Induction of tolerance in NOD mice using genetically engineered human adipose-derived mesenchymal stem cells
New Faculty I
Type I diabetes is caused by an immune-mediated process that involves the destruction of one’s own pancreatic insulin producing tissue. The mechanisms that are responsible for this self-destruction remain unclear but are thought to involve a component of the immune system known as the cytotoxic arm. A number of general immunosuppressive medications have been shown to slow down or prevent the onset and/or progression of this autoimmune destruction. However, this therapeutic option is at the expense of serious drug-induced side effects. This has led to a need for an immunosuppressive therapy with minimal side effects. Recently, a type of stem cells, known as mesenchymal stem cells, has been shown to possess immunosuppressive effects. Human clinical trials showed these cells could be used to suppress graft-versus-host-disease in patients undergoing bone marrow transplantation. This cell-based therapy was in replacement of traditional immunosuppressive medications such as cyclosporine. Although very promising, the immunosuppressive effect was only observed for two weeks, suggesting a transient nature. Our group has recently discovered a rare subpopulation of mesenchymal stem cells in the fat tissue of humans with persistent immunosuppressive effects. Further studies to characterize the underlying mechanism of immunosuppression revealed these cells block the cytotoxic arm of the immune system, providing a significant relevance for use as a therapeutic for type I diabetes. The advantages of a cell-based immunosuppressive lie in their ability to achieve these effects in the absence of end-organ damage thereby providing increased safety for patients. In addition, our preliminary experiments involved transplantation of human cells into mice with a normal immune system. In this model, human cells were not rejected, suggesting the possibility that this rare stem cell population may be used similar to drugs, in an off-the-shelf fashion, without concern for special tissue matching procedures that continue to limit commercialization of stem cells. Another limitation, however, is in the ability of stem cells to be mass produced for commercial scale use. Through the use of genetic engineering, our group has designed a tool that allows for large scale cell expansion in the tissue culture dish. This mechanism can only be turned on in the presence of a special drug that would otherwise not be present in the human body, thereby allowing for complete control of the induction mechanism. We believe that engineering of this inducible mechanism into the stem cell population with immunosuppressive effects will solve the two major hurdles currently limiting stem cell commercialization while creating a stable safe and efficacious therapeutic for type I diabetes. A mesenchymal stem cell with persistent immunosuppressive effects that can be mass produced similar to a drug will represent a major breakthrough in the field, allowing for treatment of other autoimmune diseases.
Statement of Benefit to California:
California is home to over 100,000 people afflicted with type I diabetes with current demographic trends suggesting this number will steadily increase for the next two decades. Since the onset of type I diabetes is often in childhood, the cumulative impact over a patient's lifetime is significant at a number of levels including quality of life, emotional stability, as well as the currently unavoidable late-stage sequela such as blindness, kidney damage, and cardiovascular disease. The costs associated with providing vigilant monitoring and care for patients with diabetes are high and will continue to increase barring a paradigm shift in the therapeutic approach. Much attention has been paid to the treatment of type II diabetes using regenerative medicine approaches such as islet cell transplantation using embryonic stem cells. However, unlike type II diabetes, type I diabetes is caused by an autoimmune reaction against one's own islet cells. Thus, islet cell replacement is unlikely to significantly impact the quality of life of type I diabetics in the absence of preventing the continued autoimmune destruction process. The proposed research aims to develop an innovative therapeutic stem cell approach that differs from those currently in development. Instead of utilizing stem cells to replace the destroyed islet cells, our laboratory believes we can exploit recent evidence that a particular adult-derived stem cell population possesses immunosuppressive effects. The work conducted in this project will allow for the development of a stem cell based therapeutic approach that addresses the underlying pathophysiology of type I diabetes by preventing the autoimmune destruction of insulin-producing islet cells. This approach offers the State of California and its citizens a significant advance in the therapeutic approach to type I diabetes, allowing patient's to preserve their insulin producing cells thereby preventing the significant short- and long-term problems associated with this devastating disease. If successful, this approach may be applied more broadly to all autoimmune diseases providing the State of California with the first therapeutic capable of preventing autoimmune disease safely and efficaciously, leading to a tremendous reduction in the California health care burden and improvement in the overall health and productivity of its citizens.
SYNOPSIS: The proposal aims to study and test the immunosuppressant aspects of adipocyte-derived mesenchymal stem cells (AMSC) with the goal of developing a cellular therapy that will prevent autoimmune destruction of pancreatic beta cells in type I diabetes. The proposal addresses two major roadblocks in cellular therapies for type I diabetes: 1) rejection of allogeneic cells and 2) limited in vitro expansion of adult stem cells. The PI proposes a comparison of the immunosuppressive potency of AMSC, hematopoetic stem cells (HSC) and Jurkat cells in vitro using natural killer (NK) and cytotoxic T cells from mouse and human as the effectors for quantitative comparisons, and microarray analysis and antibody arrays of these cells (and another cell line). In addition, the PI proposes to take the information from the microarrays and perform siRNA experiments as proof of concept that the differentially expressed genes are functional in the immune escape mechanisms he will identify. A second aim is to determine in vitro and in vivo how long the immune suppressant properties of the AMSC are maintained. The third aim is to genetically engineer the AMSC with a controllable immortalization gene (i.e., estrogen control over the c-myc expression), to facilitate large scale expansion of the cells. The fourth aim is to use mixed lymphocyte reaction (MLR) and immune competent and humanized mice to determine how many cells are needed for immunosuppression. The final aim is to use the conditionally immortalized AMSC to prevent autoimmune destruction of the pancreatic beta cells in NOD mice. STRENGTHS AND WEAKNESSES OF THE RESEARCH PLAN: In general, the PI recognizes some of the major hurdles facing all of translational stem cell biology—understanding the immune interactions between specific transplanted stem/progenitor cells and the host, and the need for more efficient expansion ex vivo especially for therapies in adult patients. The quality of the research plan, however, is weak. The difficulties in the study design, many at each stage, are not at all adequately addressed by the investigator and the experiments are too numerous and ambitious for the time frame proposed. It is felt that the investigator grossly underestimates the complexity of many of the proposed studies. The project generally builds on the work of others, including the striking clinical findings in Europe that stage IV graft vs. host disease after bone marrow transplantation can be transiently suppressed with third-party mesenchymal stem cell transplantation. In addition, other investigators have previously shown AMSCs to be expandable in vitro while retaining both their low immunogenicity and their immunosuppressive effects. A basic flaw in the proposal, however, is that there are many ways to prevent diabetes in a NOD mouse, but very few to correct diabetes after onset. This plan only addresses the former even though the proposal introduction suggests the latter. Another weakness is that there is no indication that the applicant or his team has the expertise to carry out these studies. The investigator proposes to compare the immunosuppressive effects of AMSCs to unsorted HSCs and Jurkat cells by isolating MSC-positive and –negative fractions, based on standard markers by flow cytometry, and test their ability to promote CTL and NK cell killing. It is not stated where they will get human NK cell or lymphocyte subsets for their in vitro assays. Furthermore, the proposal does not indicate: how many rare AMSCs can be obtained from each lipoaspirate, the frequency of lipoaspirates, and whether this is sufficient for the proposed experiments. As is abundantly clear from the preliminary data, all stem cells will elicit different immune responses, and the fate of HSC is well known. The cells chosen for comparison, then, with the ASMC are puzzling. Why not take the ‘gold standard’ for comparison, bone-marrow derived MSC, to determine which of these two would have more potency? Furthermore, the properties of the rare AMSC positive cells are not assured. The supposition that AMSCs have immunosuppressive properties is based on only expression of a few molecules (no functional data) and therefore the proposal appears to be quite risky as the PI has no direct experience in this field and essentially no preliminary data to support the proposed genetic engineering strategy that may allow for conditional induction of a reversible cancer-like state in human AMSCs. Although the applicant states that they have recently isolated a unique subpopulation of adipocyte MSCs with more persistent immunosuppressive effects than previously have been demonstrated, these data are not shown. What is shown is simply the expression of markers such as IDO, CD200 and CD47 by these and other related cell types; no studies demonstrating functional immunosuppressive effects are shown. Based on their interpretation of some existing literature and the expression of the aforementioned markers in human AMSCs, they propose the hypothesis to be tested that transplantation of engineered human AMSCs into NOD mice may be able to prevent autoimmune destruction of beta cells and restore euglycemia. The preliminary data show that AMSC can be sorted out using HLA 1b antibodies, and that the AMSC can be differentiated to mesenchymal lineages. The most interesting data is that there appeared to be MSC surviving in blood for two weeks after transplant into immune competent mice. However the data state that these were human MSC and so I presume that they are not AMSC as shown in Figure 3 (otherwise why not call them MSC). This suggests that the immune escape of AMSC has not yet been evaluated and would seem to be an essential piece of data. The investigators will further study the molecular signature of the various cell populations using microarrays. Unfortunately, there is no hypothesis here; nor is there consideration about what they might discover with these studies. It is also not clear that the microarray is the appropriate strategy to identify the genes responsible for the immune escape of the cells. The investigators also propose using an antibody array and siRNA, which represent an entirely unrealistic set of studies. The silencing studies are difficult to imagine as feasible if the phenotype of immune escape is complex, as it likely will be. It is also hard to imagine that only one gene will recapitulate the phenotype and doing multiple silencing experiments in MSC is not trivial. In aim 2, they propose to assess stability of expression of markers of MSCs over time in culture and then test the ability of MSCs to escape immune rejection in vivo in immunocompetent and humanized immune deficient mice. Unfortunately, this will not be as easy as proposed and the humanized immunodeficient mice that they propose to generate are not a well-characterized system. The methods by which they propose to study the stability of gene expression is also not well described. In Aim 3, they propose to genetically engineer an inducible self-renewal system into MSCs to overcome their in vitro senescence and allow expansion. They will use a c-Myc gene fused to mutated estrogen receptor, thereby allowing the c-Myc transgene to be induced with estrogen analogs. Following induction, they will test growth rates and tumorigenic potential of the cells in vitro and in vivo. The studies to determine whether cancers are induced by c-myc are superficially explained. Will all the organs be harvested, fixed, and examined by a trained pathologist for pre-cancerous lesions? Aim 4 will determine the expression for MHC molecules and will determine if genetically engineered AMSCs will be capable of preventing autoimmune destruction of pancreatic beta cells in NOD mice. The connection between doses in vitro that inhibit cytotoxic activity and how these doses will be translated to clinical dosing is not clear. For clinical translational relevance in Aim 5, these transplants planned are ‘preventive’, a luxury not available in clinical type I diabetes. The experimental design should have been more clinically relevant. This aim alone would be a 3 year project. The slated work force is the PI (75%), a research associate (100%) plus consultants, which seems to be completely unreasonable. More personnel should be slated for the work even if it were pared down. QUALIFICATIONS AND POTENTIAL OF THE PRINCIPAL INVESTIGATOR: The PI is currently the Director of Translational Research at Elixir Institute. He obtained his MD and PhD in 2002 from New Jersey Medical School and did a residency in Dermatology and postdoctoral fellowship at Stanford University. Since 2005, Dr. Hantash has been in a training program in Regenerative Medicine at Stanford. He has won numerous awards and uniquely, he has achieved a degree of recognition in the poetry field. He has a number of first author clinical publications in specialty journals and 3 papers (2 middle author in JBC, 1 first author in Biochemical J) from his doctoral work. His publication record is focused purely on dermatological conditions and their clinical treatment; he does not have any publications in the stem cell field. There is no real career development plan offered. He is currently well-funded through the Minnesota Jewish Foundation to characterize human adult mesenchymal stem cells while directing translational research at the Elixir Institute of Regenerative Medicine. Although the application is a new faculty award for physician-scientists, it is not clear from the application that the investigator proposes to continue with clinical activities. INSTITUTIONAL COMMITMENT TO PRINCIPAL INVESTIGATOR: This is a newly formed non-profit, extra-academic institute with no direct academic affiliations. It was formed in 2007 and therefore there is no basis for determining how they will foster faculty careers. Additionally, there is really no indication of commitment to Dr. Hantash’s career development. The company is focused on the ADMC in this proposal. The PI has his career planned as a 100% laboratory endeavor so his clinical time will not be a conflict with his employer or a barrier to giving him time for the project. Since the project appears to be at the core of the Institute’s mission, the PI should be free to explore it, as seen by his 75% time commitment. The stem cell travel is a bit much (2-3 meeting a year per person) given that many local seminars and meetings will be available to keep the investigator up to date. Infrastructure, environment and institutional commitment in terms of resources for enlarging a stem cell program appears to be limited at the Elixir Institute. DISCUSSION: Reviewers felt that this application suffered in several ways. First, the research proposal is too ambitious and complex for the timeframe proposed and presents an inadequate description of expected results and alternative strategies. Although the applicant aims in the long-term to develop a therapy for type I diabetes, the proposed experiments really focus on the prevention of the disease in a mouse model, for which there are already many successful targets. Second, reviewers felt that the PI did not present an adequate career development plan. Finally, the host institution (being newly formed) has no track record in fostering faculty careers and does not offer a clear statement of its commitment to the PI’s career development.