Different cell fates arisen from introduction of reprogramming factors. Overexpression of Oct4, Sox2, Klf4, and c-Myc results in generation of apoptotic cells, senescent cells, transformed cells, incompletely reprogrammed cells, and ESC-like iPSCs. During the course of induction of pluripotency, many cells undergo apoptosis or become senescent. A large proportion of cells remained in culture represent incompletely reprogrammed or become transformed.