Polyhistidine-tagged hepatitis B core particles as carriers of HIV-1/gp120epitopes of different HIV-1 subtypes

The hepatitis B core antigen is a widely accepted carrier particle to enhan ce the immunogenicity of foreign epitopes. From electron cryomicroscopy, th e immunodominant region between amino acid positions 79 to 81 is known to p rotrude from the surface of the shells. It can be replaced by heterologous sequences without interfering with the particle-forming capacity in many ca ses. Here we have introduced various V3 sequences of the envelope protein o f different subtypes (A, B, O) of HIV-1/gp120 in order to enhance their imm unogenicity and broaden the immune response against the virus. To improve p urification efficiency and solubility of the E. coli-expressed hybrids, six histidine residues were fused to amino acid 156. An adjustable purificatio n scheme was utilised including denaturation, Ni2+-NTA affinity chromatogra phy and particle renaturation under high salt conditions, resulting in high ly pure antigen preparations. The hybrids reacted specifically with sera of HIV-1-infected patients. They further induced an autologous, subtype-speci fic anti-HIV-1 antibody response superior to that of Keyhole limpet-haemocy anine-coupled peptides.