The role of neutralizing antibodies to interferon-β as a biomarker of persistent MRI activity in multiple sclerosis: a 7-year observational study

Purpose: During interferon-β (IFN-β) therapy, up to 45 % of patients may develop neutralizing antibodies (NAbs), associated with a decreased efficacy of the drug. We investigated in a real-life setting the impact of NAbs on magnetic resonance imaging (MRI) outcomes in a population of 567 IFN-β-treated relapsing-remitting (RR) multiple sclerosis (MS) patients up to 7 years. We also evaluated NAbs’ role as a biomarker of the persistence of MRI disease activity. Methods: Patients’ sera were tested for NAbs’ presence by cytopathic effect (CPE) assay every 6–12 months. MRI scans were performed every 12 months. Generalized hierarchical linear models accounting for within-patient correlation were used to analyze T1 gadolinium-enhancing and new T2 lesions. Moreover, further tests were carried out to assess the overall outcome difference from year 1 to year 7 according to NAb status and the possible interaction between NAb status and time of follow-up. Results: Seventy-five patients (13.2 %) became NAb positive (NAb+) during the follow-up. Considering T1 gadolinium-enhancing (GD+) lesions, we observed a significantly higher incidence in NAb+ patients (52 %, p = 0.0091). Also for new T2 lesions, we found a higher incidence in NAb+ patients (50 %, p = 0.0075). The negative impact of NAbs on the MRI outcomes considered did not change during the follow-up. Conclusions: Our 7-year results show the negative effect of NAbs on MRI measures of disease activity and confirm their role as a surrogate marker of IFN-β treatment efficacy.