IGKV1D-37 and primary progressive multiple sclerosis: This is in line with earlier observations reporting the formation of compact myelin sheaths after transplantation of O4+ iPSC-derived OPCs from four primary progressive MS (PPMS) patients into immunodeficient shiverer mice and the comparable differentiation of iPSC-derived oligodendrocytes from two PPMS patients and two controls into O4+ and MBP+ oligodendrocytes in vitro [13, 17].