Recombinant Lloviu virus as a tool to study viral replication and host responses

Next generation sequencing has revealed the presence of numerous RNA viruses in animal
reservoir hosts, including many closely related to known human pathogens. Despite their
zoonotic potential, most of these viruses remain understudied due to not yet being cultured.
While reverse genetic systems can facilitate virus rescue, this is often hindered by missing
viral genome ends. A prime example is Lloviu virus (LLOV), an uncultured filovirus that is
closely related to the highly pathogenic Ebola virus. Using minigenome systems, we complemented the missing LLOV genomic ends and identified cis-acting elements required for
LLOV replication that were lacking in the published sequence. We leveraged these data to
generate recombinant full-length LLOV clones and rescue infectious virus. Similar to other
filoviruses, recombinant LLOV (rLLOV) forms filamentous virions and induces the formation
of characteristic inclusions in the cytoplasm of the infected cells, as shown by electron
microscopy. Known target cells of Ebola virus, including macrophages and hepatocytes, are
permissive to rLLOV infection, suggesting that humans could be potential hosts. However,
inflammatory responses in human macrophages, a hallmark of Ebola virus disease, are not
induced by rLLOV. Additional tropism testing identified pneumocytes as capable of robust
rLLOV and Ebola virus infection. We also used rLLOV to test antivirals targeting multiple facets of the replication cycle. Rescue of uncultured viruses of pathogenic concern represents a valuable tool in our arsenal for pandemic preparedness