Akaluc bioluminescence offers superior sensitivity to track in vivo dynamics of SARS-CoV-2 infection (preprint)

Monitoring in vivo viral dynamics can improve our understanding of pathogenicity and tissue tropism. For positive-sense, single-stranded RNA viruses, several studies have attempted to monitor viral kinetics in vivo using reporter genomes. The application of such recombinant viruses can be limited by challenges in accommodating bioluminescent reporter genes in the viral genome. Conventional luminescence also exhibits relatively low tissue permeability and thus less sensitivity for visualization in vivo. Here we show that unlike NanoLuc bioluminescence, the improved method, termed AkaBLI, allows visualization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in Syrian hamsters. By successfully incorporating a codon-optimized Akaluc luciferase gene into the SARS-CoV-2 genome, we visualized in vivo infection, including the tissue-specific differences associated with particular variants. Additionally, we could evaluate the efficacy of neutralizing antibodies and mRNA vaccination by monitoring changes in Akaluc signals. Overall, AkaBLI is an effective technology for monitoring viral dynamics in live animals.

Virological characteristics of the SARS-CoV-2 XBB.1.5 variant (preprint)

Circulation of SARS-CoV-2 Omicron XBB has resulted in the emergence of XBB.1.5, a new Variant of Interest. Our phylogenetic analysis suggests that XBB.1.5 evolved from XBB.1 by acquiring the F486P spike (S) mutation, subsequent to the acquisition of a nonsense mutation in ORF8. Neutralization assays showed similar abilities of immune escape between XBB.1.5 and XBB.1. We determined the structural basis for the interaction between human ACE2 and the S protein of XBB.1.5, showing similar overall structures between the S proteins of XBB.1 and XBB.1.5. The intrinsic pathogenicity of XBB.1.5 in hamsters is lower than that of XBB.1. Importantly, we found that the ORF8 nonsense mutation of XBB.1.5 resulted in impairment of MHC expression. In vivo experiments using recombinant viruses revealed that the XBB.1.5 mutations are involved with reduced virulence of XBB.1.5. Together, these data suggest that the mutations in ORF8 and S could enhance spreading of XBB.1.5 in humans.