ABSTRACT
T cell-mediated elimination of malignant cells is one cornerstone of endogenous and therapeutically induced antitumor immunity. Tumors exploit numerous regulatory mechanisms to suppress T cell immunity. Regulatory T cells (T regs) play a crucial role in this process due to their ability to inhibit antitumoral immune responses and they are known to accumulate in various cancer entities. The chemokine CCL22, predominately produced by dendritic cells (DCs), regulates T reg migration via binding to its receptor CCR4. CCL22 controls T cell immunity, both by recruiting T regs to the tumor tissue and by promoting the formation of DC-T reg contacts in the lymph node. Here, we review the current knowledge on the role of CCL22 in cancer immunity. After revising the principal mechanisms of CCL22-induced immune suppression, we address the factors leading to CCL22 expression and ways of targeting this chemokine therapeutically. Therapeutic interventions to the CCL22-CCR4 axis may represent a promising strategy in cancer immunotherapy.
Subject(s)
Chemokine CCL22/metabolism , Neoplasms/immunology , Neoplasms/metabolism , Signal Transduction , Tumor Microenvironment , Animals , Humans , Neoplasms/therapy , Receptors, CCR4/metabolism , T-Lymphocytes, Regulatory/immunologyABSTRACT
Chemokines have crucial roles in organ development and orchestration of leukocyte migration. The chemokine CCL22 is expressed constitutively at high levels in the lymph node, but the functional significance of this expression is so far unknown. Studying a newly established CCL22-deficient mouse, we demonstrate that CCL22 expression by dendritic cells (DCs) promotes the formation of cell-cell contacts and interaction with regulatory T cells (T reg) through their CCR4 receptor. Vaccination of CCL22-deficient mice led to excessive T cell responses that were also observed when wild-type mice were vaccinated using CCL22-deficient DCs. Tumor-bearing mice with CCL22 deficiency showed prolonged survival upon vaccination, and further, CCL22-deficient mice had increased susceptibility to inflammatory disease. In conclusion, we identify the CCL22-CCR4 axis as an immune checkpoint that is crucial for the control of T cell immunity.
Subject(s)
Bone Marrow Cells/immunology , Cell Communication/immunology , Chemokine CCL22/immunology , Dendritic Cells/immunology , Lymph Nodes/immunology , T-Lymphocytes, Regulatory/immunology , Animals , Cell Line, Tumor , Cell Movement , Chemokine CCL22/genetics , HEK293 Cells , Humans , Lymph Nodes/cytology , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Knockout , Receptors, CCR4/metabolism , Transplantation, HomologousABSTRACT
Ewing sarcoma (EwS) is an aggressive cancer characterized by chromosomal translocations generating fusions of the EWSR1 gene with ETS transcription factors (in 85% FLI1). EWSR1-FLI1 induces gene expression via binding to enhancer-like GGAA-microsatellites, whose activity correlates with the number of consecutive GGAA-repeats. Herein we investigate the role of the secretory neuropeptide CALCB (calcitonin-related polypeptide ß) in EwS, which signals via the CGRP (calcitonin gene-related peptide) receptor complex, containing RAMP1 (receptor activity modifying protein 1) as crucial part for receptor specificity. Analysis of 2678 gene expression microarrays comprising 50 tumor entities and 71 normal tissue types revealed that CALCB is specifically and highly overexpressed in EwS. Time-course knockdown experiments showed that CALCB expression is tightly linked to that of EWSR1-FLI1. Consistently, gene set enrichment analyses of genes whose expression in primary EwS is correlated to that of CALCB indicated that it is co-expressed with other EWSR1-FLI1 target genes and associated with signatures involved in stemness and proliferation. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) data for FLI1 and histone marks from EwS cell lines demonstrated that EWSR1-FLI1 binds to a GGAA-microsatellite close to CALCB, which exhibits characteristics of an active enhancer. Reporter assays confirmed the strong EWSR1-FLI1- and length-dependent enhancer activity of this GGAA-microsatellite. Mass spectrometric analyses of EwS cell culture supernatants demonstrated that CALCB is secreted by EwS cells. While short-term RNA interference-mediated CALCB knockdown had no effect on proliferation and clonogenic growth of EwS cells in vitro, its long-term knockdown decreased EwS growth in vitro and in vivo. Similarly, knockdown of RAMP1 reduced clonogenic/spheroidal growth and tumorigenicity, and small-molecule inhibitors directed against the RAMP1-comprising CGRP receptor reduced growth of EwS. Collectively, our findings suggest that CALCB is a direct EWSR1-FLI1 target and that targeting the CALCB/RAMP1 axis may offer a new therapeutic strategy for inhibition of EwS growth.
