Accelerated vaccination for Ebola virus haemorrhagic fever in non-human primates

Abstract

Containment of highly lethal Ebola virus outbreaks poses a serious public health challenge. Although an experimental vaccine has successfully protected non-human primates against disease, more than six months was required to complete the immunizations, making it impractical to limit an acute epidemic. Here, we report the development of accelerated vaccination against Ebola virus in non-human primates. The antibody response to immunization with an adenoviral (ADV) vector encoding the Ebola glycoprotein (GP) was induced more rapidly than with DNA priming and ADV boosting, but it was of lower magnitude. To determine whether this earlier immune response could nonetheless protect against disease, cynomolgus macaques were challenged with Ebola virus after vaccination with ADV-GP and nucleoprotein (NP) vectors. Protection was highly effective and correlated with the generation of Ebola-specific CD8(+) T-cell and antibody responses. Even when animals were immunized once with ADV-GP/NP and challenged 28 days later, they remained resistant to challenge with either low or high doses of virus. This accelerated vaccine provides an intervention that may help to limit the epidemic spread of Ebola, and is applicable to other viruses.

Figure 1. Comparison of the Ebola-specific antibody responses by heterologous DNA/ADV prime–boost or ADV prime–boost vaccination in mice.

a, The time course of Ebola-specific antibody responses by DNA prime and adenovirus boost compared with adenoviral immunization alone is shown (see Methods). Data represent the relative ELISA titre to Ebola GP after immunization with DNA/ADV–GP or ADV–GP/ADV–GP in BALB/c mice using a log scale. b, Immunization schedule for previously used heterologous prime–boost vaccine (top), adenoviral prime and boost (middle), and single adenoviral virus (bottom) immunizations. Challenge was performed with a 1995 isolate of Ebola virus (Zaire) at 32, 10 or 4 weeks after the initial immunization, respectively.

Figure 2. Protection against lethal challenge in non-human primates using adenoviral priming and boosting.

Plasma viraemia in monkeys after infection with Ebola virus. Asterisks represent the time of death in control animals. The data represent the reciprocal endpoint dilution of serum for each monkey. Results are shown for four immunized animals challenged with Ebola Zaire at 13 PFUs (low dose; filled symbols, left), four immunized animals challenged at 1,500 PFUs (high dose; filled symbols, right), and five saline-injected control animals (open symbols).

Figure 3. Immune responses to adenoviral prime and boost vaccination in cynomolgus macaques.

a, Intracellular flow cytometry was performed to quantify IFN-γ production from Ebola-specific CD8 lymphocytes from saline injected (control) or ADV–GP/NP immunized (subject) monkeys at weeks 0 and 9. Immune responses before (day 0) and after (days 3, 6) challenge at week 10 are shown for CD8 cells. No substantial increases were observed in the CD4 population. Non-stimulated cells gave responses similar to those of the control subjects, at background levels. The gating strategy for FACs analysis is similar to previous analyses (Supplementary Information). b, ELISA titres of Ebola-specific antibodies in serum of vaccinated animals collected at week 0 (pre-immune, left), week 9 (pre-boost, middle) and week 10 (day of challenge, right) relative to the time of the first immunization. ELISA results represent endpoint dilution titres determined by optical density as described in Methods.

Figure 4. Protection against lethal challenge in non-human primates using a single adenoviral immunization.

a, Immunization and challenge were performed with the 1995 Zaire subtype Ebola virus as in Fig. 1b (bottom), and plasma viraemia in monkeys after challenge was measured as above (see Fig. 2 legend) for four immunized animals inoculated with 18 PFUs (low dose; filled symbols, left) and four animals injected with 1,762 PFUs (high dose; filled symbols, right) or two saline-injected controls (open symbols). b, Intracellular flow cytometry was performed using antibodies to TNF-α in CD4 and CD8 lymphocytes from immunized monkeys (subject), each panel representing an individual macaque. Immune responses before (day 0) and after (days 6, 10) challenge on day 28 are shown. Horizontal bars indicate the average value per group, and filled circles represent values for individual subjects. c, Endpoint dilution ELISA titres of Ebola-specific antibodies in serum collected two weeks after immunization with ADV–GP/NP, determined by optical density as described in Methods. d, Kaplan–Meier survival curve of macaques, immunized as indicated, and challenged with a low or high dose of PFUs of Ebola virus.