Characterizing PD-L1-Targeting Extracellular Vesicles Produced by Oncolytic Vaccinia Virus Infection

Abstract

Tumour cells evade immune responses by multiple mechanisms in the tumour microenvironment, including through the expression of immunosuppressive molecules. The programmed cell death ligand 1 (PD-L1) plays a major role in this immunosuppression, and its expression is often up regulated as a result of innate and adaptive resistance mechanisms. Recent studies have discovered that the expression of PD-L1 can also extend to the nanoparticles that are naturally released by these cells, termed extracellular vesicles (EVs). Immune checkpoint inhibitors (ICIs) have shown great promise in blocking these immune-silencing interactions, but they remain hindered by their low response rates and toxic side effects. In addition, it has been found that the presentation of PD-L1 by EVs can be resistant to these established ICI therapies, further limiting their success. Here, we report a novel technique in which the oncolytic virus, Vaccinia virus, can be engineered to produce PDL1- targeting EVs as a form of immune checkpoint blockade. Our results show that our tailored EVs can target and neutralize immunosuppressive PD-L1, leading to enhanced anti-tumour immunity. Overall, this demonstrates the potential of using this technique to generate future EV-based immunotherapies.