CD44 and pachyonychia congenita: Human PCSCs were identified as CD44+α2β1hiCD133+ [31] and CD133+ cells isolated from 22Rv1 human PC cells were enriched with a set of CSC genes (CD44, OCT4, c-MYC, and BMI1) [157]; in a set of hTERT-immortalized human primary prostate cells, CD133+ and CD133− cells comparably produced xenografts in NOD/SCID mice [158].