Lineage tracing reveals the pro-tumorigenic niche role of tissue resident macrophages in early lung cancer lesions II

To explore the diversity of the MF compartment in human non-small cell lung carcinoma lesions (NSCLC), we first performed an unbiased single cell RNA-sequencing (scRNAseq) analysis of CD45+ tumor-associated leukocytes. We identified distinct MF populations enriched in human tumors and found related MF phenotypes in mouse lung tumors. Using lineage-tracing, we discovered these discrete MF populations differ in origin and have a distinct temporal and spatial distribution in the TME. Longitudinal tumor imaging revealed that upon tumor cell seeding, TRMF accumulate in proximity to tumor cells to promote tumor cell epithelial mesenchymal transition and invasiveness, while also inducing a potent T regulatory (Treg) response that protects tumor cells from adaptive immunity. TRMF depletion prior to tumor implantation, while sparing Mo-MF, did not affect tumor cell seeding but significantly reduced Treg numbers, dampened the Treg regulatory program, promoted the accumulation of CD8+ T cells in tumor lesions, and reduced tumor invasiveness and growth. During tumor growth, TRMF redistributed at the periphery of the TME, which becomes dominated by Mo-MF both in mouse and human NSCLC lesions, and TRMF depletion in later stage tumors, had little effect on tumor growth. This study identifies the distinct contribution of the TRMF lineage to early lung cancer invasiveness and establish TRMF as a potential novel target to treat early lung cancer lesions. Overall design: Sorted lung TRMs from naïve wild type (WT) and tumor bearing mice (KP-TRMs : KP tumors harvested at d15 and at d35) were generated by deep sequencing using Illumina Nextseq 500.