Should we measure the bioavailability of interferon β in vivo in patients with multiple sclerosis?

Abstract

This commentary discusses a study by van der Voort et al. that tested the diagnostic value of in vivo interferon β (IFN-β) bioactivity screening in identifying patients with multiple sclerosis who have developed neutralizing antibodies (NAbs) to IFN-β therapy—an event that limits the efficacy of the therapy. The in vivo assay used by the authors, which measures expression of the IFN-β-stimulated gene MxA (MX1) in the peripheral blood, indicated lack of a biological response in 19 of 23 patients with high-titer NAbs following injection of IFN-β. However, an abnormal response was also observed in 18 of 55 patients who had low-titer NAbs or were NAb negative. The authors concluded that in patients treated with IFN-β a single postinjection measurement of MxA messenger RNA expression is adequate to determine the IFN-β bioactivity status. While we believe that in vivo measurement of MxA messenger RNA following IFN-β injection is a reliable test by which to identify patients with inadequate response to IFN-β, the capacity of the test to predict treatment failure must be established in a well-designed, prospective trial.