Bispecific Macrophage Nano-Engager Couples Dual Checkpoint Blockade with Stimulator of Interferon Genes Activation to Potentiate Antitumor Immunity

The immunosuppressive tumor microenvironment, characterized by impaired antigen presentation, “don’t eat me” signaling, and T-cell exhaustion, challenges effective cancer immunotherapy. Conventional T-cell-redirecting bispecific engagers (BiTEs) show limited efficacy in solid tumors because of poor T-cell infiltration, rapid clearance, and dose-limiting cytokine release associated with the CD3 agonism. Therefore, we aimed to enhance macrophage-mediated tumor clearance and T-cell priming by developing a bispecific macrophage nanoengager (nanoBIME) that integrates dual immune checkpoint blockade (anti-SIRPα and anti-PD-L1) with STING-agonist delivery (SR717) in a single poly(lactic-co-glycolic acid) nanocarrier (BIS-PLGA-NP@SR717). BIS-PLGA-NP@SR717 exhibited uniform nanoscale features, efficient SR717 encapsulation, and stable dual-antibody conjugation, enabling systemic delivery with sustained intracellular release. Dual-ligand presentation markedly enhanced receptor binding and nanoparticle uptake in macrophages and PD-L1-expressing tumor cells. BIS-PLGA-NP@SR717 synergistically promoted macrophage phagocytosis, repolarized tumor-associated macrophages toward an M1 phenotype, enhanced dendritic cell maturation, and CD8+ T-cell activation; additionally, it elevated granzyme B, perforin, and IFN-γ production, resulting in robust T-cell-dependent tumor cell killing. In CT26 tumor-bearing mice, BIS-PLGA-NP@SR717 achieved superior tumor accumulation, deep intratumoral penetration, and dose-dependent tumor regression with minimal systemic toxicity. Transcriptomic profiling further revealed the coordinated activation of phagosome-related pathways, antigen presentation, STING/IFN pathways, chemokine signaling, and T-cell receptor engagement. Collectively, BIS-PLGA-NP@SR717 represents an integrated, multiaxis immunotherapeutic nanoplatform that synchronizes innate activation, macrophage remodeling, and T-cell effector functions. Its modular architecture provides a versatile framework for next-generation immunotherapies for solid tumors.