Dynamic Change of PD-L2 on Circulating Plasma Extracellular Vesicles as a Predictor of Treatment Response in Melanoma Patients Receiving Anti-PD-1 Therapy.

Immune checkpoint inhibitors (ICIs) have provided new hope for melanoma patients, however, not all patients benefit. Furthermore, ICI-related therapies cause significant immune-related adverse events that adversely affect patient outcomes. Therefore, there is a pressing need for reliable biomarkers to identify patients most likely to benefit from these treatments. In this study, we employed an extracellular vesicles (EVs) protein expression array to explore the longitudinal membrane protein profiles of plasma-derived EVs from 32 melanoma patients receiving anti-PD-1 and anti-angiogenesis therapy at baseline and early treatment. We found that the dynamic changes in PD-L2 on the EV membrane were associated with treatment response and patient survival. The dynamic change of EV PD-L2 as an indication of treatment efficacy was validated in an independent cohort of melanoma patients treated with anti-PD-1 monotherapy. Plasma-derived PD-L2+ EVs from patients with mucosal melanoma significantly reduced the frequency of granzyme B+ CD8 T cells within the peripheral blood mononuclear cells (PBMCs) of healthy individuals. The inhibitory effect of PD-L2+ EVs on CD8 T cells was further validated using human melanoma cell lines and the B16-F10 mouse model. Although intratumoural injection of PD-L2+ EVs could promote melanoma growth in vivo, tumours with PD-L2+ EVs showed a higher response to anti-PD-1 than those without PD-L2+ EVs. Collectively, our study demonstrates that PD-L2+ EVs inhibit CD8 T cell activation and promote melanoma growth, and changes in PD-L2 on circulating EVs during early treatment could serve as a biomarker for ICI-based therapy.