Inhalable hybrid nanovaccines with virus-biomimetic structure boost protective immune responses against SARS-CoV-2 variants

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with different antigenic variants, has posed a significant threat to public health. It is urgent to develop inhalable vaccines, instead of injectable vaccines, to elicit mucosal immunity against respiratory viral infections. Methods We reported an inhalable hybrid nanovaccine (NV RBD -MLipo) to boost protective immunity against SARS-CoV-2 infection. Nanovesicles derived from genetically engineered 293T cells expressing RBD (NV RBD ) were fused with pulmonary surfactant (PS)-biomimetic liposomes containing MPLA (MLipo) to yield NV RBD -MLipo, which possessed virus-biomimetic structure, inherited RBD expression and versatile properties. Results In contrast to subcutaneous vaccination, NV RBD -MLipo, via inhalable vaccination, could efficiently enter the alveolar macrophages (AMs) to elicit AMs activation through MPLA-activated TLR4/NF-κB signaling pathway. Moreover, NV RBD -MLipo induced T and B cells activation, and high level of RBD-specific IgG and secretory IgA (sIgA), thus elevating protective mucosal and systemic immune responses, while reducing side effects. NV RBD -MLipo also demonstrated broad-spectrum neutralization activity against SARS-CoV-2 (WT, Delta, Omicron) pseudovirus, and protected immunized mice against WT pseudovirus infection. Conclusions This inhalable NV RBD -MLipo, as an effective and safe nanovaccine, holds huge potential to provoke robust mucosal immunity, and might be a promising vaccine candidate to combat respiratory infectious diseases, including COVID-19 and influenza.