Strategy to develop broadly effective multivalent COVID-19 vaccines against emerging variants based on Ad5/35 platform.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron strain has evolved into highly divergent variants with several sub-lineages. These newly emerging variants threaten the efficacy of available COVID-19 vaccines. To mitigate the occurrence of breakthrough infections and re-infections, and more importantly, to reduce the disease burden, it is essential to develop a strategy for producing updated multivalent vaccines that can provide broad neutralization against both currently circulating and emerging variants. We developed bivalent vaccine AdCLD-CoV19-1 BA.5/BA.2.75 and trivalent vaccines AdCLD-CoV19-1 XBB/BN.1/BQ.1.1 and AdCLD-CoV19-1 XBB.1.5/BN.1/BQ.1.1 using an Ad5/35 platform-based non-replicating recombinant adenoviral vector. We compared immune responses elicited by the monovalent and multivalent vaccines in mice and macaques. We found that the BA.5/BA.2.75 bivalent and the XBB/BN.1/BQ.1.1 and XBB.1.5/BN.1/BQ.1.1 trivalent vaccines exhibited improved cross-neutralization ability compared to their respective monovalent vaccines. These data suggest that the developed multivalent vaccines enhance immunity against circulating Omicron subvariants and effectively elicit neutralizing antibodies across a broad spectrum of SARS-CoV-2 variants.

Construction of the safe neutralizing assay system using pseudotyped Nipah virus and G protein-specific monoclonal antibody.

Nipah virus (NiV) is a recently emerged paramyxovirus that causes acute respiratory illness and fatal encephalitis in a broad spectrum of vertebrates, including humans. Due to its high pathogenicity and mortality rates, NiV requires handling in biosafety level-4 (BSL-4) containment facilities and no effective vaccines or therapeutic agents are currently available. Since current diagnostic tests for detecting serum neutralizing antibodies against NiV mainly employ live viruses, establishment of more safe and robust alternative diagnostic methods is an essential medical requirement. Here, we have developed a pseudotyped NiV and closely related Hendra virus (HeV) expressing envelope attachment (G) and fusion (F) glycoproteins using the Moloney murine leukemia virus (MuLV) packaging system. We additionally generated polyclonal antibodies (pAbs) against NiV-G and HeV-G and assessed their neutralizing activities for potential utilization in the pseudovirus-based neutralization assay and further application in the serum diagnostic test. To enhance the specificity of neutralizing antibody and sensitivity of the serological diagnostic test, monoclonal antibodies (mAbs) against NiV-G were generated, and among which four out of six mAb clones showed significant reactivity. Specifically, the 7G9 clone displayed the highest sensitivity. The selected mAb clones showed no cross-reactivity with HeV-G and efficient neutralizing activities against pseudotyped NiV. These results validate the safety and specificity of neutralization assays against NiV and HeV and present a useful tool to design effective vaccines and serological diagnosis.