Objective
The objective of our study is to provide a proof-of-concept (using an in vivo mouse model of T1D) that hematopoietic stem cells modified to express beta cell antigens directed at both CD4+ and CD8+ T cells can serve as an inexhaustible source of immune cells capable to engaging and tolerizing pathogenic T cells in T1D. This project will build on older studies and aims to demonstrate better efficacy with reduced or absent conditioning for stem cell engraftment (powerful conditioning regimens would be highly undesirable for T1D patients). With our unique platform to express antigens, we aim to demonstrate that the promotion of regulatory CD4+ T cells contributes to better efficacy. Finally, we aim to show that protection from disease will be permanent for the great majority of treated animals.
Background Rationale
Although much progress has been made in better controlling the delivery of exogenous insulin in Type 1 diabetes (T1D) patients (e.g., with the help of pumps), the process of daily insulin administration is tedious, particularly with children, and glycemic control is not optimal, with long-term complications still occurring. Thus, maintaining or rescuing endogenous insulin production is crucial, whether it is from residual islets or transplanted islets. Even with the prospect of one day generating insulin-producing beta-cells from the patient’s own stem cells that are not subject to rejection on the basis of mismatched tissue markers, there will always be a need to restrain the immune system that continuously seeks to eliminate these insulin-producing cells. Current immune modifying therapies do not discriminate between pathogenic T cells and other T cells; and as a result, their implementation is fraught with increased susceptibility to infections and malignancies. Pathogenic T cells may be engaged specifically using their own specific antigens and be reprogramed when engaged under the right conditions, which include lack of inflammation and sustained antigen presentation as critical determinants. Beta cell antigens are recognized by specific T cells only in the pancreas-draining lymph nodes, which are inflamed in T1D, leading to their stimulation as pathogenic T cells. In contrast, our immune system is tolerant to ubiquitous antigens that are exposed all over the body. The goal of antigen-specific therapy is to overwhelmingly engage these T cells in non-inflamed sites (other lymph nodes, spleen, liver). Current approaches, still at the preclinical and early clinical stages, rely on continuous administration of antigens in order for these T cells to become tolerant and ignore the beta cells, and this may also become a tedious process in the long run. One way to maintain a continuous, uninterrupted and omnipresent display of disease-related antigens is to express them in the stem cells that give rise to immune cells. These stem cells self-renew and can produce a large number antigen-expressing immune cells for the rest of the patient’s life. The largely non-inflammatory context of persistent engagement of pathogenic T cells should result in their removal or inactivation. The rationale and feasibility of the proposed approach is supported by past studies, which were nonetheless hampered by technical limitations that can now be overcome thanks to major advances in field (e.g., use of modified stem cells for the treatment of sickle cell disease) and in our lab (e.g., use of antigen-encoding constructs optimized for CD4+ T cell engagement).
Description of Project
Although much progress has been made in better controlling the delivery of exogenous insulin in Type 1 diabetes (T1D) patients (e.g., with the help of pumps), the process of daily insulin administration is tedious, particularly with children, and glycemic control is not optimal, such that complications continue to develop in the long term. Thus, maintaining or rescuing endogenous insulin production is crucial, whether it is from residual islets or transplanted islets. Even with the prospect of one day generating insulin-producing beta-cells from the patient’s own stem cells that are not subject to rejection on the basis of mismatched tissue markers, there will always be a need to restrain the immune system that continuously seeks to eliminate these insulin-producing cells. Current immune modifying therapies do not discriminate between pathogenic T cells and other T cells; and as a result, their implementation is fraught with increased susceptibility to infections and malignancies. Pathogenic T cells may be engaged using their own specific antigens and be reprogramed when engaged under the right conditions, which include lack of inflammation and sustained antigen presentation as critical determinants. Beta cell antigens are recognized by specific T cells only in the pancreas-draining lymph nodes, which are inflamed in T1D, leading to their stimulation as pathogenic T cells. In contrast, our immune system is tolerant to ubiquitous antigens that are exposed all over the body. The goal of antigen-specific therapy is to overwhelmingly engage these T cells in non-inflamed sites (other lymph nodes, spleen, liver). Current approaches, still at the preclinical and early clinical stages, rely on continuous administration of antigens in order for these T cells to become tolerant and ignore the beta cells, and this may also become a tedious process in the long run.
Another way to ensure the omnipresence and persistence of these autoantigens is to express them in a tiny fraction of the early precursors of the immune cells, the hematopoietic stem cells, which give rise to a large number and variety of antigen-presenting cells. Previous studies in mice naturally developing T1D have shown that this approach can be highly effective at permanently blunting the response of pathogenic T cells. However, several hurdles made this approach difficult at the time, including the need of viral vectors to introduce the antigen-encoding constructs into the stem cells, the fact that expressed antigens were primarily presented to CD8+ T cells with no or little effect on CD4+ T cells, and the treatments needed for the modified stem cells to engraft long-term. We now have the ability to surmount these challenges as proposed in this project that will include proof-of-concept experiments in the mouse model. Our goal is to show the successful long-term engraftment of modified (antigen-expressing) stem cells, the persistence engagement and neutralization of autoreactive T cells and the permanent protection of residual beta cells, following a single intervention.
Anticipated Outcome
Once the patient’s own stem cells have been safely modified to introduce our unique construct and re-infused, we anticipate that these stem cells will give rise to a large number of antigen-expressing and presenting immune cells capable of engaging diabetogenic T cells throughout the body, eliminating or neutralizing them before they can harm beta cells. Importantly, with our unique construct, not only CD8+ but also CD4+ cells among diabetogenic T cells will be engaged, which is expected to also result in the induction of a subset of regulatory cells capable of suppressing other diabetogenic T cells. The proposed approach follows the most fundamental principles of successful tolerance establishment with omnipresent and persistent antigen exposure, overwhelmingly under non-inflammatory conditions. We expect to demonstrate efficacy in a mouse model of T1D, with 0.1-1% of immune cells originating from the successfully engrafted modified stem cells, whereby efficacy will be measured based on protection from diabetes and the ability to generate stable regulatory T cells.
Relevance to T1D
Although much progress has been made in better controlling the delivery of exogenous insulin in Type 1 diabetes (T1D) patients (e.g., with the help of pumps), the process of daily insulin administration is tedious, particularly with children, and glycemic control is not optimal, such that complications continue to develop in the long term. Thus, maintaining or rescuing endogenous insulin production is crucial, whether it is from residual islets or transplanted islets. Even with the prospect of one day generating insulin-producing beta-cells from the patient’s own stem cells that are not subject to rejection on the basis of mismatched tissue markers, there will always be a need to restrain the immune system that continuously seeks to eliminate these insulin-producing cells. Current immune modifying therapies do not discriminate between pathogenic T cells and other T cells; and as a result, their implementation is fraught with increased susceptibility to infections and malignancies. This project aims to provide proof-of-concept that this approach is viable, ultimately leading to an autologous cell therapy that is safe (no/minimal conditioning) and could lead to a potentially complete and permanent control of autoreactive T cells in T1D patients. Unlike other cell therapies considered for T1D, the cells used in this case self-renew, such that only one treatment should be required for permanent protection.