There are several challenges to the successful implementation of a cellular therapy for insulin dependent diabetes derived from Human Embryonic Stem Cells (hESCs). Among these are the development of functional insulin-producing cells, a clinical delivery method that eliminates the need for chronic immunosuppression, and assurance that hESC-derived tumors do not develop in the patient.
We have recently developed methods to efficiently generate such insulin-producing cells from Human Embryonic Stem Cells that can prevent diabetes in mouse models of the disease. The results demonstrated for the first time that Human Embryonic Stem Cells could indeed serve as a source of cellular therapy for diabetes. However, the clinical use of Human Embryonic Stem Cell-derived cell products is hampered by safety concerns over the potential growth of unwanted cell types and the formation of tumors.
Encapsulation of cellular transplants has the potential to reduce or eliminate the need for immunosuppression. Moreover, a durable immunoprotective device which prevented cell escape could serve as a platform for safely administering Human Embryonic Stem Cell-derived therapies. The [REDACTED] device, a planar polytetrafluorethylene (PTFE) pouch-like encapsulation device, features 100% encapsulation and is fully retrievable. We and others have demonstrated in various animal models that the device provides obust protection of transplanted cells against immune attack from the host, [REDACTED] -encapsulated insulin-producing cells can correct diabetes in animals, and the device can prevent the escape and spread of cancer cells.
Therefore, the goal of the proposed studies is to evaluate the retrievable [REDACTED] cell encapsulation device in combination with Human Embryonic Stem Cell-derived pancreatic progenitor cells for the treatment of diabetes in mice.
With a current prevalence of greater than 170 million individuals world-wide, diabetes has attained epidemic proportions. The widespread secondary complications of kidney failure, cardiovascular disease, peripheral nerve disease, and severe retinopathies, this disease extracts a relentless and costly toll on the patients and the health care establishments required for their treatment. Current estimates are that California spends minimally $12 billion on diabetes not including lost wages. There are more than 300,000 diabetes related hospitalizations costing $3.4 billion annually. To date, cellular replacement has been performed either by transplantation of whole pancreas organs, or via infusion of isolated primary pancreatic islets into the portal vein . While effective, the availability of such procedures is severely limited for the treatment of the general diabetes population since it relies upon the extremely limited supply of pancreas organs from deceased donors and usually requires life-long administration of immuno-suppressive drugs.
Recent advances in human embryonic stem cell research indicate that the production of a virtually unlimited supply of functional insulin-producing cells is possible. However, much research is required to determine how to safely administer such cells as a therapy because they could give rise to tumors. The animal studies proposed in this application address this with a device that could both protect the therapeutic cells from host immune attack, and protect the host from tumor formation. If successful, our research would provide a possible opportunity for safely administering a diabetes therapy derived from human embryonic stem cells.
Currently, the shortage of donor organ tissue and risks associated with lifelong immunosuppression limit islet transplantation to only the most severely impacted brittle patients with diabetes. Thus, successful development of a universal cell therapy to treat diabetes requires a renewable safe source of glucose responsive human islet cells and a means for their delivery without the use of chronic immunosuppression. While human embryonic stem cells (hESCs) represent an excellent starting material for the generation of numerous islet cells, the clinical use of hESC-derived cell products is hampered by safety concerns over the potential growth of unwanted cell types and the formation of teratomas. A cell delivery system that allows for both segregation of the hESC-derived graft from host tissues and complete retrieval of the engrafted cells would provide an additional level of safety for hESC-derived cell therapies. The rationale behind this proposal, therefore, is to evaluate an immunoisolation device in combination with hESC-derived pancreatic progenitors as a means for the widespread treatment of diabetes without immunosuppression.
Immunoisolation involves the encapsulation of therapeutic graft cells in a membrane (essentially a sealed pouch) thereby protecting the graft from direct contact with the host immune cells and potentially reducing and/or eliminating the need for chronic co-administration of potent anti-rejection drugs for the life of the graft. The encapsulating membrane physically separates the graft cells from host tissues and vasculature. Therefore, to maintain viability and functional metabolism of the graft, the membrane must permit adequate diffusion of oxygen, nutrients, and waste-products, while also preventing exposure to host immune cells. Finally, an encapsulating membrane ideally allows for the timely delivery of insulin at levels that maintain safe and stable blood sugar levels.
Our hESC-derived pancreatic progenitor cells are first implanted and the cells complete their maturation to fully functional glucose-responsive islet cells several weeks after engraftment into a host animal. One of the notable achievements over the past year has been the demonstration that the encapsulation device can not only sustain the viability of the pancreatic progenitor cells, but also supports the maturation of those cells to fully functional glucose responsive endocrine tissue. We also have demonstrated that encapsulated grafts prevent the development of diabetes in animals that are treated with a toxin that selectively kills their endogenous pancreatic insulin producing beta cells. The encapsulated grafts maintained normal blood sugar levels in these animals, essentially functioning in place of their beta cells. Finally, all of the encapsulated grafts were fully contained in the interior of the device and there were no breached or ruptured devices observed, even when highly proliferative cells were encapsulated in the device. These results suggest that such an encapsulation device may be a viable system to safely deliver an hESC-derived cell therapy for diabetes.
During the second year of our grant we have determined two important features:
1- The encapsulation device we assessed here allows for the efficient development of functional insulin-producing grafts derived from differentiated human embryonic stem cells. We show that in the vast majority of implanted mice (93%) robust insulin-production was detected. Moreover, supporting their potential therapeutic value, in 19 of 19 animals that were challenged with the chemical destruction of their own insulin-producing cells the encapsulated grafts prevented the onset of diabetes.
2- We have used an imaging technology and genetically modified human embryonic stem cells to assess the grafts of differentiated embryonic stem cells in animals as the functional insulin delivery capacity develops over time. These studies showed that the encapsulation device fully contains the grafts: no hESC-derived cells were found outside of the implanted encapsulation device. This supports the premise that the device can be used to safely administer a population of cells derived from hESC.