Identifying metabolic targets to reinvigorate T cell exhaustion

Johns Hopkins University, Baltimore MD

Investigators

Abstract

PROJECT SUMMARY CD8+ T cells are a critical component of the adaptive immune system and play an essential role in immune defense against viruses, bacteria, and tumors. To achieve such a critical function in many different contexts, CD8+ T cells have evolved to be highly adaptive by modulating cellular metabolism. Activated effector T cells require high metabolic flux through anabolic growth-promoting pathways, while quiescent or more resting states engage catabolic processes for ATP generation. After prolonged antigen exposure, CD8+ T cells can become dysfunctional as they enter a distinct differentiation state known as T-cell exhaustion. This dysfunctional state of T cells is characterized by stable expression of inhibitory surface receptors, poor response to tumor antigens, and low cell proliferation and persistence of T cells in vivo, dampening immunity and causing poor responsiveness to immune checkpoint inhibitors. Growing evidence indicates that exhausted T cells are ‘metabolically insufficient’ with altered signaling cascades and transcriptional and epigenetic landscapes. Metabolites are not simply byproducts of the differentiation of T cells, but metabolism itself may dictate T cell exhaustion. Hence, modulating metabolism might reprogram or rewire certain states of T cell differentiation. However, how metabolic rewiring drives and defines the differentiation of T cell exhaustion remains unclear. We applied an untargeted liquid chromatography-mass spectrometry-based metabolomics approach and found exhausted T cells display a distinct metabolic profile compared to functional effector T cells. We thus hypothesize that chronic TCR stimulation imposes unique constraints on T cell metabolism that can be targeted to reinvigorate exhausted T cells by overexpressing metabolic genes. Encouraged by a striking metabolic difference between exhausted T cells and effector T cells, we will use unbiased genetic and systems approaches to understand the functional relevance of metabolic pathways in CD8+ T cell immunity. Several loss-of-function (LOF) screen studies have recently identified that remodeling metabolism is intrinsically linked to cellular development, activation, function, differentiation, and survival in T- cell biology. However, the comprehensive discovery of regulators requires both gain-of-function (GOF) and LOF approaches. In Aim 1, we performed a functional genomic screen in vitro using a metabolism-focused CRISPR activation library to identify potential gain-of-function metabolic targets that limit T cell persistence. In Aim 2, we will determine the molecular mechanism by which the newly revealed GOF candidates reinvigorate T cell exhaustion. The interactive analysis of the collected data will allow us to define the molecular mechanisms by which metabolic pathways regulate T cell exhaustion. Collectively, we hope that our work will provide insight into how to therapeutically modulate metabolism to restore exhausted T cells.