The majority of persistent ground-glass nodules (GGNs) are ultimately identified as early-stage lung adenocarcinoma (LUAD). Investigating the molecular mechanisms driving the malignant progression of GGNs could support the development of preventive and therapeutic approaches to block the development and progression of early LUAD. Macrophages (Macs) play a key role in establishing an immunosuppressive tumor microenvironment (TME). Yet, their specific contribution to the progression of early-stage LUAD presenting as mixed ground-glass nodules (mGGNs) remains unclear. Through single-cell RNA sequencing (scRNA-seq) of normal lung tissue, ground-glass areas, and solid components from mGGNs, along with validation via multicolor immunohistochemistry (mIHC) and flow cytometry, we observed elevated levels and accumulation around tumors of immunosuppressive SPP1+ alveolar macrophages and monocyte-derived macrophages (Mo-Macs), particularly the latter. This buildup at the tumor edge may hinder immune cell infiltration into the tumor interior, thereby facilitating the malignant shift of GGNs. SPP1+ Macs exhibit a senescent profile while also showing the ability to promote tumor metastasis and new blood vessel formation. Analysis of clinical LUAD tissue microarrays and the TCGA-LUAD dataset indicated that a higher proportion of tumoral SPP1+ Macs correlates with worse patient outcomes. Moreover, SPP1+ Macs contribute to an immunosuppressive TME by interacting with other immune populations. Experiments in cell cultures and animal models demonstrated that knocking out SPP1 suppressed the immunosuppressive polarization and senescence in Macs, restored a less suppressive TME, and slowed the expansion of LUAD xenograft tumors. These results suggest a novel therapeutic avenue targeting SPP1+ Macs to potentially slow or prevent the conversion of GGNs into early-stage LUAD.
