KLF4 and lung adenocarcinoma: We transduced OCT3/4, SOX2, and KLF4 (hereafter, OSK) or EGFP into a KRAS-mutated (G12S) human lung adenocarcinoma cell line (A549) using retrovirus vectors, then cultured the cells in 10% fetal bovine serum (FBS) containing Dulbecco’s modified Eagle’s medium (DMEM).