In human patients with MS, granulocyte–macrophage colony-stimulating factor (GM-CSF) and CXCR4 define a T-helper cells signature in MS, emphasizing CXCR4 and GM-CSF signaling as a potent mechanism stimulating T cell transmigration into the CNS (Galli et al., 2019). Here, CXCR4 is linked to myeloid sarcoma.