Chemokine-Driven Intercellular Crosstalk in the Osteosarcoma Microenvironment After Neoadjuvant Chemotherapy: A...

Background/Objectives: Osteosarcoma (OS) is an aggressive bone malignancy with a complex tumor microenvironment (TME) that influences therapeutic outcomes and resistance. How neoadjuvant chemotherapy (NACT) reshapes the OS TME at single-cell resolution remains largely undefined. This study aimed to characterize cellular heterogeneity in the OS TME after NACT and identify chemokine-mediated intercellular crosstalk driving chemoresistance. Methods: Single-cell RNA sequencing was performed on surgical specimens from 12 OS patients (6 treatment-naive and 6 post-NACT). After quality control, 77,616 cells (36,214 from naive patients, 41,402 from post-NACT samples) were analyzed through the Seurat pipeline. Unsupervised clustering, differential expression analysis, and cell-cell communication network construction were performed, and candidate signaling axes were validated using transwell assays and Western blotting. Results: Cells were classified into 10 major cell types. Osteoblasts, identified as malignant cells, were partitioned into 11 subpopulations with marked transcriptional heterogeneity and differential PI3K/Akt pathway activity. Post-NACT, stromal and vascular components underwent molecular and functional remodeling, shaping an immune-activated microenvironment. Mononuclear phagocytes resolved into three discrete clusters-monocytes, macrophages, and dendritic cells-with differentiation gradients. Endothelial cells maintained robust CXCL2 expression throughout the therapeutic course. Functional validation via transwell assays and Western blotting confirmed that endothelial-derived CXCL2 promoted macrophage chemotaxis via CXCR2, with corresponding CXCR2 upregulation in macrophages. Conclusions: Collectively, these findings suggest the complex cellular and transcriptional heterogeneity of the OS microenvironment and its chemokine-driven molecular remodeling after NACT, indicating that TME dynamics may be a determinant of therapeutic response and chemoresistance.