Dual checkpoint inhibition in M2 macrophages via anti-PD-L1 and siRNA-Loaded M1-Exosomes: Enhancing tumor immunity...

The interaction between a cluster of differentiation 47 (CD47) on cancer cells and signal regulatory protein alpha (SIRPα) on macrophages is thought to hinder macrophage phagocytic activity, which can be blocked by combining siRNAs targeting SIRPα (siSIRPα) with simultaneous involvement of activating receptors like FcRs (Fc receptors) using anti-programmed death-ligand 1 (anti-PD-L1). For this study, M1 macrophage-derived exosomes isolated from lipopolysaccharide (LPS)-stimulated RAW264.7 cells were used to deliver the siRNAs, and electroporated with siSIRPα. The exosomes were characterized and used to treat M2 macrophages (RAW264.7 cells triggered by interleukin-4 (IL-4)), and the polarization of macrophages was evaluated using flow cytometry, real-time PCR, ELISA, and phagocytosis assays. The anti-tumor functions of treated macrophages were assessed by co-culturing them with 4T1 cells, evaluating the migration and invasion of 4T1 cells, and examining the phagocytosis of 4T1 cells by macrophages. The results showed that siSIRPα-loaded M1-exosomes caused polarization of M2 macrophage toward M1 phenotype and enhanced anti-tumor effects by reducing migration and invasion of 4T1 cells and enhancing phagocytosis of 4T1 cells by macrophages, especially with combination of anti-PD-L1. This study suggests that blocking the SIRPα-CD47 interaction and the PD-1/PD-L1 pathway in M2 macrophages could be a promising therapeutic approach to enhance anti-tumor immune responses.