Oligodendrocyte progenitor cells (OPC) in MS patients with IgG+/IgM+ RRMS decrease their ability to repair demyelinated regions, due of lack of sufficient energy to repair neuronal damage, which leads to a poor clinical prognosis in contrast to IgG+/IgM− RRMS patients [145,146]. The gene discussed is CD40LG; the disease is myeloid sarcoma.