Tools and Technologies II
Transplantation of liver cells, or hepatocytes, could potentially cure many of the 100,000 Americans with genetic diseases in which the liver fails to produce molecules essential for survival. In other severe liver diseases, hepatocyte transplantation might also help patients stay alive long enough for a liver transplant. However, the supply of hepatocytes from adult donors is only enough for a few of the patients who need them. Many more patients would be saved if we could derive transplantable hepatocytes from human stem cells. To fulfill this promise, we need to overcome four main problems: 1. The ethical dilemmas surrounding stem cells derived from human embryos. 2. Cell purity: Making sure that the cells injected into the patient are not contaminated by unwanted types of cells that can develop into tumors. 3. Rejection of transplanted cells by the patient's immune system. 4. The extraordinary fragility of hepatocytes, which makes them difficult to work with, and to keep alive in the laboratory. Only the last of these problems is specific to hepatocytes. The others are common to most research on stem cells. We recently demonstrated a new technique that addresses each of these problems. The new system is inherently designed to minimize the number of unwanted cells. It minimizes stresses on cells, and may help to keep hepatocytes alive longer in the laboratory. Unlike most current techniques for deriving desired types of cells from stem cells, the new system produces similar results from several different lines of stem cells. That ability to work with a wider range of cell lines may ultimately make it easier to provide transplantable cells that are genetically compatible with the patient's immune system. In addition to the embryonic stem cells used in much of today's stem-cell research, the new system also works with a special type of stem cell, called human parthenogenetic stem cells (hpSC). hpSC are derived from unfertilized eggs, so that they do not involve destroying a human embryo. They can also be produced in a special genetic form, called HLA-homozygous stem cells, which offer an alternative strategy for overcoming problems of immune rejection. Our results show that this system can produce high-purity cells that perform some of the functions typical of liver cells, have similar structures and produce some of the same proteins that are hallmarks of hepatocytes. The proposed program aims to show that this new technology can produce fully mature, functional hepatocytes. In pursuing this goal, we will be testing new methods to control the process of transforming stem cells into a desired type of cell. If successful, this program will not only take a key step toward the transplantation of liver cells, but demonstrate new approaches to the problems of ethical controversy, cell purity and immune rejection that stand in the way of other potentially life-saving applications of stem cells.
Statement of Benefit to California:
This project will benefit California patients, provide new revenue sources for California's healthcare industry and expand California's biotechnology industry. The research will lead to the derivation of liver cells that can be transplanted into patients. Liver-cell transplantation may cure genetic diseases in which the liver fails to produce molecules essential for life. These diseases affect 100,000 Americans, roughly 10,000 of whom live in California. Transplanted liver cells may also benefit the nearly 4,000 Californians now waiting for a liver transplant . Cures for these patients will save lives while contributing to California's healthcare and biotechnology industries. However, this program's benefits go well beyond liver disease. California scientists are now working intensively with human stem cells because of their potential to cure many intractable diseases including diabetes, liver disease, retinal disease, Alzheimer's disease, muscular dystrophy, Parkinson's disease and many others. Many of these potential cures depend on the derivation of functional cells - liver cells, pancreatic islet cells, retinal pigment cells and others - that can be transplanted into patients. Two key problems holding back progress in all of these areas are the rejection of transplanted cells by the immune system and the danger of creating tumors because of unwanted cell types that contaminate the transplanted cells. This program will demonstrate new methods to overcome both of these key problems. These methods will help California scientists to develop new products to cure a wide range of diseases. These new products will benefit California patients with these diseases, and provide new revenue sources for California hospitals and clinics based on the new modes of treatment. The new products will also create a new industry based on the production, marketing and distribution of transplantable cells derived from stem cells. Much of that activity will happen in California because so much of the world's biotechnology industry is based here. The new stem-cell products will be sold worldwide, bringing new sources of income into the state. Research using this program's new methods will also generate California-based intellectual property that will be licensed by stem-cell researchers around the world. This intellectual property will increase the valuation of California research organizations, leading to increased investment, employment and tax revenues. In summary, this program will benefit California by providing a new source of transplantable liver cells that can cure metabolic liver disease and assist patients waiting for liver transplants. It will benefit the state even more by demonstrating new methods to overcome the problems of cell purity and immune rejection that are currently impeding the development of California's stem-cell industry.
The goal of this application is to use a novel three-dimensional (3D) differentiation device to derive functional, mature hepatocytes from multiple lines of human embryonic and human parthenogenic stem cells (hESC and hpSC). To develop this device, the applicants will first determine the critical components required at each stage of differentiation into hepatocytes. Then, a protocol for derivation and cultivation of functional hepatocytes will be developed. Finally, the optimized differentiation protocol will be tested to see if it yields functional, mature hepatocytes. The reviewers agreed that the proposal aims to overcome a significant bottleneck, the need for transplantable human pluripotent stem cell-derived hepatocytes, and that the approach aims to address the problems of cell purity, immune rejection and cell fragility that stand in the way of many stem cell applications including the transplantation of stem cell-derived mature hepatocytes. The reviewers commented that the basic notion of recapitulating the three-dimensional architecture of the liver to create mature hepatocytes is an attractive experimental approach, although not particularly innovative. However, while the overall goal is significant, reviewers were not convinced that the proposed studies or the device would significantly improve current methods to generate human hepatocytes from embryonic stem cells. In addition, reviewers questioned the scalability of the device for large-scale purification of hepatocytes, and hence, the translatability of the approach. They concluded that this application would not have a significant impact in advancing the use of human hepatocytes for regenerative medicine. Reviewers were unenthusiastic about both the proposal’s preliminary data and experimental design. They commented that the preliminary data do not demonstrate any advance beyond the current state of the art, or support the goal of differentiating human pluripotent cells into transplantable hepatocytes. This lack of supporting preliminary data cast serious doubt on the likelihood of success of the proposal. Reviewers described the overall strategies, methodologies and analyses as well-reasoned but not particularly well developed. Important details were missing throughout the experimental design. For example, it is unclear as to what quantitative measures will be used to determine if the aims and objectives of the project have been achieved, making it difficult to assess if substantially meaningful results will be generated. In addition, there are no potential pitfalls discussed or alternative plans identified. The omission of details throughout the description of the experimental design significantly reduced the reviewers’ confidence that meaningful results would be generated. The Principal Investigator (PI) is qualified to oversee the project, although there is no obvious track record in liver biology. The research team is integrative and complementary and provides the expertise and commitment necessary to carry out the proposed studies. In summary, this application proposes a 3D cell culture device to derive fully mature hepatocytes for clinical transplantation. Although the reviewers felt that the application addresses a key bottleneck, they raised several serious concerns regarding the lack of compelling preliminary data and absence of detail in the experimental design that led them to doubt the likelihood of success. They also viewed the proposal as not sufficiently innovative. This application was therefore not recommended for funding.