CXCR3/CXCL10 Signaling Pathway Drives T-ALL into the CNS/Meningeal Microenvironment
Authors: Sharma Nitesh D. , Keewan Esra'a , Ornatowski Wojciech , Nysus Monique , Paul Silpita , Jacquez Quiteria , Myers Bianca L. , Kang Huining , Zychowski Katherine E. , Winter Stuart S , Hunger Stephen P. , Loh Mignon L. , Castillo Eliseo , Vue Tou , Jones Nicholas , Ntziachristos Panagiotis , Matlawska-Wasowska Ksenia 
Published: December 2023

Cure rates for T-cell acute lymphoblastic leukemia (T-ALL) have improved significantly, but central nervous system (CNS) involvement leads to a poor prognosis. Understanding the mechanisms underlying CNS involvement could lead to more effective therapies. The CXCR3/CXCL10 signaling pathway mediates T cell movement across the blood-CSF barrier during neuroinflammation, but its role in T-ALL colonization of the CNS/meninges remains unclear. In our study, we hypothesized that T-ALL cells exploit normal T-cell function to infiltrate the meninges. We examined CXCR3 expression in thymic CD4+CD8+ double positive (DP) cells of ∆E-NOTCH1 T-ALL and control mice. Levels of CXCR3 were higher in CD4 +CD8 + DP cells of T-ALL mice compared to controls. Furthermore, leukemic cells in the meninges, bone marrow (BM), and thymus had higher CXCR3 levels compared to other organs ( p &lt; 0.01), suggesting an organ-specific CXCR3 expression in infiltrating T-ALL cells. Additionally, primary T-ALL samples (n = 24) had elevated CXCR3 mRNA levels compared to normal thymocytes. Using CRISPR-Cas9, we deleted CXCR3 in the KOPTK1 and PER117 cell lines and in two primary patient samples. CXCR3 deletion resulted in decreased proliferation, delayed cell cycle progression in S/G2/M phases but did not affect apoptotic cell death. CXCR3 inactivation led to decreased activation of AKT, ERK1/2, JNK, and reduced the expression of cell motility regulators. Notably, T-ALL cells migrated more efficiently to CXCL10 than to CXCL9 and CXCL11, which was reduced upon CXCR3 silencing ( p &lt; 0.01). Mechanistically, we demonstrated that USP7, a ubiquitin-specific protease, regulates and stabilizes the CXCR3 protein via deubiquitination. To explore the role of CXCR3 in T-ALL in vivo, we transplanted CXCR3 KO and control KOPTK1 cells into NSG mice (8 mice/group). Mice with CXCR3 KO had increased survival and significantly lower leukemia burden in the BM and extramedullary tissues compared to the control group ( p &lt; 0.01). We next analyzed the levels of CXCR3 ligands, CXCL9, CXCL10, and CXCL11, in the blood serum and CSF of ∆E-NOTCH1 and control mice (5 mice/group). T-ALL mice had elevated CXCL10 levels in both blood serum and CSF, with higher levels in the CSF, suggesting compartmentalization of the immune response between the CSF and blood ( p &lt; 0.01). CXCL9 and CXCL11 expression were minimal or undetectable. Remarkably, upon injecting ∆E-NOTCH1-transformed hematopoietic progenitors into CXCL10 knockout ( CXCL10 KO) and control B6 mice (5 mice/group), tissue analysis revealed a significant decrease in T-ALL meningeal infiltration in the CXCL10 KO mice, but not in other organs ( p &lt; 0.01). Conversely, control mice exhibited high levels of leukemic cells in all tested organs. We found that meningeal stromal cells (PDGFR+, CD13+, CD31-, CD45-) expressed CXCL10 in ∆E-NOTCH1 mice, unlike hematopoietic (CD45+) and endothelial cells (CD31+, CD45-), compared to control mice. We further observed upregulation of CXCL10 in human meningeal stromal cells co-cultured with KOPTK1, PER117, and primary samples. Treatment with a CXCR3 antagonist or knockout of CXCR3 reduced leukemic cell migration to the meningeal stromal cells compared to controls ( p &lt; 0.01). Conversely, migration of T-ALL cells to the tested stromal cells was reduced upon treatment with a CXCL10 neutralizing antibody or by CXCL10 deletion in stromal cells. Additionally, we identified that the CXCR3/CXCL10 signaling pathway regulated the expression of VLA-4 and VCAM-1, promoting T-ALL cell adhesion to the meningeal stroma. Genetic inactivation or pharmacological inhibition of CXCR3 in T-ALL cells or CXCL10 in meningeal stromal cells reduced cell-cell adhesion and the expression of VLA-4 and VCAM-1 in T-ALL and meningeal stroma, respectively, further supporting the role of CXCL10-CXCR3 in regulating T-ALL adhesion. Lastly, we investigated whether inflammatory cytokines derived from T-ALL induce CXCL10 in the meningeal microenvironment. We found elevated expression of Ifng, Tnf and Il27 in T-ALL cells infiltrating the meninges, but not other organs of ΔE-NOTCH1 mice ( p &lt; 0.01). Silencing these genes in human T-ALL cells resulted in reduced CXCL10 expression and secretion, along with reduced leukemic cell migration to the tested meningeal stromal cells. In summary, our study emphasizes the key role of CXCR3-CXCL10 signaling in T-ALL progression and meningeal infiltration.