CD15 expression does not identify a phenotypically or genetically distinct glioblastoma population

Recent research has focused on the hypothesis that the growth and regeneration of glioblastoma (GB) is sustained by a subpopulation of self-renewing stem-like cells. This has led to the prediction that molecular markers for cancer stem cells in GB may provide a treatment target. One candidate marker is CD15: we wanted to determine if CD15 represented a credible stemcell marker in GB.Wefirst demonstrated that CD15-positive (CD15+) cells were less proliferative than their CD15-negative (CD15–) counterparts in 10 patient GB tumors. Next we compared the proliferative activity of CD15+ and CD15–cells in vitro using tumor-initiating primary GB cell lines (TICs) and found no difference in proliferative behavior. Furthermore, TICs sorted for CD15+ and CD15– were not significantly different cytogenetically or in terms of gene expression profile. Sorted single CD15+ and CD15– cells were equally capable of reconstituting a heterogeneous population containing both CD15+ and CD15–cells over time, and both CD15+ and CD15–cells were able to generate tumors in vivo. No difference was found in the phenotypic or genomic behavior ofCD15+cellscomparedwithCD15–cells fromthesame patient. Moreover, we found that in vitro, cells were able to interconvert between the CD15+ and CD15– states. Our data challenge the utility of CD15 as a cancer stem cell marker.