CXCR4-positive subset of glioma is enriched for cancer stem cells

CXC chemokine receptor 4 (CXCR4) is a cell surface molecule expressed in a distinct subset of glioma cells with enhanced tumorigenicity, and it is related to many important biological activities of the tumor. We supposed that this receptor might be a cell surface "marker" for glioma stem cells. This hypothesis was tested both in vitro and in vivo. The CXCR4+ and CXCR4- subsets were sorted from three human malignant glioma specimens. They were tested for the capability of colony formation in soft agar, generation of tumorosphere, self-renewal, and multipotent differentiation in vitro, and the capability of xenograft tumor in vivo. Drug and radiation resistance and coexpression with CD133 were studied for each subset. CXCR4+ glioma cells, but not CXCR4- cells, were capable of generating tumorospheres in serum-free medium. In addition, these spheres were able to self-renew after passage, and had multipotent differentiation after being induced in serum-containing medium. In soft agar assay, CXCR4+ cells generate much more colonies. The animal experiment revealed that CXCR4+ subpopulation had stronger tumorigenicity than the unsorted parental glioma cells, while the CXCR4- cells did not generate xenograft tumor. CXCR4-possitive cells were more resistant to temozolomide and radiation treatment. Both CXCR4+ and CXCR4- subsets contained very few CD133+ cells. The CXCR4+ subsets of glioma cells fulfill the standard of "cancer stem cell".