New chimaeric hepatitis B virus core particles carrying hantavirus (serotype Puumala) epitopes: immunogenicity and protection against virus challenge

Virus-like particles generated by the heterologous expression of virus stru ctural proteins are able to potentiate the immunogenicity of foreign epitop es presented on their surface. In recent years epitopes of various origin h ave been inserted into the core antigen of hepatitis B virus (HBV) allowing the formation of chimaeric HBV core particles. Chimaeric core particles ca rrying the 45 N-terminal amino acids of the Puumala hantavirus nucleocapsid protein induced protective immunity in bank voles, the natural host of thi s hantavirus. Particles applied in the absence of adjuvant are still immuno genic and partially protective in bank voles. Although a C-terminally trunc ated core antigen of HBV (HBcAg Delta) tolerates the insertion of extended foreign sequences, for the construction of multivalent vaccines the limited insertion capacity is still a critical factor. Recently, we have described a new system for generating HBV 'mosaic particles' in an Escherichia coil suppressor strain based on a readthrough mechanism on a stop linker located in front of the insert. Those mosaic particles are built up by both HBcAg Delta and the HBcAg Delta/Puumala nucleocapsid readthrough protein. The par ticles formed presented the 114 amino acid (aa) long hantavirus sequence, a t least in part, on their surface and induced antibodies against the hantav irus sequence in bank voles. Variants of the stop linker still allowed the formation of mosaic particles demonstrating that stop codon suppression alo ne is sufficient for the packaging of longer foreign sequences in mosaic pa rticles. Another approach to increase the insertion capacity is based on th e simultaneous insertion of different Puumala nucleocapsid protein sequence s (aa 1-45 and aa 75-119) into two different positions (aa 78 and behind aa 144) of a single HBcAg molecule. The data presented are of high relevance for the generation of multivalent vaccines requiring a high insertion capac ity for foreign sequences. (C) 1999 Elsevier Science B.V. All rights reserv ed.