Objective
In assessing unmet areas of immunoengineering for beta cell replacement in type 1 diabetes (T1D), Drs. Phelps (PI) and Russ (Co-PI) have been collaborating on strategies for local control of autoimmunity in type 1 diabetes. This proposal furthers this goal by pursuing novel sources of local immunomodulation to drive tolerance towards grafted stem cell derived beta-like cells (sBCs). In addition to our published sBC tolerance approach, we have been investigating the potential use of immunomodulatory signals from pregnancy. An understudied signal with respect to immune engineering, but central molecular regulator of pregnancy tolerance adaptation is the hormone human chorionic gonadotropin (hCG). hCG is transcribed from the earliest stages of the blastocyst and later by the placenta promoting tolerance. This project extends our existing and established collaborative efforts synergizing engineered hydrogel platform technologies with our expertise in cell engineering of immune privileged, mature sBCs. We have extensive experience in genome engineering and functional testing of immune modular molecules (and other genes) expressed on sBCs in vitro and in vivo. This project also pushes forward the state-of-the-art in islet replacement therapy modeling by expanding our innovative use of humanized mice to investigate not only allogenic (or xenogenic) but also beta cell specific autoimmune responses to sBC grafts in a matched manner.
Background Rationale
Clinical onset of T1D represents the culmination of a prodromal period of chronic beta cell autoimmunity, inflammation, destruction and antigen spreading. Onset of disease takes place when the majority of beta cells have been destroyed and remaining beta cells are no longer able to produce sufficient insulin for maintaining glucose homeostasis. Pancreatic islet transplantation to replace functional beta cell mass has been able to provide some patients with a few years of temporary relief from insulin injections but is insufficient to permanently cure a human T1D patient due to eventual graft failure. Thus, there is a critical need for approaches that combine islet replacement through renewable sources of beta cells with immunomodulation to counter recurrence of autoimmunity.
Our proposed solution is designed to promote localized, instead of systemic antigen-specific tolerance for all islet autoantigen responding T cells, by taking advantage of the fact that our strategy will interface with the full repertoire of islet-invading T cells at the site of transplantation. Thus, we do not require prior knowledge of the autoantigen subset (the majority of which is currently not known) to which the autoreactive T cells are reacting in a particular patient. By localizing immunomodulatory presentation, we will target only those T cells reacting to the islet, avoiding systemic immune suppression. Further, the solution we propose is compatible with islet revascularization, and will not compromise islet tissue integration to achieve immunomodulation.
Description of Project
Human pregnancy presents a source of potent immunomodulatory signals to protect the fetus from the maternal immune system that hold potential for inducing localized tolerance in beta cell replacement. Immune tolerance in pregnancy is maintained through multiple pathways including signaling molecules, lack of HLA-A and HLA-B expression in the placental trophoblast and induction of unique immune cell subsets. Of key importance, the hormone hCG is transcribed from the earliest stages of the blastocyst and later by the placenta and is the hormone detected by over-the-counter pregnancy tests. hCG is an essential signal required for development of maternal-fetal immune tolerance. Systemic administration of hCG prevents T-cell mediated autoimmunity in NOD mice, demonstrating activity of hCG outside of pregnancy and in mouse models of autoimmune T1D. Our own in vitro co-culture experiment provide proof of principle that hCG inhibits insulin-specific, human T cells. Here, we propose to localize presentation of hCG to the microenvironment of transplanted stem cell derived human beta cells using engineered biomaterials and genome engineering. These systems will be tested in humanized mouse models of autoimmune diabetes.
Anticipated Outcome
This project will be the first to investigate hCG in the context of islet graft tolerance. Importantly, we propose the innovative use of a humanized mouse model of T1D to test our combined immunotolerance therapy in both allogenic rejection and autoimmune settings specifically. Notably, this work can easily incorporate or substitute additional immune modulatory approaches including those already established (PD-L1, TRAIL, FasL and HLA Class-I knock out) as alternative strategies. Thus, the success of our project does not solely depend on the desired complete efficacy of the highly novel hCG approach. In addition, the microporous architecture of engineered delivery hydrogel is compatible with direct islet revascularization, a critical feature for proper beta cell function, currently not readily achieved using various other encapsulation strategies.
Relevance to T1D
Of the 37 million Americans with diabetes (11.3% of the population), 1.9 million children and adults have type 1 diabetes (T1D). T1D is an autoimmune disease marked by infiltration of the pancreatic islets by self-reactive CD4+ and CD8+ T cells, which mediate the selective destruction of the insulin-producing beta cells. T1D results in life-long dependence on exogenous insulin for survival, which is particularly limiting for those affected at a young age. Current T1D treatments are inadequate at responding accurately to short-term metabolic imbalances and cannot prevent severe chronic diabetes-related complications. Therefore, a curative therapy that targets the underlying disease process is desperately needed. Several approaches for manipulating the mechanisms of central and peripheral tolerance have been attempted to treat T1D autoimmunity. However, a majority of clinically translated immunotherapies for T1D have focused on systemic delivery of global immunomodulatory molecules or immune cells. None has yet proven particularly effective for preventing the onset of T1D in humans. The research proposed here presents a rationally designed, localized immunomodulatory strategy to promote immune tolerance in a beta cell replacement setting.