Hepatitis C virus (HCV) chronically infects 300 million people world-wide. Current treatments for HCV cause severe debilitating side effects and have limited efficacy. No vaccines have been developed to prevent HCV infection to date because of the need to provide protection against the 7 circulating genotypes that differ by up to 30% at the nucleotide level. HCV encodes two envelope glycoproteins, E1 and E2. While the function of E1 remains unclear, the N-terminal 277 amino acids of E2 constitute the receptor-binding domain (RBD) which interacts with the major cell surface receptor CD81. Within the RBD are three variable regions, the immunodominant hypervariable region 1 (HVR1) and two variable regions of unknown function, HVR2 and the intergenotypic variable region (igVR). Antibodies directed towards HVR1 can prevent infection by homologous strains of virus but do not cross-react with heterologous strains, driving immune escape. It has been suggested that HVR1 acts as an immune decoy. Using a recombinant form of the E2 RBD, we have demonstrated that all 3 variable regions can be deleted from the RBD (Delta3) whilst retaining its native fold and the ability to interact with CD81 (1). Delta3 therefore comprises the conserved E2 core domain. To compare the immunogenicity of intact E2 and Delta3, we conducted vaccine trials in mice and guinea pigs. Delta3 increases the titre of antibody capable of inhibiting the interaction between E2 and CD81 and elicits higher titres of antibody capable of neutralising heterologous strains of HCV compared to intact E2 RBD. Delta3 refocusses the immune response towards the conserved E2 core domain including conserved neutralization epitopes. We propose that HVR2 and the igVR shield the underlying conserved CD81 binding site and neutralization epitopes. Delta3 is expressed as a mixture of different disulphide-linked oligomeric forms. Gel filtration was used to purify these different oligomeric forms and antibodies were generated. Monomeric and dimeric forms of Delta3 only neutralize homologous strains of virus while trimeric and larger forms of Delta3 elicit potent cross-neutralizing antibodies. These studies suggest that the Delta3 antigen is a lead vaccine candidate for the prevention of HCV.