Anti-JC virus antibodies in a large German natalizumab-treated multiple sclerosis cohort

To investigate the rate of seropositivity of anti-JC virus (JCV) antibodies in a German multiple sclerosis (MS) cohort treated with natalizumab in the postmarketing setting and to assess anti-JCV serostatus in samples obtained before diagnosis of progressive multifocal leukoencephalopathy (PML).

This was a blinded, retrospective cross-sectional and longitudinal analysis for anti-JCV antibodies using a confirmatory 2-step ELISA on 2,782 blood samples obtained from 2,253 patients nationwide for routine testing for anti-natalizumab antibodies during open-label treatment between 2007 and 2010.

Of the natalizumab-treated patients with MS, 58.8% tested positive for anti-JCV antibodies. The rate of seropositivity was higher in males and increased with age, with a plateau between age intervals 20-29 and 30-39 years. In longitudinal analyses, 19 of 194 (9.8%) patients converted from anti-JCV antibody-negative to seropositive status over 7.7 months; 4.7% reverted from antibody-positive to seronegative status over 7.9 months. Antibody levels, especially in the latter group, were low, indicating fluctuations around the lower cut point of the assay. Neither anti-JCV serostatus nor antibody levels were associated with immunosuppressive pretreatment, duration of natalizumab treatment, or anti-natalizumab antibodies. All samples obtained from 10 patients who developed PML were seropositive (13 samples before PML diagnosis [2.0-37.6 months]; 2 samples at diagnosis). Antibody levels in these samples were higher than those in samples from seropositive patients who did not develop PML.

These data argue for the potential clinical utility of JCV serology for PML risk stratification. However, further investigations of fluctuations in serostatus and of antibody levels for a more precise understanding of the predictive value are warranted.