Priming biologically active antibody responses against an isolated, conformational viral epitope by DNA vaccination

The immunodominant, conformational "a" determinant of hepatitis B surface Ag (HBsAg) elicits Ab responses. We selectively expressed the Ab-binding, glycosylated, native a determinant (residue 120-147) of HBsAg in a fusion protein containing C-terminally the HBsAg fragment SII (residue 80-180) fused to a SV40 T-Ag-derived hsp73-binding 77 aa (T₇₇) or non-hsp-binding 60 aa (T₆₀) N terminus. A DNA vaccine encoding non-hsp-binding secreted T₆₀-SII fusion protein-stimulated murine Ab responses with a similar efficacy as a DNA vaccine encoding the secreted, native, small HBsAg. A DNA vaccine encoding hsp73-binding, intracellular T₇₇-SII fusion protein-stimulated murine Ab responses less efficiently but comparable to a DNA vaccine encoding the intracellular, native, large HBsAg. HBsAg-specific Abs elicited by either the T₆₀-SII-expressing or the T₇₇-SII-expressing DNA vaccine suppressed HBsAg antigenemia in transgenic mice that produce HBsAg from a transgene in the liver; hence, a biologically active B cell response cross-reacting with the native, viral envelope epitope was primed by both DNA vaccine constructs. HBsAg-specific Ab and CTL responses were coprimed when an S_20-50 fragment (containing the immunodominant, L^d-binding epitope S_28-39) of HBsAg was fused C-terminally to the pCI/T₇₇-SII sequence (pCI/T₇₇-SII-L^d DNA vaccine). Chimeric, polyepitope DNA vaccines encoding conformational, Ab-binding epitopes and MHC class I-binding epitopes can thus efficiently deliver antigenic information to different compartments of the immune system in an immunogenic way.