Monoclonal antibody therapy is a new treatment strategy for many types of 
diseases including cancers and autoimmune diseases, realizing a high efficacy 
and tolerability. In multiple sclerosis (MS) and neuromyelitis optica (NMO) 
spectrum disorders, several monoclonal antibodies have been suggested to 
decrease the incidence of clinical relapse and the disease activity. In MS, 
anti-α4 integrin (natalizumab), anti-CD52 (alemtuzumab), anti-CD25 (daclizumab) 
and anti-CD20 (ocrelizumab) have been shown to effectively reduce the relapses 
in randomized controlled trials and have been approved by the Food and Drug 
Administration. Specifically, ocrelizumab is the first drug that has shown 
significant suppression of brain volume loss and suppression of chronic 
disability progression. In NMO, though there have yet to be any approved 
monoclonal antibodies, rituximab, anti-complement C5 (eculizumab), anti-IL-6 
receptor (tocilizumab), anti-CD19 (inebilizumab) and non-pathogenic 
anti-aquaporin 4 (aquaporumab) have been suggested to be effective, and some of 
these are now under clinical trials. Aquaporumab is a non-pathogenic recombinant 
human monoclonal antibody that competitively inhibits the binding of the 
pathogenic auto-antibody against aquaporin 4 in NMO patients; thus, it is 
expected to be highly disease specific with less non-specific adverse events. 
Some of these monoclonal antibodies in MS and NMO are known to cause several 
notable adverse events. Natalizumab and rituximab increase the risk of 
progressive multifocal leukoencephalopathy. Eculizumab increases the risk of 
meningococcal infection. Tocilizumab is known to cause intestinal diverticulitis 
that can cause intestinal perforation. In this review, we summarize the 
characteristics of, evidence for and notable adverse events of each monoclonal 
antibody in MS and NMO.