CD133+ STA-ET-8.2 cells are more tumorigenic than CD133- cells. (A): CD133+ STA-ET-8.2 cells readily form colonies in soft agar while CD133- STA-ET-8.2 cells form significantly fewer colonies. In contrast, no difference in colony formation is seen in FACS-sorted TC71 cells. Images are representative of 6 wells/experiment from 3 separate experiments. (B): Analysis of CD133 expression in FACS-sorted cells prior to injection confirms significant enrichment of CD133+ cells in CD133+ fraction. (C): Variable tumorigenicity of sorted and unsorted STA-ET-8.2 cells is demonstrated by xenograft assays (left panel). In particular, unsorted STA-ET-8.2 cells reliably form tumors in NOD-SCID mice whereas cells that have been FACS-sorted are highly inefficient. Among sorted populations, only CD133+ cells generated tumors. CD133+ cell-derived xenografts demonstrate the classic small round blue cell ESFT phenotype and contain both CD133+ and CD133- cells (right panel).