This method, also known as transdifferentiation or direct conversion, consists in overexpressing one or several factors, usually transcription factors, introduced in the cells.[1] The starting material can be either pluripotent stem cells (PSCs), or either differentiated cell type such as fibroblasts. The principle was first demonstrated in 1987 with the myogenic factors MyoD.[9] A drawback of this approach is the introduction of foreign nucleic acid in the cells and the forced expression of transcription factors which effects are not fully understood.