Robust and durable prophylactic protection conferred by RNA interference in preclinical models of SARS-CoV-2 (preprint)

RNA interference is a natural antiviral mechanism that could be harnessed to combat SARS-CoV-2 infection by targeting and destroying the viral genome. We screened lipophilic small-interfering RNA (siRNA) conjugates targeting highly conserved regions of the SARS-CoV-2 genome and identified leads targeting outside of the spike-encoding region capable of achieving [≥]3-log viral reduction. Serial passaging studies demonstrated that a two-siRNA combination prevented development of resistance compared to a single-siRNA approach. A two-siRNA combination delivered intranasally protected Syrian hamsters from weight loss and lung pathology by viral infection upon prophylactic administration but not following onset of infection. Together, the data support potential utility of RNAi as a prophylactic approach to limit SARS-CoV-2 infection that may help combat emergent variants, complement existing interventions, or protect populations where vaccines are less effective. Most importantly, this strategy has implications for developing medicines that may be valuable in protecting against future coronavirus pandemics.

Maturation signatures of conventional dendritic cells in COVID-19 reflect direct viral sensing (preprint)

Growing evidence suggests that conventional dendritic cells (cDCs) undergo aberrant maturation in COVID-19, and this adversely affects T cell activation. Here, we find that cDC2 subtypes show similar infection-induced gene signatures with an increasing gradient of expression of interferon-stimulated genes from mild to severe patients and a down-regulation of major histocompatibility complex class II (MHC class II) molecules and some inflammatory cytokines compared to the baseline level of healthy donors. In vitro, the direct exposure of cDC2s to the virus recapitulates the type of activation observed in vivo. Our findings provide evidence that SARS-CoV-2 can directly interact with cDC2s and, by down-regulating crucial molecules required for T cell activation, implements an efficient immune escape mechanism.

The circulating SARS-CoV-2 spike variant N439K maintains fitness while evading antibody-mediated immunity (preprint)

SARS-CoV-2 can mutate to evade immunity, with consequences for the efficacy of emerging vaccines and antibody therapeutics. Herein we demonstrate that the immunodominant SARS-CoV-2 spike (S) receptor binding motif (RBM) is the most divergent region of S, and provide epidemiological, clinical, and molecular characterization of a prevalent RBM variant, N439K. We demonstrate that N439K S protein has enhanced binding affinity to the hACE2 receptor, and that N439K virus has similar clinical outcomes and in vitro replication fitness as compared to wild- type. We observed that the N439K mutation resulted in immune escape from a panel of neutralizing monoclonal antibodies, including one in clinical trials, as well as from polyclonal sera from a sizeable fraction of persons recovered from infection. Immune evasion mutations that maintain virulence and fitness such as N439K can emerge within SARS-CoV-2 S, highlighting the need for ongoing molecular surveillance to guide development and usage of vaccines and therapeutics.

Transfer transcriptomic signatures for infectious diseases (preprint)

The modulation of the transcriptome is among the earliest responses to infection, and vaccination. However, defining transcriptome signatures of disease is challenging because logistic, technical and cost factors limit the size and representativeness of samples in clinical studies. These limitations lead to poor performance of signatures when applied to new datasets or varying study settings. Using a novel approach, we leverage existing transcriptomic signatures as classifiers in unseen datasets from prospective studies, with the goal of predicting individual outcomes. Machine learning allowed the identification of sets of genes, which we name transfer transcriptomic signatures, that are predictive across diverse datasets and/or species (rhesus to humans) and that are also suggestive of activated pathways and cell type composition. We demonstrate the usefulness of transfer signatures in two use cases: progression of latent to active tuberculosis, and severity of COVID-19 and influenza A H1N1 infection. The broad significance of our work lies in the concept that a small set of archetypal human immunophenotypes, captured by transfer signatures, can explain a larger set of responses to diverse diseases.

Type III interferons disrupt the lung epithelial barrier upon viral recognition (preprint)

Lower respiratory tract infections are a leading cause of mortality driven by infectious agents. RNA viruses such as influenza virus, respiratory syncytial virus and the new pandemic coronavirus SARS-CoV-2 can be highly pathogenic. Clinical and experimental evidence indicate that most severe and lethal cases do not depend on the viral burden and are, instead, characterized by an aberrant immune response. In this work we assessed how the innate immune response contributes to the pathogenesis of RNA virus infections. We demonstrate that type III interferons produced by dendritic cells in the lung in response to viral recognition cause barrier damage and compromise the host tissue tolerance. In particular, type III interferons inhibit tissue repair and lung epithelial cell proliferation, causing susceptibility to lethal bacterial superinfections. Overall, our data give a strong mandate to rethink the pathophysiological roles of this group of interferons and their possible use in the clinical practice against endemic as well as emerging viral infections.

Structural and functional analysis of a potent sarbecovirus neutralizing antibody (preprint)

SARS-CoV-2 is a newly emerged coronavirus responsible for the current COVID-19 pandemic that has resulted in more than one million infections and 73,000 deaths1,2. Vaccine and therapeutic discovery efforts are paramount to curb the pandemic spread of this zoonotic virus. The SARS-CoV-2 spike (S) glycoprotein promotes entry into host cells and is the main target of neutralizing antibodies. Here we describe multiple monoclonal antibodies targeting SARS-CoV-2 S identified from memory B cells of a SARS survivor infected in 2003. One antibody, named S309, potently neutralizes SARS-CoV-2 and SARS-CoV pseudoviruses as well as authentic SARS-CoV-2 by engaging the S receptor-binding domain. Using cryo-electron microscopy and binding assays, we show that S309 recognizes a glycan-containing epitope that is conserved within the sarbecovirus subgenus, without competing with receptor attachment. Antibody cocktails including S309 along with other antibodies identified here further enhanced SARS-CoV-2 neutralization and may limit the emergence of neutralization-escape mutants. These results pave the way for using S309 and S309-containing antibody cocktails for prophylaxis in individuals at high risk of exposure or as a post-exposure therapy to limit or treat severe disease.