Objective
The main objective of this study is to demonstrate the proof of concept in established murine models of T1D for a novel sub 100 micron diameter (less than one tenth of a millimeter) biocompatible microbead that releases protease resistant CXCL12 (prCXCL12) to enable long term function of a co-transplanted alloislet graft without systemic immune suppression. Secondary aims include exploration of the co-transplantation of releasing the immunomodulatory protein called CD47 with microbeads releasing prCXCL12 in this context and confirmation of the way in which our new therapeutic approach to T1D works in our mouse models.
Background Rationale
Transplant of islets from other people or islet-like cells derived from stem cells, can reverse the effects of type 1 diabetes. However, these implants need to be protected from attack by the recipient’s immune attack. This is currently done using drugs that systemically suppress immune response. This protects islet implants but the drugs must be taken for the rest of the recipient’s life. This approach is expensive and is not good for the recipient’s long-term health given the increased risk of cancer and infections. Investigators are currently exploring whether using stem cells that have been genetically-modified to evade immune system rejection may be a solution to this problem, but this is also a complex and expensive solution and may not be appropriate or accessible for the majority of people living with type 1 diabetes.
Over the last two years we have been exploring with collaborators whether co-implantation of tiny beads coated with specific human proteins that modify the immune response along with the islet transplant can ward off immune attack locally around the islets long-term, enabling the islets to cure diabetes without needing additional systemic immune suppression. Our prior study showed that a combination of two different proteins—a degradation-resistant protein called prCXCL12 and another human protein called Fas ligand—can accomplish this goal in a mouse model to T1D. However, we also discovered that microbeads (larger than a tenth of a millimeter in diameter) coated with prCXCL12 by itself greatly extended the functional life of implanted islets alone even if it did not enable long-term (6 month) islet survival and function. Because our laboratory has shown in the past that CXCL12 by itself can protect islets from immune attack over the long-term when there is enough of the protein in the local area around islets, we believe that the use of prCXCL12 by itself did not work in these first experiments because the microbead size was too large to provide a sufficient density of prCXCL12 in and around the islets. We are therefore now proposing to test the effect of using novel smaller beads (below a tenth of a millimeter in diameter) capable of carrying and releasing much more prCXCL12 in established murine models of T1D without the concurrent use of systemic immune suppression.
Description of Project
Transplantation of islets obtained from other people, or transplant of islet-like cells derived from stem cells, has been repeatedly shown to reverse the effects of type 1 diabetes. However, these donor islet implants need to be protected from attack by the recipient’s immune system. This is currently done using drugs that suppress the body’s immune response. This approach protects islet implants from the recipient’s immune system, but the immune suppressive medications must be taken for the rest of the recipient’s life. This is an expensive and complex approach and is not good for recipient’s long-term health because the immune suppressive agents put the treated individual at significantly increased risk for cancer and infectious diseases.
We plan to develop a new method and technology that could enable islet transplantation without systemic immune suppression. We plan to transplant insulin producing islets along with novel tiny biocompatible beads called microbeads that are engineered to release a human protein called CXCL12 which we have made resistant to breakdown in the body, termed protease- resistant CXCL12 or prCXCL12. We have previously demonstrated both in mouse and non human primate models of T1D that the naturally occurring CXCL12 protein can protect islet transplants from immune attack without the need for systemic immune suppression when the islets are completely embedded in a naturally occurring gel containing CXCL12. However, this approach is complex and the coating of islets with the gel can impair the function of the insulin-producing cells. We therefore propose that if we combine and surround the islet graft with very small microgels (less than a 10th of a millimeter in diameter) that are engineered to release prCXCL12 this will allow the islets to function normally and resist immune attack for the long term and without systemic immune suppression. In a previous study, the original microbeads we used were much larger, (greater than one tenth of a millimeter), but still showed promise when they were engineered to release prCXCL12 in combination with microbeads releasing a second immune suppressive human protein, called Fas ligand. Our proposed study will focus on a further simplification of this approach to be more relevant to the clinical situation by testing whether prCXCL12 alone in microgels is sufficient to provide a protective local immune environment that allows the islets to produce enough insulin to eliminate diabetes over a long period of time without any systemic immune suppression. To this end, we will test this new material and method in two widely accepted mouse models of T1D and also confirm how are new technology is working. Furthermore, if this proposed study is successful we would test this approach next in diabetic non human primates to check that it is a safe approach and is therapeutic. Our proposed project involves an active collaboration between experienced and expert islet transplant immunologists at Massachusetts General Hospital and leading microgel bioengineers at Brigham and Women’s Hospital and MIT. All necessary expertise, materials and experimental animal models along with a highly experienced project manager are currently available to complete this proposed project to time and cost in 2 years. Our inventions here are covered by intellectual property which also makes it significantly more likely that our technology could ultimately be developed as a commercial clinically applicable product for individuals with T1D.
Anticipated Outcome
We anticipate that when the right size and composition of the microbeads (less than a tenth of a millimeter in diameter) are identified, implanting these beads coated with degradation-resistant CXCL12 along with islets into a mouse with diabetes will create a zone of immune protection around the islets that lets them function long-term (greater than 6 months), producing insulin that cures the diabetic condition of the mice, without the need for any systemic immune suppression. We will potentially also see that the effect of the degradation resistant CXCL12 can be augmented by incorporation of a second immune protective molecule into the microbeads, namely CD47, to prevent immune cells from killing insulin producing cells. We expect to demonstrate that the mechanism of action of the degradation resistant CXCL12 involves both the reduction of entry of immune cells that can kill beta cells into the graft and the increase of immune cells that suppress the immune response to beta cells in the graft itself. We also expect to demonstrate that our novel approach results in local immune protection of the islet graft and not overall suppression of the animal’s immune system.
Relevance to T1D
Replacement of islets lost to immune attack in individuals with type 1 diabetes has shown promise in reversing diabetes in the long-term but currently requires concurrent lifelong, systemic immune suppression. This approach is complex and expensive and presents long-term risks to the patient’s health including increased susceptibility to cancer and infectious diseases. Currently proposed solutions to eliminating the need for such immune suppression involve taking stem cells, transforming them into islet-like cells, and genetically modifying these cells to evade the immune system. While these approaches may have promise for eliminating the need for immune suppression, they are also complex and expensive and not likely appropriate or accessible for most people living with type 1 diabetes.
If successful, our proposed simpler approach, which involves including a mixture of tiny biocompatible beads coated with a degradation-resistant form of the immune protective naturally occurring protein CXCL12 along with the islets, would enable transplantation of islets without systemic immune suppression and could expand the use of islet transplant safely and effectively to the majority of people living with type 1 diabetes. This approach would be far less complex and expensive than genetic modification of islets or beta cells and could be used with any kind of islet source. It therefore has potential to make islet transplantation available to a much wider group of people with type 1 diabetes without the need for immune suppression.
The important caveat here is that the work we propose to do is purely experimental and involves proving our novel concept and technology in mouse models of T1D that resemble but are not identical to the human disease. Consequently, if our proposed study is successful, our next step would be to apply our novel microbead technology to islet transplantation in nonhuman primates with T1D, which we are well equipped to do in the future. We would have to demonstrate both safety and efficacy of our approach in these large animals with T1D, which more closely resemble humans than do mice, before considering and being permitted to test the safety and then efficacy of our novel microbeads that release the degradation resistant and immune protective CXCL12 in the context of islet transplantation in human individuals with T1D.