ABCG2 and cancer: The expression of previously-reported candidate marker genes, such as CD133, CD44 and ABCG2, which are argued to be related to cancer stem cells, and the transduced genes OCT3/4, SOX2 and KLF4 were not significantly different among the parental A549, OSK-A549-Colony and OSK-A549-SN cells (Figure S4A,B).