Pseudotyped Viruses for Influenza

We have developed an influenza hemagglutinin (HA) pseudotype (PV) library encompassing all influenza A (IAV) subtypes from HA1-HA18, influenza B (IBV) subtypes (both lineages), representative influenza C (ICV), and influenza D (IDV) viruses. These influenza HA (or hemagglutinin-esterase fusion (HEF) for ICV and IDV) pseudotypes have been used in a pseudotype microneutralization assay (pMN), an optimized luciferase reporter assay, that is highly sensitive and specific for detecting neutralizing antibodies against influenza viruses. This has been an invaluable tool in detecting the humoral immune response against specific hemagglutinin or hemagglutinin-esterase fusion proteins for IAV to IDV in serum samples and for screening antibodies for their neutralizing abilities. Additionally, we have also produced influenza neuraminidase (NA) pseudotypes for IAV N1-N9 subtypes and IBV lineages. We have utilized these NA-PV as surrogate antigens in in vitro assays to assess vaccine immunogenicity. These NA PV have been employed as the source of neuraminidase enzyme activity in a pseudotype enzyme-linked lectin assay (pELLA) that is able to measure neuraminidase inhibition (NI) titers of reference antisera, monoclonal antibodies, and postvaccination sera. Here we show the production of influenza HA, HEF, and NA PV and their employment as substitutes for wild-type viruses in influenza serological and neutralization assays. We also introduce AutoPlate, an easily accessible web app that can analyze data from pMN and pELLA quickly and efficiently, plotting inhibition curves and calculating half-maximal concentration (IC₅₀) neutralizing antibody titers. These serological techniques coupled with user-friendly analysis tools are faster, safer, inexpensive alternatives to classical influenza assays while also offering the reliability and reproducibility to advance influenza research and make it more accessible to laboratories around the world.

A CRISPR screen for factors regulating SAMHD1 degradation identifies IFITMs as potent inhibitors of lentiviral particle delivery

The InterFeron Induced TransMembrane (IFITM) proteins are interferon stimulated genes that restrict many viruses, including HIV-1. SAMHD1 is another restriction factor blocking replication of HIV-1 and other viruses. Some lentiviruses evolved Vpx/Vpr proteins to degrade SAMHD1. However, this viral antagonism can be perturbed by host mechanisms: a recent study showed that in interferon (IFN) treated THP1 cells, Vpx is unable to degrade SAMHD1. In the present work, we designed an Interferon Stimulated Genes (ISGs)-targeted CRISPR knockout screen in order to identify ISGs regulating this phenotype. We found that IFITM proteins contribute to the IFNα-mediated protection of SAMHD1 by blocking VSV-G-mediated entry of the lentiviral particles delivering Vpx. Consistent with this, IFNα treatment and IFITM expression had no effect when the A-MLV envelope was used for pseudotyping. Using an assay measuring viral entry, we show that IFNα and IFITMs directly block the delivery of Vpx into cells by inhibiting VSV-G viral fusion. Strikingly, the VSV-G envelope was significantly more sensitive to this IFNα entry block and to IFITMs than HIV-1's natural envelope. This highlights important differences between VSV-G pseudotyped and wild-type HIV-1, in particular relative to the pathways they use for viral entry, suggesting that HIV-1 may have evolved to escape restriction factors blocking entry.

Retrovirus-Based Surrogate Systems for BSL-2 High-Throughput Screening of Antivirals Targeting BSL-3/4 Hemorrhagic Fever-Causing Viruses

The majority of viruses causing hemorrhagic fever in humans are Risk Group 3 or 4 pathogens and, therefore, can only be handled in biosafety level 3 or 4 (BSL-3/4) containment laboratories. The restricted number of such laboratories, the substantial financial requirements to maintain them, and safety concerns for the laboratory workers pose formidable challenges for rapid medical countermeasure discovery and evaluation. BSL-2 surrogate systems are a less challenging, cheap, and fast alternative to the use of live high-consequence viruses for dissecting and targeting individual steps of viral lifecycles with a diminished threat to the laboratory worker. Typical surrogate systems are virion-like particles (VLPs), transcriptionally active ("infectious") VLPs, minigenome systems, recombinant heterotypic viruses encoding proteins of target viruses, and vesiculoviral or retroviral pseudotype systems. Here, we outline the use of retroviral pseudotypes for identification of antivirals against BSL-4 pathogens.

Ebola virus mediated infectivity is restricted in canine and feline cells

Ebolaviruses and marburgviruses belong to the Filoviridae family and often cause severe, fatal hemorrhagic fever in humans and non-human primates. The magnitude of the 2014 outbreak in West Africa and the unprecedented emergence of Ebola virus disease (EVD) in the United States underscore the urgency to better understand the dynamics of Ebola virus infection, transmission and spread. To date, the susceptibility and possible role of domestic animals and pets in the transmission cycle and spread of EVD remains unclear. We utilized infectious VSV recombinants and lentivirus pseudotypes expressing the EBOV surface glycoprotein (GP) to assess the permissiveness of canine and feline cells to EBOV GP-mediated entry. We observed a general restriction in EBOV-mediated infection of primary canine and feline cells. To address the entry mechanism, we used cells deficient in NPC1, a host protein implicated in EBOV entry, and a pharmacological blockade of cholesterol transport, to show that an NPC1-dependent mechanism of EBOV entry is conserved in canine and feline cells. These data demonstrate that cells of canine and feline origin are susceptible to EBOV GP mediated infection; however, infectivity of these cells is reduced significantly compared to controls. Moreover, these data provide new insights into the mechanism of EBOV GP mediated entry into cells of canine and feline origin.