The goal of this proposal is to use adult cells that would normally be discarded after routine surgical procedures, or blood cells, to generate stem cells for regenerative medicine applications. Stem cells will develop into any of the tissues of the body under the proper conditions and will eventually be used to develop laboratory models of human disease and for drug discovery or for medical implantation. Stem cells are important because they are a renewable cell source and will eventually overcome the sourcing issues caused by the shortage of donated organs.
We propose to induce these stem cells to become liver cells (hepatocytes) using a unique laboratory model of human liver tissue. In this model, hepatocytes are grown together with the other cells found in the liver (microenvironmental cells) in three dimensions (as in the body), forming a liver tissue. The microenvironmental cells support the hepatocytes and allow them to function for a long time in the laboratory. Because of this, certain measurements that could not be performed on hepatocytes alone (which survive for only a short time in the laboratory) are possible using these 3D liver tissue cultures (3DLC), for example, the assessment of the effects of chronic drug exposure and the replication of hepatitis viruses C and D for testing prospective antiviral drugs.
Since certain “feeder” cells can influence stem cells to form specific types of tissue cells, we will use microenvironmental cells from adult or fetal liver to support the development of stem cells into hepatocytes. We will also do genetic profiling of stem cells and fetal and adult liver cells to identify genes that are important for hepatocytes to develop from stem cells. These genes can then be inserted into the stem cells to direct them to become hepatocytes.
At present, drug discovery is studied using hepatocytes isolated from livers that are donated for transplant but found to be unsuitable for clinical use. These livers come from a pool of donors of diverse ages, genders, health status and ethnic backgrounds and their overall quality can also be highly variable. Regardless of overall quality, it is unusual for hepatocytes to survive in a highly functional state for more than a week in the laboratory and this severely limits the evaluation of new drugs and, in the case of hepatitis C, the development of antiviral therapies. Stem cell-derived hepatocytes would provide a renewable source of genetically-defined, reproducible, disease- and patient-specific hepatocytes for drug discovery and disease modeling using 3DLC. In addition, a database could be developed that, with time, could be used to identify such patient-specific outcomes as differential drug efficacy, idiosyncratic toxicity and adverse drug reactions. We have already produced 3DLC using mouse stem cell-derived hepatocytes and mouse liver microenvironmental cells indicating that this approach is feasible.
The goal of this proposal is to develop a stem cell-based human liver tissue model for use in the laboratory to study human disease, to facilitate the development of new drug therapies and to directly treat human conditions such as organ failure. For example, one prospective use of this model system is to advance new HCV antiviral therapies to the clinic. The incidence of hepatitis C (HCV) in the United States has been estimated at 1.8% , and more recently at 2.5% from a population-based sample of young women living in poorer neighborhoods in California , the state with the greatest number of HCV+ people. Computer modeling projects 165,900 deaths from chronic liver disease, 27,200 deaths from hepatocellular carcinoma, and $10.7 billion in direct medical expenditures for HCV from the year 2010 through 2019 . During this period, HCV may lead to 720,700 years of de-compensated cirrhosis and hepatocellular carcinoma and to the loss of 1.83 million years of life in those younger than 65 at a societal cost of $21.3 and $54.2 billion, respectively . HCV causes an estimated 8,000 to 10,000 deaths annually in the U.S. and accounts for 60 - 70 percent of chronic hepatitis cases, and 30 percent of cirrhosis, end-stage liver disease, and liver cancer cases. At least 75 percent of patients with acute hepatitis C ultimately develop chronic infection, and most of them have accompanying chronic liver disease. Liver failure from hepatitis C is the most common reason for a liver transplant. Currently, it is estimated there are about 180 million people worldwide who are infected with HCV, 4 million of those are in the United States.
In addition to this direct benefit to the citizens of California, indirect benefits include development of novel core facilities and shared equipment resources, experienced collaborative research teams that can attract millions of dollars of additional funding to the state, spinout companies from new technology development, and employment opportunities resulting from this new technology as well as increased tax revenues.
The program would also create a collaborative team spanning major liver research and clinical centers throughout California, facilitating patient access to treatments and the teams access to normal and diseased, and fetal and adult tissues and multiple clinical trial sites. The research teams involved have been successful largely because of the strong biotechnology community in California enabling partnership to expedite product commercialization. These partnerships have brought millions of dollars of government grants to California as well as the promise of a growing, profitable tissue engineering and stem cell industry that will deliver innovative cell and tissue technologies to revolutionize patient care. There are few cities in the US that have the biotechnology infrastructure and collaborative environment to foster multidisciplinary teams and expedite discovery.