Boosting breast cancer immunotherapy through targeted siRNA delivery and sequential chemotherapy.

Cancer continues to be a major public health challenge due to therapeutic resistance, rising incidence and financial burden. Although anti-programmed cell death-ligand 1 (PD-L1) immunotherapy has revolutionised cancer treatment, its efficacy as monotherapy remains limited. Combining chemotherapy with immunotherapy offers the potential to amplify therapeutic outcomes and reduce side effects. Paclitaxel can induce immunogenic cell death (ICD) and improve tumour response to anti-PD-L1 therapy, thereby improving immunotherapy effectiveness. Meanwhile, small interfering RNA (siRNA) therapy can selectively suppress PD-L1 expression on the cell membrane and in the cytoplasm, though efficient delivery remains a challenge. We developed nanoparticles composed of trimethyl chitosan (TMC) and hyaluronic acid (HA) for delivering PD-L1 siRNA. These spherical nanoparticles (∼190 nm) demonstrated favourable physicochemical properties, high siRNA encapsulation efficiency, robust serum stability, a non-toxic nature and effective internalisation by cancer cells. The sequential therapy of sub-therapeutic doses of paclitaxel with siRNA PD-L1 in a 4T1 Balb/c mouse model compared to each monotherapy led to a substantial boost to antitumor immunity, suppression of tumour growth and increased infiltration of effector CD8+ T-cells within the tumour microenvironment. This study presents a novel siRNA delivery system and therapeutic approach that enhances the efficacy of breast cancer immunotherapy.