A Modular Bacteriophage T4 Nanoparticle Platform Enables Rapid Design of Dual COVID-19-Flu Mucosal Vaccines

A multivalent, rapidly deployable, mucosal vaccine platform is desperately needed to prevent acquisition and transmission of respiratory infections during epidemics and pandemics. No such approved platform currently exists and virtually all under investigation use infectious viruses that have safety concerns and are not amenable for multivalent engineering. Herein, a non-infectious biomaterial platform is presented, the bacteriophage T4 nanoparticle endowed with unique features for modular engineering, which is exploited to design dual COVID-Flu mucosal vaccines. By leveraging T4's natural affinity to nasal mucosa, in vivo CRISPR engineering, and in vitro SpyCatcher-SpyTag conjugation, hundreds of antigen molecules are incorporated from SARS-CoV-2 and influenza viruses into one nanoparticle. These include spike and hemagglutinin trimers and M2e peptides decorating the capsid while encapsulating matrix or nucleocapsid proteins inside, thereby achieving unprecedented antigen density and diversity, a pinnacle nanoparticle design. Intranasal administration of this adjuvant-free T4-CoV-Flu vaccine induces remarkable mucosal immunity against both respiratory pathogens, including high-titer neutralizing antibodies and secretory IgA, lung-resident CD4⁺/CD8⁺ T cells, diverse memory B cells, and complete protection against SARS-CoV-2 and influenza challenges. Coupled with its scalability in bacterial systems, thermostability, and adjuvant- and needle-free delivery, T4 presents an extraordinary platform to design potent mucosal vaccines against pandemic threats.