C3d enhancement of antibodies to hemagglutinin accelerates protection against influenza virus challenge

Abstract

The ability of the C3d component of complement to enhance antibody responses and protective immunity to influenza virus challenges was evaluated using a DNA vaccine encoding a C3d fusion of the hemagglutinin (HA) from influenza virus. Plasmids were generated that encoded a transmembrane HA (tmHA), a secreted form of HA (sHA), or a sHA fused to three tandem copies of the murine homologue of the C3d (sHA-3C3d). Analysis of the titers, avidity maturation, and hemagglutinin-inhibition activity of raised antibody revealed that immunizations with sHA-3C3d DNA accelerated both the avidity maturation of antibody to HA and the appearance of hemagglutinin-inhibition activity. These accelerated antibody responses correlated to a more rapid appearance of protective immunity. They also correlated to complete protection from live virus challenge by a single vaccination at a dose ten times lower than the protective dose for non-C3d forms of HA.

C3d Enhances Immune Responses Using Low Doses of DNA Expressing the HIV-1 Envelope from Codon-Optimized Gene Sequences

“…2). As previously reported [16,31,32], mice vaccinated with wt-gp120-mC3d 3 -DNA elicited significantly higher titers of anti-Env specific antibody compared to mice vaccinated with wt-gp120-DNA (p>0.05) (Fig. 2A).…”

“…The molecular adjuvant, C3d, has been shown to enhance the immunogenicity of viral, bacterial, and self antigens (T-dependent and T-independent) when inoculated as either DNA or protein in both inbred and outbred mice strains [4,5,12,16,17,19,21,24,31,32,35,36,38,39]. Overall, the inoculation of C3d fused antigens as protein immunogens seems to produce more consistent results than DNA expressing the same protein in-vivo.…”

“…In order to enhance the immune responses elicited by a DNA vaccine, we used two effective approaches which, independently, enhance antibody titer and cellular responses against HIV-1 envelope glycoproteins; the use of C3d as a molecular adjuvant [5,16,19,21,24,31,32] and enhanced protein expression from codon-optimized gene sequences [2,3,10,37,41]. Therefore, in this study, DNA vaccines expressing one of four gp120 molecules from wild type HIV-1 gene sequences or sequences that were optimized for expression in mammalian cells (codonoptimized) were used to immunize mice.…”

“…Plasmid DNA pTR600, a eukaryotic expression vector, has been described previously [31,32]. Briefly, the vector was constructed to contain the cytomegalovirus immediate-early promoter (CMV -IE) plus intron A (IA) for initiating transcription of eukaryotic inserts and the bovine growth hormone polyadenylation signal (BGH poly A) for termination of transcription.…”

“…Independently, each approach enhances antibody titer and cellular responses against Env compared to DNA plasmidsexpressing wild-type (wt) env gene inserts only. The fusion of C3d to an antigen results in enhanced immunogenicity to the fused antigen [5,16,17,19,21,24,31,32,35,36]. Rodents inoculated with DNA plasmids expressing HIV-1 Env fused to multiple copies of human or murine C3d (mC3d) had enhanced anti-Env specific IgG titers and accelerated affinity maturation of antibody [16].…”