PROM1 and ovarian cancer: We previously showed that these are PD-L1+, and that PD-L1lo ES2 cells proliferated more slowly in vitro versus control ES2.3 ALDH1hiCD133+ is an accepted human ovarian cancer TIC phenotype.15,16 As we found that ES2 cells expressed negligible CD133 by flow cytometry (not shown), we used ALDHhi expression to identify ES2 TICs in vitro.