Humoral and CD4(+) T helper (Th) cell responses to the hepatitis C virus non-structural 3 (NS3) protein: NS3 primes Th 1-like responses more effectively as a DNA-based immunogen than as a recombinant protein

The non-structural 3 (NS3) protein is one of the most conserved proteins of hepatitis C virus, and T helper 1 (Th1)-like responses to NS3 in humans co rrelate with clearance of infection. Several studies have proposed that DNA -based immunizations are highly immunogenic and prime Th1-like responses, a lthough few head-to-head comparisons with exogenous protein immunizations h ave been described. A full-length NS3/NS4A gene was cloned in eukaryotic ve ctors with expression directed to different subcellular compartments. Inbre d mice were immunized twice in regenerating tibialis anterior (TA) muscles with either plasmid DNA or recombinant NS3 (rNS3), After two 1-10 mug DNA i mmunizations, specific antibody titres of up to 12960 were detected at week 5, dominated by IgG2a and IgG2b, NS3-specific CD4(+) T cell responses in D NA-immunized mice peaked at day 1 3, as measured by proliferation and IL-2 and IFN-gamma production. Mice immunized with 1-10 mug rNS3 without adjuvan t developed antibody titres comparable to those of the DNA-immunized mice, but dominated instead by IgG1, CD4+ T cell responses in these mice showed p eaks of IL-2 response at day 3 and IL-6 and IFN-gamma responses at day 6, W ith adjuvant, rNS3 was around 10-fold more immunogenic with respect to spee d and magnitude of the immune responses, Thus, immunization with rNS3 in ad juvant is superior to DNA immunization with respect to kinetics and quantit y in priming specific antibodies and CD4+ T cells. However, as a DNA immuno gen, NS3 elicits stronger Th1-like immune responses, whereas rNS3 primes a mixed Th1/Th2-like response regardless of the route, dose or adjuvant.