Dual-Engineered Phage\nVaccine Platform Facilitates\nSTING Activation for Influenza Protection

Influenza epidemics remain a global public health challenge.\nVaccination\nwith nucleic acid-based vaccines, which trigger strong cellular and\nhumoral immune responses, represents a promising approach for preventing\nvirus infection. However, its effectiveness relies on efficient delivery\nand an immunoadjuvant. Here, we constructed a gene- and nanoengineered\nvaccine delivery platform via modifying MnO<sub>2</sub> nanoparticles\n(NPs) onto the surface of the M13 phage, which carried the hemagglutinin\nstem gene of influenza A virus preceded by a eukaryotic initial transcriptional\nregion. Specifically, the M13 phage protected the inserted nucleic\nacid vaccine against degradation due to the existence of capsid proteins.\nMnO<sub>2</sub> NPs released Mn<sup>2+</sup> ions under the acidic\ncondition of endolysosomes, thereby promoting the cytoplasmic delivery\nof phage vaccines, which significantly improved the antigen expression.\nMoreover, Mn<sup>2+</sup> acted as a potent adjuvant for dendritic\ncell maturation by activating the cGAS/STING pathway. Immunization\nwith the engineered phage vaccine induced CD4<sup>+</sup> T cell,\nCD8<sup>+</sup> T cell, and humoral immune responses in mice. In infected\nmouse models, the vaccines ameliorated weight loss, survival rate,\nlung virus titers, and pulmonary pathologies and conferred full protection\nagainst influenza viruses. Collectively, we developed a dual-engineered\nphage vaccine platform, offering an alternative regimen for optimizing\nnucleic acid vaccines, which may have broad applications in the rational\ndesign of vaccine formulations.