Species-specific immunogenicity and protective efficacy of a vesicular stomatitis virus-based Sudan virus vaccine: a challenge study in macaques

Abstract

Background: The recent Sudan virus (SUDV) outbreak in Uganda highlights the need for rapid response capabilities, including development of vaccines against emerging viruses with high public health impact. We aimed to develop a Sudan virus-specific vaccine suitable for emergency use during outbreaks.

Methods: We generated and characterised a vesicular stomatitis virus (VSV)-based vaccine, VSV- SUDV, and evaluated the protective efficacy following a single-dose vaccination against lethal SUDV infection in non-human primates (NHPs). We used male and female cynomolgus macaques (n=11) aged 6-11 years and weighing 3·8-9·0 kg. Animals received a 1 mL intramuscular injection for vaccination containing either 1 × 10⁷ plaque forming units (PFU) VSV-SUDV or 1 × 10⁷ PFU of a VSV-based vaccine against Marburg virus (control; five NHPs). NHPs were challenged intramuscularly 28 days after vaccination with 1 × 10⁴ TCID₅₀ SUDV-Gulu. We assessed anaesthetised NHPs on days 28, 21, 14, and 7 before challenge; days 0, 3, 6, 9, 14, 21, 28, and 35 after challenge; and at euthanasia (day 40 for survivors). As we repurposed NHPs from a successful VSV-Ebola virus (EBOV) vaccine efficacy study, we also investigated VSV-EBOV's cross-protective potential against SUDV challenge.

Findings: Of the six NHPs given VSV-SUDV, none showed any signs of disease in response to the challenge. Four of the five NHPs in the control group developed characteristic clinical signs of Sudan virus diseases. SUDV glycoprotein-specific IgG concentrations peaked 14 days after vaccination (titre of >1:10 000) and reached their highest concentrations at 6 days after challenge (1:25 600-1:102 400). Although the NHPs developed cross-reactive humoral responses to SUDV after VSV-EBOV vaccination and EBOV challenge, there was little cross-protection.

Interpretation: These data emphasise the need for species-specific vaccines for each human-pathogenic Ebolavirus. Furthermore, although previous VSV-EBOV immunity is boosted through VSV-SUDV vaccination, it only has a small effect on the immunogenicity and protective efficacy of VSV-SUDV vaccination against SUDV challenge.

Funding: Intramural Research Program, US National Institute of Allergy and Infectious Diseases, National Institutes of Health.

Figure 1:. Survival and clinical changes in NHPs after SUDV challenge

Two groups of NHPs were vaccinated with VSV-SUDV (six NHPs) or control vaccine (VSV-MARV; five NHPs) and challenged 4 weeks later with SUDV. Survival (A), clinical scores (B), lymphocytes (C), and viraemia by real-time quantitative PCR (D) and titration (E) are shown. Serum concentrations of aspartate aminotransferase (F), alanine phosphatase (G), blood urea nitrogen (H), and albumin (I) were measured. Significant differences in the survival curves were determined using log-rank analysis. See appendix (pp 2–3) for details of TCID₅₀ equivalents. MARV=Marburg virus. NHP=non-human primate. SUDV=Sudan virus. TCID₅₀=median tissue culture infectious dose. VSV=vesicular stomatitis virus.

Figure 2:. Histopathology after SUDV challenge

(A) At the time of euthanasia, liver and spleen necropsy samples were collected (day 6–7 after challenge for the control group; 40 days after challenge for the vaccinated group), inactivated, processed, and stained with haematoxylin and eosin (upper row of images). Immunohistochemistry of samples is shown in the bottom row of images. SUDV antigen (VP40) was detected in control NHPs only. Immunoreactive cells are brown. Sections from a representative animal in each group are shown. Magnification ×200; scale bar 50 μm. (B) SUDV titres in control NHPs at the time of euthanasia. NHP=non-human primate. SUDV=Sudan virus. TCID₅₀=median tissue culture infectious dose.

Figure 3:. Humoral immune responses after vaccination and SUDV challenge

Serum IgG concentrations specific for EBOV glycoprotein (A), SUDV glycoprotein (B), and VSV (C) were measured over time. Geometric mean and geometric SD are shown. Statistical significance was determined by two-way ANOVA with Tukey’s multiple comparisons test. (D) Serum neutralisation presented as FRNT₅₀ of green fluorescence protein-positive cells at the time of vaccination (day 28 before challenge), challenge (day 0 after challenge), and euthanasia (day 40 after challenge [study end]). The dotted line shows the limit of detection. EBOV=Ebola virus. FRNT₅₀=50% fluorescence reduction. SUDV=Sudan virus. VSV=vesicular stomatitis virus.