CXCL12 and glioblastoma: This observation was supported and highlighted in a recent study showing, in five different CSC cultures, that the distinctive properties of original GBM are retained in vitro, including CXCR4 expression and CXCL12 secretion, but were highly variably among cultures, with a general inverse relationship between receptor expression and ligand secretion levels (Gatti et al., 2013).