Engineered Bacteriophages in Cancer Immunotherapy: Emerging Concepts and Potential Integration with CAR-T Cell...

Due to antigen heterogeneity, restricted immune cell trafficking and an immunosuppressive, nutrient-restricted tumour microenvironment, solid tumours remain resistant to modern immunotherapies. Engineered bacteriophages offer a modular framework to overcome these obstacles: programmable virus-like particles with scalable production. Through genome engineering, capsid decoration with mammalian cell-targeting ligands, or hybrid AAV/phage systems, engineered bacteriophages can display tumour-associated antigens, enhance receptor-mediated uptake and deliver therapeutic payloads such as cytokines, chemokines and suicide genes without naturally infecting mammalian cells. These features support their use as vaccine platforms, immunological adjuvants and targeted gene-delivery vehicles. These may enable more precise, tumour-localized therapeutic intervention. Phages can engage innate immune pathways, including TLR9, TLR3/7/8, cGAS-STING and AIM2, promoting dendritic cell maturation and inflammatory mediators that may convert immunologically "cold" tumours into inflamed microenvironments. Their multivalent antigen display enhances B- and T-cell priming, while cDC1-mediated cross-presentation supports cytotoxic CD8+ T-cell responses and immunological memory. In CAR-T therapy, engineered phages may improve tumour homing through chemokine modulation, support persistence through local cytokine delivery, reduce antigen escape by presenting multiple tumour epitopes, and limit T-cell exhaustion through dominant-negative receptor strategies or local checkpoint blockade. This review summarizes engineering approaches, delivery systems, manufacturing, biodistribution, dosing, and safety issues, including immunogenicity, pre-existing anti-phage antibodies and horizontal gene transfer. It also distinguishes therapeutic engineered phage particles from phage display technologies used for molecular discovery. Despite encouraging results integrating modified bacteriophages with CAR-T cell therapy, the evidence remains mostly preclinical, indicating both substantial translational prospects and crucial obstacles for future clinical development.