Tumor Cell-Induced Platelet Aggregation Accelerates Hematogenous Metastasis of Malignant Melanoma by Triggering Macrophage Recruitment

Background Tumor cell-induced platelet aggregation (TCIPA) is not only a recognized mechanism for paraneoplastic thrombocytosis but also a potential breakthrough alternative for a low response to immune checkpoint inhibitors (ICIs) in hematogenous metastasis of malignant melanoma (MM). However, there is no TCIPA-specific model for further investigation of the relationship among TCIPA, the tumor immune microenvironment (TIME), and metastasis. Methods We developed a TCIPA metastatic melanoma model with advanced hematogenous metastasis and enhanced TCIPA characteristics. We also investigated the pathway for TCIPA in the TIME. Results We found that TCIPA triggers the recruitment of tumor-associated macrophages (TAMs) to lung metastases by secreting B16 cell-educated platelet-derived chemokines such as CCL2, SDF-1, and IL-1β. Larger quantities of TAMs in the TCIPA model were polarized to the M2 type by B16 cell reprocessing, and their surface programmed cell death 1 ligand 1 (PD-L1) expression was upregulated, ultimately assisting B16 cells in escaping host immunity and accelerating MM hematogenous metastasis. Conclusions TCIPA accelerates MM lung metastasis via tumor-educated platelets (TEPs), triggering TAM recruitment, promoting TAM polarization (M2), and remodeling the suppressive TIME in lung metastases.