Design of the Recombinant Influenza Neuraminidase Antigen is Crucial for its Biochemical Properties and Protective Efficacy

Supplementing influenza vaccines with recombinant neuraminidase (rNA) antigens remains a promising approach for improving the suboptimal vaccine efficacy. However, correlations among rNA designs, properties, and protection have not been systematically investigated. Here, we performed a comparative analysis of several rNAs produced using the baculovirus/insect cell system. The rNAs were designed with different tetramerization motifs and NA domains from a recent H1N1 vaccine strain (A/Brisbane/02/2018) and were compared for enzymatic property, antigenicity, stability, and protection in mice. We found that distinct enzymatic properties are associated with rNAs containing the NA head-domain versus the full-ectodomain, formation of higher order rNA oligomers is tetramerization domain-dependent, whereas protective efficacy is more contingent on the combination of the tetramerization and NA domains. Following single-dose immunizations, a rNA possessing the full-ectodomain and the tetramerization motif from the human vasodilator-stimulated phosphoprotein provided much better protection than a rNA with ∼10-fold more enzymatically active molecules that is comprised of the head-domain and the same tetramerization motif. In contrast, these two rNA designs provided comparable protection when the tetramerization motif from the tetrabrachion protein was used instead. These findings demonstrate that individual rNAs should be thoroughly evaluated for vaccine development, as the heterologous domain combination can result in rNAs with similar key attributes but vastly differ in protection. IMPORTANCE For several decades it has been proposed that influenza vaccines could be supplemented with recombinant neuraminidase (rNA) to improve the efficacy. However, some key questions for manufacturing stable and immunogenic rNA remain to be answered. We show here that the tetramerization motifs and NA domains included in the rNA construct design can have a profound impact on the biochemical, immunogenic and protective properties. We also show that the single-dose immunization regimen is more informative for assessing the rNA immune response and protective efficacy, which is surprisingly more dependent on the specific combination of NA and tetramerization domains than common attributes for evaluating NA. Our findings may help to optimize the design of rNAs that can be used to improve or develop influenza vaccines.