The majority of the CCHFV-M vaccinated mice developed both IgG1 and IgG2c responses following three vaccinations.

<p>Prior to challenge, CCHFV-specific antibody isotypes and the antibody avidity were examined by ELISA against the CCHF_VLP. A) The CCHFV-specific IgG1 and IgG2c response in individual mice following three vaccinations. Pooled sera from IFNAR^-/- and WT C57BL/6 mice vaccinated with empty vector were tested concurrently and had no detectable signal. B) The avidity of the CCHFV-specific antibody response in vaccinated mice following three vaccinations was measured. For (A) and (B) mice that died after CCHFV challenge are shown in red. *Two-way ANOVA, confidence intervals were set to 95%.</p

CCHFV-M vaccinated mice developed CCHFV-specific neutralizing antibodies following three vaccinations, and the response was enhanced with the addition of complement.

<p>Prior to challenge, neutralization titers were measured against the CCHF_VLP, with and without complement. Mice that died following challenge are highlighted in red. *Two-way ANOVA confidence intervals were set to 95%.</p

<i>In vitro</i> expression of the glycoprotein genes from the CCHFV-M DNA vaccine plasmid.

<p>A) The total (permeabilized cells) and surface presence (non-permeabilized cells) of G_C was examined 44 h after transfection of COS-7 cells with wild-type CCHFV-M, optimized CCHFV-M, or empty vector, the maximum expression was seen at 250 ng of each plasmid (shown). B) <i>In vitro</i> expression by Western blot of G_N (37 kDa) and G_C (75 kDa) in COS-7 cells 44 h after transfection of CCHFV-M or empty vector, 250 ng of each plasmid.</p

N-specific antibodies in post-challenge sera of CCHFV-M vaccinated mice.

<p>Sera from vaccinated mice that survived CCHFV challenge (28 days post-challenge) were examined by ELISA for antibodies against N.</p

A DNA vaccine for Crimean-Congo hemorrhagic fever protects against disease and death in two lethal mouse models

<div><p>Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus capable of causing a severe hemorrhagic fever disease in humans. There are currently no licensed vaccines to prevent CCHFV-associated disease. We developed a DNA vaccine expressing the M-segment glycoprotein precursor gene of CCHFV and assessed its immunogenicity and protective efficacy in two lethal mouse models of disease: type I interferon receptor knockout (IFNAR^-/-) mice; and a novel transiently immune suppressed (IS) mouse model. Vaccination of mice by muscle electroporation of the M-segment DNA vaccine elicited strong antigen-specific humoral immune responses with neutralizing titers after three vaccinations in both IFNAR^-/- and IS mouse models. To compare the protective efficacy of the vaccine in the two models, groups of vaccinated mice (7–10 per group) were intraperitoneally (IP) challenged with a lethal dose of CCHFV strain IbAr 10200. Weight loss was markedly reduced in CCHFV DNA-vaccinated mice as compared to controls. Furthermore, whereas all vector-control vaccinated mice succumbed to disease by day 5, the DNA vaccine protected >60% of the animals from lethal disease. Mice from both models developed comparable levels of antibodies, but the IS mice had a more balanced Th1/Th2 response to vaccination. There were no statistical differences in the protective efficacies of the vaccine in the two models. Our results provide the first comparison of these two mouse models for assessing a vaccine against CCHFV and offer supportive data indicating that a DNA vaccine expressing the glycoprotein genes of CCHFV elicits protective immunity against CCHFV.</p></div

CCHFV-specific IgG ELISA titers increase following each vaccination.

<p>The CCHFV-specific ELISA titers following three vaccinations are similar in IFNAR^-/- and WT C578BL/6 mice before challenge. A) Mouse sera were pooled in each vaccination group and the CCHFV-specific IgG antibodies were measured by CCHF_VLP ELISA following each vaccination with the optimized CCHFV-M vaccine. Vaccinations were performed at weeks 0, 3, and 6. B) The CCHFV IgG ELISA titers for individual mice 1 week prior to challenge; mice that died after CCHFV challenge are shown in red. *One-way ANOVA, confidence intervals were set to 95%.</p