MOG and primary progressive multiple sclerosis: Abbreviations: MS = multiple sclerosis, RRMS = relapsing-remitting multiple sclerosis, PPMS = primary progressive multiple sclerosis, EAE = experimental autoimmune encephalomyelitis, MOG = myelin oligodendrocyte glycoprotein, PLP = proteolipid protein, MSCs = mesenchymal stem cells, CNS = central nervous system, IT = intrathecal, ALS = amyotrophic lateral sclerosis, MSC-NPs = mesenchymal stem cell-neural progenitors, EDSS = expanded disability status score.