Macrophage-T Cell Crosstalk in PSC Resistance
Background: Pulmonary sarcomatoid carcinoma (PSC) is a rare and aggressive NSCLC  subtype. This study is the first  to identify the mechanisms of PSC in immunotherapeutic resistance to propose reversal strategies. Methods: The tumourtumor immune microenvironment (TIME) in treatment naïveenaïve and immune-resistant PSC specimens was detected by single-cell RNA sequencing (scRNA-seq). Findings were validated via multi-immunofluorescence or immunohistochemistry staining on tissues, and flow cytometry/ELISA on peripheral blood from ICI-treated PSC patients. Potential therapies were tested in PSC patient-derived xenograft (PDX) models and murine lung adenocarcinoma models (LLC and KL). Sorted CD45+  tumor-infiltrating lymphocytes (TILs) from PSC-PDX were cultured in vitro under various conditions with subsequent scRNA-seq and flow cytometry. Results: scRNA-seq revealed terminally exhausted T cells and macrophages with dual pro-angiogenic and immunosuppressive roles in resistant tumors. SLC8A1? /FOLR2? macrophage subsets were key resistance mediators, facilitating intercellular crosstalk via CCL3-CCL1/CCL5-CCR5 signaling. This axis activatedion triggered an upregulation of the immunosuppressive MIF-CD74 and NECTIN2-TIGIT networks. CCR1/CCR5 blockade combined with anti-PD-1 significantly suppressed tumor growth by reversing T-cell exhaustion and macrophage polarization in PSC-PDX models, LLC, and KL. Relative findings were validated in an immunohistochemistry cohort of resectable PSC, bulk RNA-seq and scRNA-seq of common lung cancers receiving immunotherapy. In vitro inhibition of CCR1/CCR5 reduced MIF/TIGIT signaling and restored progenitor-like T-cell states. Clinically, elevated serum CCL3/CCL5/MIF levels and increased SLC8A1?/FOLR2? macrophage proportions in PBMCs and tissues correlated with disease progression. Conclusions: Dual CCR1/CCR5 inhibition represents a novel therapeutic strategy to overcome resistance in PSC and other common NSCLC.