C–C Motif Chemokine Ligand 4 Positive (CCL4+) Neutrophils Negatively Influence the Tumor Immune Microenvironment by Regulating Macrophages

Abstract

Epidemiological studies have revealed that the incidence of most cancers increases with age. However, the relationship between the two remains obscure owing to the complexity and heterogeneity of the tumor microenvironment (TME). By analyzing 10 × single-cell ribonucleic-acid sequencing data derived from subcutaneous tumor tissues in old (17–22 months) and young (6–8 weeks) mice, we found an increase in C–C Motif Chemokine Ligand 4 positive (CCL4+) neutrophils in aged mice compared with those in their younger counterparts. The expression levels of genes encoding protumor chemokines, such as CXCL2, CCL3, and CCL4, were significantly higher in old mice. Kyoto Encyclopedia of Genes and Genomes analysis showed that the differentially expressed genes were enriched mainly in NF-κB signaling, a well-established facilitator of tumor progression and metastasis. We also observed a multiple communication between neutrophils and immnunosuppressive immune cells. CCL4+ neutrophils adversely enriched in the TME, interacted with Spp1+ macrophages, promoted progression and metastasis. Our findings provided novel insights in the role of CCL4+ neutrophils in tumor pathogenesis and progression.