Extramedullary infiltration of leukemic cells to the meninges (CNS disease/relapse) is a poor prognostic factor for patients with T-cell acute lymphoblastic leukemia (T-ALL). To date, few studies have investigated the roles of chemokine receptors and other mediators of signal transduction in driving T-ALL influx to the meninges. The CXCR3-CXCL10 signaling axis plays a critical role in regulating the entry of specific leukocyte subsets into inflamed meninges. However, its role in regulating leukemic cell migration and trafficking to the meninges remains poorly understood. The focus of this proposal is on a unique mechanism by which leukemic cells hijack an inflammatory pathway to pave the way to the meninges/CNS. We discovered upregulation of CXCR3 chemokine receptor levels in a subset of high-risk T-ALL with CNS disease. Our preliminary findings provide strong evidence that CXCR3 potentiates T-ALL cell migration and meningeal infiltration. We have compelling evidence that, in the meningeal microenvironment, T-ALL cells migrate to the meningeal pericytes, which induce CXCL10 in response to leukemia-derived cytokines. The goal of this study is to address how the CXCR3-CXCL10 axis mediates T-ALL trafficking to the meninges. We hypothesize that T-ALL exploits the inflammatory CXCR3-CXCL10 pathway to facilitate meningeal infiltration. Our rationale is that leukemic cells may adopt pro-inflammatory signaling governing normal T-cell influx during meningitis and neuroinflammation to trigger meningeal colonization. Using ΔE Notch1-induced T-ALL mouse model and a panel of well- characterized T-ALL patient derived xenografts we propose to study how the CXCR3-CXCL10 signaling axis regulates T-ALL cell migration and influx into the meninges. In addition, we will seek to establish a proof of principle for the therapeutic potential of targeting this signaling pathway for the treatment of CNS-involved T- ALL. Furthermore, we propose to use microfluidic 3D cell culture systems to model T-ALL cell migration in the meningeal niche. In Aim 1, we will determine the roles of CXCR3 in T-ALL trafficking to the meninges and will conduct mechanistic studies unraveling the roles of USP7/TAL1 in regulating CXCR3 expression in migrating T-ALL cells. In Aim 2, we will investigate how leukemic cells induce a pro-inflammatory phenotype in meningeal pericytes and how pericyte-derived CXCL10 confers T-ALL tropism to the meninges. Our goal will be to demonstrate that disseminated leukemic cells induce pro-inflammatory chemokine CXCL10 in the meningeal microenvironment, forming a supportive niche for leukemic cell influx and colonization. The identification of the mechanism by which leukemic cells infiltrate the meninges will lead to the development of novel therapies.