Inhibition of interferon signaling improves rabbit calicivirus replication in biliary organoid cultures.

The Rabbit hemorrhagic disease virus (RHDV) was discovered 40 years ago. This highly pathogenic virus threatens the integrity of ecosystems in the European rabbit's native range, while in Australia, it is used as a biocontrol tool to manage overabundant populations of feral European rabbits. Little is known about the life cycle of this virus due to the absence of a reliable cell culture system. In 2023, we developed a rabbit liver-derived organoid cell culture system that supports RHDV replication but is unable to sustain serial passaging in culture. Here, we report that the interferon signaling pathway inhibitor Ruxolitinib increases virus replication in organoid-derived monolayer cells and, for the first time, enables the serial passaging of RHDV in cell culture. Four consecutive passages were achieved with viral titers reaching the concentration of the initial virus stock as measured by real-time quantitative PCR. Immunofluorescence analysis showed that more cells are infected in the presence of Ruxolitinib. Furthermore, we noted that cells grew faster and formed healthier monolayers in the presence of the interferon inhibitor. To determine the cellular composition of the monolayers, we used single-cell RNA sequencing, revealing that our organoids consist largely of RHDV-permissive cholangiocytes. IMPORTANCE: In this work, we describe the use of an interferon inhibitor to enhance the permissiveness of our recently developed rabbit liver-derived organoid cell culture system for rabbit hemorrhagic disease viruses. The data show that interferon inhibitors offer a simple and cost-effective approach to increase the replication of difficult-to-grow viruses in culture systems that are not interferon-deficient.