Self-assembly of the domestic cat hepadnavirus core antigen (DCHcAg) into virus-like particles (VLPs).

Domestic cat hepadnavirus (DCHBV) is an emerging Orthohepadnavirus associated with chronic hepatitis and hepatocellular carcinoma in cats, sharing structural similarity with human hepatitis B virus (HBV). We successfully expressed the DCHBV core antigen (DCHBVcAg) in a baculovirus-insect cell system and demonstrated its self-assembly into virus-like particles (VLPs). Full-length DCHBVc and C-terminally truncated DCHBVc (residues 1-149) were expressed in Sf9 cells, formed dimers, and purified by sucrose gradient ultracentrifugation. Transmission electron microscopy showed both constructs assembled into icosahedral, non-enveloped VLPs with diameters of 30.2 ± 2.0 nm (DCHBVc) and 26.0 ± 2.4 nm (DCHBVc), confirming that the N-terminal assembly domain is sufficient for capsid formation. Due to its phylogenetic distance from HBV and likely lack of pre-existing immunity in non-feline species, DCHBVcAg offers a novel VLP scaffold for chimeric vaccine development, epitope display, and hepadnavirus research without anti-HBc antibody interference. This establishes DCHBVcAg-based VLPs as a versatile tool for veterinary vaccinology and comparative virology.