Pre-clinical Vaccine Development for Respiratory Viruses

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Human paramyxoviruses and pneumoviruses are widespread pathogens, cause considerable disease burden. Parainfluenza virus types 1-4 (PIV1-4) are highly infectious human pathogens, of which PIV3 is most commonly responsible for severe respiratory illness in newborns, elderly, and immunocompromised individuals. Based on a cryoelectron microscopy structure of an engineered PIV3 F prefusion-stabilized trimer, we engineered in additional mutations different from our previous published modifications in each of the four PIV fusion (F) glycoproteins to further stabilize their metastable prefusion states. The vaccine candidates were able to elicit murine PIV type-specific response, with little cross-neutralization of other PIVs. We evaluated the neutralization responses of the vaccine candidates in nonhuman primates (NHPs). We applied similar concept and designs to hMPV F proteins. We designed various mutations to further stabilize the PIV F prefusion trimers and hMPV prefusion trimers. In addition, we designed expression the modified trimers on the surface of different nanoparticles as vaccine immunogens. In the past year, we investigate the impact of further stabilizing HMPV F in the pre-F state. We replaced the furin-cleavage site with a flexible linker, creating a single chain F that yielded increased amounts of pre-F stabilized trimers, enabling the generation and assessment of F trimers stabilized by multiple disulfide bonds. Immunogenicity assessments in nave mice showed the triple disulfide-stabilized pre-F trimer could elicit high titer neutralization than elicited by post-F. Immunogenicity assessments in pre-exposed rhesus macaques showed the triple disulfide-stabilized pre-F could recall high neutralizing titers after a single immunization, with little discrimination in the recall response between pre-F and post-F. Collectively, these results suggest single-chain triple disulfide-stabilized pre-F trimers to be promising HMPV-vaccine antigens.