Figure 1. From fibroblast to functional hepatocyte. Fibroblasts from individuals with mutant a1-antitrypsin (AAT; A1AT; SERPINA1) are transformed into induced pluripotent stem (iPS) cells using reprogramming factors expressed by Sendai virus vectors, an integration-free method [a]. Homologous recombination is initiated with zinc finger nucleases (ZFNs) and a piggyBac transposon (blue arrow) to correct A1AT [b]. piggyBac is removed with piggyBac transposase, leaving wild-type A1AT [c]. iPS cells are differentiated into functional hepatocyte-like cells [d].