Disease Team Research I
Because there is still considerable morbidity and mortality associated with the process of whole liver transplantation, and because more than a thousand people die each year while on the liver transplantation list, and tens of thousands more never get on the list because of the lack of available livers, it is evident that improved and safer liver transplantation would be valuable, as would approaches that provide for an increased number of transplantations in a timely manner. A technology that might address these issues is the development of a human liver cell line that can be employed in liver cell transplantation or in a bioartificial liver. Developing such a cell line from human embryonic stem cells (hESC) would provide a valuable tool for pharmacology studies, as well as for use in cell-based therapeutics. The objective of this proposal is to focus a team effort to determine which differentiated hESC will be the most effective liver-like cells in cell culture and in animal studies, and to then use the best cells in clinical trials of cell transplantation in patients with advanced liver disease. In the proposed studies, the team will differentiate hESC so that they act like liver cells in culture. Once it has been established that the cells are acting like liver cells by producing normal human liver proteins, and that they do not result in tumors, the cells will be assessed in clinically-relevant models using techniques that can then be adapted to future human clinical trials. One of the ways cells can be evaluated is to label the cells which will provide a means to monitor them with various imaging systems. The intent in these studies is to determine which will be the most effective cells to use in human clinical trials. Once this is determined, the best cells can then be employed in human patients. If the studies are successfully undertaken, we will have established a clinically useful and viable liver cell line that could be used to repopulate an injured liver in a safer and less expensive manner than with whole liver transplantation. Moreover, all people who have liver failure or an inherited liver disease could be treated, because there would be an unlimited supply of liver cells.
Statement of Benefit to California:
In California, as in all parts of the US, there are not enough livers available for transplantation for all the people who need them. The result is that many more people die of liver failure than is necessary. One way to improve this situation is the transplantation of liver cells rather than whole organ transplantation. We are attempting to develop liver cell lines from stem cells that will act like normal liver cells. If the cells that we develop function well and do not act like cancer cells in culture, the cells will be assessed in clinically-relevant models using techniques that can then be adapted to future human clinical trials. In our studies, we will compare human embryonic stem cells with other stem cells to determine which will be the most effective cells to transplant into people. Finally, we will employ the best cells in clinical trials in humans. If the studies are successfully undertaken, we will have established a clinically useful and viable liver cell line that could be used to repopulate an injured liver in a safer and less expensive manner than with whole liver transplantation. Moreover, all people who have liver failure or an inherited liver disease could be treated, because there would be an unlimited supply of liver cells.
This application proposes to develop human embryonic stem cells (hESCs)-derived hepatocytes for therapy of patients with end stage liver failure. End stage liver disease is currently best treated by solid organ transplantation, but the number of patients in need of a liver exceeds the number of available donor organs. Specifically, this group includes patients requiring large liver resections for malignant disease and patients with acute liver failure who are not candidates for solid organ transplantation. In order to achieve this, the applicant team will optimize differentiation approaches to increase the purity and safety of hESC-derived hepatocytes. The second and third years of the project will include preclinical studies in two clinically relevant animal models to determine the efficacy, safety and graft acceptance. GMP scale-up, optimization of cell manufacturing process, source material verification, and toxicology testing will start in the third year. Filing the IND and creation of a certificate of analysis for the final cellular product will be completed by the fourth year. Overall, reviewers were not enthusiastic about this proposal. While they appreciated the recent scientific progress in the differentiation of hepatocytes by the applicant team and the long-term goal of this proposal, they raised a number of concerns about the scientific rationale and the preliminary data that lead them to question the project’s scientific maturity and feasibility. Specifically, reviewers felt that the applicant had not demonstrated compelling evidence of disease-modifying activity, and that an IND application was not likely to be achieved in the four year time frame. Reviewers questioned the scientific rationale of the project, in particular whether the target profile of the proposed therapeutic was appropriate. Reviewers noted that, although evidence supports the possibility of generating hepatocytes from hESCs, liver cell therapy is not yet an established clinical modality (unlike islet cell transplantation in diabetes). hESC replacement of liver cells is unlikely to address the significant associated pathophysiology of each targeted condition. For example, acute liver failure involves not only a loss of liver-specific functions, but also a significant inflammatory response, including the recruitment of immune cells to the damaged liver and amplification of cytokine secretion. Similarly, the complications of overly aggressive liver resections are not simply the loss of hepatocellular mass but also secondary damage to the liver that occurs as portal hyperperfusion syndrome. Neither of the secondary conditions would be addressed by hESC-derived cell replacement. In light of this, the panel would have been more enthusiastic about a candidate population with inborn errors of metabolism for cell transplantation. One reviewer raised the possibility of using such cells in a bioreactor setting as a bridge to transplantation, similar to hemodialysis for end stage renal failure patients. The reviewers commented that based on the preliminary data, this project was judged to be at an earlier stage of development than one qualified for this RFA. First, the application did not include compelling evidence for disease-modifying activity of hESC-derived hepatic lineage cells in a clinically-relevant model. Such activity is claimed in the application, but supporting data were not fully convincing. The preliminary efficacy data are derived from a model in which there is such a strong selection pressure for the transplanted cells, that it is likely to overestimate potency of the engrafted hESC-derived hepatic lineage cells. The application did include data showing that the applicants could make hepatocyte-like cells, based on expression data and functional assays. However, reviewers were not convinced that the team could achieve scale-up of processes to achieve the estimated one billion hepatocytes per patient (an optimistic lower limit) with currently available technologies. With such a large number of cells required for each patient, elimination of tumorigenic cells is a key issue. Reviewers noted the applicant presented strategies to address this issue, with early efforts underway. For example, efficacy of a gene modifying vector to eliminate undesired cell populations from the cellular product has not been demonstrated in a relevant cell system. The research and development plan was judged to be logically sequenced, but issues surfaced with the experimental approach and design. The applicant proposes preclinical models in two species with which the team has considerable experience. One reviewer noted that the murine model may be able to demonstrate proliferation and function of hESC-derived hepatocytes, but does not reflect the disease to be ultimately treated. Reviewers praised inclusion of the clinically relevant large animal models and noted that immune suppression strategies were already worked out in this model, but suggested that these studies are premature. Timelines were not clear, and milestones and success criteria required more specificity for efficiency of differentiation and purity of the derived hepatocytes, functional properties of the cells, acceptable levels on non-hepatocytes, and tumorigenesis. From a regulatory perspective, inclusion of a gene modification approach to eliminate potentially tumorogenic cells adds complexity to achieving an IND approval for cellular therapy. Finally, reviewers questioned the need for the additional cell selection approach outlined in the project. While an interesting research project, the justification that this is on critical path to the development of a robust cell therapy product was judged inadequate. Reviewers found the PI and research team to be well-qualified, with appropriate experience, including GMP manufacturing and successful IND filing. The PI is well-established in liver cell biology, and has published several papers in peer-reviewed journals on the generation of hepatocytes from hESCs. Leading hepatologists are engaged as consultants. A clinical team is enlisted from another institution. Collaborators supported by a CIRM Collaborative Funding Partner will work with the team to determine the optimal cell line and processes for transplantation. Reviewers agreed that the resources and facilities are more than adequate to complete the proposed project. Collaborations bring together strengths in stem cell biology, preclinical studies and clinical medicine. Strong letters of support from the participating institutions are included in the application. Overall, while reviewers appreciated the long-term goal of this proposal they raised a number of concerns about the scientific rationale and the preliminary data that led them to question the project’s scientific maturity and feasibility. Specifically, reviewers judged an IND application was not likely to be achieved in the four year time frame. It appeared a worthwhile research project, but not one that was ready for the development stage specified in the RFA.
- Andrew Balber