Objective
The recent FDA approval of the T cell-targeting drug, teplizumab (marketed as TZIELD) highlights the potential for drugs that modify immune system function (immunotherapies) in preventing or treating type 1 diabetes (T1D). Unfortunately, teplizumab-mediated protection against diabetes is transient. Our overarching goal is to complete the fundamental research necessary to continue expanding the arsenal of drugs available to provide a durable T1D cure.
Islet autoantibodies are among the most powerful biomarkers for predicting T1D risk and are thought to arise when T and B lymphocytes “talk” to each other in special immune structures called germinal centers. B lymphocytes instruct CD4+ T lymphocytes to encourage CD8+ T lymphocytes to kill islet beta cells. Our data from mouse models of T1D show that the key germinal center protein, BCL6, supports this destructive communication, with genetic deletion of BCL6 in T cells providing complete protection against diabetes development. We will test two different classes of available small molecule inhibitors of BCL6: 1) FX1-nanobody conjugates, to inhibit BCL6 function in B lymphocytes, but not T lymphocytes, and 2) ARV-393, which degrades BCL6 in both B and T lymphocytes. Our specific objectives are therefore:
1) Engineer nanobody-FX1 drug conjugates that selectively target BCL6 in B lymphocytes and test the effect of this drug on B lymphocyte activation and pro-inflammatory T cell responses in T1D-prone mice.
2) Identify the impact of ARV-393-mediated BCL6 inhibition on autoimmune germinal center formation, pathologic T and B lymphocyte activity, and diabetes development in T1D-prone mice.
Background Rationale
Type 1 diabetes (T1D) occurs when the immune system mistakenly launches an attack against beta cells in pancreatic islets. The origins of this misguided autoimmune assault against self-tissues are still not entirely clear. We know that T and B lymphocytes are two types of immune cells that cooperate with each other to cause destruction of pancreatic beta cells. One outcome of this nefarious T and B lymphocyte cooperation is that islet autoantibodies are produced, which are among the best predictive biomarkers of T1D. Blocking communication between these self-reactive T and B lymphocytes without disrupting protective immune responses is thus a major therapeutic goal. Studying these autoimmune interactions in humans is complicated by the inaccessibility of the pancreas in living individuals. Mouse models of T1D circumvent this challenge by allowing access to pancreas tissue at various stages of the pre-diabetes interval (i.e., when autoimmune T/B cell interactions are active, but before diabetes onset). Preclinical studies in mice allow us to vet ideas to ensure only the most promising candidates move on to human clinical trials. To illustrate the importance of mouse models in advancing T1D research, proof-of-concept studies in T1D mouse models were an essential step in reaching FDA approval of teplizumab (marketed as TZIELD). This proposal will harness the power of mouse models to advance our understanding of immune pathways we can disrupt to block T1D.
Protective immune responses can evolve following infection or vaccination to be better, faster, and stronger by continuing to “train and retain” the very best T and B lymphocytes. This “elite immune system training” happens in specialized immune structures called germinal centers. Protective germinal centers help you fight infection, but autoreactive germinal centers can be dangerous. Our published data show that germinal centers help to unleash islet-reactive T and B lymphocytes to promote beta cell attack in T1D. Specifically, we found that blocking BCL6 function in T cells led to complete protection against diabetes in a T1D mouse model. Importantly, blocking BCL6 does not completely block protective immune responses; protective antibodies can still form, enabling pathogen clearance. Teplizumab is a recently FDA-approved drug that delays T1D onset for an average of two years by broadly disrupting T cell function. T1D prevention via teplizumab is unfortunately not durable, in part because it is given as a single course to limit chronic immunosuppression. Whereas teplizumab targets the majority of T cells, targeting BCL6 will only disrupt the function of a small proportion of T and B lymphocytes, and should thus be less immunosuppressive. T1D onset can range from infancy to adulthood, likely driven at least in part by differences in the underlying autoimmune response that causes disease. Increasing the arsenal of different immunotherapies available to treat T1D could allow for greater personalization of therapy in the future.
We will develop a new therapy to enhance the selectivity of which immune cells are targeted by a drug (using B lymphocyte-targeting nanobodies) and to direct BCL6 inhibitors to specific cell targets. We will separately test a second small molecule inhibitor of BCL6 (with a different mechanism of action). These studies will increase our mechanistic understanding of how T1D autoimmunity develops and build preclinical rationale for BCL6 as a new therapeutic target in T1D.
Description of Project
Our immune systems are designed to protect us against germs such as viruses and bacteria. T and B lymphocytes are specialized immune cells that target specific germs to keep us healthy. Unfortunately, in autoimmune diseases like type 1 diabetes (T1D), T and B lymphocytes inappropriately direct their attack at self-tissues such as pancreatic beta cells. This immune cell attack on beta cells in islets can occur for years or even decades before symptoms are noticed, and T1D is diagnosed in the clinic. The good news is this long pre-symptomatic period provides an opportunity to therapeutically intervene before diabetes develops. For example, teplizumab (marketed as TZIELD) is a recently FDA-approved drug which suppresses T lymphocytes to delay diabetes onset in at-risk individuals. This diabetes protection is unfortunately only transient and works by causing immune suppression against both self (good) and germs (bad). Such broad immune suppression is particularly problematic in children, as they have not yet had the opportunity to form immune memory against the common germs they are likely to encounter throughout life. We are therefore focused on identifying immunotherapies that adequately control the dangerous, islet-reactive lymphocytes that are less disruptive to host protective immune responses against germs and cancer.
Certain types of immune responses come from germinal center reactions, specialized immune structures in which specialized immune cells, T and B lymphocytes, interact to help each other strengthen their attack against an invading germ. We find that genetically deleting the key germinal center protein, BCL6, in T cells completely protects against diabetes in a mouse model of T1D. To support future translation of this finding to people, this proposal will perform key preclinical studies to develop and test different pharmacologic strategies of BCL6 inhibition for their impact on preventing T1D. Importantly, primary immune responses are retained even when BCL6 function is blocked, which means this drug will likely be less immunosuppressive than drugs like teplizumab. As a separate approach, we will develop nanobody-drug conjugates that offer the advantage of linking a BCL6 inhibitor to a nanobody (a tiny version of an antibody) which will direct the inhibitor to a specific immune cell type (to enhance therapy selectivity) and enhance tissue penetration to block pathologic B cell function at the site of autoimmune attack. Preserving protective immune responses is especially important in children, as their immune system is still growing, just like they are, and thus has less complete coverage against the typical germs they might encounter compared to an adult.
Overall, this research will teach us about how the immune response against beta cells develops and will generate foundational knowledge necessary to support future clinical translation of new therapies directed against BCL6.
Anticipated Outcome
We were the first to show T cell expression of BCL6 is essential for type 1 diabetes (T1D) to develop in T1D-prone mice. To support future clinical translation of these findings, these studies will capitalize on unique resources and team strengths including 1) new nanobody-drug conjugate technology and 2) over twenty years of research experience dedicated to enhancing our understanding how autoreactive B and T lymphocytes interact to drive T1D. The proposed experiments will enable the following outcomes:
Aim 1 experiments will take advantage of new nanobody-drug conjugate technology developed by our team to selectively cause BCL6 blockade in B lymphocytes. We will monitor pro-pathogenic changes in islet-reactive B and T lymphocytes in response to treatment with this emerging class of drug.
Aim 2 experiments will evaluate the ability of the small molecule BCL6 inhibitor, ARV-393, to disrupt pro-pathogenic B and T lymphocyte interactions and block diabetes development in a classic T1D mouse model. These studies will determine whether ARV-393 can prevent early, pathogenic immune changes and downstream development of diabetes.
Overall, these studies will examine how BCL6 inhibition in B cells (Aim 1) and B cells and T cells (Aim 2) control islet autoimmunity in T1D-prone mice. This will increase our understanding of how T1D develops, with potential impact on future biomarker discovery/validation campaigns in human T1D to predict risk of T1D progression and track individual response to immunotherapy. Clinicians could use this information to tailor and more rapidly adapt T1D treatments if and when they are not working as desired for a given individual.
The nanobody-drug conjugate platform we will develop in Aim 1 is a “plug and play” modular system that can be easily modified to target different immune cell types and tissues (via the nanobody domain) and target different proteins (by changing the drug payload) which could be harnessed in many different ways to develop new immunotherapies for T1D.
Relevance to T1D
Clinical type 1 diabetes (T1D) develops as a result of immune system attack on pancreatic beta cells in islets. This immune attack is orchestrated by T and B lymphocytes which are specialized immune cells that go rogue and attack self-tissues, instead of germs and cancer cells, as intended. Within general T and B lymphocytes, there are “elite” subsets that are intimately associated with generating protective immune responses. These “elite” B and T cell subsets depend on BCL6 for their transition into “lean, mean, fighting machines”. Our published studies using mouse models of T1D identify an essential role for BCL6 in driving islet autoimmunity and diabetes. The proposed experiments will evaluate two distinct classes of BCL6 inhibitors to provide preclinical rationale for this new type of immunotherapy in T1D.
The recent approval of teplizumab (which impacts T cells broadly) highlights the power that immunotherapy holds for T1D prevention and treatment. Translation of new, more selective drugs like BCL6 inhibitors to the clinic hold potential to prolong the transient protection conferred by teplizumab or might serve as a less immunosuppressive alternative therapy. Dr. Bonami (PI) is a Type 1 Diabetes TrialNet Investigator at Vanderbilt and leads A) mechanistic studies using mouse models and B) translational studies in people at risk for T1D. Dr. John Wilson (Co-PI) is a bioengineer at Vanderbilt with expertise in nanobody-drug conjugate design, which he has successfully applied to cancer models, and who also has experience with T1D research. This cross-disciplinary experience positions our team perfectly for the “bench to bedside” research required to most rapidly translate this and other promising new immunotherapies to the clinic.
Translation of Bcl6 inhibitors to the clinic could help:
People at risk for T1D. BCL6 inhibitors could delay or prevent diabetes onset in people at risk for T1D by stopping beta cell attack in its tracks.
People with established T1D. Insulin production could be normalized through successful beta cell transplant or regeneration in people with long-standing T1D. The autoimmune response that destroyed beta cells initially would likely also attack and destroy nascent beta cells if they are not protected from further attack. BCL6 inhibitors could provide this protection against continued autoimmunity to provide durable protection against T1D.