A Single Dose of Modified Vaccinia Ankara expressing Ebola Virus Like Particles Protects Nonhuman Primates from Lethal Ebola Virus Challenge

Abstract

Ebola virus (EBOV), isolate Makona, was the causative agent of the West African epidemic devastating predominantly Guinea, Liberia and Sierra Leone from 2013-2016. While several experimental vaccine and treatment approaches have been accelerated through human clinical trials, there is still no approved countermeasure available against this disease. Here, we report the construction and preclinical efficacy testing of a novel recombinant modified vaccinia Ankara (MVA)-based vaccine expressing the EBOV-Makona glycoprotein GP and matrix protein VP40 (MVA-EBOV). GP and VP40 form EBOV-like particles and elicit protective immune responses. In this study, we report 100% protection against lethal EBOV infection in guinea pigs after prime/boost vaccination with MVA-EBOV. Furthermore, this MVA-EBOV protected macaques from lethal disease after a single dose or prime/boost vaccination. The vaccine elicited a variety of antibody responses to both antigens, including neutralizing antibodies and antibodies with antibody-dependent cellular cytotoxic activity specific for GP. This is the first report that a replication-deficient MVA vector can confer full protection against lethal EBOV challenge after a single dose vaccination in macaques.

Figure 1

MVA-EBOV vaccine construction and expression. (a) Schematic of MVA-EBOV vaccine expressing EBOV-like particles. I8R and G1L, conserved vaccinia sequences flanking the insertion site for gp; A50R and B1R, conserved sequences flanking the insertion site for vp40. P_mH5, modified early late H5 vaccinia promoter. Numbers indicate positions in the MVA genome which is abbreviated and not to scale. (b) Western blot showing expression of EBOV GP (monoclonal Ab c6D8) and VP40 (polyclonal Ab) in 293 T cell lysates (LYS) and supernatants (SUP). Molecular weight markers are indicated to the left of blots. (c) Thin section electron micrograph showing the expression of EBOV-like particles. Arrows in (c) show examples of immunogold staining for GP. (d) Magnified thin section electron micrograph showing the immunogold staining of GP (black dots) without arrows.

Figure 2

MVA-EBOV protection study in guinea pigs. (a) Survival curves for animals primed at week 0 and boosted at week 4 with MVA-EBOV or MVAwt. Controls are unvaccinated animals. At 8 weeks (day 0) all animals were challenged with the EBOV-Mayinga-based GPA-EBOV. (b) Body weight changes post challenge. (c) Anti-GP-specific Ab measured pre-immunization (pre), at 4 weeks after the prime (Wk4) and 2 weeks after the boost (Wk6). (d) Neutralizing Ab measured as 50% focus reduction neutralization titer (FRNT₅₀). Significance levels are indicated as follows: p < 0.05 (*), p < 0.01 (**), p < 0.001 (***) and p < 0.0001 (****).

Figure 3

MVA-EBOV protection study in rhesus macaques. (a) Survival curves of animals receiving prime or prime/boost with MVA-EBOV or MVAwt (control) and challenge with EBOV-Makona on day 0. Viremia levels determined in whole blood samples over time by (b) virus titration and (c) RT-qPCR. (d) Counts of platelets in macaque whole blood samples over time. Levels of (e) aspartate amino transferase (AST) and (f) blood urea nitrogen (BUN) in the serum of challenged macaques over time. (g) EBOV titers in selected tissue samples of MVAwt control animals at the time of euthanasia. Significance levels are indicated as follows: p < 0.05 (*), and p < 0.01 (**). All other results are not statistically significant.

Figure 4

Humoral responses after vaccination and challenge. (a) EBOV GP-specific and (b) EBOV VP40-specific IgG during the immunization and challenge phases of the study. Arrows indicate days of vaccination (V; day −56, −28) and challenge (C, day 0). (c) Neutralizing titers on day 0 and 42 of the study. (d) ADCC activity pre-immunization (day −28 for prime group and day −56 for prime/boost group) and on day −7 (pre-challenge). Significance level is indicated as p < 0.05 (*); all other results are not statistically significant.