Objective
In this proposed study, we plan to explore strategies of protecting transplanted stem cell derived islet cells from the recipient immune system in the large animal model pig. In order to achieve immune-cloaking we will genetically modify islet cells derived from pig induced pluripotent stem cells (piPSCs) to be less visible to the immune system. This will involve modulating the expression of cell surface recognition molecules, such as deleting specific swine leucocyte antigens (SLAs) and expressing factors that mediate the adaptive T cell response. Such hypoimmunogenic piPSC-derived islet cells will be transplanted into fully immunocompetent pigs followed by analysis of the resulting host immune response to the graft as well as functionality of the transplanted islets over time. Promising candidates of hypoimmunogenic piPSC-islets will also be transplanted in diabetic pigs and their ability to reduce insulin dependency and restore normal blood glucose levels will be assessed. By employing pig pluripotent stem cells and pigs as recipients we are thus developing a novel model system of allogeneic immune rejection of stem cell derived islets that closely resembles the human counterpart and allows unprecedented insight into how these transplanted cells can be protected for replacement therapies. These efforts have clear implication to optimize human stem cell therapies for patients with Type 1 Diabetes.
Background Rationale
Type 1 diabetes (T1D) is a chronic illness characterized by elevated blood glucose levels caused by autoimmune destruction of insulin-producing beta cells. More than 3 million individuals in the United States have been diagnosed with T1D, accounting for 5-10% of all diabetes cases. Current treatment largely involves the exogenous injection of insulin but can only achieve an imperfect control of blood glucose levels and life-threatening hypoglycemic events and vascular complications persist. Another option is to replace the lost beta cells by transplantation of cadaveric islets with simultaneous long-term immunosuppression. Since the demand for cadaveric islets far outstrips the supply, stem cell-based replacement therapy has recently emerged as a promising alternative source for restoring islet function in diabetic patients. Stem cell-derived islet cells can be efficiently generated by differentiation from pluripotent stem cells and are already being tested in a Phase 1/2 clinical trial in T1D patients.
The long-term protection of transplanted islets from the recipient immune system however remains a major obstacle for replacement therapy. Continuous immunosuppression presents with its own complications and impedes widespread application of these therapies. It is therefore essential to develop novel strategies that protect the stem cell-derived islets from immunogenic attack. Progress in this area is currently hampered by the lack of appropriate model systems that fully reflect and allow assessment of the full spectrum of the allogeneic immune response after transplantation. The large animal model pig is a suitable system which closely resembles the human situation and has many advantages over other models such as humanized mice or non-human primates. We thus propose to utilize stem cells derived from pig fibroblasts to generate islet clusters and transplant them into recipient pigs to assess the allogeneic immune response to the graft and develop strategies of preventing immunogenic destruction of these clusters.
Description of Project
Stem cell islet therapies are emerging as a clear alternative for treatment of patients with Type 1 Diabetes (T1D). While tremendous progress has been made over the recent years, in particular regarding the generation of functional islet cells from stem cells, concerns remain about how such cells can be protected in the long run from immune destruction caused by the recipient immune system. In part, this problem arises due to the absence of model systems fully replicating the scenarios experienced after stem cell transplantation. For example, human stem cell derived islets transplanted into humanized mice experience cross-species specific responses (xenogeneic), while other parts of the immune response are lacking. Here, we propose to use the pig as an optimized model system to study the full immune response that occurs after stem cell derived islet transplantation. We will follow approaches previously described in human stem cells to cloak derivatives against immune recognition and elimination. This work is now possible due to the fact that pig induced pluripotent stem cells are available, that such cells can be differentiated into pancreatic cell types, that the pig immune system has been well characterized, and that our group includes world experts in generating and analyzing genetically modified pigs for the study of human diseases, including diabetes. Importantly, the pig is considered to be closer to human than other models, including rodents, and also has metabolic traits closer to human situation than non-human primates. Thus, we expect that our approach will generate novel information that can be used to rapidly test how various immune cloaking strategies protect stem cell derived cells from destruction in fully immune competent animals. This unique approach will accelerate translation of stem cell therapies for patients with T1D.
Anticipated Outcome
We anticipate identifying molecules that can be modulated in order to protect transplanted stem cell derived islet cells from immune recognition and subsequent destruction. The pig as a novel model system will further lead to critical new insights into how allogeneic rejection is mediated in a fully immunocompetent host that shares many similarities with humans. An iterative experimental approach will allow us to directly translate findings from initial studies into further improved hypoimmunogenic stem cell derived islets. We thus expect to understand which sets of immunomodulatory molecules need to be modified to achieve effective immune-cloaking. These findings will be highly relevant for human stem cell therapies.
Relevance to T1D
Stem cell-based islet replacement therapy is rapidly advancing towards broad application in patients with Type 1 Diabetes (T1D). One major obstacle is the requirement for long-term immunosuppression following allogenic transplantation, a treatment that carries significant risk for uncontrolled viral infections and cancer formation. Developing novel strategies of protecting the transplanted islets from the recipient’s immune system is therefore paramount. Our proposed work directly addresses this need and could lead to significant advances in our understanding of how to circumvent immunogenic rejection in patients after transplantation. By testing modified hypoimmunogenic islet cells in a fully immunocompetent model system closely resembling that of humans, knowledge gained from our studies should have potential direct application for patients with T1D.