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Thread: Tysabri screening test may be unreliable

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    Distinguished Community Member agate's Avatar
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    Default Tysabri screening test may be unreliable

    It seems that the test for the JC virus may not be totally reliable. From MedPage Today, June 5, 2013:



    Quote:
    Tysabri Screening Test May Be Unreliable

    By John Gever, Deputy Managing Editor, MedPage Today

    Reviewed by Zalman S. Agus, MD; Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania

    About one-third of multiple sclerosis patients testing negative for antibodies against the JC virus -- suggesting that natalizumab (Tysabri) would be relatively safe -- were found to have active viremia, researchers said.

    The report, published in the June 6 issue of the New England Journal of Medicine, raises the specter that patients with negative JC serology results could be given natalizumab when they may actually be at high risk for progressive multifocal leukoencephalopathy (PML), an often fatal type of brain inflammation.

    PML is caused by JC virus becoming active in the brain. Natalizumab appears to contribute to reactivation of latent JC virus infections. MS patients with such infections face a PML risk while on natalizumab ranging from about 0.01% to 0.1% depending on the presence of other risk factors

    Eugene O. Major, PhD, of the National Institute of Neurological Disorders and Stroke in Bethesda, Md., and colleagues reported having tested blood samples from 49 patients for anti-JC virus antibodies and for JC virus DNA.

    In 26 of the patients, the samples were obtained immediately before starting on natalizumab. Samples from the other 23 were obtained after at least 2 years of periodic natalizumab infusions.

    Ten patients in the first group were found to have JC viral DNA in their blood, with four lacking a positive result in anti-JC virus antibody testing. (Seronegativity was defined as antibody titers of less than 2,560 units.)

    In the group of 23 patients tested after 2 years of natalizumab treatment, seven were found to be viremic and two were seronegative, the researchers reported.

    Overall, they indicated, six of 17 patients (35%) showing JC viremia were seronegative with the antibody test.

    Fisher's exact test indicated that the rate of viremia in the 49 patients was significantly greater than in 18 healthy volunteers also undergoing viral DNA testing (P=0.003), in whom none showed evidence of the virus in blood.

    "The relatively high percentage of patients who had viremia and were seronegative appears to be greater than the false negative rate identified previously," Major and colleagues wrote.

    Currently, the FDA and natalizumab's label recommend JC virus antibody testing before the drug is started in MS patients. The risk of PML is believed to be virtually nil for patients without JC virus infection, but false-negative serological test results would lead to incorrect PML risk prediction.

    "To establish risk-stratification algorithms for PML in patients who receive potent immunomodulatory therapies, a single measurement of viral activity, such as a test for antibodies to JC virus, may be useful but not sufficient to assess risk," the researchers wrote. They recommended "a more comprehensive risk-mitigation strategy" that involves periodic testing during natalizumab treatment.

    Natalizumab's label now calls for repeat serology testing every 6 months, citing the risk of new JC virus infections that may occur during treatment. Infections are relatively common in the general population. In the current study, 12 of the 18 healthy volunteers were seropositive.

    On the other hand, a positive test result is not an absolute contraindication to natalizumab. "The risks and benefits of continuing treatment with Tysabri should be carefully considered in patients who are found to be anti-JCV antibody positive and have one or more additional risk factors," it says. Such risk factors include duration of natalizumab therapy and prior history of immunosuppressant treatment.
    _____________________________________

    The study had no commercial funding.

    One co-author reported relationships with Biogen Idec (maker of natalizumab), Teva, Genzyme, Abbott, Acorda, and Novartis. Other authors were NINDS employees and had no disclosures.

    Primary source: New England Journal of Medicine

    Source reference:
    Major E, et al "JC Viremia in natalizumab-treated patients with multiple sclerosis" New Engl J Med 2013; 368: 2240-2241.
    Last edited by agate; 06-07-2013 at 10:14 PM.
    MS diagnosed 1980. Avonex 2002-2005. Copaxone 6/07 - 5/10.
    Member of this MS board since 2001.

  2. #2

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    i just replied to a post re long term tysabri patients with jc virus -- and mentioned that my doc said something about spectrum of jc virus -- he may have been referring to this paper -- i will give him a copy of this article -- so sorry to have been redundant in the message i just posted . .

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