Tysabri (natalizumab) is a treatment for relapsing-remitting multiple sclerosis (RRMS) and Crohn’s disease. Tysabri is manufactured by Biogen and is approved both in the U.S. and the European Union.

How Tysabri works

Multiple sclerosis (MS) is a progressive immune-mediated neurodegenerative disorder. Immune cells cross the blood-brain barrier (the endothelial cells that form the blood vessels in the brain and provide a barrier between the brain and the blood) and attack the protein coat called myelin that protects the nerve cells. Without myelin, nerve impulses are interrupted or poorly transmitted, which results in impaired vision and loss of muscle control and balance, among other symptoms. RRMS is the most common form of MS where patients go through periods of worsening neurological symptoms (relapse) followed by periods of partial or complete recovery (remission).

Tysabri is an antibody therapy which treats RRMS by blocking the entry of immune cells into the brain.

Ordinarily, in order to cross the blood-brain barrier, immune cells must interact with a protein complex found on the surface of endothelial cells that make up blood-brain barrier. This complex is made up of two proteins, VCAM-1 and alpha-4-beta-1-integrin. Tysabri contains an antibody that recognizes and binds to alpha-4-beta-1-integrin, preventing binding to VCAM-1 and blocking entry of immune cells to the brain.

Tysabri is administered by intravenous injection once every 28 days.

Tysabri in clinical trials

A literature review of a Phase 3 clinical trial data of Tysabri in patients with RRMS was published in the journal Therapeutics and Clinical Risk Management. The study found that, after two years of Tysabri treatment, the average relapse rate was reduced by 68 percent in patients with RRMS compared to placebo. Moreover, the number of new or enlarging MS lesions was decreased by 83 percent compared to placebo. Six percent of patients developed an immune response to the treatment itself, which resulted in a loss of treatment effectiveness.

An observational clinical trial (NCT00493298) is currently recruiting 6,000 RRMS patients in Europe, Australia, Canada, and Argentina to assess Tysabri’s long-term safety and effect on disease activity and progression. The number of patients who experience severe adverse events will be recorded, as well as the annual relapse rate (a measure of disease progression), for 10 years after beginning Tysabri treatment.

Preliminary results from the first five years of the trial were published in the Journal of Neurology, Neurosurgery, and Psychiatry. Of the 4,821 patients enrolled, 468 were followed for at least four years, and 2,496 for at least two years. No new safety concerns have been raised, and a lower annual relapse rate was observed, which remained low at five years. Many patients discontinued treatment (25 percent) or withdrew from the study (15 percent). The most common reason for patients withdrawing from the study was an infection. Fifty-one patients discontinued treatment following serious adverse events.

Other information

Tysabri increases the risk of a rare type of brain infection called progressive multifocal leukoencephalopathy (PML). Patients with a weakened immune system (either through an illness like HIV or from taking immune-suppressing medications) are at higher risks to develop PML. Patients who  previously have been or are currently infected with John Cunningham Virus (JCV) also are at higher risk. Long-term treatment with Tysabri (more than two years) may increase the risk of developing PML.

Side effects of Tysabri include headaches, nausea, urinary tract infections, depression, and joint pain.


Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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Patrícia holds her PhD in Medical Microbiology and Infectious Diseases from the Leiden University Medical Center in Leiden, The Netherlands. She has studied Applied Biology at Universidade do Minho and was a postdoctoral research fellow at Instituto de Medicina Molecular in Lisbon, Portugal. Her work has been focused on molecular genetic traits of infectious agents such as viruses and parasites.


  1. Frank Carlin says:

    I would like to know the consequences of not receiving proscribed monthly infusion treatments. I am trying to convince someone with MS to go for their monthly infusion.

    • Andi Anderson says:

      I think the greatest risk when skipping treatment is that your immune system is weak (from immunosuppressive infusions) AND is not monitored by a physician.

      The more concerning question to ask is why someone suddenly wants to stop or skip treatment. Regardless of the answer, it needs to be reported to their doctor(s) so the M.D.s can access the situation. The medication, a virus, or sooooo many other things in their body could be causing bad symptoms.

      Tell your friend that it is ok to stop or skip treatment, but as a rational adult who cares about their own health, they need to DISCUSS their decision for wanting to end/skip treatment to one or more of their doctors first.

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