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 correlate with clearance of
infection. Several studies have proposed that
DNA-based immunizations are highly immunogenic and prime Th1-like responses, although few head-to-head comparisons with exogenous
protein immunizations have been described. A full-length NS3/NS4A gene was cloned in eukaryotic vectors with expression directed to different subcellular compartments. Inbred mice were immunized twice in regenerating tibialis anterior (TA) muscles with either plasmid
DNA or recombinant NS3 (rNS3). After two 100 micrograms
DNA immunizations, specific antibody titres of up to 12960 were detected at week 5, dominated by
IgG2a and
IgG2b. NS3-specific CD4(+) T cell responses in
DNA-immunized mice peaked at day 13, as measured by proliferation and
IL-2 and IFN-gamma production. Mice immunized with 1-10 micrograms rNS3 without adjuvant developed antibody titres comparable to those of the
DNA-immunized mice, but dominated instead by
IgG1. CD4(+) T cell responses in these mice showed peaks of
IL-2 response at day 3 and
IL-6 and IFN-gamma responses at day 6. With adjuvant, rNS3 was around 10-fold more immunogenic with respect to speed and magnitude of the immune responses. Thus, immunization with rNS3 in adjuvant is superior to
DNA immunization with respect to kinetics and quantity in priming specific
antibodies and CD4(+) T cells. However, as
a DNA immunogen, NS3 elicits stronger Th1-like immune responses, whereas rNS3 primes a mixed Th1/Th2-like response regardless of the route, dose or adjuvant.