Drug resistance mutations of hepatitis B virus (HBV) influence the yield of the virions of the human hepatitis delta virus (HDV) and their infectivity

This work analyzed 30 drug resistance mutations (DRMs) in the surface antigen of hepatitis B virus (HBV) (i.e., HBsAg) selected by several FDA-approved anti-HBV nucleos(t)ide analogs. All DRM-bearing HBsAg variants supported the formation and secretion of hepatitis delta virus (HDV), and only 13/30 DRMs considerably decreased the yield of secreted HDV virions. However, the majority of DRMs (23/30) greatly reduced HDV infectivity, and four of them even caused the complete loss of infectivity, which was determined by analyzing the levels of HDV RNA genomes in the infected cells, and the fraction of HDV-infected cells. The ability to inhibit HDV infectivity was observed for DRMs located in the large cytosolic loop (LCL), major antigenic loop (MAL), HDV-binding site (HDV-BS), and the transmembrane domains II, III, and IV of HBsAg, which suggested that DRMs mediate their inhibitory influence by both direct and indirect mechanisms that could alter the attachment/entry, post-entry trafficking, and/or subsequent uncoating of the virions. This report also established the transmembrane domains II, III, and IV as critical regulators of the overall infectivity of HDV virions. It became apparent that in the settings of natural HBV/HDV infection, DRMs can therefore greatly reduce the spread/superinfection of HDV and diminish the size of the HDV reservoir in chronically infected livers. Overall, our findings advanced the understanding of how anti-HBV drug treatments influence the HDV life cycle, the roles of HBV envelope proteins in facilitating the assembly and infectivity of HDV, and the mechanism of complex HBV-HDV interactions. IMPORTANCE: The study showed that the drug resistance mutations (DRMs) in the surface antigen of hepatitis B virus (HBsAg) can greatly reduce hepatitis delta virus (HDV) assembly and infectivity. Since most of the tested DRMs considerably reduced HDV infectivity, and four of them resulted in a complete loss of the infectivity, such effects can lead to suppression of HDV spread/superinfection and reduction of the HDV reservoir in the infected liver. If most detrimental for infectivity DRMs are present on the majority of HBsAg molecules, this could facilitate substantial suppression of chronic HDV infection and possibly reduce HDV-associated liver pathogenesis. It was also determined that DRMs located in the transmembrane domains II, III, and IV of HBsAg could critically alter HDV infectivity. Our findings therefore suggest that different HBsAg regions work in the intramolecular coordinating concert, facilitating the assembly and infectivity of the virions, and that certain short- and long-distance interactions between different regions of HBsAg take place.