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Antibody-based therapies are a promising treatment option for managing ebolavirus infections. Several Ebola virus (EBOV)-specific and, more recently, pan-ebolavirus antibody cocktails have been described. Here, we report the development and assessment of a Sudan virus (SUDV)-specific antibody cocktail. We produced a panel of SUDV glycoprotein (GP)-specific human chimeric monoclonal antibodies (mAbs) using both plant and mammalian expression systems and completed head-to-head in vitro and in vivo evaluations. Neutralizing activity, competitive binding groups, and epitope specificity of SUDV mAbs were defined before assessing protective efficacy of individual mAbs using a mouse model of SUDV infection. Of the mAbs tested, GP base-binding mAbs were more potent neutralizers and more protective than glycan cap- or mucin-like domain-binding mAbs. No significant difference was observed between plant and mammalian mAbs in any of our in vitro or in vivo evaluations. Based on in vitro and rodent testing, a combination of two SUDV-specific mAbs, one base binding (16F6) and one glycan cap binding (X10H2), was down-selected for assessment in a macaque model of SUDV infection. This cocktail, RIID F6-H2, provided protection from SUDV infection in rhesus macaques when administered at 50 mg/kg on days 4 and 6 postinfection. RIID F6-H2 is an effective postexposure SUDV therapy and provides a potential treatment option for managing human SUDV infection.

Newly emerged pathogens such as SARS-CoV-2 highlight the urgent need for assays that detect levels of neutralizing antibodies that may be protective. We studied the relationship between anti-spike ectodomain (ECD) and anti-receptor binding domain (RBD) IgG titers, and SARS-CoV-2 virus neutralization (VN) titers generated by two different in vitro assays using convalescent plasma samples obtained from 68 COVID-19 patients, including 13 who donated plasma multiple times. Only 23% (16/68) of donors had been hospitalized. We also studied 16 samples from subjects found to have anti-spike protein IgG during surveillance screening of asymptomatic individuals. We report a strong positive correlation between both plasma anti-RBD and anti-ECD IgG titers, and in vitro VN titer. Anti-RBD plasma IgG correlated slightly better than anti-ECD IgG titer with VN titer. The probability of a VN titer ≥160 was 80% or greater with anti-RBD or anti-ECD titers of ≥1:1350. Thirty-seven percent (25/68) of convalescent plasma donors lacked VN titers ≥160, the FDA-recommended level for convalescent plasma used for COVID-19 treatment. Dyspnea, hospitalization, and disease severity were significantly associated with higher VN titer. Frequent donation of convalescent plasma did not significantly decrease either VN or IgG titers. Analysis of 2,814 asymptomatic adults found 27 individuals with anti-RBD or anti-ECD IgG titers of ≥1:1350, and evidence of VN ≥1:160. Taken together, we conclude that anti-RBD or anti-ECD IgG titers can serve as a surrogate for VN titers to identify suitable plasma donors. Plasma anti-RBD or anti-ECD titer of ≥1:1350 may provide critical information about protection against COVID-19 disease.

Category A agents, such as Ebola virus, pose a great risk to national security because of high rates of transmission and mortality and the gravity of impact to public health. The use of Ebola virus as a bioweapon is a significant concern, and rapid diagnostics, safe vaccines, and efficacious therapeutics are needed. The Mucosal Tissue Equivalent (MTE) component of the MIMIC™ lung mucosal model is an in vitro/ex vivo respiratory tissue model comprised of human lung epithelial cells that mimics the vascularized lower airway alveolar tissue micro-environment. The use of the MTE allows for the inclusion of human immune components, which may be a better predictor of the human immune response than animal models. In this study, Ebola virus was applied at the air-liquid interface of the differentiated human epithelium and expression of cytokines was measured. Peripheral blood mononuclear cells (PBMCs) were applied to apical layer of the MTEs prior to inoculation with Ebola virus (Kikwit). We quantified cytokines and chemokines using supernatants serially collected on days 0, 3, 6, 9, and 15 post infection. In the infected MTEs containing human PBMCs, we detected pro-inflammatory cytokines, colony stimulating factors and endothelial growth factors. This “cytokine storm” would be expected to play a role in inflammation, recruitment of cells to the site of infection, and induction of a specific immune response to acute viral infection in humans. This human lung infection model will be used to evaluate existing therapeutic antibody and vaccine candidates for Ebola virus. Going forward, this system may provide a more rapid, relevant and cost effective means to evaluate vaccine candidates than can be accomplished by using animal models.

Ebola virus causes a severe and often fatal hemorrhagic fever in people, for which no approved vaccines or therapeutics are available. Disease pathogenesis and countermeasure studies are typically performed using animal models; however, ex vivo models recapitulating human immune responses may provide valuable information. We optimized engineered lung tissue constructs comprised of human lung epithelial cells and human endothelial cells that mimic the vascularized lower airway alveolar tissue micro-environment to study the human innate immune response to Ebola virus Kikwit (EBOV/Kik). Human lung tissue macrophages are difficult to obtain due to practical and ethical considerations, so macrophages were chemically derived from human monocytes. We inoculated the constructs, in the presence and absence of monocyte derived macrophages (MDM), and quantified cytokines/chemokines secreted on days 0, 3, 6, 9, and 15 post-infection using 29-plex and 1-plex human cytokine/chemokine kits. Prior to infection, MDM were secreting IL-13, MCP-1, MIP-1a, MIP-1b; however, these levels rapidly declined by day 3 post-infection (pi). The MDM secreted peak levels of IL-4, IFN-a2, Eotaxin, IL-12P40, and IFNg at day 6pi, and IL-1ra peaked at day 9 pi. In response to EBOV/Kik, the human lung epithelial cells in the engineered lung tissue construct secreted G-CSF, IL-1ra, IL-8, IP-10, and PDGF-AA/BB. G-CSF and IL-8, cytokines known to mobilize hematopoietic progenitors from bone marrow to blood and recruit neutrophils to sites of infection, were abundantly secreted by both endothelial cells and macrophages in response to infection. This model system may be a valuable resource to the field to study human immune responses during acute infections.

The progress of filovirus vaccines has advanced greatly due in part to the urgent need to develop countermeasures for the unprecedented Ebolavirus (EBOV) outbreak in West Africa. While a variety of vaccination approaches have been moved into clinical trials, the understanding of what constitutes a protective response after vaccination is still under investigation. Our approach to addressing immune correlates has involved the use of various mouse models to first test whether or not protection is afforded in the absence of a cell population. To this end, wild type (wt), β2m−/− and μMT−/− mouse models were used to assess the protective efficacy of vaccination with a Venezuelan Equine Encephalitis Virus replicon bearing the EBOV glycoprotein (GP). Vaccinated β2m−/− mice, despite lacking CD8 T cells, enjoyed full protection against mouse-adapted (ma) EBOV exposure. Vaccinated μMT−/− mice, on the other hand, succumbed to maEBOV exposure, similar to unvaccinated control mice. A flow cytometry analysis of T cell responses in Wt, β2­m−/− and μMT−/− mice revealed all mice mounted CD4 T cell responses, whereas only wt mice generated CD8 T cell responses. Antibody responses to EBOV GP were predictably lacking in μMT−/− mice after vaccination, but were present at high titers in wt and β2m−/− mice. We were able to achieve protection in vaccinated μMT−/−, but not unvaccinated μMT−/− mice, given serum from vaccinated wt mice before and after maEBOV exposure. These data indicate that T cell responses in this model can contribute to protection when given antibody help. Ultimately, antibody responses appear to be the best protective correlate in this model, though we also provide evidence that T cell responses can be essential in certain conditions.