Deep generative models predict SARS-CoV-2 Spike infectivity and foreshadow neutralizing antibody escape (preprint)

Recurrent waves of SARS-CoV-2 infection, driven by the periodic emergence of new viral variants, highlight the need for vaccines and therapeutics that remain effective against future strains. Yet, our ability to proactively evaluate such therapeutics is limited to assessing their effectiveness against previous or circulating variants, which may differ significantly in their antibody escape from future viral evolution. To address this challenge, we developed deep learning methods to predict the effect of mutations on fitness and escape from neutralizing antibodies and used this information to engineer a set of 68 unique SARS-CoV-2 Spike proteins. The designed constructs, which incorporated novel combinations of up to 46 mutations relative to the ancestral strain, were infectious and evaded neutralization by nine well-characterized panels of human polyclonal anti-SARS-CoV-2 immune sera. Designed constructs on previous SARS-CoV-2 strains anticipated the antibody neutralization escape of variants seen subsequently during the COVID-19 pandemic. We demonstrate that designed Spike constructs using data available at the time of the implementation of the 2022 bivalent mRNA booster vaccine foretold the level of neutralizing antibody escape observed in the most recently emerging variants. Our approach provides extensive datasets of antigenically diverse escape variants to evaluate the protective ability of vaccines and therapeutics to inhibit future variants. This approach is generalizable to other viral pathogen

S:D614G and S:H655Y are gateway mutations that act epistatically to promote SARS-CoV-2 variant fitness (preprint)

SARS-CoV-2 variants bearing complex combinations of mutations have been associated with increased transmissibility, COVID-19 severity, and immune escape. S:D614G may have facilitated emergence of such variants since they appeared after S:D614G had gone to fixation. To test this hypothesis, Spike sequences from an immunocompromised individual with prolonged infection, and from the major SARS-CoV-2 variants of concern, were reverted to the ancestral S:D614. In all cases, infectivity of the revertants was compromised. Rare SARS-CoV-2 lineages that lack S:D614G were identified and the infectivity of these was dependent upon S:Q613H or S:H655Y. Notably, Gamma and Omicron variants possess both S:D614G and S:H655Y, each of which contributed to infectivity of these variants. All three mutations, S:Q613H, S:D614G, and S:H655Y, stabilized Spike on virions, consistent with selection of these mutations by a common molecular mechanism. Among sarbecoviruses, S:Q613H, S:D614G, and S:H655Y are only detected in SARS-CoV-2, which uniquely possesses a polybasic S1/S2 cleavage site. Results of genetic and biochemical experiments here demonstrated that S:D614G and S:H655Y are likely adaptations to the cleavage site. CryoEM revealed that both mutations shift the Spike receptor binding domain towards the open conformation required for ACE2-binding and Spikes bearing either S:D614G or S:H655Y spontaneously mimic the smFRET signal that ACE2 induces in the parental molecule. Data from these orthogonal experiments demonstrate that S:D614G and S:H655Y are convergent adaptations to the polybasic S1/S2 cleavage site, which stabilize S1 on the virion in the open RBD conformation that is on-pathway for target cell fusion, and thereby act epistatically to promote the fitness of variants bearing complex combinations of clinically significant mutations.

Innate lymphoid cells and disease tolerance in SARS-CoV-2 infection (preprint)

BACKGROUNDRisk of severe coronavirus disease 2019 (COVID-19) increases with age, is greater in males, and is associated with decreased numbers of blood lymphoid cells. Though the reasons for these robust associations are unclear, effects of age and sex on innate and adaptive lymphoid subsets, including on homeostatic innate lymphoid cells (ILCs) implicated in disease tolerance, may underlie the effects of age and sex on COVID-19 morbidity and mortality. METHODSFlow cytometry was used to quantitate subsets of blood lymphoid cells from people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), comparing those hospitalized with severe COVID-19 (n=40) and those treated as outpatients for less severe disease (n=51). 86 healthy individuals served as controls. The relationship between abundance of specific blood lymphoid cell types, age, sex, hospitalization, duration of hospitalization, and elevation of blood markers for systemic inflammation, was determined using multiple regression. RESULTSAfter accounting for effects of age and sex, hospitalization for COVID-19 was associated with 1.78-fold fewer ILCs (95%CI: 2.34-1.36; p = 4.55 x 10-5) and 2.31-fold fewer CD16+ natural killer (NK) cells (95%CI: 3.1-1.71; p = 1.04 x 10-7), when compared to uninfected controls. Among people infected with SARS-CoV-2, the odds ratio for hospitalization, adjusted for age, sex, and duration of symptoms, was 0.413 (95%CI: 0.197-0.724; p = 0.00691) for every 2-fold increase in ILCs. In addition, higher ILC abundance was associated with less time spent in the hospital and lower levels of blood markers associated with COVID-19 severity: each two-fold increase in ILC abundance was associated with a 9.38 day decrease in duration of hospital stay (95% CI: 15.76-3.01; p= 0.0054), and decrease in blood C-reactive protein (CRP) by 46.29 mg/L (95% CI: 71.34-21.24; p = 6.25 x 10-4), erythrocyte sedimentation rate (ESR) by 11.04 mm/h (95% CI: 21.94-0.13; p = 0.047), and the fibrin degradation product D-dimer by 1098.52 ng/mL (95% CI: 1932.84-264.19; p = 0.011). CONCLUSIONSBoth ILCs and NK cells were depleted in the blood of people hospitalized for severe COVID-19, but, among lymphoid cell subsets, only ILC abundance was independently associated with the need for hospitalization, duration of hospital stay, and severity of inflammation. These results indicate that, by promoting disease tolerance, homeostatic ILCs protect against morbidity and mortality in SARS-CoV-2 infection, and suggest that reduction in the number of ILCs with age and in males accounts for the increased risk of severe COVID-19 in these demographic groups.

SARS-CoV-2 Spike protein variant D614G increases infectivity and retains sensitivity to antibodies that target the receptor binding domain (preprint)

The SARS-CoV-2 spike (S) protein variant D614G supplanted the ancestral virus worldwide in a matter of months. Here we show that D614G was more infectious than the ancestral form on human lung cells, colon cells, and cells rendered permissive by ectopic expression of various mammalian ACE2 orthologs. Nonetheless, D614G affinity for ACE2 was reduced due to a faster dissociation rate. Assessment of the S protein trimer by cryo-electron microscopy showed that D614G disrupts a critical interprotomer contact and that this dramatically shifts the S protein trimer conformation toward an ACE2-binding and fusion-competent state. Consistent with the more open conformation, neutralization potency of antibodies targeting the S protein receptor-binding domain was not attenuated. These results indicate that D614G adopts conformations that make virion membrane fusion with the target cell membrane more probable but that D614G retains susceptibility to therapies that disrupt interaction of the SARS-CoV-2 S protein with the ACE2 receptor.