Publications

Background: Intranasal (I.N.) vaccination holds promise to elicit mucosal immunity that counters respiratory pathogens at the site of infection. For subunit protein vaccines, immunostimulatory adjuvants are typically required. Methods: We screened a panel of 22 lipid-phase adjuvants to identify which ones elicited antigen-specific IgA with I.N. immunization of liposome-displayed SARS-CoV-2 receptor-binding domain (RBD). Results: Initial screening showed the TLR-4 agonist Kdo2-Lipid A (KLA) effectively elicited RBD-specific IgA. A second round of screening identified further inclusion of the invariant NKT cell ligands α-Galactosylceramide (α-GalCer) and its synthetic analog 7DW8-5 as complementary adjuvants for I.N. immunization, resulting in orders-of-magnitude-greater mucosal IgA response relative to intramuscular (I.M.) immunization. The inclusion of cationic lipids conferred capacity for mucosal adhesion and maintained immune responses. In K18 hACE2 transgenic mice, vaccination significantly reduced viral replication and prevented mortality from SARS-CoV-2 challenge. Conclusions: These results point towards the potential for the use of KLA and α-GalCer for I.N. subunit vaccines.

Influenza viruses cause mild to severe lower respiratory infections, sometimes resulting in hospitalization and death. Vaccination remains the primary prophylactic strategy. Live attenuated influenza vaccines (LAIVs) efficiently induce antiviral immune responses and contain temperature-sensitive and cold-adapted mutations that render them safe. These mutations are principally located in the PB1 and PB2 subunits of the viral RNA polymerase, but the mechanism by which they attenuate the virus is unclear. We introduced the PB1 and PB2 mutations from two LAIV backbones, A/Ann Arbor/6/1960 H2N2 (AA) and A/Leningrad/134/17/1957 H2N2 (Len), into the model influenza strain A/Puerto Rico/8/1934 H1N1 (PR8). In contrast to the wild-type (WT) PR8 polymerase, the two "PR8-LAIV" polymerase complexes demonstrated maximal activity at cold temperatures (30-32 °C) and greatly reduced activity at elevated temperatures (>37 °C). To further understand the impact of the LAIV mutations, we infected MDCK cells with WT and mutated PR8 viruses that contain the Len and AA LAIV mutations in PB1 and PB2. The PR8-LAIV mutant viruses exhibited a selective, temperature-dependent defect in the replicase activity of the viral RNA polymerase relative to WT PR8, while also demonstrating a temperature-dependent enhancement in the transcriptional activity of the enzyme. In addition, the PR8-LAIV mutant viruses produced similar levels of viral proteins to WT PR8 at 37 °C, but greatly (2-3 log10) reduced levels of infectious viral progeny. Collectively, these data show that LAIV mutations selectively alter influenza viral RNA polymerase function, favoring transcription over genome synthesis at 37 °C, thereby preserving viral antigen production while also contributing to viral attenuation.

Over the past two decades, betacoronaviruses (β-CoVs) have caused two epidemics and a pandemic and remain a high risk for future outbreaks through zoonotic transmissions, highlighting the need for broad biomedical countermeasures. Here, we describe a convalescent human monoclonal antibody (mAb 1871) that targets the S2 subunit of the coronavirus spike protein, with broad β-CoVs binding and sarbecovirus neutralization. Cryo-electron microscopy analysis revealed that mAb 1871 binds the upstream helix of the S2 subunit, interacting with partially conserved residues, providing a molecular basis for its cross-reactivity. Though less potent than receptor-binding domain-directed antibodies-approximately 500-fold lower neutralization potency than the emergency use authorized receptor-binding domain (RBD)-directed Pemgarda mAb against wild-type SARS-CoV-2-mAb 1871 provides protective efficacy in a mouse model. Notably, Fc effector functions are critical for its in vivo protection. This study further highlights the Fc dependence of S2-directed antibodies for in vivo protection and identifies a conserved epitope in the S2 subunit as a potential target of broad-β-CoVs countermeasures.IMPORTANCEBats and pangolins are natural reservoirs of betacoronaviruses (β-CoVs) and continue to pose a significant risk for future outbreaks through zoonotic transmissions. This highlights the need for effective countermeasures to prevent future pandemics. While neutralizing antibodies targeting the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) received emergency use authorization, many have lost efficacy as the virus evolved, and authorizations have been revoked. In contrast to the S1 subunit, the spike protein S2 subunit is more conserved across β-CoVs, making it an attractive target for the development of broadly neutralizing antibodies. Here, we describe a human mAb that targets a conserved epitope in the S2 subunit, demonstrating broad β-CoV binding, sarbecovirus neutralization, and in vivo protection mediated by Fc effector functions in a mouse model. These findings have important implications for pan-β-CoVs therapeutics and vaccine development.

Influenza A viruses (IAVs) infect a wide range of mammalian and bird species and are responsible for seasonal outbreaks and occasional pandemics of great consequences in humans. Studying IAVs requires methods to detect the presence of the virus in infected cells or animal models. Recombinant IAV-expressing fluorescent proteins has allowed monitoring of viral infection in cultured cells and ex vivo in the organs of infected animals. However, fluorescent-expressing IAVs are often attenuated and are not suited for the imaging of infected animals using in vivo imaging systems (IVISs). To overcome this limitation, we generated a recombinant pandemic influenza A/California/04/2009 H1N1 (pH1N1)-expressing nanoluciferase (Nluc) from the non-structural viral segment, hereafter referred to as pH1N1-Nluc. The pH1N1-Nluc replicates efficiently in vitro, with growth kinetics and plaque morphology comparable to wild-type pH1N1 (pH1N1-WT). We used this pH1N1-Nluc to demonstrate its ability to effectively identify neutralizing monoclonal antibodies and antivirals, with neutralization and inhibition results comparable to pH1N1-WT. In mice, pH1N1-Nluc was able to induce similar body weight loss and mortality, and viral titers comparable to pH1N1-WT, results that were also recapitulated in a ferret model of IAV infection. Using IVIS, pH1N1-Nluc enabled non-invasive, real-time tracking of viral infection in vivo and ex vivo following infection of mice with viral titers in tissues comparable to pH1N1-WT. The flexibility of this approach was further demonstrated by the generation of a Nluc-expressing recombinant A/Puerto Rico/8/1934 H1N1 (PR8-Nluc). Altogether, our results demonstrate that Nluc-expressing recombinant IAVs represent a valuable tool for in vitro and in vivo studies, including the identification of antivirals and/or neutralizing antibodies, and to assess the protective efficacy of vaccines.IMPORTANCEInfluenza A viruses (IAVs) pose a threat to human and animal health. Mechanisms that control IAV replication and pathogenesis are incompletely understood due to the lack of experimental approaches to visualize and quantify viral dynamics in real time. The use of replication-competent fluorescent-expressing IAV in vivo has been challenging because such viruses typically have reduced replication fitness and are not suited for imaging of entire animals. Herein, we developed replication-competent recombinant IAV-expressing nanoluciferase (Nluc) that can be used to visualize viral infection in living animals. Infection with Nluc-expressing IAV could be monitored in real time using in vivo imaging systems. Importantly, the Nluc reporter overcomes several shortcomings of fluorescent proteins and provides a new and sensitive tool to interrogate viral dynamics and immune responses in vitro and in vivo. This technology can be applied to advance studies and accelerate the development of new prophylactics and therapeutics against IAV.

Monoclonal antibodies (mAbs) that recognize and inhibit a diverse range of influenza viruses, although relatively rare, have been isolated following infection or vaccination. Study of their ontology and mechanisms of action informs universal vaccine and therapeutic development. We have previously described a potent and broad neuraminidase (NA)-neutralizing human mAb, 1122A11, that neutralizes a wide range of H3N2 viruses. Here, further characterization of 1122A11 reveals reactivity to cross-group influenza A virus NAs, including group-1 N1 and N8, and group-2 N2 and N3 NAs. Recent H3N2 viruses have acquired Asn245 glycosylation on the active site rim. Crystal structures of an N2 NA from A/Singapore/INFIMH-16-0019/2016 (H3N2) at 2.3 Å (apo) and 2.2 Å (Fab bound) resolution showed that 1122A11 binding causes local changes to the periphery of NA active site to accommodate the glycan. The CDRH3 of 1122A11 inserts into the active site and mimics the substrate sialic acid. We then determined that the ability of 1122A11 to protect from lethal challenge in mice is not dependent on Fc-effector function. These results highlight the therapeutic potential of 1122A11 as a broad protective anti-viral and reinforce pursuit of immunogen development of NA antibodies toward achieving more universal influenza protection.

The host range of HPAIV H5N1 was recently expanded to include ruminants, particularly dairy cattle in the United States (US). Shortly after, human H5N1 infection was reported in a dairy worker in Texas following exposure to infected cattle. Herein, we rescued the cattle-origin influenza A/bovine/Texas/24-029328-02/2024(H5N1, rHPbTX) and A/Texas/37/2024(H5N1, rHPhTX) viruses, identified in dairy cattle and human, respectively, and their low pathogenic forms, rLPbTX and rLPhTX, with monobasic HA cleavage sites. Intriguingly, rHPhTX replicated more efficiently than rHPbTX in mammalian and avian cells. Still, variations in the PA and NA proteins didn't affect their antiviral susceptibility to PA and NA inhibitors. Unlike rHPbTX and rLPbTX, both rHPhTX and rLPhTX exhibited higher pathogenicity and efficient replication in infected C57BL/6J mice. The lungs of rHPhTX-infected mice produced higher inflammatory cytokines/chemokines than rHPbTX-infected mice. Our results highlight the potential risk of HPAIV H5N1 virus adaptation in human and/or dairy cattle during the current multistate/multispecies outbreak in the US.

The current situation with H5N1 highly pathogenic avian influenza virus (HPAI) is causing a worldwide concern due to multiple outbreaks in wild birds, poultry, and mammals. Moreover, multiple zoonotic infections in humans have been reported. Importantly, HPAI H5N1 viruses with genetic markers of adaptation to mammals have been detected. Together with HPAI H5N1, avian influenza viruses H7N9 (high and low pathogenic) stand out due to their high mortality rates in humans. This raises the question of how prepared we are serologically and whether seasonal vaccines are capable of inducing protective immunity against these influenza subtypes. An observational study was conducted in which sera from people born between years 1925-1967, 1968-1977, and 1978-1997 were collected before or after 28 days or 6 months post-vaccination with an inactivated seasonal influenza vaccine. Then, hemagglutination inhibition, viral neutralization, and immunoassays were performed to assess the basal protective immunity of the population as well as the ability of seasonal influenza vaccines to induce protective responses. Our results indicate that subtype-specific serological protection against H5N1 and H7N9 in the representative Spanish population evaluated was limited or nonexistent. However, seasonal vaccination was able to increase the antibody titers to protective levels in a moderate percentage of people, probably due to cross-reactive responses. These findings demonstrate the importance of vaccination and suggest that seasonal influenza vaccines could be used as a first line of defense against an eventual pandemic caused by avian influenza viruses, to be followed immediately by the use of more specific pandemic vaccines.IMPORTANCEInfluenza A viruses (IAV) can infect and replicate in multiple mammalian and avian species. Avian influenza virus (AIV) is a highly contagious viral disease that occurs primarily in poultry and wild water birds. Due to the lack of population immunity in humans and ongoing evolution of AIV, there is a continuing risk that new IAV could emerge and rapidly spread worldwide, causing a pandemic, if the ability to transmit efficiently among humans was gained. The aim of this study is to analyze the basal protection and presence of antibodies against IAV H5N1 and H7N9 subtypes in the population from different ages. Moreover, we have evaluated the humoral response after immunization with a seasonal influenza vaccine. This study is strategically important to evaluate the level of population immunity that is a major factor when assessing the impact that an emerging IAV strain would have, and the role of seasonal vaccines to mitigate the effects of a pandemic.

2'-O-ribose methylation of the first transcribed base (adenine or A1 in SARS-CoV-2) of viral RNA mimics host RNAs and subverts the innate immune response. How nsp16, with partner nsp10, assembles on the 5'-end of SARS-CoV-2 mRNA to methylate A1 is not fully understood. We present a ∼2.4 Å crystal structure of the heterotetrameric complex formed by the cooperative assembly of two nsp16/nsp10 heterodimers with one 10-mer Cap-1 RNA (product) bound to each. An aromatic zipper-like motif in nsp16 and the N-terminal regions of nsp10 and nsp16 orchestrate oligomeric assembly for efficient methylation. The front catalytic pocket of nsp16 stabilizes the upstream portion of the RNA while downstream RNA remains unresolved, likely due to flexibility. An inverted nsp16 dimer extends the positively charged surface for longer RNA to influence catalysis. Additionally, a non-specific nucleotide-binding pocket on the backside of nsp16 plays a critical role in catalysis, contributing to enzymatic activity.

Monoclonal antibodies (mAbs) that recognize and inhibit a diverse range of influenza viruses, although relatively rare, have been isolated following infection or vaccination. Study of their ontology and mechanisms of action informs universal vaccine and therapeutic development. We have previously described a potent and broad neuraminidase (NA)-neutralizing human mAb, 1122A11, that neutralizes a wide range of H3N2 viruses. Here, further characterization of 1122A11 reveals reactivity to cross-group influenza A virus NAs, including group-1 N1 and N8, and group-2 N2 and N3 NAs. Recent H3N2 viruses have acquired Asn245 glycosylation on the active site rim. Crystal structures of an N2 NA from A/Singapore/INFIMH-16-0019/2016 (H3N2) at 2.3 Å (apo) and 2.2 Å (Fab bound) resolution showed that 1122A11 binding causes local changes to the periphery of NA active site to accommodate the glycan. The CDRH3 of 1122A11 inserts into the active site and mimics the substrate sialic acid. We then determined that the ability of 1122A11 to protect from lethal challenge in mice is not dependent on Fc-effector function. These results highlight the therapeutic potential of 1122A11 as a broad protective anti-viral and reinforce pursuit of immunogen development of NA antibodies toward achieving more universal influenza protection.

The ongoing outbreak of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b has affected at least 989 dairy herds across 17 states in the United States (U.S.) and resulted in 70 confirmed human infections, underscoring the urgent need to understand the pathogenesis and therapeutic interventions of emerging H5N1 viruses. In this study, we modelled infection with a highly pathogenic recombinant human A/Texas/37/2024 H5N1 (rHPh-TX H5N1) strain using human airway organoids (HAO) to investigate viral replication, innate immune response, infection-induced fibrogenesis, and potential therapeutic interventions. rHPh-TX H5N1 replicated efficiently in HAO, eliciting a robust interferon (IFN) response and pro-inflammatory cytokine production. Prolonged infection led to the accumulation of fibroblast-like cells surrounding infected regions, marked by increased alpha-smooth muscle actin (α-SMA) expression and upregulation of transforming growth factor-beta (TGF-β), indicative of fibroblast activation and extracellular matrix (ECM) remodelling. Compared to organoids infected with the pandemic A/California/04/09 H1N1 (pH1N1) strain, rHPh-TX H5N1 induced significantly higher expression of fibrosis-associated markers, including fibronectin (FN), collagen 1A (COL1A), collagen 3A (COL3A), metalloproteinases 2 and 9 (MMP2, and MMP9). Notably, the inhibition of Rho-associated coiled-coil-forming protein kinases (ROCK) signalling reduced fibrogenesis, with ROCK1 inhibition being more effective than ROCK2 inhibition. These findings highlight the potential of targeting ROCK signalling to mitigate H5N1-induced lung fibrosis, informing therapeutic strategies for severe influenza infections.