This assumption is supported by the findingthat tumor initiating cell populations can be isolated based on expression ofmarkers that are often associated with immature cell types in a variety of tissues.For example only the CD133+ fraction of glioblastoma cells, whichmake up approximately 1% of the total tumor cell load, is capable ofinitiating growth of a new glioblastoma upon transplantation. This evidence concerns the gene PROM1 and glioblastoma.