Augmenting Regulatory T Cell Reconstitution during GVHD

About This Grant

Graft versus host disease (GVHD) is the major complication associated with allogeneic hematopoietic stem cell transplantation (HSCT). A critical element of the pathophysiology of GVHD is the failure to reconstitute the regulatory T cell compartment which has been shown to be important for the mitigation of GVHD severity. Re- establishment of an effective regulatory network to counterbalance the pro inflammatory milieu by enhancing regulatory T cell (Treg) survival and suppressive capability therefore remains a major challenge in the field. In preliminary studies, we have demonstrated that the interleukin 27 (IL-27)/IL-27 receptor (IL-27R) signaling pathway plays a critical role in the regulation of CD4+ Treg survival and suppressive capability, and that blockade of IL-27 or the IL-27R results in significantly reduced GVHD lethality, increased CD4+ Treg reconstitution, stabilization of Foxp3 expression, and an increase in CD4+ Treg mitochondrial fitness. In addition, our studies have uncovered a previously unappreciated role for the lysosomal glycoprotein, gamma interferon lysosomal thiol reductase (GILT), by revealing that the regulation of IL-27/IL-27R signaling in CD4+ Tregs is mediated by downstream expression of this glycoprotein. Based on these studies, the overall goal of this proposal is to delineate mechanistic pathways by which absence of IL-27R signaling in CD4+ Tregs promotes their survival, enhances their suppressive capability, and alters the alloreactive donor T cell repertoire. Our overall hypothesis is that signaling through the IL-27R regulates CD4+ Treg survival and that blockade of this pathway augments Treg reconstitution and enhances metabolic fitness. Studies in Specific Aim 1 will delineate mechanistic pathways by which blockade of IL-27R signaling in CD4+ Tregs enhances their ability to prevent GVHD-induced lethality. To address this question, we will employ genetically modified murine models to examine the functional relevance of the mTor and autophagy pathways in mediating the suppressive effects of CD4+ IL-27R/ Tregs as well as determine the effect of IL-27R signaling blockade on mitochondrial metabolism. Experiments in Specific Aim 2 will define the role of GILT in the regulation of CD4+ Treg survival and functional suppressive capability and determine the extent to which absence of GILT phenocopies what is observed with CD4+ IL-27R/ Tregs. We will also delineate the effect of lysosomal expression of GILT on mitochondrial function and oxidative phosphorylation in CD4+ Tregs. Studies in Specific Aim 3 will characterize how absence of IL-27R signaling in CD4+ Tregs alters the alloreactive and regulatory T cell repertoires during GVHD. To address this question, we will employ newly developed bioinformatic pipelines that utilize both single cell paired alpha/beta T cell receptor RNA sequencing and single cell RNA transcriptomics to provide integrated clonal definition and transcriptional profiles for donor T cells residing in GVHD tissue sites. The overall objective of these studies is to develop new insights into the pathophysiology and regulation of GVHD that will foster the development of clinically relevant strategies to mitigate this complication in allogeneic HSCT recipients.