Generating a Human Liver from Stem Cells
Monday, September 25, 2023

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Since the discovery of embryonic stem cells in1981, decades of laboratory studies have failed to generate a complex vascularized organ such as liver from pluripotent stem cells (PSCs), giving rise to the prevailing belief that in vitro recapitulation of the complex interactions among cells and tissues during organogenesis is considered to be essentially impractical. Here, we challenge this notion by focusing on the earliest process of organogenesis, i.e. cellular interactions during "organ bud" development.


 Generation of Liver Bud from Pluripotent Stem Cells by Mimicking Early Organogenesis

During the early liver organogenesis, liver progenitor cells delaminate from the foregut endodermal sheet and form a three-dimensional liver bud (LB) (Figure1), a condensed tissue mass that is soon vascularized. Such large-scale morphogenetic changes depend on the orchestration of signals between liver, mesenchymal and endothelial progenitors prior to blood perfusion. These observations led us to hypothesise that three-dimensional (3D) liver bud formation can be mimicked in vitro by culturing hepatic endoderm cells with endothelial and mesenchymal lineages.


 Self-Formation of Three-Dimensional Liver Bud from Human iPSC in Vitro

Here, we found that, although cells were plated on 2D conditions, hiPSC-derived liver progenitos organised into macroscopically visible 3D liver bud (hiPSC-LBs, or "rudimentary liver") by cultivating with human endothelial cells and human mesenchymal cells, presumably mimicking the above stated early developmental interactions (Figure2, upper). Surprisingly, we observed a formation of developing endothelial networks along with homogenously distributed hiPSC-liver progenitors even in vitro (Figure2, lower). Immunostaining and gene expression analyses revealed resemblance between in vitro grown hiPSC-LBs and in vivo liver buds.


Therapeutic Potential of in Vitro Grown hiPSC-LB by Mesenteric

Transplantation Model

Transplantation of hiPSC-LBs resulted in a formation of functional human vasculatures in l by connecting to the host vessels just within 48 hours (Figure3, left). The formation of functional vasculatures stimulated the maturation of hiPSC-LBs into tissue resembling the adult liver with multiple liver-specific functions such as protein production and human-specific drug metabolism. Furthermore, mesenteric transplantation of hiPSC-LBs rescued the drug-induced lethal liver failure model (Figure3, right). Thus, to our knowledge, we firstly demonstrated that the generation of functional human organ from pluripotent stem cells.

Future Perspectives:

Manipulation of iPSCs holds great promise for regenerative medicine. However, clinical trials of "cell transplantation", that is a current main target of stem cell-based approach, have presented unsatisfactory results. Our study demonstrates a proof-of-concept that "organ bud transplantation" offers an alternative approach resulting in the generation of a 3D, vascularized organ. These results highlight the enormous therapeutic potential using in vitro grown organ bud transplantation for treating organ failure.


The liver is significantly active in metabolizing compounds and the major target for toxicity caused by drugs. Liver toxicity and alterations of hepatic physiology are frequently occurring reasons for preclinical failure during drug development. Prioritization of compounds based on human hepatotoxicity potential is currently a key unmet need in drug discovery. Current hepatocyte model systems include primary human hepatocytes harvested from cadavers, immortalized cell lines, hiPSC-derived hepatocyte-like cells and animal models. However, each of these model systems presents limitations in functionality, reproducibility, and/or availability. Our results represent the potential for predicting humanized profile of drug metabolism mimicking in vivo human physiology. Fully functioning hepatocytes differentiated from hiPSCs in liver bud will aid to assess the drug safety and efficacy for preclinical drug discovery, hepatotoxicity testing, and disease research.