Therapeutic Targeting of Macrophage Plasticity Remodels the Tumor-Immune Microenvironment

Although the majority of patients with advanced lung adenocarcinoma (LUAD) are eligible to receive immune checkpoint blockade, approximately 80% of these tumors are resistant to this therapeutic approach. Insights at the single-cell level into mechanisms that drive LUAD tumorigenesis and the relationship of LUAD histologic heterogeneity to response to immune checkpoint blockade could help identify biomarkers and potential combinational approaches to improve immunotherapy efficacy. Here, we used a genetically engineered mouse model that replicates the development of human LUAD through a spectrum of preinvasive to invasive adenocarcinoma histologic subtypes. A systems onco-immunology approach of integrating the analytical power and unique, complementary capabilities of time-of-flight mass cytometry (CyTOF) and imaging mass cytometry was leveraged to identify cellular and spatial immune contextures in LUAD. Comprehensive investigation of mouse and human LUAD using these single-cell proteomics platforms showed that LUAD progression is associated with spatiotemporal evolution of tumor-associated macrophages in the tumor-immune microenvironment, which governs tumor response to immunotherapy. PD-1 was expressed in a highly plastic tumor-promoting subtype of tumor-associated macrophages that develops during tumor progression from preinvasive to invasive adenocarcinoma, controls the lymphocyte-depleted niche of invasive tumors, and protects tumor cells in the solid histologic components of the tumor. Longitudinal, multidimensional single-cell analyses of LUAD tumorigenesis revealed dynamic alteration of immunoregulatory PD-1–expressing tumor-associated macrophages that can be targeted to overcome resistance to checkpoint immunotherapy. Significance: Comprehensive single-cell proteomics analyses of lung adenocarcinoma progression reveal the role of tumor-associated macrophages in resistance to PD-1 blockade therapy.