Silencing of hepatic fate-conversion factors induce tumorigenesis in reprogrammed hepatic progenitor-like cells

Felipe Serrano, Maria García-Bravo, Marina Blazquez, Josema Torres, Jose V. Castell, Jose C. Segovia, Roque Bort

Several studies have reported the direct conversion of mouse fibroblasts to hepatocyte-like cells with different degrees of maturation by expression of hepatic fate-conversion factors. We have used a combination of lentiviral vectors expressing hepatic fate-conversion factors with Oct4, Sox2, Klf4, and Myc to convert mouse embryonic fibroblasts into hepatic cells. We have generated hepatic cells with progenitor-like features (iHepL cells). iHepL cells displayed basic hepatocyte functions but failed to perform functions characteristic of mature hepatocytes such as significant Cyp450 or urea cycle activities. iHepL cells expressed multiple hepatic-specific transcription factors and functional genes characteristic of immature hepatocytes and cholangiocytes, as well as high levels of Foxl1, Cd24a, and Lgr5, specific markers of hepatic progenitor cells. When transplanted into partial hepatectomized and hepatic irradiated mice, they differentiated into hepatocytes and cholangiocytes. However, iHepL cells formed malignant non-teratoma cell aggregations in one out of five engrafted livers and five out of five xenografts assays. All the cells in these tumors had silenced key hepatic fate-conversion factors, and lost hepatic features. This study highlights the dangers of using pluripotency factors in reprogramming strategies when fate-conversion factors are silenced in vivo, and urges us to perform extensive tumorigenic tests in reprogrammed cells.