The hepatitis B core antigen is a widely accepted carrier particle to enhance the immunogenicity of foreign epitopes. From electron cryomicroscopy, the immunodominant region between amino acid positions 79 to 81 is known to protrude from the surface of the shells. It can be replaced by heterologous sequences without interfering with the particleforming capacity in many cases. Here we have introduced various V3 sequences of the envelope protein of different subtypes (A, B, O) of HIV-1/gp120 in order to enhance their immunogenicity and broaden the immune response against the virus. To improve purification efficiency and solubility of the E. coliexpressed hybrids, six histidine residues were fused to amino acid 156. An adjustable purification scheme was utilised including denaturation, Ni[2+]NTA affinity chromatography and particle renaturation under high salt conditions, resulting in highly pure antigen preparations. The hybrids reacted specifically with sera of HIV-1- infected patients. They further induced an autologous, subtypespecific anti HIV-1 antibody response superior to that of Keyhole limpethaemocyaninecoupled peptides.
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