SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes and CD8 + T cells for optimal clinical and virological benefit. Thus, potently neutralizing mAbs utilize Fc effector functions during therapy to mitigate lung infection and disease.

Human monoclonal antibodies are safe, preventive and therapeutic tools, that can be rapidly developed to help restore the massive health and economic disruption caused by the coronavirus disease 2019 (COVID-19) pandemic. By single cell sorting 4,277 SARS-CoV-2 spike protein specific memory B cells from 14 COVID-19 survivors, 453 neutralizing antibodies were identified. The most potent neutralizing antibodies recognized the spike protein receptor binding domain, followed in potency by antibodies that recognize the S1 domain, the spike protein trimer and the S2 subunit. Only 1.4% of them neutralized the authentic virus with a potency of 1-10 ng/mL. The most potent monoclonal antibody, engineered to reduce the risk of antibody dependent enhancement and prolong half-life, neutralized the authentic wild type virus and emerging variants containing D614G, E484K and N501Y substitutions. Prophylactic and therapeutic efficacy in the hamster model was observed at 0.25 and 4 mg/kg respectively in absence of Fc-functions.

The digestive and respiratory tracts of chickens are colonized by bacteria that are believed to play important roles in the overall health and performance of the birds. Most of the current research on the commensal bacteria (microbiota) of chickens has focused on broilers and gut microbiota, and less attention has been given to layers and respiratory microbiota. This research bias has left significant gaps in our knowledge of the layer microbiome. This study was conducted to define the core microbiota colonizing the upper respiratory tract (URT) and lower intestinal tract (LIT) in commercial layers under field conditions. One hundred eighty-one chickens were sampled from a flock of Ͼ80,000 birds at nine times to collect samples for 16S rRNA gene-based bacterial metabarcoding. Generally, the body site and age/farm stage had very dominant effects on the quantity, taxonomic composition, and dynamics of core bacteria. Remarkably, ileal and URT microbiota were compositionally more related to each other than to that from the cecum. Unique taxa dominated in each body site yet some taxa overlapped between URT and LIT sites, demonstrating a common core. The overlapping bacteria also contained various levels of several genera with well-recognized avian pathogens. Our findings suggest that significant interaction exists between gut and respiratory microbiota, including potential pathogens, in all stages of the farm sequence. The baseline data generated in this study can be useful for the development of effective microbiome-based interventions to enhance production performance and to prevent and control disease in commercial chicken layers. IMPORTANCE The poultry industry is faced with numerous challenges associated with infectious diseases and suboptimal performance of flocks. As microbiome research continues to grow, it is becoming clear that poultry health and production performance are partly influenced by nonpathogenic symbionts that occupy different habitats within the bird. This study has defined the baseline composition and overlaps between respiratory and gut bacteria in healthy, optimally performing chicken layers across all stages of the commercial farm sequence. Consequently, the study has set the groundwork for the development of interventions that seek to enhance production performance and to prevent and control infectious diseases through the modulation of gut and respiratory bacteria.

The vast majority of people already have preexisting immune responses to influenza viruses from one or more subtypes. However, almost all preclinical studies evaluate new influenza vaccine candidates in immunologically naive animals. Recently, our group demonstrated that priming naive ferrets with broadly reactive H1 COBRA HA-based vaccines boosted preexisting antibodies induced by wild-type H1N1 virus infections. These H1 COBRA hemagglutinin (HA) antigens induced antibodies with HAI activity against multiple antigenically different H1N1 viral variants. In this study, ferrets, preimmune to historical H3N2 viruses, were vaccinated with virus-like particle (VLP) vaccines expressing either an HA from a wild-type H3 influenza virus or a COBRA H3 HA antigen (T6, T7, T10, or T11). The elicited antisera had the ability to neutralize virus infection against either a panel of viruses representing vaccine strains selected by the World Health Organization or a set of viral variants that cocirculated during the same time period. Preimmune animals vaccinated with H3 COBRA T10 HA antigen elicited sera with higher hemagglutination inhibition (HAI) antibody titers than antisera elicited by VLP vaccines with wild-type HA VLPs in preimmune ferrets. However, while the T11 COBRA vaccine did not elicit HAI activity, the elicited antibodies did neutralize antigenically distinct H3N2 influenza viruses. Overall, H3 COBRA-based HA vaccines were able to neutralize both historical H3 and contemporary, as well as future, H3N2 viruses with higher titers than vaccines with wild-type H3 HA antigens. This is the first report demonstrating the effectiveness of a broadly reactive H3N3 vaccine in a preimmune ferret model. IMPORTANCE After exposure to influenza virus, the host generates neutralizing anti-hemagglutinin (anti-HA) antibodies against that specific infecting influenza strain. These antibodies can also neutralize some, but not all, cocirculating strains. The goal of next-generation influenza vaccines, such as HA head-based COBRA, is to stimulate broadly protective neutralizing antibodies against all strains circulating within a subtype, in particular those that persist over multiple influenza seasons, without requiring an update to the vaccine. To mimic the human condition, COBRA HA virus-like particle vaccines were tested in ferrets that were previously exposed to historical H3N2 influenza viruses. In this model, these vaccines elicited broadly protective antibodies that neutralized cocirculating H3N2 influenza viruses isolated over a 20-year period. This is the first study to show the effectiveness of H3N3 COBRA HA vaccines in a host with preexisting immunity to influenza.

Influenza virus mutants that encode C-terminally truncated NS1 proteins (NS1-truncated mutants) are attractive candidates for avian live attenuated influenza vaccine (LAIV) development because they are both attenuated and immunogenic in chickens. We previously showed that a high protective efficacy of NS1-truncated LAIV in chickens corresponds with induction of high levels of type I interferon (IFN) responses in chicken embryonic fibroblast cells. In this study, we investigated the relationship between induction of IFN and IFN-stimulated gene responses in vivo and the immunogenicity and protective efficacy of NS1-truncated LAIV. Our data demonstrates that accelerated antibody induction and protective efficacy of NS1-truncated LAIV correlates well with upregulation of IFN-stimulated genes. Further, through oral administration of recombinant chicken IFN alpha in drinking water, we provide direct evidence that type I IFN can promote rapid induction of adaptive immune responses and protective efficacy of influenza vaccine in chickens.