Search

Ebola virus (EBOV) causes severe and often fatal hemorrhagic fever in humans and nonhuman primates (NHPs). Currently, there are no licensed vaccines or therapeutics for human use. Recombinant vesicular stomatitis virus (rVSV)-based vaccine vectors, which encode an EBOV glycoprotein in place of the VSV glycoprotein, have shown 100% efficacy against homologous Sudan ebolavirus (SEBOV) or Zaire ebolavirus (ZEBOV) challenge in NHPs. In addition, a single injection of a blend of three rVSV vectors completely protected NHPs against challenge with SEBOV, ZEBOV, the former Côte d'Ivoire ebolavirus, and Marburg virus. However, recent studies suggest that complete protection against the newly discovered Bundibugyo ebolavirus (BEBOV) using several different heterologous filovirus vaccines is more difficult and presents a new challenge. As BEBOV caused nearly 50% mortality in a recent outbreak any filovirus vaccine advanced for human use must be able to protect against this new species. Here, we evaluated several different strategies against BEBOV using rVSV-based vaccines. Groups of cynomolgus macaques were vaccinated with a single injection of a homologous BEBOV vaccine, a single injection of a blended heterologous vaccine (SEBOV/ZEBOV), or a prime-boost using heterologous SEBOV and ZEBOV vectors. Animals were challenged with BEBOV 29–36 days after initial vaccination. Macaques vaccinated with the homologous BEBOV vaccine or the prime-boost showed no overt signs of illness and survived challenge. In contrast, animals vaccinated with the heterologous blended vaccine and unvaccinated control animals developed severe clinical symptoms consistent with BEBOV infection with 2 of 3 animals in each group succumbing. These data show that complete protection against BEBOV will likely require incorporation of BEBOV glycoprotein into the vaccine or employment of a prime-boost regimen. Fortunately, our results demonstrate that heterologous rVSV-based filovirus vaccine vectors employed in the prime-boost approach can provide protection against BEBOV using an abbreviated regimen, which may have utility in outbreak settings. Author Summary: Ebola viruses (EBOV), of which there are five species, are categorized as Category A Priority Pathogens and Tier 1 Select Agents by several US Government agencies as a result of their high mortality rates and potential for use as agents of bioterrorism. Currently, there are no vaccines or therapeutics approved for human use. Replication-competent, recombinant vesicular stomatitis virus (rVSV) vectors expressing filovirus glycoproteins (GP), in place of the VSV glycoprotein have shown promise in lethal nonhuman primate (NHP) models of filovirus infection as both single injection preventive vaccines and as post-exposure treatments. The recent outbreak of the fifth recognized EBOV species, Bundibugyo ebolavirus (BEBOV), demonstrates the need for vaccines that can be rapidly deployed to combat an outbreak of a new filovirus species. To date, rVSV-filovirus GP-based vaccines have only been able to protect against challenge with a homologous species of EBOV. Here, we show that the two heterologous rVSV-based filovirus vaccines available at the time of the original BEBOV outbreak can protect NHPs against BEBOV challenge using a short prime-boost vaccination strategy. While the prime-boost strategy was successful, a single injection blended vaccination strategy with the same vaccine vectors failed to provide protection. These data suggest that an abbreviated prime-boost regimen of 36 days may have utility for quickly responding to outbreaks caused by new species of EBOV. [ABSTRACT FROM AUTHOR]

The filoviruses, Marburg virus and Ebola virus, cause severe hemorrhagic fever with high mortality in humans and nonhuman primates. Among the most promising filovirus vaccines under development is a system based on recombinant vesicular stomatitis virus (rVSV) that expresses an individual filovirus glycoprotein (GP) in place of the VSV glycoprotein (G). The main concern with all replication-competent vaccines, including the rVSV filovirus GP vectors, is their safety. To address this concern, we performed a neurovirulence study using 21 cynomolgus macaques where the vaccines were administered intrathalamically. Seven animals received a rVSV vector expressing the Zaire ebolavirus (ZEBOV) GP; seven animals received a rVSV vector expressing the Lake Victoria marburgvirus (MARV) GP; three animals received rVSV-wild type (wt) vector, and four animals received vehicle control. Two of three animals given rVSV-wt showed severe neurological symptoms whereas animals receiving vehicle control, rVSV-ZEBOV-GP, or rVSV-MARV-GP did not develop these symptoms. Histological analysis revealed major lesions in neural tissues of all three rVSV-wt animals; however, no significant lesions were observed in any animals from the filovirus vaccine or vehicle control groups. These data strongly suggest that rVSV filovirus GP vaccine vectors lack the neurovirulence properties associated with the rVSV-wt parent vector and support their further development as a vaccine platform for human use. Author Summary: Ebola and Marburg viruses are categorized as Category A priority pathogens by several US Government agencies as a result of their high mortality rates and potential for use as agents of bioterrorism. There are currently no vaccines or therapeutics approved for human use. A replication-competent, recombinant vesicular stomatitis virus (rVSV) vector expressing filovirus glycoproteins (GP), in place of the VSV G protein has shown promise in lethal nonhuman primate models of filovirus infection as both a single-injection preventive vaccine and a postexposure treatment. Replication-competent vaccines that are intended for use in humans usually undergo neurovirulence testing as was done for measles virus, mumps virus, yellow fever virus, and poliovirus vaccines. Here we used a conventional neurovirulence test to evaluate the safety of our rVSV-based Zaire ebolavirus and Lake Victoria marburgvirus GP vaccines in cynomolgus macaques. Importantly, we demonstrate for the first time that these rVSV filovirus GP vectors lack neurovirulence when compared to a rVSV wild-type vector. [ABSTRACT FROM AUTHOR]