Targeted exosomes for co-delivery of siFGL1 and siTGF-β1 trigger combined cancer immunotherapy by remodeling immunosuppressive tumor microenvironment

Immune checkpoint therapy encounters significant challenges in clinic, including low response rate, acquired resistance and immune-related adverse events. Combination immunotherapy targeting multiple independent but complementary pathways in immune evasion has the potential to enhance therapeutic efficacy. Herein, a combination therapeutic strategy that dually inhibiting FGL1, a recently discovered main ligand for immune checkpoint LAG-3, and TGF-β1, an immunosuppressive cytokine, is firstly reported for colorectal cancer immunotherapy by blocking immune checkpoint and modulating tumor microenvironment simultaneously. We established a cRGD-modified exosome with high siFGL1 and siTGF-β1 loading efficiency (cRGD-Exo/siMix) to realize the co-silence of FGL1 and TGF-β1. The constructed cRGD-Exo/siMix showed a significant anti-tumor effect both in vitro and in vivo. Analysis of the tumor immune microenvironment demonstrated an increased number of tumor infiltration CD8+ T cells while a decreased number of immunosuppressive cells, implying that this therapeutic approach boosted anti-tumor immunity by reshaping the tumor microenvironment. This work provides a new strategy for siRNA delivery and its applications in combined cancer immunotherapy.