KLF4 and cancer: We retrovirally transduced a set of defined factors, Octamer-binding transcription factor 3/4 (OCT3/4), Kruppel-like factor 4 (KLF4), and SRY-box transcription factor 2 (SOX2) into human colon [13] and lung [14] cancer cells, followed by culturing with a conventional serum-containing medium, but not a human embryonic stem cell medium.