Safety and immunogenicity of DNA vaccines encoding Ebolavirus and Marburgvirus wild-type glycoproteins in a phase I clinical trial

Abstract

Background: Ebolavirus and Marburgvirus cause severe hemorrhagic fever with high mortality and are potential bioterrorism agents. There are no available vaccines or therapeutic agents. Previous clinical trials evaluated transmembrane-deleted and point-mutation Ebolavirus glycoproteins (GPs) in candidate vaccines. Constructs evaluated in this trial encode wild-type (WT) GP from Ebolavirus Zaire and Sudan species and the Marburgvirus Angola strain expressed in a DNA vaccine.

Methods: The VRC 206 study evaluated the safety and immunogenicity of these DNA vaccines (4 mg administered intramuscularly by Biojector) at weeks 0, 4, and 8, with a homologous boost at or after week 32. Safety evaluations included solicited reactogenicity and coagulation parameters. Primary immune assessment was done by means of GP-specific enzyme-linked immunosorbent assay.

Results: The vaccines were well tolerated, with no serious adverse events; 80% of subjects had positive enzyme-linked immunosorbent assay results (≥30) at week 12. The fourth DNA vaccination boosted the immune responses.

Conclusions: The investigational Ebolavirus and Marburgvirus WT GP DNA vaccines were safe, well tolerated, and immunogenic in this phase I study. These results will further inform filovirus vaccine research toward a goal of inducing protective immunity by using WT GP antigens in candidate vaccine regimens.

Clinical trials registration: NCT00605514.

Keywords: DNA; ebola; ebolavirus; filovirus; marburg; marburgvirus; vaccine.

Figure 1.

Schematic diagram of study design, vaccination schedule and follow-up showing screening, enrollment, and follow-up. The original protocol design included 3 study vaccinations at day 0 and weeks 4 and 8, with 32 weeks of follow-up. An optional fourth vaccination was added by amendment with 12 weeks of additional follow-up. Abbreviation: WT, wild-type.

Figure 2.

Glycoprotein (GP)-specific mean antibody responses assessed by enzyme-linked immunosorbent assay (ELISA) for GP (AN), GP (S), and GP (Z). Mean titers with upper 95% confidence intervals are shown for 3 time points: 4 and 24 weeks after the third vaccination and 4 weeks after the fourth DNA vaccination. The threshold for positivity in this assay was a reciprocal dilution of 30 and is indicated by a dashed line.

Figure 3.

Ebolavirus and Marburgvirus neutralization as the percentage of infection in the presence of subject serum samples relative to control infection. Neutralization is represented as the percentage of infection in the presence of subject serum samples relative to control infection in the absence of serum samples. Results are shown for 9 of 10 EBO vaccinees (A) and 9 of 10 MAR vaccinees (B) at 3 time points: at baseline (preimmune) and after the third and fourth DNA vaccinations.

Figure 4.

Frequency of CD4⁺ and CD8⁺ T-cell responses by intracellular cytokine staining and enzyme-linked immunospot assay (ELISPOT) analysis. The percentage of responders is shown for each vaccine antigen at 4 time points for CD4⁺ and CD8⁺ intracellular cytokine staining and ELISPOT.