A biomimetic VLP influenza vaccine with interior NP/exterior M2e antigens constructed through a temperature shift-based encapsulation strategy

Here we present a biomimetic strategy towards an influenza vaccine design based on hepatitis B virus core virus-like particles (HBc VLP). To this end, a temperature-shift based encapsulation process based on analysis of the unique thermal-associated structural flexibility of HBc VLP nanocages was proposed and proved efficient for encapsulation of antigen inside the VLP. By displaying a matrix protein 2 ectodomain (M2e) antigen on the exterior of HBc VLP through genetic fusion, and encapsulate a conserved internal nucleoprotein (NP) antigen peptide inside the VLP, a biomimetic dual-antigen influenza vaccine with interior NP/exterior M2e was constructed. For comparison, another non-biomimetic dual-antigen vaccine with interior M2e/exterior NP, and other four VLP-based single-antigen vaccines with NP or M2e either being encapsulated inside or genetically displayed outside the VLP were also constructed. Upon intraperitoneal immunization in mice, the dual-antigen VLP influenza vaccine elicited both NP and M2e-specific antibodies, which were stronger than those elicited by the single-antigen vaccines. Most importantly, after a lethal challenge of H1N1 virus, the biomimetic dual-antigen vaccine conferred the mice 100% protection without noticeable body weight loss in the absence of any adjuvant. While the protective efficacy conferred by the non-biomimetic one was only 62.5%, accompanying 12.5% body weight loss in the immunized mice. Besides the high level of antigen-specific antibodies, more efficient formation of total germinal center (GC) B cells and a higher level of effector memory CD8⁺ T cell population were observed in the biomimetic vaccine group, as compared with the non-biomimetic one. All these results demonstrate that VLP assembly and display of antigens in a biomimetic manner making this a promising strategy for the production of efficient universal vaccines to influenza and other rapidly emerging pathogens.