Representative dose-dependent Clostridium perfringens enterotoxin (CPE)-mediated cytotoxicity of multiple CD44+ cancer stem cell (CSC) populations and CSC clones, positive control cells (ie, VERO cells), negative controls including normal ovarian epithelium (NOVA), normal cervical keratinocytes (NORM CX), normal human fibroblasts (FIBRO), and lymphoblastoid B cells (LCL) after 24 hours incubation with CPE is shown. With no exception, all 8 CD44+ CSC populations tested were found highly sensitive to CPE exposure in vitro (P = .001). Viability was determined by counting the number of trypan blue-positive cells and the total cell number and comparing such numbers to those of the untreated control cells (ie, 100% viable cells).