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.

Profound Treg perturbations correlate with COVID-19 severity (preprint)

The hallmark of severe COVID-19 disease has been an uncontrolled inflammatory response, resulting from poorly understood immunological dysfunction. We explored the hypothesis that perturbations in FoxP3+ T regulatory cells (Treg), key enforcers of immune homeostasis, contribute to COVID-19 pathology. Cytometric and transcriptomic profiling revealed a distinct Treg phenotype in severe COVID-19 patients, with an increase in both Treg proportions and intracellular levels of the lineage-defining transcription factor FoxP3, which correlated with poor outcomes. Accordingly, these Tregs over-expressed a range of suppressive effectors, but also pro-inflammatory molecules like IL32. Most strikingly, they acquired similarity to tumor-infiltrating Tregs, known to suppress local anti-tumor responses. These traits were most marked in acute patients with severe disease, but persisted somewhat in convalescent patients. These results suggest that Tregs may play nefarious roles in COVID-19, via suppressing anti-viral T cell responses during the severe phase of the disease, and/or via a direct pro-inflammatory role.

Identification of eight SARS-CoV-2 ORF7a deletion variants in 2,726 clinical specimens (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ORF7a, the ortholog of SARS-CoV ORF7a, is a type I transmembrane protein and plays an important role in virus-host interactions. Deletion variants in ORF7a may influence virulence, but only a few such isolates have been reported. Here, we report 8 unique ORF7a deletion variants of 6 to 96 nucleotides in length identified from 2,726 clinical specimens collected in March of 2020.

SARS-CoV-2 Viral Load is Associated with Increased Disease Severity and Mortality (preprint)

The relationship between SARS-CoV-2 viral load and risk of disease progression remains largely undefined in coronavirus disease 2019 (COVID-19). We quantified SARS-CoV-2 viral load from participants with a diverse range of COVID-19 severity, including those requiring hospitalization, outpatients with mild disease, and individuals with resolved infection. SARS-CoV-2 plasma RNA was detected in 27% of hospitalized participants and 13% of outpatients diagnosed with COVID-19. Amongst the participants hospitalized with COVID-19, higher prevalence of detectable SARS-CoV-2 plasma viral load was associated with worse respiratory disease severity, lower absolute lymphocyte counts, and increased markers of inflammation, including C-reactive protein and IL-6. SARS-CoV-2 viral loads, especially plasma viremia, were associated with increased risk of mortality. SARS-CoV-2 viral load may aid in the risk stratification of patients with COVID-19 and its role in disease pathogenesis should be further explored.

Point-of-care testing for COVID-19 using SHERLOCK diagnostics (preprint)

The recent outbreak of the novel coronavirus SARS-CoV-2, which causes COVID-19, can be diagnosed using RT-qPCR, but inadequate access to reagents and equipment has slowed disease detection and impeded efforts to mitigate viral spread. Alternative approaches based on combinations of isothermal amplification and CRISPR-mediated detection, such as the SHERLOCK ( S pecific H igh S ensitivity E nzymatic R eporter Un LOCK ing) technique, offer reduced dependence on RT-qPCR equipment, but previously reported methods required multiple fluid handling steps, complicating their deployment outside clinical labs. Here we developed a simple test chemistry called STOP (SHERLOCK Testing in One Pot) for detecting SARS-CoV-2 in one hour that is suitable for point-of-care use. This simplified test, STOPCovid, provides sensitivity comparable to RT-qPCR-based SARS-CoV-2 tests and has a limit of detection of 100 copies of viral genome input in saliva or nasopharyngeal swabs per reaction. Using lateral flow readout, the test returns result in 70 minutes, and using fluorescence readout, the test returns result in 40 minutes. Moreover, we validated STOPCovid using nasopharyngeal swabs from COVID-19 patients and were able to correctly diagnose 12 positive and 5 negative patients out of 3 replicates. We envision that implementation of STOPCovid will significantly aid "test-trace-isolate" efforts, especially in low-resource settings, which will be critical for long-term public health safety and effective reopening of the society.