Fig. 3.

(A) Indirect reprogramming of human biopsy samples requires the generation of an intermediate pluripotent population and can leverage both transgenic and transgene-free methods. Retroviral and lentiviral vectors can be used for the delivery and integration of reprogramming factors, whereas adenoviral vectors, Sendai vectors, episomal vectors, mRNA, protein and small molecules utilize transgene-free cellular reprogramming approaches. (B) Direct reprogramming bypasses a pluripotent intermediate stage, and can produce post-mitotic neurons from terminally-differentiated somatic cells using lentiviral microRNA transduction.