Generating Exogenic Organs for Transplantation without the Use of Immunosuppression

At present there are more than 25,000 patients waiting to receive liver transplants. The number is increasing due to an aging US population accompanied by an increasing incidence of chronic liver diseases associated with such disorders as alcoholic liver disease, hepatitis, MAFLD and NASH. In spite of efforts to persuade people to serve as organ donors, the demand increasingly outstrips the supply for organ transplantation. One solution to this problem is the ability to generate human livers in animals for liver as well as hepatocyte transplantation. Although there are numerous protocols to differentiate human embryonic stem cells (hESCs), and inducible pluripotent stem cells (iPSCs) ex vivo to a variety of cell types, they have encountered significant challenges in translation to the clinic. However, it is now possible to regenerate the replica of organs/cells from one species of animal within the body of a second species. This involves the knockout (KO) of specific developmental genes in the blastocyst of species two; and the intra-blastocyst injection of pluripotent stem cells from species one to generate offspring that carry organs/cell types derived from that donor. The translation of this approach requires an efficient gene-editing technology. In fact, novel TALEN/CRISPR/Cas9 technologies provide such a rapid, and cost-effective means to generate genetically modified animals. Accordingly, we propose to employ gene-editing technology to knockout specific genes associated with liver development in the mouse embryo. We hypothesize that rat liver can be generated in the mouse by the injection of rat ESCs or PSCs into CRISPR-genetically engineered murine blastocysts and transplanted back into syngeneic rats. The studies represent a first step of interspecies development of exogenic organs for transplantation without immunosuppression. We have designed three Specific Aims to test our central hypothesis. Specifically, we will characterize (1) intra- and interspecies exogenic liver and endothelium derived from HHEX KO embryos; (2) the immunology and function of interspecies exogenic liver and endothelial development derived from HHEX KO embryos; and (3) several approaches to enhance the generation of interspecies chimeras that include humanization of morphogen ligand- receptor interactions. The resulting exogenic rat liver and endothelium will be transplanted back into syngeneic rats to evaluate graft survival and functionality. The generation of whole livers that are comprised primarily of rat hepatic and endothelial cells derived from implanted rat ESCs or PSCs would represent a paradigm shift and provide the necessary preclinical evidence for ultimately creating human livers in animals. If successful, the proposed research would be a game-changer that could conceivably pave the way for an alternate source of human livers for organ and/or hepatocyte transplantation that is tailored to specific patients. In addition, this novel, albeit somewhat high-risk approach circumvents many of the problems associated with research on xenotransplantation. The potential impact on improved health care in the U.S. and worldwide for liver diseases is great and represents a major step towards the goal of individualized medicine.