Antigen-Loaded Extracellular Vesicles Induce Responsiveness to Anti-PD-1 and Anti-PD-L1 Treatment in a Checkpoint Refractory Melanoma Model

Extracellular vesicles (EV) are important mediators of intercellular communication and are potential candidates for cancer immunotherapy. Immune checkpoint blockade, specifically targeting the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis, mitigates T-cell exhaustion, but is only effective in a subset of patients with cancer. Reasons for therapy resistance include low primary T-cell activation to cancer antigens, poor antigen presentation, and reduced T-cell infiltration into the tumor. Therefore, combination strategies have been extensively explored. Here, we investigated whether EV therapy could induce susceptibility to anti-PD-1 or anti-PD-L1 therapy in a checkpoint-refractory B16 melanoma model. Injection of dendritic cell-derived EVs, but not checkpoint blockade, induced a potent antigen-specific T-cell response and reduced tumor growth in tumor-bearing mice. Combination therapy of EVs and anti-PD-1 or anti-PD-L1 potentiated immune responses to ovalbumin- and α-galactosylceramide-loaded EVs in the therapeutic model. Moreover, combination therapy resulted in increased survival in a prophylactic tumor model. This demonstrates that EVs can induce potent antitumor immune responses in checkpoint refractory cancer and induce anti-PD-1 or anti-PD-L1 responses in a previously nonresponsive tumor model.