PD-L2-RGMb interaction modulates anti-cancer immunity through swinging the shift of Th1/Th2 cell balance

Immune checkpoint blockade has revolutionized gastric cancer (GC) treatment, yet primary and acquired resistance remain major clinical challenges. Here, we identified extracellular vesicles (EVs) expressing programmed death-ligand 2 (PD-L2-EVs) as a key determinant of anti-PD1 response in GC. Through profiling the extracellular vesicle protein expression profiles in plasma samples from a retrospective cohort of 76 patients, we demonstrated that high baseline PD-L2-EV levels correlate with improved immunotherapy response and survival. Using multiple immunocompetent murine models, we showed that PD-L2-EVs synergize with anti-PD1 to suppress tumor growth by remodeling the tumor immune microenvironment, enhancing CD8 + T cell and NK cell infiltration while reducing immunosuppressive cell populations. Mechanistically, PD-L2 possesses differential binding dynamics between PD1 and repulsive guidance molecule b (RGMb), its binding to the latter mediates Th1 differentiation through promoting STAT4-signaling and augments CD8 + T cell's anti-tumor immunity. On the other hand, AFP reduces cancer cell's expression of PD-L2 and impaired Th1 differentiation, which explained the resistance to immunotherapy for the subtype of AFP-GC. Importantly, through shifting T helper 1/2 cells' balance towards Th1 under PD1 blockade, PD-L2-EV enhances the efficacy of anti-PD1 but not for anti-PD-L1 therapy. Our work nominated PD-L2-EVs as a predictive biomarker in guiding the selection of different types of immunotherapy and potentiates engineered PD-L2-EV as a candidate for therapeutic combination, particularly in AFP-positive patients.