A distinct subpopulation within CD133 positive brain tumor cells shares characteristics with endothelial progenitor cells.

The cell surface marker CD133 has been proposed as a brain tumor stem cell marker. However, there have been substantial controversies regarding the necessity and role of CD133 in tumorigenesis. This study aimed to characterize CD133(+) cells in brain tumors. Human brain tumor specimens and whole blood were collected from the same patients (N=12). We carried out dual FACS staining for CD133/CD34 and functional tumorigenesis and angiogenesis analyses of CD133(+) cells from different origins. We also investigated the in vivo tumorigenic potential and histological characteristics of four distinct groups on the basis of expression of CD133/CD34 markers (CD133(+), CD133(+)/CD34(+), CD133(+)/CD34(-), and CD133(-)). CD133(+) brain tumor cells coexpressed significantly higher positivity for CD34 (70.7±5.2% in CD133(+) vs. 12.3±4.2% in CD133(-) cells, P<0.001). CD133(+) brain tumor cells formed neurosphere-like spheroids and differentiated into multiple nervous system lineages unlike CD133(+) blood cells. They showed biological characteristics of endothelial cells, including vWF expression, LDL uptake and tube formation in vitro, unlike CD133(-) brain tumors cells. Pathologic analysis of brains implanted with CD133(+) cells showed large, markedly hypervascular tumors with well-demarcated boundary. CD133(+)/CD34(-) cells produced smaller but highly infiltrative tumors. Notably, pure angiogenic cell fractions (CD133(+)/CD34(+)) and CD133(-) tumor cells did not generate tumors in vivo. Our data suggest the presence of a distinct subpopulation of CD133(+) cells isolated from human brain tumors, with characteristics of endothelial progenitor cells (EPCs).