The overall goal of this project was to establish a stable, expandable source of hepatocytes for use in cell transplantation therapy for liver disease. The specific goal was to determine if human hepatocyte progenitor cells (HPCs), which exist in the normal adult liver, can be maintained and expanded in vitro while maintaining regenerative capacity after transplantation.

The work was based on earlier findings that  HPCs exist in the mouse liver. With this CIRM award, we identified human counterparts of HPCs through gene expression studies and demonstrated both their in vitro proliferative capacity and in vivo regenerative capacity.  We successfully established a  robust cell culture system to propagate HPCs, isolated from cadaveric human hepatocytes samples, over many passages while maintaining the proliferative  status of the cells. We achieved growth rates that would theoretically support the generation of billions of dividing HPCs, with ample proliferative capacity.  These expanded cells maintained a gene expression profile similar to endogenous HPCs. 

We  succeeded in engrafting cultured human HPCs in a mouse liver injury model, although the efficiency of engraftment was lower than the mouse HPCs.  We found that the engrafted and repopulating human HPCs have hallmarks of  differentiation without evidence of tumor formation. 

We continue to study further factors contributing to adult human HPC engraftment and regeneration following expansion. Thus, under this CIRM award, we developed a solid foundation to support ongoing patient-specific cell therapy-based approaches to liver diseases.