Targeting Regulatory T cells for Factor VIII Tolerance

Stanford University, Stanford CA

Investigators

Abstract

PROJECT SUMMARY Children and adults with the inherited bleeding disorder hemophilia A are reliant on infusions of coagulation protein factor VIII (FVIII) to treat bleeding episodes. The most significant complication of FVIII replacement therapy is the formation of neutralizing antibodies called inhibitors against the infused FVIII protein. Inhibitors increases the risk of bleeding episodes that are difficult to control, which ultimately affects quality of life. However, the advent of novel non-factor therapies used to prevent bleeding has dramatically changed the treatment paradigm for persons with hemophilia A (PwHA) and inhibitors. Despite the tremendous advancements in treatment options for PwHA, none of the current therapies prevent the development of inhibitors. Moreover, PwHA and inhibitors are still dependent on bypassing agents with reduced hemostatic efficacy than FVIII for bleeding and surgical management. Although there have been extensive studies into understanding the adaptive immune response to FVIII, the mechanism(s) that drive inhibitor formation are still poorly understood. It is known that CD4+ T cells are responsible for activating B cells and plasma cells that produce FVIII antibodies. It is also established that regulatory T cells (Tregs) are an important element of central and peripheral tolerance to antigens, including FVIII tolerance achieved with successful immune tolerance induction therapy. It is postulated that FVIII inhibitor formation results from an imbalance or failure in Treg-mediated immune regulatory processes. Whether Tregs are reduced, dysfunction, or incapable of expanding in FVIII adaptive immunity warrants further investigation. The long-term goal of this work is to illuminate key mechanisms of FVIII immune responses to develop targeted and low burden therapies for inhibitor prevention during early FVIII exposure. We hypothesize that FVIII inhibitor development is associated with reduced and dysfunctional Tregs, which is prevented with Treg expansion in vivo. To test our hypothesis, we will use a combination of mouse and human model systems to understand the Treg profile in FVIII deficiency and inhibitor development. In Aim 1, we will perform rigorous Treg phenotyping in mouse models of hemophilia A with different in inhibitor responses and Tregs isolated from pediatric and adult PwHA based on inhibitor status. We will additionally generate a human-derived spleen organoid model to study the effect of FVIII on Treg responses at the primary site of FVIII interface with immune cells. In Aim 2, we will determine the effect of engaging the erythropoietin (EPO) receptor with recombinant EPO, a known Treg inducer in models of autoimmunity and solid-organ transplantation, on inhibitor responses in naive hemophilia A mice. In Aim 3, we will evaluate EPO-mediated Treg expansion capacity based on age using isolated Tregs from children with chronic kidney disease initiating EPO therapy and EPO-stimulated Tregs in vitro from PwHA naïve T cells and in the spleen organoid model. This proposal represents a new direction as an early-stage investigator that will identify mechanisms of the failed immunoregulatory responses with early FVIII exposure and investigate an innovative and alternative approach to Treg expansion for inhibitor prevention.