A proof-of-concept of using induced pluripotent stem cells (iPSCs) to generate human organ for transplantation was reported by researchers from Japan. Human ‘ liver buds’ (iPSC-LBs) were grown from a mixture of three different kinds of stem cells: hepatocytes (for liver function) coaxed from iPSCs; endothelial stem cells (to form lining of blood vessels ) from umbilical cord blood ; and mesenchymal stem cells (to form connective tissue ). This new approach allows different cell types to self-organize into a complex organ, mimicking the process in fetal development . After growing in vitro for a few days, the liver buds were transplanted into mice where the ‘liver’ quickly connected with the host blood vessels and continued to grow. Most importantly, it performed regular liver functions including metabolizing drugs and producing liver-specific proteins. Further studies will monitor the longevity of the transplanted organ in the host body (ability to integrate or avoid rejection ) and whether it will transform into tumors .   Using this method, cells from one mouse could be used to test 1,000 drug compounds to treat liver disease, and reduce animal use by up to 50,000.