It is well known that both rodent and human stem cells, in the presence of growth factors, cytokines, chemical compounds, hepatocytes, or nonparenchymal liver cells, are able to differentiate into hepatic progenitor cells (HPC) or hepatocytes in vitro, but it is still controversial whether stem cell transplantation can completely regenerate injured liver in vivo. Here, A. T. Yang and colleagues report that TGF-β1 displays time-dependent dual effect on interplay between HPC and hepatic stellate cells in vitro and in animal model of liver fibrosis. Here, TGFB1 is linked to Hepatic fibrosis.