Nucleic acid vaccines against hepatitis viruses.

Direct DNA intramuscular or intradermal injection of plasmids containing viral genes under the control of viral promoters is an efficient means of stimulating both class I and class II-mediated antiviral responses. Viral hepatitis B and C are suitable candidates for this approach, particularly as therapeutic immunogens for chronically infected individuals. Several groups have shown that the S gene of HBV is expressed in murine muscle and stimulates a high titre and long-lasting anti-HBs response. Uniquely, CD8+ CTL responses are also induced to HBsAg. No vaccine exists for HCV. Therefore the structural genes (C + E1 + E2) have been cloned as a 2,831 bp fragment from a genotype la isolate into the vector pcDNA3. The resulting plasmid DNA was injected directly into the quadriceps muscle of three-week-old BALB/c mice. Intracellular-expressed E1 and E2 proteins thus represent the complete spectrum of native structural epitopes, including those dependent on glycosylation and protein folding. Mouse antisera were tested for reactivity against conserved sequences using overlapping 7-mer peptides. Two conserved, overlapping epitopes were identified in E2 spanning residues 581-591 and 590-603. This domain represents one of seven major E2 antigenic domains recognized by HCV human antibodies, one of three with antigenic homologies to related flavivirus proteins. Thus antigen is presented with high efficiency following DNA injection and offers the potential of high rates of seroconversion and virus clearance in those predisposed to virus-induced chronic liver disease.