader of a growing movement dedicated to creating a world free of MS. The Society funds cutting-edge research for a cure, drives change through advocacy and provides programs and services to help people affected by MS live their best lives. Connect to learn more and get involved:, Facebook, X, formerly known as Twitter, Instagram, YouTube or 1-800-344-4867.


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