Development and characterisation of recombinant hepatitis delta virus-likeparticles

Injection of particulate hepatitis B virus surface antigen (HBsAg) in mice leads to the induction of a HBsAg-specific class-I-restricted cytotoxic T l ymphocyte (CTL) response. It is proposed that any protein internal to HBsAg will also be able to elicit a specific CTL response. In this study, severa l carboxy-terminal truncations of hepatitis C virus (HCV) core protein were fused to varying lengths of amino-terminal truncated large hepatitis delta antigen (L-HDAg). These constructs were analysed for their ability to be e xpressed and the particles secreted in the presence of HBsAg after transfec tion into HuH-7 cells. The secretion efficiency of the various HCV core-HDA g chimeric proteins was generally poor. Constructs containing full length H DAg appeared to be more stable than truncated versions and the length of th e inserted protein was restricted to around 40 amino acids. Thus, the use o f L-HDAg as a chimera to package foreign proteins is limited. Consequently, a polyepitope (polytope) containing a B-cell epitope from human papillomav irus (HPV 16) and multiple T-cell epitopes from the HCV polyprotein was use d to create the construct, L-HDAg-polyB. This chimeric protein was shown to be reliant on the co-expression of HBsAg for secretion into the cell cultu re fluid and was secreted more efficiently than the previous HCV core-HDAg constructs. These L-HDAg-polyB virus-like particles (VLPs) had a buoyant de nsity of similar to 1.2 g/cm(3) in caesium chloride and similar to 1.15 g/c m(3) in sucrose. The VLPs were also immunoprecipitated using an anti-HBs bu t not an anti-HD antibody. Thus, these recombinant VLPs have similar biophy sical properties to L-HDAg VLPs.