Understanding PML, JCV, and the potential risks

What is PML?

  • Progressive multifocal leukoencephalopathy (PML) is a rare brain infection that usually leads to death or severe disability
  • There is no known treatment, prevention, or cure for PML

JCV is something you may or may not have in your body

  • Typically, people with JCV are infected during childhood
  • JCV is common and is harmless in most people, but can cause PML in people who have weakened immune systems, such as people taking TYSABRI
  • Your doctor may do a blood test to check if you have antibodies to JCV before you start receiving TYSABRI or during your treatment

A standard blood test can determine if you have antibodies to JCV

  • The JCV antibody test shows if you have developed antibodies to JCV, which is a natural response from your immune system
    • If the test is positive for JCV antibodies, your risk of developing PML is increased

People who are JCV negative should be retested periodically

  • It's possible to come into contact with JCV and have it enter your body after being tested
  • There's a possibility of a false-negative result. Even if you test negative for JCV antibodies, you could still be at risk of developing PML*

*There's a possibility (3%) of a false-negative test result, which occurs when the blood test wrongly indicates JCV antibodies have not been detected.

A closer look at the estimated risk of PML

People who test negative for JCV antibodies are at a lower risk for developing PML. No one can predict who will get PML, but we can estimate the risk based on 3 known factors.

  • JCV antibody positive test result
  • Prior use of certain medicines that can weaken your immune system
  • Length of time taking TYSABRI
    • Especially for more than 2 years

Your risk of getting PML is greatest if you have all 3 risk factors listed above. There may be other risk factors for getting PML during TYSABRI treatment that we do not know about yet.

Even if you test positive for JCV antibodies, you and your doctor can decide if TYSABRI is right for you.

Your chance of getting PML increases if you have antibodies to the JCV (John Cunningham Virus)

  • The presence of JCV in people taking TYSABRI® (natalizumab) can potentially cause PML

Estimated United States Incidence of PML Stratified by Risk Factor

 antibody dosage table

Notes: The risk estimates are based on postmarketing data in the United States from approximately 69,000 TYSABRI exposed patients.
Data beyond 6 years of treatment are limited.
The anti-JCV antibody status was determined using an anti-JCV antibody test (ELISA) that has been analytically and clinically validated and is configured with detection and inhibition steps to confirm the presence of JCV-specific antibodies with an analytical false negative rate of 3%.


Learn about potential side effects associated with TYSABRI... More >>

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TYSABRI® (natalizumab) is a prescription medicine used to treat adults with relapsing forms of multiple sclerosis (MS) to slow the worsening of symptoms common in people with MS and to decrease the number of flare-ups (relapses). TYSABRI increases the risk of progressive multifocal leukoencephalopathy (PML). When starting and continuing treatment with TYSABRI, it is important to discuss with your doctor whether the expected benefit of TYSABRI is enough to outweigh this risk.

Important Safety Information

TYSABRI increases your risk of getting a rare brain infection—called progressive multifocal leukoencephalopathy (PML)—that usually leads to death or severe disability.

Before receiving TYSABRI, it is important to tell your doctor:
TYSABRI can cause serious side effects. If you have any of the symptoms listed below, call your doctor right away:
The most common side effects of TYSABRI are:
These are not all of the possible side effects of TYSABRI. For more information, ask your doctor. To report side effects to FDA, please call 1-800-FDA-1088.

Please see Full Prescribing Information (PDF) including Boxed Warning and Patient Medication Guide (PDF).

This information is not intended to replace discussions with your healthcare provider.