Human herpesvirus 6 and effectiveness of interferon beta 1b in multiple sclerosis patients

Background: Human herpesvirus 6 (HHV-6) and Epstein-Barr virus (EBV) have been repeatedly associated with multiple sclerosis (MS) pathogenesis. Also, it has been speculated that, besides its immunomodulatory properties, the efficacy of interferon beta (IFN-beta) in treating the disease may be related to its antiviral properties. The objectives of this study were to evaluate the in vivo antiviral effect of IFN-beta-1b over HHV-6 and EBV and to analyze whether such effect could be involved in its effectiveness in MS. Methods: A total of 54 patients with MS were included in an observational, multicentric, 24-month study. HHV-6 and EBV were detected by qPCR in blood and serum samples. IFN-beta-1b effectiveness was evaluated by presence, number and severity of relapses, reduction in the relapse rate, disability progression, and response to the treatment. Results: Patients with HHV-6 in blood had a higher risk of severe relapses (P = 0.01) and bad response (P = 0.03). HHV-6 was detected more frequently during relapses than in remission in blood (P = 0.024) and in serum (P = 0.0002). Patients with HHV-6 in serum had more relapses (P = 0.02), lesser reduction in the relapse rate (P = 0.04), and a lower proportion of responders (P = 0.02) than those without HHV-6 active replication. However, any association between EBV and clinical parameters could not be found. Conclusions: We concluded that presence of HHV-6 in blood and serum during IFN-beta treatment could be a good marker of poor response.