A novel toolbox for the in vitro assay of hepatitis D virus infection

Hepatitis D virus (HDV) is a defective RNA virus that requires the presence of hepatitis B virus (HBV) for its life cycle. The in vitro HDV infection system is widely used as a surrogate model to study cellular infection with both viruses owing to its practical feasibility. However, previous methods for running this system were less efficient for high-throughput screening and large-scale studies. Here, we developed a novel method for the production of infectious HDV by adenoviral vector (AdV)-mediated transduction. We demonstrated that the AdV-based method yields 10-fold higher viral titers than the transient-transfection approach. The HDV-containing supernatant derived from AdV-infected Huh7 cells can be used as the inoculum in infectivity assays without requiring further concentration prior to use. Furthermore, we devloped a chemiluminescent immunoassay (HDV-CLEIA) to quantitatively determine intracellular HDAg with a dynamic range of 5-11,000 pg/mL. HDV-CLEIA can be used as an alternative approach to assess HDV infection. The advantages of our updated methodology were demonstrated through in vitro HDV infection of HepaRG cells and by evaluating the neutralization activity using antibodies that target various regions of the HBV/HDV envelope proteins. Together, the methods presented here comprise a novel toolbox of in vitro assays for studying HDV infection.