The present invention deals with compounds and compositions for preventing and/or treating a detrimental mechanism, which blocks the endogenous myelin repair capacity of the adult nervous system (NS) in diseases associated with the expression of HERV-W envelope protein (ENV), in particular of its MSRV subtype. The present invention further relates to a pharmaceutical composition comprising an anti-MSRV/HERV-W/ENv antibody (GNbAC1) and at least one Nitric Oxide radical inhibitory drug (L-NAME, SMT or DMF).