Objective
To accelerate the widespread availability of insulin producing beta (β)–cell replacement therapies for the treatment of type 1 diabetes (T1D) by: exploring the improvements in vascularization and oxygenation of the cellular contents of SC implanted, nonimmunoisolating, vascularizing devices (ONID). An improved, accelerated neovasculature would allow better islet survival and engraftment and earlier termination of supplemental oxygen to the device. Because the supply of human islets for implantation is the major limitation to providing this therapy to T1D patients, we will explore – under the same protocols – the use of human stem cell derived islets (hSC-islets). In the same series of experiments, we will evaluate supporting technologies for noninvasively imaging the SC implanted cell chamber and its vasculature, both outside and within the chamber.
Background Rationale
The large-scale implementation of insulin producing beta (β)-cell replacement therapies as the standard of care for patients suffering with type 1 diabetes (T1D) is currently limited by insufficient human islet availability, and the insufficiency of the portal vein route of delivery. A SC implanted, vascularizing, nonimmunoisolating device, the ONID, is otherwise ideal – except for the need of supplemental oxygen prior to neovascularization is achieved. Adding a vascularizing matrix to the cells may drastically improve survival and engraftment and enable faster vascularization (resulting in supportive oxygen concentrations allowing faster oxygen termination). To address the shortage of donated islets, we will test human stem cell-derived islets in the same device system. Finally, exploring noninvasive imaging as a modality supporting the objective, sequential evaluation of the vascularization and oxygenation of SC implanted devices. This is another advantage over the portal route; imaging will facilitate experimental studies and will be essential for future clinical trials.
Description of Project
Although the transplantation of insulin producing beta (β)-cells within islets is a proven, potentially curative treatment of Type 1 Diabetes (T1D), its widespread application to the many millions of patients who could benefit from it, is practically limited by the very limited numbers of human pancreas donations from which islets are isolated. The shortage of human islets can be partially ameliorated by improving transplanted β-cell survival and function – thus conserving cells - by using a subcutaneously (SC) implanted, oxygenated encapsulation device that reduces overall device footprint yet maintains cell viability and potency. The transient supply of exogenous oxygen from a small external oxygen generator prevents lethal hypoxia until the device is sufficiently well vascularized for the β-cells to survive without supplemental oxygen.
A far more potent and widely applicable solution to the supply/demand dilemma, however, is the exploitation of virtually unlimited supplies of β-cells derived from human stem cells. The numbers of these cells can be expanded nearly without limit in culture. Because of the possible, albeit unlikely, need to retrieve the cells sometime after implantation, encapsulating cells in the SC space is desirable. Quite unfortunately, the sensitivity to hypoxia of human stem cell derived islets (hSC-islets) is even greater than that of islets; therefore, stem cells will also require supplemental oxygen until they are well-vascularized.
Two of our collaborating laboratories have developed hydrogel matrices which accelerate the vascularization and improve survival of β cells injected into various anatomic sites, including the SC tissue. Both the hydrogels and our implantable, vascularizing devices themselves accelerate the ingrowth of blood vessels; we postulate that using our device with one or the other matrix will additively or synergistically accelerate neovascularization and thus foreshorten the duration of requisite oxygen supplementation. We will test the matrices in combination with both human, donated islets and hSC-islets, seeking an improved approach for either cell source.
A technical dilemma – both experimentally and ultimately, clinically – is non-invasive monitoring and visualization of the cellular cargos of SC-implanted devices. Accordingly, this proposal will also test three imaging modalities: Contrast enhanced micro-Computed Tomography (microCT) to image neovasculature, both surrounding and within devices; Photoacoustic (PA) analysis of hemoglobin oxygenation state; and Ultrasound (US) imaging of blood borne nanovesicles to assess perfusion. The intent of investigating these supporting technologies is to identify which one(s) provides the greatest accuracy and ease of use, by which to assess the state of neovascularization of the cells with the device. These images and quantitative data derived from them will be invaluable in determining when to halt the flow of supplemental oxygen and to remove the oxygen generator. This will – quite obviously – be useful in planning and executing experimental schemata; more importantly, clinical trials will require a means of monitoring, not only β cell survival and function, but their requirement for oxygen supplementation.
Finally, the proposed study will provide pre-clinical data required by regulatory agencies to approve clinical investigations of human islets or stem cell-derived β cells encapsulated within retrievable devices temporarily supplied with oxygen from an external generator.
Successful completion of the Specific Aims within this proposal will represent significant progress toward the BT1D goal of establishing a widely applicable strategy for curative therapy of T1D.
Anticipated Outcome
This project will be guided by two objectives. First, to demonstrate diabetes reversal using human stem cell derived islets (hSC-islets) in diabetic rats, cells are tightly packed in non-immunoisolating devices with an external oxygen delivery source. Then, once blood vessels are established within the device, oxygen delivery is terminated, after which maintenance of a non-diabetic status (normoglycemia) is demonstrated. To further improve hSC-islet survival and engraftment and hasten the moment of oxygen termination, the proposal will test the synergy of adding vascularizing matrices to the cells before loading and implanting the device. The critical endpoint is persistent, durable reversal of diabetes in previously diabetic rats after terminating the external oxygen supplementation.
Relevance to T1D
Type 1 diabetes (T1D) is a lifelong metabolic disorder that demands viable treatment options. Insulin producing beta (β)-cell replacement is a practical approach to the treatment of T1D but cannot be widely implemented to treat the millions of people in need due to human donated islet shortages. Encapsulated β-cell therapy – with human stem cell derived islets (hSC-islets) – is less invasive and less expensive than islet transplantation in the liver. It is more efficacious and convenient than insulin pumps due to the cells’ ability to monitor blood glucose and respond to that glucose level. Ultimately, this project will allow for a quicker and more efficient clinical translation of encapsulated cell therapy for the treatment of type 1 diabetes using fewer cells, by improving – with matrix - encapsulated cell viability and function and by providing supplemental oxygen until blood vessel formation can be achieved. The proposed noninvasive imaging is a potentially valuable tool for evaluating the vasculature of the implant.