Multiple sclerosis: Skin-induced antigen-specific immune tolerance

Multiple sclerosis (MS) is a highly prevalent demyelinating disorder, presumed to be driven by an autoimmune response toward the central nervous system (CNS) components. All currently available treatments modulate the immune system globally and besides the reduction of disease activity, they may also impose considerable disturbances on the immune protective mechanisms. Thus, induction of antigen-specific immune tolerance remains the ultimate goal of MS therapy. Such approach carries promising therapeutic perspectives and, above all, a desirable safety profile. Several studies have been performed to evaluate highly selective, antigen-induced, therapies for experimental autoimmune encephalomyelitis (EAE) and MS. These trials have also indicated the importance of the antigen administration route. The continued efforts to develop efficient and safe MS therapy gave rise to the idea of incorporating the skin immune system in order to modulate autoimmunity in MS. Skin is the largest immunological organ of human body, and thus provides ample opportunities to modify immune responses. Skin dendritic cells have a significant ability to modulate the immune reactions, promoting either immunity or tolerance. Their capacity to induce tolerance has already been described in several experimental models of MS. In a one-year, double-blinded, placebo-controlled study assessing the effectiveness of transdermal myelin peptides patches, significant changes in the morphology of Langerhans cells (LCs) and shifts in the dendritic cell (DC) populations in the draining lymph nodes have been observed. In addition, patients treated with myelin patches showed a decreased brain inflammatory activity on MRI and a reduced relapse rate. In this review, we further discuss the potential to use skin-induced immune tolerance for MS treatment, with a particular focus on dermal DCs.