Generation of chimeric HBc proteins with epitopes in E.coli: Formation of virus-like particles and a potent inducer of antigen-specific cytotoxic immune response and anti-tumor effect in vivo

The major aim of the project was to develop the virus-like particles (VLPs) displaying single or multi-epitope of hepatocellular carcinomas (HCC) in Escherichia coli and to evaluate the effect on inducing Ag-specific CD8+ T cell response and antitumor efficacy as candidate vaccines. To this end, hepatitis B virus core (HBc) particles were used as a carrier of HCC epitopes. Four HCC epitopes MAGE-1(278–286aa), MAGE-3(271–279aa), AFP1 (158–166aa) or AFP2 (542–550aa) were fused to the 3′ terminus of the truncated HBV core gene, respectively, or conjunctively. Not all recombinant plasmids led to expression of chimeric proteins in expression strain E. coli BL21 (DE3), but chimeric proteins which are expressed in inclusion bodies resulted in the formation of complete “mature” VLPs. E. coli-derived truncated HBc(1–144) chimeric protein self-assembled into VLPs that both morphologically and physically are similar to the wild-type ones and they still remained activity after purification and refolding from 6 M urea solution. We also showed that they could be internalized and presented by DCs in vitro. Additionally, DCs pulsed with the chimeric HBc-VLPs could induce stronger CTL activity and greater IFN-γ secretion by responding T cells compared with peptid-pulsed DCs. In the B16-pIR-HH tumor therapy model, the growth of established tumors was significantly inhibited by immunization using VLP-pulsed DCs, resulting in significantly higher survival rate of immunized animals. Thus, the results of the current study have demonstrated the principal possibility of using VLP on the basis of HBcAg for creation of a new type of HCC-specific immunogen.