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In recent years the wide-spanning applications of stem cells in biomedical research have been commonly acknowledged. The primary goal of this proposal is to boost stem cell research towards clinical application. Although excellent progress has been made in the past with regard to understanding stem cell specification into tissue-specific cells and also the mechanisms of their self-renewal, major hurdles on the way to the clinic still exist. One of them – the risk for immune rejection - will be addressed in this proposal. Since embryonic stem cells (ESCs) are harvested from an early embryonic stage of a 'donor', ESC transplantation will always be allogenic (related, but sufficiently different genetic make-up). The implication is that the patient will have to be on immunosuppressants for the rest of their life to prevent immune rejection of the transplanted cells - a medical treatment associated with serious side effects. In the past years, many laboratories have worked on circumventing the rejection problem with lesser or greater success. Finally, the recent discovery of induced pluripotent cell (iPS) technology promises the possible generation of cells with the patient's own genetic make-up, but with pluripotent potential. Such pluripotent have the ability to be expanded in culture in an unlimited fashion and bring about all possible cell types that the adult body consists of, something that is not possible with other types of stem cells harvested from the patient's own body. But how do we know whether or not iPS cells will work better and without resulting in immune rejection? The FDA requires that human trials always have to be preceeded by animal experiments, but how do we test the response of a human immune system in an animal model? To answer these questions, our consortium proposes to engineer a human immune system in a mouse. In its entirety, our strategy is composed of two subsequent transplantations. In the first, we will kill the mouse's blood stem cells, which usually give rise to the immune cells. Then human blood stem cells will be transplanted that reconstitute the blood and the immune cells - expect these are now of human origin. In a second transplantation then, we will transplant human ESCs and human iPSCs into this humanized mouse model and characterize the type of immune response by testing for typical immunological parameters. As the second transplantation model, we chose a bone defect. This model is readily available to us, but more importantly, the specialization of human ESCs and iPSCs into bone forming cells in culture is, in contrast to other tissue models, a robust and standardized process. Ultimately, we will be able to measure the human-specific immune reaction caused by either ESCs or iPSCs. Our research will bring stem cell transplantations closer to the clinic, which in turn would help to reduce the economic burden on the Californian healthcare system associated with conventional medical treatment options.
Statement of Benefit to California:
During the last few years, the profound implications of pluripotent stem cells for biomedicine have been widely recognized. While adult stem cells (ASCs) have been used in clinical trials to treat bony injuries, the autologous transplantation of ASCs (stem cells harvested from self) for the treatment of osteoporosis, which is a degenerative disease caused by malfunctioning stem cells, may be limited by the quality of the patient's own cell material. In other cases, the number of ASCs that can be harvested and expanded in culture may not be sufficient to treat the patient. Given the recent advances in many research fields, the consortium that we have assembled for this research project is now in a position to move the frontier of stem cell research to the next level towards clinical application -1) characterizing whether osteoprogenitors derived from an unlimited cell source - pluripotent stem cells (PSCs) - can repair bone tissue and 2) understanding the immune responses that are elicited by such PSCs. The research proposed in this application will provide tangible benefits to Californians. The success of the approach of our proposal should create a platform on which stem cell treatment of other degenerative diseases can build. Osteoporosis is only one of the diseases for which the concept of replacing destroyed or dysfunctional cells is a practical goal, but there is many more. Overall however, once it has been understood what immunological consequences the transplantation of progenitor cells derived from PSCs has, the clinical use of stem cells would undoubtedly help to reduce the economic burden on the Californian healthcare system associated with conventional reparative options. Our proposal covers aspects of high quality applied research and timely applications to real-world biomedical problems. Therefore, the impact of our research is four-fold: it will make important contributions or SCIENTIFIC IMPACT, regarding the definition of immune responses typically to be expected after autologous and allogenic stem cell transplantation. We achieve this by creating STRUCTURAL and MULTIDISCIPLINARY SYNERGIES inside the team and the outside world through incorporating unique knowledge that is only available outside of California, even the United States, by partnering with German experts. It will create novel Intellectual Property, which will BOOST THE INDUSTRY SECTOR and facilitate translation into the clinic by setting Californian STANDARDS for the clinical application of stem cells. Crucially, however, the proposed research will significantly benefit California by training highly qualified personnel for future careers in academic research or the biomedical industry (i.e. Genentech). These trained professionals will have the skills to develop new therapeutic strategies in a broad range of applications, improving patient quality of life and positively impacting the Californian healthcare system.
The ultimate goal of this proposal is to determine whether human induced pluripotent stem cells (hiPSCs), which are first differentiated to the osteogenic lineage, can be transplanted without rejection and contribute to the repair of bone defects. In the first Aim, a preclinical model for the adaptive human immune system will be developed. Next, the applicant will characterize the immune response elicited by transplantation of osteoprogenitors (OPCs) derived from either allogeneic human embryonic stem cells (hESCs) (Aim 2), or functionally autologous hiPSCs (Aim 3). The ability of these grafts to contribute to bone repair will be evaluated. The reviewers believed the proposal is modestly innovative but would have limited impact. While they acknowledged the creativity of the preclinical model, their enthusiasm for its significance was tempered by uncertainties about its robustness as well the increasing availability of commercial alternatives. In addition, verification that autologously derived cells could escape immune rejection was not considered to be a high priority to the field. While agreeing that such information could be useful, the reviewers were disappointed that the investigators did not propose a path forward should they find evidence that the functionally autologous cells are rejected. Reviewers had mixed impressions about the feasibility of the research plan. Many reviewers felt the overall application and study design were poorly constructed. With respect to Aim 1, reviewers questioned whether it would be possible to generate the proposed model on a consistent basis, given the known difficulties with human engraftment in the designated strain as well as the presence of natural killer (NK) cells in this model. The general lack of details and discussion surrounding the methods to be used also contributed to this sense of uncertainty. Finally, reviewers questioned whether meaningful results would be obtained from Aims 2 and 3, given the descriptive nature of these studies and the lack of a cohesive, underlying hypothesis to provide context for their interpretation. The principal investigator (PI) was described as a talented young scientist with expertise in stem cells and the mesenchymal lineage. The co-investigators were considered highly qualified in the areas of hiPSC biology and bone repair, and the collaborative funding partner provides valuable experience with immunology. Despite these strengths, the reviewers noted a lack of specific expertise in the area of immune tolerance. Furthermore, they questioned the extent to which such a large and dispersed collaboration could be effectively managed. In summary, reviewers felt this proposal addresses an interesting question but one that is not likely to have great impact on the field. The feasibility was in doubt due to a lack of clear underlying hypothesis as well as uncertainties about the experimental design and execution.