Ebola virus-like particles

Ebola virus (EBOV) and Nipah virus (NiV) infection of humans can cause fatal disease and constitutes a public health threat. In contrast, EBOV and NiV infection of fruit bats, the putative (EBOV) or proven (NiV) natural reservoir, is not associated with disease, and it is currently unknown how these animals control the virus. The human interferon (IFN)-stimulated antiviral effector protein tetherin (CD317, BST-2) blocks release of EBOV- and NiV-like particles from cells and is counteracted by the EBOV glycoprotein (GP). In contrast, it is unknown whether fruit bat tetherin restricts virus infection and is susceptible to GP-driven antagonism. Here, we report the sequence of fruit bat tetherin and show that its expression is IFN stimulated and associated with strong antiviral activity. Moreover, we demonstrate that EBOV- GP antagonizes tetherin orthologues of diverse species but fails to efficiently counteract fruit bat tetherin in virus-like particle (VLP) release assays. However, unexpectedly, tetherin was dispensable for robust IFN-mediated inhibition of EBOV spread in fruit bat cells. Thus, the VLP-based model systems mimicking tetherin-mediated inhibition of EBOV release and its counteraction by GP seem not to adequately reflect all aspects of EBOV release from IFN-stimulated fruit bat cells, potentially due to differences in tetherin expression levels that could not be resolved by the present study. In contrast, tetherin expression was essential for IFN-dependent inhibition of NiV infection, demonstrating that IFN-induced fruit bat tetherin exerts antiviral activity and may critically contribute to control of NiV and potentially other highly virulent viruses in infected animals. IMPORTANCE Ebola virus and Nipah virus (EBOV and NiV) can cause fatal disease in humans. In contrast, infected fruit bats do not develop symptoms but can transmit the virus to humans. Why fruit bats but not humans control infection is largely unknown. Tetherin is an antiviral host cell protein and is counteracted by the EBOV glycoprotein in human cells. Here, employing model systems, we show that tetherin of fruit bats displays higher antiviral activity than human tetherin and is largely resistant against counteraction by the Ebola virus glycoprotein. Moreover, we demonstrate that induction of tetherin expression is critical for interferon-mediated inhibition of NiV but, for at present unknown reasons, not EBOV spread in fruit bat cells. Collectively, our findings identify tetherin as an antiviral effector of innate immune responses in fruit bats, which might allow these animals to control infection with NiV and potentially other viruses that cause severe disease in humans.

There are currently no approved therapeutics or vaccines to treat or protect against the severe hemorrhagic fever and death caused by Ebola virus (EBOV). Ebola virus-like particles (EBOV VLPs) consisting of the matrix protein VP40, the glycoprotein (GP), and the nucleoprotein (NP) are highly immunogenic and protective in nonhuman primates against Ebola virus disease (EVD). We have constructed a modified vaccinia virus Ankara-Bavarian Nordic (MVA-BN) recombinant coexpressing VP40 and GP of EBOV Mayinga and the NP of Tai Forest virus (TAFV) (MVA-BN-EBOV-VLP) to launch noninfectious EBOV VLPs as a second vaccine modality in the MVA-BN-EBOV-VLP-vaccinated organism. Human cells infected with either MVA-BN-EBOV-VLP or MVA-BN-EBOV-GP showed comparable GP expression levels and transport of complex N-glycosylated GP to the cell surface. Human cells infected with MVA-BN-EBOV-VLP produced large amounts of EBOV VLPs that were decorated with GP spikes but excluded the poxviral membrane protein B5, thus resembling authentic EBOV particles. The heterologous TAFV NP enhanced EBOV VP40-driven VLP formation with efficiency similar to that of the homologous EBOV NP in a transient-expression assay, and both NPs were incorporated into EBOV VLPs. EBOV GP-specific CD8 T cell responses were comparable between MVA-BN-EBOV-VLP- and MVA-BN-EBOV-GP-immunized mice. The levels of EBOV GP-specific neutralizing and binding antibodies, as well as GP-specific IgG1/IgG2a ratios induced by the two constructs, in mice were also similar, raising the question whether the quality rather than the quantity of the GP-specific antibody response might be altered by an EBOV VLP-generating MVA recombinant. IMPORTANCE The recent outbreak of Ebola virus (EBOV), claiming more than 11,000 lives, has underscored the need to advance the development of safe and effective filovirus vaccines. Virus-like particles (VLPs), as well as recombinant viral vectors, have proved to be promising vaccine candidates. Modified vaccinia virus Ankara-Bavarian Nordic (MVA-BN) is a safe and immunogenic vaccine vector with a large capacity to accommodate multiple foreign genes. In this study, we combined the advantages of VLPs and the MVA platform by generating a recombinant MVA-BN-EBOV-VLP that would produce noninfectious EBOV VLPs in the vaccinated individual. Our results show that human cells infected with MVA-BN-EBOV-VLP indeed formed and released EBOV VLPs, thus producing a highly authentic immunogen. MVA-BN-EBOV-VLP efficiently induced EBOV-specific humoral and cellular immune responses in vaccinated mice. These results are the basis for future advancements, e.g., by including antigens from various filoviral species to develop multivalent VLP-producing MVA-based filovirus vaccines.