A metalloprotein nanoparticle scaffold co-delivers antigens and adjuvants with metal-enhanced STING activation for vaccination preventing viral infections

Co-delivery of antigens and adjuvants in a nanoparticle format could be beneficial for subunit vaccine devel- opment. Herein, we develop a nanovaccine comprising lactoferrin-Mn-PEG-diABZI-2-antigen, termed LaMP-A-antigen. Featuring a metalloprotein core, LaMP securely localizes manganese (Mn) in confined spaces formed by lactoferrin-PEG conjugates. LaMP efficiently coordinates imidazole-containing adjuvants (diABZI-2), yielding LaMP-A, which is subsequently functionalized by numerous his-tagged viral-derived antigenic proteins or pep- tides by simple admixture. Compared to regular metal chelation, LaMP-A-antigen is more physiologically stable and can be lyophilized and stored at room temperature without change in physical and immunological properties for months. Following screening of ten common metal ions, manganese and cobalt are found to enhance the adjuvant effect of diABZI-2 by activation of stimulator of interferon genes (STING). In particular, Mn2+ achieves a 39-fold adjuvant dose sparing effect. When the SARS-CoV-2 receptor-binding domain (RBD) is used as a model antigen, immunization with LaMP-A-RBD elicits strong mucosal, humoral and cellular immunity. Following a single intranasal administration of LaMP-A-RBD in hamsters, antigen-specific T cells as well as natural killer (NK) cells are induced, along with RBD-specific IgG and secretory IgA (sIgA), leading to rapid neutralization in a reporter pseudovirus challenge. Thus, the LaMP-A system represents a novel vaccine adjuvant system that dis- plays antigens, and exploits metalloimmune responses via the cGAS-STING pathway to improve vaccine immunogenicity.