CD133⁺ niches and single cells in glioblastoma have different phenotypes

Putative CD133⁺ brain tumor stem cells have been shown to be located in niches and as single cells. This is the first study providing insight into the different phenotypes of CD133⁺ cells in glioblastoma according to localization. Paraffin sections were stained by double immunofluorescence with CD133 and the candidate stem cell markers Sox2, Bmi-1, EGFR, podoplanin and nestin, the proliferation marker Ki67 and the endothelial cell markers CD31, CD34, and VWF. Cell counting showed that the CD133⁺ cells in the niches had a significantly higher expression of Sox2, EGFR and nestin compared to CD133⁺ single cells, but only a 3% Ki67 labeling index versus 14% found for CD133⁺ single cells. Only low endothelial cell marker expression was found in the niches or the CD133⁻ tumor areas, while 43% CD133⁺/CD31⁺ and 25% CD133⁺/CD34⁺ single cells were found. CD133⁺ blood vessels within CD133⁺ niches were less proliferative and more often Bmi-1⁺ than CD133⁺ blood vessels outside niches. In conclusion, different CD133⁺ cell phenotypes exist according to the in situ localization, and also the phenotype of CD133⁺ blood vessels vary according to the localization. CD133⁺ niches contain stem-like cells with a lower proliferation index than CD133⁺ single cells, which have an endothelial differentiation profile suggesting a role in angiogenesis.