Polytope DNA vaccine development against hepatitis C virus: a streamlined approach from in silico design to in vitro and primary in vivo analyses in BALB/c mice.

For chronic viral infections like Hepatitis C, CD8-CTLs have emerged as important protective tools. Hence, isolated dominant epitopes arranged as polytope DNA or peptide vaccines represent a promising approach. However, because of controversial rules governing the polytope construction and epitope processing, proper design and primary analysis of such vaccines are prior to the costly transgenic animal studies. In this study, based on in silico epitope selection, four HLA-A2 (C132, E614 and N1406) and H-2d (E405 and C132) immunodominant CD8-epitopes of HCV were selected. The codon optimized nucleotide sequences of the epitopes were assembled by overlap extension PCR in three different sequential tandems for the best proteasomal cleavage predictions and cloned into pcDNA3.1 vector. In addition, to enhance particulate formation, three other plasmids containing the fusion of polytopes with hepatitis B surface antigen gene (HBsAg) were also constructed. Proper expression of all constructs in transfected Cos-7 cells was verified by RT-PCR, immunofluorescence, Western-blot, ELISA and dot blot techniques. Moreover, particle formation of HBsAg-fused polytopes was manifested by their secretion to the culture media albeit in lesser amounts compared to sole HBsAg protein. Finally, the positive delayed-type hypersensitivity (DTH) response of vaccinated mice indicated the in vivo expression of all constructs and efficient stimulation of immune response, which was stronger for HBsAg fusion constructs. In addition, proper processing of the epitopes was evidenced by the DTH response towards H-2d epitopic peptides. These data provide enough support and merit for the further evaluation of the designed constructs in HLA-A2 transgenic mice.