Oral Delivery of siSIRPα via Yeast-Derived β-Glucan Particles Enhances Macrophage-Mediated Antitumor Immunity by Blocking the CD47-SIRPα Axis.

[INTRODUCTION] The CD47-SIRPα Axis functions as a key innate immune checkpoint that enables tumors to evade phagocytosis and immune surveillance. Blockade of this interaction has emerged as a promising anticancer immunotherapy strategy.

[OBJECTIVE] The study aimed to develop a macrophage-targeting delivery system using whole β-glucan particles (WGPs) with an immune-stimulatory property to deliver small interfering RNA against SIRPα (siSIRPα), thereby abrogating SIRPα-mediated phagocytosis inhibition and enhancing antitumor immunity.

[METHODS] Dectin-1-dependent uptake of WGP-siSIRPα was confirmed with bone marrow derived macrophages (BMDMs) from WT and Dectin-1 using immunofluorescences and flow cytometry. Cytoskeletal dynamics and lysosomal escape of siSIRPα in BMDMs were visualized by immunofluorescences. Phenotype of BMDMs was characterized via transcriptomics, flow cytometry, ELISA and ROS detection. WGP-siSIRPα mediated T-cell activation was assessed using flow cytometry. In vitro phagocytosis of macrophages was evaluated by confocal microscopy. Therapeutic efficacy was evaluated in subcutaneous B16 melanoma (C57BL/6 mice) and 4 T1 breast cancer (BALB/c mice) models following oral administration of WGP-siSIRPα.

[RESULTS] WGP-mediated siSIRPα delivery, dependent on Dectin-1 receptor, achieved robust SIRPα silencing and significantly downregulated expression of SIRPα in macrophages, accompanied by cytoskeletal reorganization and effective lysosomal escape. WGPs promoted M0-to-M1 polarization in macrophages, which synergistically augmented T-cell responses through enhanced antigen presentation. Enhanced phagocytosis of tumor cells with high CD47 expression was observed following siSIRPα delivery. Orally administered WGP-siSIRPα significantly inhibited tumor growth in both B16 melanoma and 4 T1 breast cancer models, associated with decreased SIRPα expression in tumor-associated macrophages (TAMs) and increased M1 polarization within the tumor microenvironment (TME).

[CONCLUSION] These findings establish a proof-of-concept for an oral WGP-based delivery platform and demonstrate a novel siRNA-mediated approach to CD47-SIRPα blockade, which potentiates macrophage-driven antitumor immune responses.