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. Here, PROM1 is linked to ovarian carcinoma.