KRT15 and hydrops fetalis: Potential markers for the epithelial HF SCs include β1 integrin, keratin 15 and 19 (K15, K19), α6 integrin, the transferrin receptor (CD71), p63 and CD34; however there is still considerable debate over how to distinguish the least committed, slow-cycling eSCs from their immediate progeny (i.e., rapidly proliferating, but more committed transit amplifying cells) [23–27].