GNbAC1 is a humanized monoclonal antibody targeting MSRV-Env, an endogenous retroviral protein, which is expressed inmultiple sclerosis (MS) lesions, is pro-inflammatory and inhibits oligodendrocyte precursor cell differentiation. This paper describes the open-label extension up to 12 months of a trial testing GNbAC1 in 10 MS patients at 2 and 6 mg/kg. The primary objective was to assess GNbAC1 safety, and other objectives were pharmacokinetic and pharmacodynamic assessments. During the extended study, no safety issues occurred in the 8 remaining patients. No anti-GNbAC1 antibodies were detected. GNbAC1 appears well tolerated. ; GeNeuro SA, Geneva, Switzerland. ; http://www.elsevier.com/locate/jneuroim ; 2016-09-30 ; hb2015