The ratio between SARS-CoV-2 RNA viral load and culturable viral titer differs depending on stage of infection (preprint)

Analysis of incident, longitudinal RNA viral loads in saliva and nasal swabs and culturable viral titers in nasal swabs collected twice-daily by a tricenarian male infected with SARS-CoV-2 revealed the ratio between viral load and viral titer can be five orders of magnitude higher during early infection than late infection.

Modulation of type I interferon responses potently inhibits SARS-CoV-2 replication and inflammation in rhesus macaques (preprint)

Type-I interferons (IFN-I) are critical mediators of innate control of viral infections, but also drive recruitment of inflammatory cells to sites of infection, a key feature of severe COVID-19. Here, and for the first time, IFN-I signaling was modulated in rhesus macaques (RMs) prior to and during acute SARS-CoV-2 infection using a mutated IFN2 (IFN-modulator; IFNmod), which has previously been shown to reduce the binding and signaling of endogenous IFN-I. In SARS-CoV-2-infected RMs, IFNmod reduced both antiviral and inflammatory ISGs. Notably, IFNmod treatment resulted in a potent reduction in (i) SARS-CoV-2 viral load in Bronchoalveolar lavage (BAL), upper airways, lung, and hilar lymph nodes; (ii) inflammatory cytokines, chemokines, and CD163+MRC1- inflammatory macrophages in BAL; and (iii) expression of Siglec-1, which enhances SARS-CoV-2 infection and predicts disease severity, on circulating monocytes. In the lung, IFNmod also reduced pathogenesis and attenuated pathways of inflammasome activation and stress response during acute SARS-CoV-2 infection. This study, using an intervention targeting both IFN- and IFN-{beta} pathways, shows that excessive inflammation driven by type 1 IFN critically contributes to SARS-CoV-2 pathogenesis in RMs, and demonstrates the potential of IFNmod to limit viral replication, SARS-CoV-2 induced inflammation, and COVID-19 severity.

Dynamics of SARS-CoV-2 VOC neutralization and novel mAb reveal protection against Omicron (preprint)

To evaluate SARS-CoV-2 variants we isolated SARS-CoV-2 temporally during the pandemic starting with first appearance of virus in the Western hemisphere near Seattle, WA, USA, and isolated each known major variant class, revealing the dynamics of emergence and complete take-over of all new cases by current Omicron variants. We assessed virus neutralization in a first-ever full comparison across variants and evaluated a novel monoclonal antibody (Mab). We found that convalescence greater than 5-months provides little-to-no protection against SARS-CoV-2 variants, vaccination enhances immunity against variants with the exception of Omicron BA.1, and paired testing of vaccine sera against ancestral virus compared to Omicron BA.1 shows that 3-dose vaccine regimen provides over 50-fold enhanced protection against Omicron BA.1 compared to a 2-dose regimen. We also reveal a novel Mab that effectively neutralizes Omicron BA.1 and BA.2 variants over clinically-approved Mabs. Our observations underscore the need for continued vaccination efforts, with innovation for vaccine and Mab improvement, for protection against variants of SARS-CoV-2. SummaryWe isolated SARS-CoV-2 temporally starting with emergence of virus in the Western hemisphere. Neutralization analyses across all variant lineages show that vaccine-boost regimen provides protection against Omicron BA.1. We reveal a Mab that protects against Omicron BA.1 and BA.2 variants.

Replicating RNA platform enables rapid response to the SARS-CoV-2 Omicron variant and elicits enhanced protection in naïve hamsters compared to ancestral vaccine (preprint)

In late 2021, the SARS-CoV-2 Omicron (B.1.1.529) variant of concern (VoC) was reported with many mutations in the viral spike protein that were predicted to enhance transmissibility and allow viral escape of neutralizing antibodies. Within weeks of the first report of B.1.1.529, this VoC has rapidly spread throughout the world, replacing previously circulating strains of SARS-CoV-2 and leading to a resurgence in COVID-19 cases even in populations with high levels of vaccine- and infection-induced immunity. Initial studies have shown that B.1.1.529 is less sensitive to protective antibody conferred by previous infections and vaccines developed against earlier lineages of SARS-CoV-2. The ability of B.1.1.529 to spread even among vaccinated populations has led to a global public health demand for updated vaccines that can confer protection against B.1.1.529. We report here the rapid development of a replicating RNA vaccine expressing the B.1.1.529 spike and show that this B.1.1.529-targeted vaccine is immunogenic in mice and hamsters. Interestingly, we found that mice previously immunized with A.1-specific vaccines failed to elevate neutralizing antibody titers against B.1.1.529 following B.1.1.529-targeted boosting, suggesting pre-existing immunity may impact the efficacy of B.1.1.529- targeted boosters. Furthermore, we found that our B.1.1.529-targeted vaccine provides superior protection compared to the ancestral A.1-targeted vaccine in hamsters challenged with the B.1.1.529 VoC after a single dose of each vaccine.

T cell response to intact SARS-CoV-2 includes coronavirus cross-reactive and variant-specific components (preprint)

SARS-CoV-2 provokes a brisk T cell response. Peptide-based studies exclude antigen processing and presentation biology and may influence T cell detection studies. To focus on responses to whole virus and complex antigens, we used intact SARS-CoV-2 and full-length proteins with DC to activate CD8 and CD4 T cells from convalescent persons. T cell receptor (TCR) sequencing showed partial repertoire preservation after expansion. Resultant CD8 T cells recognize SARS-CoV-2-infected respiratory cells, and CD4 T cells detect inactivated whole viral antigen. Specificity scans with proteome-covering protein/peptide arrays show that CD8 T cells are oligospecific per subject and that CD4 T cell breadth is higher. Some CD4 T cell lines enriched using SARS-CoV-2 cross-recognize whole seasonal coronavirus (sCoV) antigens, with protein, peptide, and HLA restriction validation. Conversely, recognition of some epitopes is eliminated for SARS-CoV-2 variants, including spike (S) epitopes in the alpha, beta, gamma, and delta variant lineages.

SARS-CoV2 variant-specific replicating RNA vaccines protect from disease and pathology and reduce viral shedding following challenge with heterologous SARS-CoV2 variants of concern (preprint)

Despite mass public health efforts, the SARS-CoV2 pandemic continues as of late-2021 with resurgent case numbers in many parts of the world. The emergence of SARS-CoV2 variants of concern (VoC) and evidence that existing vaccines that were designed to protect from the original strains of SARS-CoV-2 may have reduced potency for protection from infection against these VoC is driving continued development of second generation vaccines that can protect against multiple VoC. In this report, we evaluated an alphavirus-based replicating RNA vaccine expressing Spike proteins from the original SARS-CoV-2 Alpha strain and recent VoCs delivered in vivo via a lipid inorganic nanoparticle. Vaccination of both mice and Syrian Golden hamsters showed that vaccination induced potent neutralizing titers against each homologous VoC but reduced neutralization against heterologous challenges. Vaccinated hamsters challenged with homologous SARS-CoV2 variants exhibited complete protection from infection. In addition, vaccinated hamsters challenged with heterologous SARS-CoV-2 variants exhibited significantly reduced shedding of infectious virus. Our data demonstrate that this vaccine platform elicits significant protective immunity against SARS-CoV2 variants and supports continued development of this platform.

Endomembrane targeting of human OAS1 p46 augments antiviral activity (preprint)

Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from host cell innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense viral RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flavivirus, picornavirus, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform strongly associates with COVID-19 severity. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests early control of SARS-CoV-2 replication through OAS1-p46 is an important determinant of COVID-19 severity.

SARS-CoV-2 infects human pluripotent stem cell-derived cardiomyocytes, impairing electrical and mechanical function (preprint)

Global health has been threatened by the COVID-19 pandemic, caused by the novel severe acute respiratory syndrome coronavirus (SARS-CoV-2)1. Although considered primarily a respiratory infection, many COVID-19 patients also suffer severe cardiovascular disease2-4. Improving patient care critically relies on understanding if cardiovascular pathology is caused directly by viral infection of cardiac cells or indirectly via systemic inflammation and/or coagulation abnormalities3,5-9. Here we examine the cardiac tropism of SARS-CoV-2 using human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and three-dimensional engineered heart tissues (3D-EHTs). We observe that hPSC-CMs express the viral receptor ACE2 and other viral processing factors, and that SARS-CoV-2 readily infects and replicates within hPSC-CMs, resulting in rapid cell death. Moreover, infected hPSC-CMs show a progressive impairment in both electrophysiological and contractile properties. Thus, COVID-19-related cardiac symptoms likely result from a direct cardiotoxic effect of SARS-CoV-2. Long-term cardiac complications might be possible sequelae in patients who recover from this illness.

SARS-CoV-2 Serologic Assays in Control and Unknown Populations Demonstrate the Necessity of Virus Neutralization Testing. (preprint)

BackgroundTo determine how serologic antibody testing outcome links with virus neutralization of SARS-CoV-2 to ascertain immune protection status, we evaluated a unique set of individuals for SARS-CoV-2 antibody detection and viral neutralization. MethodsHerein, we compare several analytic platforms with 15 positive and 30 negative SARS-CoV-2 infected controls followed by viral neutralization assessment. We then applied these platforms in a clinically relevant population: 114 individuals with unknown histories of SARS-CoV-2 infection. ResultsIn control populations, the best performing antibody detection assays were SARS-CoV-2 receptor binding domain (RBD) IgG (specificity 87%, sensitivity 100%, PPV 100%, NPV 93%), spike IgG3 (specificity 93%, sensitivity 97%, PPV 93%, NPV 97%), and nucleocapsid (NP) protein IgG (specificity 93%, sensitivity 97%, PPV 93%, NPV 97%). Neutralization of positive and negative control sera showed 100% agreement. 20 unknown individuals had detectable SARS-CoV-2 antibodies with 16 demonstrating virus neutralization. The antibody assays that best predicted virus neutralization were RBD IgG (misidentified 2), spike IgG3 (misidentified 1), and NP IgG (misidentified 2). ConclusionThese data suggest that meaningful evaluation of antibody assay performance requires testing in an unknown population. Further, these results indicate coupling of virus neutralization analysis to a positive antibody test is required to categorize patients based on SARS-CoV-2 immune protection status following virus exposure or vaccine administration. One of the antibody detection platforms identified in this study followed by the pseudoneutralization or focus reduction assay would provide a practical testing strategy to assess for SARS-CoV-2 antibodies with optimal prediction of correlates to neutralizing immunity. FundingSupported by NIH grants AI148684, AI151698, AI145296, and UW funds to the Center for Innate Immunity and Immune Disease.

Functional SARS-CoV-2-specific immune memory persists after mild COVID-19 (preprint)

The recently emerged SARS-CoV-2 virus is currently causing a global pandemic and cases continue to rise. The majority of infected individuals experience mildly symptomatic coronavirus disease 2019 (COVID-19), but it is unknown whether this can induce persistent immune memory that might contribute to herd immunity. Thus, we performed a longitudinal assessment of individuals recovered from mildly symptomatic COVID-19 to determine if they develop and sustain immunological memory against the virus. We found that recovered individuals developed SARS-CoV-2-specific IgG antibody and neutralizing plasma, as well as virus-specific memory B and T cells that not only persisted, but in some cases increased numerically over three months following symptom onset. Furthermore, the SARS-CoV-2-specific memory lymphocytes exhibited characteristics associated with potent antiviral immunity: memory T cells secreted IFN-γ and expanded upon antigen re-encounter, while memory B cells expressed receptors capable of neutralizing virus when expressed as antibodies. These findings demonstrate that mild COVID-19 elicits memory lymphocytes that persist and display functional hallmarks associated with antiviral protective immunity.

De novo design of ACE2 protein decoys to neutralize SARS-CoV-2 (preprint)

There is an urgent need for the ability to rapidly develop effective countermeasures for emerging biological threats, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the ongoing coronavirus disease 2019 (COVID-19) pandemic. We have developed a generalized computational design strategy to rapidly engineer de novo proteins that precisely recapitulate the protein surface targeted by biological agents, like viruses, to gain entry into cells. The designed proteins act as decoys that block cellular entry and aim to be resilient to viral mutational escape. Using our novel platform, in less than ten weeks, we engineered, validated, and optimized de novo protein decoys of human angiotensin-converting enzyme 2 (hACE2), the membrane-associated protein that SARS-CoV-2 exploits to infect cells. Our optimized designs are hyperstable de novo proteins ([~]18-37 kDa), have high affinity for the SARS-CoV-2 receptor binding domain (RBD) and can potently inhibit the virus infection and replication in vitro. Future refinements to our strategy can enable the rapid development of other therapeutic de novo protein decoys, not limited to neutralizing viruses, but to combat any agent that explicitly interacts with cell surface proteins to cause disease.

Single-dose replicating RNA vaccine induces neutralizing antibodies against SARS-CoV-2 in nonhuman primates (preprint)

The ongoing COVID-19 pandemic, caused by infection with SARS-CoV-2, is having a dramatic and deleterious impact on health services and the global economy. Grim public health statistics highlight the need for vaccines that can rapidly confer protection after a single dose and be manufactured using components suitable for scale-up and efficient distribution. In response, we have rapidly developed repRNA-CoV2S, a stable and highly immunogenic vaccine candidate comprised of an RNA replicon formulated with a novel Lipid InOrganic Nanoparticle (LION) designed to enhance vaccine stability, delivery and immunogenicity. We show that intramuscular injection of LION/repRNA-CoV2S elicits robust anti-SARS-CoV-2 spike protein IgG antibody isotypes indicative of a Type 1 T helper response as well as potent T cell responses in mice. Importantly, a single-dose administration in nonhuman primates elicited antibody responses that potently neutralized SARS-CoV-2. These data support further development of LION/repRNA-CoV2S as a vaccine candidate for prophylactic protection from SARS-CoV-2 infection.