Objective
Therapeutic approaches to developing tolerance to transplanted islets generally focus on promoting the activation and proliferation of regulatory immune cells such as CD4+ regulatory T (Treg) cells and tolerogenic dendritic cells (tolDCs). These cells promote tolerance in secondary lymphoid organs (e.g., lymph nodes and spleen) and specific tissues by deleting self-reactive lymphocytes. Unfortunately, only very few approaches have demonstrated success in inducing immune tolerance to prevent rejection of allogeneic organs. The Engleman group at Stanford recently discovered that the erythropoietin receptor (EpoR) expressed on type I dendritic cells (cDC1s) strongly directs immune tolerance, including tolerance to alloantigens. Based on this work, we hypothesize that EpoR signaling in cDC1s can be exploited to induce tolerance to transplanted islets for the treatment of T1D provided appropriate locoregional co-presentation of these signals and the islets can be achieved. The Appel lab has developed a simple-to-implement self-assembled and injectable hydrogel depot technology enabling the controlled codelivery of diverse therapeutic cargoes, including both proteins and cells. These materials can be easily administered with standard syringe/needle or catheter delivery approaches, and they form depots in the body upon administration that simply dissolve away over timeframes tunable from days to months depending on the hydrogel formulation. These hydrogels are uniquely capable of prolonged administration of complex mixtures of biologic compounds, such as in the case of vaccines, and they can act as local inflammatory niches for recruitment, infiltration, and activation of immune cells. The Appel lab has recently shown that co-delivery of autoantigens (e.g., insulin) and chemokines (e.g., GM-CSF) in this hydrogel depot implanted subcutaneously leads to formation of a privileged immune niche that induces antigen-specific tolerance and mitigates the onset of T1D in NOD mice, a well-established T1D mouse model.
In this work we will leverage this injectable hydrogel depot technology for sustained locoregional co-delivery of tolerogenic cargo and allogeneic islets to treat diabetes. We have promising proof-of-concept data in mice that demonstrate the effectiveness of EpoR signaling in host cDC1s for induction of tolerance as well as preliminary data in NOD mice wherein T1D onset was mitigated using hydrogel-based tolerogenic vaccines. We will evaluate the effectiveness of using hydrogel-based islet transplantation therapy to reduce auto- and alloimmunity and enable robust engraftment of transplanted islets. We believe this novel therapeutic approach has the potential to yield unprecedented islet transplantation success and catalyze the development of a powerful regimen for the management of diabetes affording as yet unrealized therapeutic impacts.
Background Rationale
Type 1 Diabetes (T1D) arises from autoimmune destruction of pancreatic β cells. Transplantation of human replacement islet cells, including cadaveric donor pancreatic islets, or progeny of human stem cell lines, offers restoration of β cell mass in people with T1D, affording opportunities for prevention and reversal of complications from diabetes. Unfortunately, islet graft recipients must maintain life-long immunosuppression regimens with drugs that can lead to complications like secondary malignancy, and opportunistic infections. These immunosuppressive drugs also induce β cell dysfunction or death. There is therefore a huge clinical need for development of tolerogenic regimens that eliminate the need for immunosuppression and facilitate wider application of islet transplantation options for T1D.
Immune tolerance is an active state of unresponsiveness of the immune system to antigen (Ag) that have the potential to induce an immune response. Such tolerance is beneficial in avoiding autoimmunity and rejection of organ transplants, but detrimental in cancer. The antigen-presenting cells called type 1 conventional dendritic cells (cDC1s) have unique properties (like 'efferocytosis' and 'cross-presention'), enabling them to promote T cell-mediated immunity or tolerance. However, the mechanisms underlying the tolerogenic function of cDC1s remain largely unknown. The Engleman group at Stanford has discovered that the erythropoietin receptor (EpoR) acts as a critical switch that determines the tolerogenic state of cDC1s and the threshold of Ag-specific T cell responses. The functional state of cDC1s coupled with Ag uptake and subsequent Ag presentation dictates both the direction (i.e., immunogenic versus tolerogenic) and intensity of an Ag-specific immune response. The acquisition of apoptotic cells by cDC1s not only initiates both CD4+ and CD8+ T cell priming and activation but can also result in tolerogenic programming of cDC1s, leading to the induction of Ag-specific Tregs and deletion of Ag-specific CD8+ T cells. We hypothesize that controlled co-transplantation of islets, Epo, and immunomodulatory cargo targeting cDC1s can manipulate these cells in vivo to induce tolerance to transplanted islets to effective treat T1D.
The Appel group at Stanford has developed an injectable hydrogel depot technology enabling the controlled codelivery of diverse therapeutic cargoes, including both immunomodulatory proteins and cells. These hydrogels are easily formed by simple mixing with therapeutic cargo (like islet cells), and they are easily injectable and highly biocompatible. Importantly, these materials can be readily administered with standard syringe/needle or catheter delivery approaches, and they form depots in the body upon administration that simply dissolve away over specific timeframes (days to months) depending on the hydrogel formulation. Thus, the duration and intensity of drug delivery through hydrogels can be 'tuned' for optimal impacts. Importantly, these hydrogel depots permit immune cell infiltration to generate an immune niche for the modulation of immune cells. The Appel lab has recently shown that hydrogel co-delivery of auto-antigens (e.g., insulin) and chemokines in subcutaneous sites leads to formation of a privileged immune niche that induces antigen-specific tolerance and mitigates the onset of autoimmune diabetes in NOD mice, an established model of human T1D.
We hypothesize that controlled co-delivery of islets and immunomodulatory factors (e.g., chemokines such as GM-CSF and recombinant Epo) in our injectable hydrogels will result in the formation of an immune-privileged niche that will drive robust and durable allograft tolerance to the transplanted islets. These immunomodulatory hydrogel depots for islet transplantation can be implanted in tissues where islets are typically implanted (e.g., kidney capsule in mice and omentum in primates), while driving the development of peripheral tolerance. We will engineer a safe and effective biomaterial for the transplantation of islet cells co-delivered with tolerogenic agents that will promote immune tolerance and improve allograft survival for the treatment of diabetes.
Description of Project
Type 1 Diabetes (T1D) from autoimmune destruction of pancreatic β cells leads to deficits in endogenous insulin output. Transplantation of human pancreatic islet cells and restoration of β cell mass in people with T1D, affords opportunities for prevention and reversal of complications. Unfortunately, islet transplant recipients require lifelong immunosuppression with toxic drugs, including agents that damage β cells. Thus, there is a critical unmet need for new strategies for 'targeted' immune tolerance that eliminate systemic immunosuppression and facilitate wider application of islet transplantation for T1D. The Engleman group at Stanford recently discovered that the erythropoietin receptor (EpoR) expressed on type I dendritic cells (cDC1s) strongly directs immune tolerance, including tolerance to alloantigens. In mice treated with total lymphoid irradiation and donor bone marrow to induce allogeneic tolerance, activation of EpoR signaling in host cDC1s induced expansion of regulatory T cells (Tregs) that are essential for achieving allotolerance. Based on this work, we hypothesize that EpoR signaling in cDC1s can be exploited to induce tolerance to transplanted islets for the treatment of T1D, provided these signals can be maintained in the local environment with transplanted islets over relevant timeframes.
The Appel group at Stanford has recently developed an injectable hydrogel depot technology enabling the controlled codelivery of diverse therapeutic cargo, including both proteins and cells. These materials can be easily administered with standard syringe/needle or catheter delivery approaches, and they form depots in the body upon administration that simply dissolve away over timeframes tunable from days to months. Leveraging this technology, the Appel group have recently shown that co-delivery of auto-antigens like insulin, and chemokines that recruit dendritic cells, like GM-CSF, leads to formation of a privileged immune niche that induces antigen-specific tolerance and mitigates the onset of autoimmune diabetes in NOD mice, a well-established model of T1D. For example, 80% of NOD mice receiving hydrogel-based vaccine formulations remained non-diabetic compared to only 40% in control groups.
Based on these promising proof-of-concept studies, we hypothesize that controlled co-delivery of islets and immunomodulatory factors (e.g., chemokines such as GM-CSF and recombinant erythropoietin, Epo) in our injectable hydrogels will result in the formation of an immune-privileged niche that will drive robust and durable allograft tolerance to the transplanted islets. These immunomodulatory hydrogel depots can be implanted in standard islet engraftment sites (e.g., kidney capsule in mice and omentum in primates), while driving the development of islet tolerance. Further, we hypothesize that antigen-specific vaccines can augment the tolerogenic islet niche to overcome both auto- and alloimmunity, thereby inducing long-term transplant viability and function. We have assembled a superb team (Engleman, Kim, and Appel groups at Stanford) with relevant expertise to successfully achieve our research goals. The novel therapeutic strategies we propose should be translatable and dramatically improve islet transplantation success to reverse T1D.
Anticipated Outcome
The proposed work will generate promising novel drug product candidates that can be applied during islet transplantation therapies to obviate the need for systemic immunosuppression and improve islet engraftment. We anticipate that the novel hydrogel depot-based drug products developed through work here will catalyze the development of a powerful new strategies for durable cell-based treatment of T1D. By the end of the proposed work, we anticipate having robust preliminary data demonstrating the feasibility of our approach for clinical translational studies. Ultimately, we hope to advance these drug product candidates to clinical practice and provide a cell-based cure for T1D. Our Stanford team has a prior record of developing clinically-useful therapeutics, including work by Appel and Engleman.
Relevance to T1D
Type I Diabetes (T1D) is characterized by the inability to produce endogenous insulin and amylin after an autoimmune response destroys the pancreatic β-cells. Transplantation of human pancreatic islet cells offers restoration of β cell mass in people with T1D, affording opportunities for prevention and reversal of complications from this disease. Unfortunately, islet graft recipients must maintain immunosuppression regimens for their entire lives with drugs that can be toxic to the recipient, and which may induce peripheral insulin resistance. There is therefore a huge clinical need for development of tolerogenic regimens that obviate the need for immunosuppression and facilitate more wide application of islet transplantation as a cure for T1D. To address the challenges of islet transplant rejection, we will develop novel therapies for inducing robust and durable auto- and allotolerance by leveraging a unique self-assembled and injectable hydrogel depot technology that enables co-transplantation of islets and immunomodulatory cargo to create an immune privileged niche that will promote immune tolerance and improve allograft survival for the treatment of diabetes.