Myelin-specific Th1-like Th17 cells increased in both peripheral blood and CSF of patients with MS [121,122] and Th17.1 cells, a Th1-like Th17 subpopulation expressing high levels of IFN-γ, GM-CSF, very late antigen 4 (VLA-4), and low levels of IL-17, have been associated with the disease activity in RRMS patients [123]. The gene discussed is IL17A; the disease is myeloid sarcoma.