Development of HBc virus-like particles as modular nanocarrier by intein-mediated trans-splicing

Hepatitis B virus core protein (HBc) spontaneously assembles as Virus-like particles (VLPs) in Escherichia coli (E. coli) which is extensively used as a nanocarrier to boost antigen immunogenicity. Genetic fusion of cargo protein with HBc occasionally forms inclusion bodies instead of properly assembled VLPs. To this end, we devised HBc VLPs as a modular nanocarrier for antigen delivery by intein-mediated trans-splicing (TS). We introduced split intein (int) to the C-terminus of split HBc N-core to employ intein-mediated TS technology to HBc VLPs. Split HBc with the insertion of int at N-core C-terminus (designated as HBc N-int-C) existed in inclusion bodies. Interestingly, introduction of a soluble tag, gb1, to int C-terminus remarkably improved the solubility of recombinant protein (named HBc N-int-gb1-C). Moreover, newly designed recombinant spontaneously assembled as VLPs and endowed efficiently coupling two different model antigens onto HBc N-int-gb1-C VLPs. Furthermore, model antigens delivered by HBc VLPs induced a dramatically enhanced antigen-specific immune responses. Antigen proteins mainly elicited Th2 IgG responses while antigens delivered by HBc VLPs steered Th1/Th2 balanced IgG responses. Taken together, intein-mediated TS was amenable to decorate HBc VLPs with antigens and showed good potential for antigen delivery.