Background: Treatment with natalizumab, a monoclonal antibody against the adhesion molecule very late activation antigen 4, an α4β1 integrin, was recently associated with the development of progressive multifocal leukoencephalopathy, a demyelinating disorder of the central nervous system caused by JC virus infection. Objective: To test the effect of natalizumab treatment on the CD4+/CD8+ T-cell ratios in cerebrospinal fluid (CSF) and peripheral blood. Design: Prospective longitudinal study. Setting: Academic and private multiple sclerosis centers. Patients: Patients with multiple sclerosis (MS) treated with natalizumab, untreated patients with MS, patients with other neurologic diseases, and human immunodeficiency virus-infected patients. Main Outcome Measures: CD4+ and CD8 + T cells were enumerated in CSF and peripheral blood. The mean fluorescence intensity of unbound α4 integrin on peripheral blood CD4 + and CD8+ T cells was analyzed before and after natalizumab therapy. Results: Natalizumab therapy decreased the CSF CD4 +/CD8+ ratio of patients with MS to levels similar to those of human immunodeficiency virus-infected patients. CD4+/ CD8+ ratios in peripheral blood in patients with MS progressively decreased with the number of natalizumab doses, but they remained within normal limits. Six months after the cessation of natalizumab therapy, CSF CD4 +/CD8+ ratios normalized. The expression of unbound α4 integrin on peripheral blood T cells decreases with natalizumab therapy and was significantly lower on CD4+ vs CD8+ T cells. Conclusions: Natalizumab treatment alters the CSF CD4+/CD8 + ratio. Lower expression of unbound α4 integrin on CD4 + T cells is one possible mechanism. These results may have implications for the observation that some natalizumab-treated patients with MS developed progressive multifocal leukoencephalopathy.
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