Pazopanib-associated remodeling of platelet-immune cell crosstalk and immune suppressive platelet-derived extracellular vesicles in metastatic RCC.

[BACKGROUND] Antiangiogenics promote immune activation by reducing myeloid-derived suppressor cells (MDSCs) and enhancing natural killer (NK) and T cell functions in metastatic RCC patients. However, these effects are transient, leading to compensatory immunosuppression. Platelets (PLT) and their extracellular vesicles (PLT-EVs) modulate immune and angiogenic pathways, suggesting a role in immune reprogramming during therapy.

[METHODS] Circulating EVs were longitudinally profiled in metastatic RCC patients (n=8) undergoing Pazopanib therapy. EVs, isolated by differential ultracentrifugation from baseline, 3- and 6-month plasma samples, were characterized by bead-based multiplex assay and nanoparticle tracking analysis. Results were correlated with blood counts, RNA-seq and flow cytometry immune profiles.

[RESULTS] Pazopanib induced temporally structured EV compartment alterations. After three months, EVs were enriched in immune markers (CD8, CD56, CD19, CD1c, HLA-DR), consistent with immune activation, whereas PLT-derived markers (CD41b, CD42a, CD29) were diminished. By six months, PLT-EV markers recovered, with CD62P and CD29 EVs co-expressing immunoregulatory and angiogenic molecules (CD209, CD105). PLT-EV abundance correlated with the expansion of regulatory T cells (Tregs), PD-L1 monocytes and MDSCs, together with suppression of NK cells. PLT activation and PDGF signaling pathways decreased in PBMC from patients with clinical benefit.

[CONCLUSIONS] Despite the small sample size and absence of functional experiments, our results suggest that Pazopanib promotes cytotoxic immune programs but, by six months, reprograms PLT-EVs towards different adhesion characteristics contributing to Treg and MDSC expansion while suppressing NK activity. PLT-EVs may influence the balance between immune activation and suppression during anti-angiogenic therapy, suggesting PLT-EVs as biomarkers and therapeutic targets in mRCC.