Liver transplantation is currently definitive therapy for patients with end-stage liver disease. However, the full potential for liver transplants is severely compromised due to shortages in the number of suitable donor livers. Today, partial liver transplants in which a piece of the liver (known as a split-liver graft) is used, has become a popular strategy to solve the problem of organ shortage. However, several problems and risks still exist. One such problem is the size of the grafts with many grafts too small to adequate liver function (i.e. “small-for-size” grafts). Another problem is the decreasing quality of donor grafts, primarily due to the aging of general population. Therefore, enhancing the quality and function of the liver grafts for transplantation is of major importance for the overall success of this life-saving therapy. Poor quality liver grafts are particularly susceptible to injuries that are sustained when the graft is harvested and then transplanted into the host. These injuries, known as a damage due to ischemia and reperfusion, or IRI, represent one of the most understudied yet critical problems in liver transplantation. Our Laboratory has been at the forefront of liver IRI research for the last 20 years and our studies have suggested that IRI may be the result of the recipient’s immune system. Since the immune system can dictate the transplant outcome, the logical question arises as to how can we modify the host’s immune system to improve the quality and function of these liver grafts following their transplantation. Over the years, striking advances in modifying the immune system’s response to transplanted organs has occurred. There is a general consensus that real progress in one of the most challenging areas of transplantation, i.e., the acquisition of tolerance to the donated tissue is now within reach. This proposal is aimed at applying state-of-the-art immunosuppression concepts with the burgeoning field of stem cells in order to improve the outcome of liver transplants. Specifically this, application proposes that liver grafts transplanted together with stem cells and combined with directed suppression of the host’s immune system may promote the ability of these stem cells to regenerate liver tissue and improve the quality of the transplanted graft. Based on the findings of this proposal the ultimate goal is to proceed to clinical trials and translate our data from the bench to bedside in liver transplant patients.
Statement of Benefit to California:
While liver transplantation has been established as the definitive therapy for patients with end-stage liver disease, its full potential is far from being realized due to the increasing numbers of recipients who vie for a limited donor supply. Indeed, in the last decade the number of liver transplants has grown by 2.5-fold, whereas the number of patients on waiting list has increased by 15-fold. As patients wait for their transplant, the cost of patient care increases exponentially. As some of these costs are too great for the patient to pay, the decreasing availability of suitable livers for transplantation, places a large burden on the state’s health care system. Although advances in surgical technique have allowed the use split donor livers from cadavers, this practice is not suited for the majority of cases. Partial liver transplantation using liver grafts from live donors is a valuable strategy to solve the problem of organ shortage. However, the quality and the size of the graft remain problems. Importantly, these “sub-optimal” livers not only contribute to the shortage of organs available for transplantation, but also experience higher incidence of both early acute and late chronic dysfunction once transplanted. Hence, enhancing the quality of the donated organ is of major importance, as it should improve the outcome of liver transplantation, decreasing the need and cost of post-surgical care. This application combines state-of-the-art immunosuppression techniques with the burgeoning field of stem cells in order to improve the outcome of liver transplants. Specifically, this application proposes that liver grafts transplanted together with stem cells and combined with directed suppression of the host’s immune system may promote the ability of these stem cells to regenerate liver tissue and improve the quality of the transplanted graft. Based on the findings of this proposal, the goal is to proceed to clinical trials and translate our data from the bench to bedside where it could potentially solve the growing problem of inadequate organ liver supply in the State of California.
The goal of this proposal is to explore the use of stem cells as immune modulators in clinical liver transplantation. Liver transplantation is a life-saving intervention for individuals with end stage liver diseases, however, a shortage of liver donors has led to the practice of grafting small liver segments that can regenerate the tissue, rather than whole livers and often, liver graft quality can be problematic. In this grant application, the principal investigator (PI) proposes to utilize a small-for-size liver injury model and a ischemic and reperfusion injury (IRI) liver transplant model in conjunction with mesenchymal or adipose stem cells to determine whether the stem cells can engraft and assist with hepatic reconstitution by either immune methods or by replacement of hepatocytes. Experiments will begin with allogenic transplants and progress to xenogeneic transplants. The expectation is that xenogeneic stem cells will be rejected, so published tolerogenic protocols will be tested to improve stem cell acceptance. Reviewers were enthusiastic about this project’s innovation and complemented the PI and research team for their transplant and immunology experience. However, they were critical of the use of mesenchymal stem cells (MSCs) for the proposed experiments, given the lack of data supporting the differentiation of MSCs into mature hepatocytes and a lack of clarity on the effects of MSCs on immune function. In this context, they pointed to the research team’s lack of stem cell expertise and the weak data on stem cells throughout the application. Overall, reviewers expert in the field of hepatic cell differentiation doubted the feasibility of this project and were unconvinced that it would yield significant data. Most reviewers commented that this was an innovative proposal addressing an urgent clinical need, as the shortage of suitable liver donors is a challenging roadblock to therapy. The goal of this research is to increase the success of liver fragment grafts, thus expanding the number of patients who can benefit from the limited supply of tissue. If successful, the impact of this proposal would be significant and near-term. Reviewers strongly questioned the feasibility of this largely speculative proposal, and in particular, the choice of MSCs and adipose stem cells for these experiments. The preliminary data in this application recapitulates published data showing that MSCs can be induced to express low levels of certain hepatic markers. However, reviewers commented that there is a lack of experimental evidence in the field that these cells can generate mature, functional hepatocytes. Specifically, there is little to no published evidence that MSC-derived hepatocytes can approach mature liver levels of critical hepatic functions such as drug metabolism and conjugation, ammonia metabolism, bile acid production, conjugation of bilirubin, or synthesis of clotting factors. Significant basic research needs to be done to establish whether these cells can function as hepatocytes, but none of the studies proposed in this application would address these issues. On the other hand, there is strong evidence that MSCs can modulate immunological systems in the host, and it is likely that an immunological mechanism is responsible for the reversal of hepatic function in the publications cited, rather than transdifferentiation to hepatocytes. Reviewers commented that previously published studies show that while MSCs can influence the recovery from hepatic damage, cells become less effective in this regard when they undergo a hepatic differentiation program in vitro. It was also pointed out that MSC modulation of the immune system is being intensely studied by numerous groups around the world. The studies proposed in this application would not add much to the current base of knowledge concerning these cells. The PI on this application was described as an expert in transplantation immunobiology, with extensive experience in cellular and molecular biology. The PI has a world-wide reputation as an outstanding contributor to our understanding of IRI and the use of immunosuppressive/tolerogenic regimens in solid organ transplantation. The laboratory is exceedingly well funded by NIH. The application generally applies the immunological approaches utilized by the applicant on other transplant protocols to stem cells and the immunological aspects of the study are generally straightforward and well within the capabilities of the team. However, the team does not have experience with stem cell transplantation into the liver. Although the potential impact of this innovative proposal was considered high, reviewers felt that the choice of cells was not appropriate due to the lack of evidence indicating these cells can become mature, functional hepatoytes, and, therefore, the project as proposed lacked feasibility. Furthermore, the fact that MSCs are immunomodulatory complicates the scientific analysis and feasibility of this project and this issue was not appropriately addressed in the experimental plan. These fundamental flaws led reviewers to conclude that the proposal would be unlikely to significantly advance the field. PROGRAMMATIC REVIEW A motion was made to move this application into Tier 1, Recommended for Funding. During programmatic discussion, reviewers noted that responsiveness to the RFA was high, suggesting that it might be appropriate to move into Tier 1. Due to insufficient support by the Grants Working Group, the motion was withdrawn.