Although expression patterns of CXCR4 and its CXCL12 ligand have been extensively investigated during CNS development and in healthy and injured adult CNS [7, 10, 11, 21], few studies have analyzed functions of CXCL12 in the context of CNS demyelinating diseases such as EAE/MS [7, 8, 22]. Here, CXCR4 is linked to myeloid sarcoma.