A single-nucleus and spatial transcriptomic atlas of the COVID-19 liver reveals topological, functional, and regenerative organ disruption in patients

The molecular underpinnings of organ dysfunction in acute COVID-19 and its potential long-term sequelae are under intense investigation. To shed light on these in the context of liver function, we performed single-nucleus RNA-seq and spatial transcriptomic profiling of livers from 17 COVID-19 decedents. We identified hepatocytes positive for SARS-CoV-2 RNA with an expression phenotype resembling infected lung epithelial cells. Integrated analysis and comparisons with healthy controls revealed extensive changes in the cellular composition and expression states in COVID-19 liver, reflecting hepatocellular injury, ductular reaction, pathologic vascular expansion, and fibrogenesis. We also observed Kupffer cell proliferation and erythrocyte progenitors for the first time in a human liver single-cell atlas, resembling similar responses in liver injury in mice and in sepsis, respectively. Despite the absence of a clinical acute liver injury phenotype, endothelial cell composition was dramatically impacted in COVID-19, concomitantly with extensive alterations and profibrogenic activation of reactive cholangiocytes and mesenchymal cells. Our atlas provides novel insights into liver physiology and pathology in COVID-19 and forms a foundational resource for its investigation and understanding.

Limit of Detection for Rapid Antigen Testing of the SARS-CoV-2 Omicron Variant

There has been debate in the literature about the ability of antigen tests to detect the SARS-CoV-2 Omicron variant including indication on the US Food and Drug administration website that antigen tests may have lower sensitivity for the Omicron variant without provision of data or the potential scale of the issue (see https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/sars-cov-2-viral-mutations-impact-covid-19-tests-omicronvariantimpact, accessed 1/27/2022). Here we determined the limit of detection (LoD) for the Omicron variant compared with the WA1 strain used for LoD studies described in the Instructions for Use for all Emergency Use Authorization (EUA)-approved antigen tests. Using live virus (to avoid artifactual findings potentially obtained with gamma-irradiated or heat-killed virus) quantified by plaque forming units (PFU), we examined the analytical sensitivity of three antigen tests widely used in the United States: the Abbott Binax Now, the AccessBio CareStart, and LumiraDx antigen tests. We found that the 95% detection threshold (LoD) for antigen tests was at least as good for Omicron as for the WA1 strain. Furthermore, the relationship of genome copies to plaque forming units for Omicron and WA1 overlap. Therefore, the LoD equivalency also applies if the quantitative comparator is genome copies determined from live virus preparations. Taken together, our data support the continued ability of the antigen tests examined to detect the Omicron variant.

SARS-CoV-2 Antigen Tests Predict Infectivity Based on Viral Culture: Comparison of Antigen, PCR Viral Load, and Viral Culture Testing on a Large Sample Cohort

The relationship of SARS-CoV-2 antigen testing results, viral load, and viral culture detection remains to be fully defined. Presumptively, viral culture can provide a surrogate measure for infectivity of sampled individuals, and thereby inform how and where to most appropriately deploy available diagnostic testing modalities. We therefore determined the relationship of antigen testing results from three lateral flow and one microfluidics assay to viral culture performed in parallel in 181 nasopharyngeal swab samples positive for SARS-CoV-2. Sample viral loads, determined by RT-qPCR, were distributed across the range of viral load values observed in our testing population. We found that antigen tests were predictive of viral culture positivity, with the LumiraDx method showing enhanced sensitivity (90%; 95% confidence interval (95% CI) 83-94%) compared with the BD Veritor (74%, 95% CI 65-81%), CareStart (74%, 95% CI 65-81%) and Oscar Corona (74%, 95% CI 65-82%) lateral flow antigen tests. Antigen and viral culture positivity were also highly correlated with sample viral load, with areas under the receiver-operator characteristic curves (ROCs) of 0.94-0.97 and 0.92, respectively. In particular, a viral load threshold of 100,000 copies/mL was 95% sensitive (95% CI, 90-98%) and 72% specific (95% CI, 60-81%) for predicting viral culture positivity. Taken together, the detection of SARS-CoV-2 antigen identified highly infectious individuals, some of whom may harbor 10,000-fold more virus in their samples than those with any detectable infectious virus. As such, our data support use of antigen testing in defining infectivity status at the time of sampling.

Saliva Is Comparable to Nasopharyngeal Swabs for Molecular Detection of SARS-CoV-2

BackgroundThe continued need for molecular testing for SARS-CoV-2 and potential for self-collected saliva as an alternative to nasopharyngeal (NP) swabs for sample acquisition led us to compare saliva to NP swabs in an outpatient setting, without restrictions to avoid food, drink, smoking, or tooth-brushing. MethodsA total of 385 pairs of NP and saliva specimens were obtained, the majority from individuals presenting for initial evaluation, and were tested on two high-sensitivity RT-PCR platforms: the Abbott m2000 and Abbott Alinity m (both with limits of detection [LoD] of 100 copies of viral RNA/mL). ResultsConcordance between saliva and NP was excellent overall (Cohens {kappa}=0.93), for both initial and followup testing, for both platforms, and for specimens treated with guanidinium transport medium as preservative as well as for untreated saliva ({kappa}=0.88-0.95). Viral loads were on average 16x higher in NP specimens than saliva specimens, suggesting that only the relatively small fraction of outpatients ([~]8% in this study) who present with very low viral loads (<1,600 copies/mL from NP swabs) would be missed by testing saliva instead of NP swabs, when using sensitive testing platforms. Special attention was necessary to ensure leak-resistant specimen collection and transport. ConclusionsThe advantages of self-collection of saliva, without behavioral restrictions, will likely outweigh a minor potential decrease in clinical sensitivity in individuals less likely to pose an infectious risk to others for many real-world scenarios, especially for initial testing. Key pointsSaliva has comparable sensitivity and specificity to nasopharyngeal swabs for RT-PCR-based COVID-19 testing (concordance, {kappa}=0.93; n=385 participants), albeit with slightly lower recovery of viral RNA. Treatment with a readily available guanidinium preservative within 24 hours of sample collection improves recovery.

Verification of the Abbott Alinity m Resp-4-Plex Assay for detection of SARS-CoV-2, influenza A/B, and respiratory syncytial virus

COVID-19 symptomology may overlap with other circulating respiratory viruses that may also cause severe disease and for which there are specific and potentially life-saving treatments. The Abbott Alinity m Resp-4-Plex assay is a multiplex PCR assay that simultaneously detects and differentiates infection with SARS-CoV-2, influenza A, influenza B, and respiratory syncytial virus (RSV). We characterized its accuracy, precision, and analytical sensitivity. All were found to be robust for measures examined. In the context of sample-to-answer, near random access automation on the Alinity m platform, we believe that the Resp-4-Plex assay offers significant utility in addressing the current needs of the SARS-CoV-2 pandemic and future needs during anticipated endemic circulation of SARS-CoV-2 with other respiratory viruses.

A single-cell and spatial atlas of autopsy tissues reveals pathology and cellular targets of SARS-CoV-2

The SARS-CoV-2 pandemic has caused over 1 million deaths globally, mostly due to acute lung injury and acute respiratory distress syndrome, or direct complications resulting in multiple-organ failures. Little is known about the host tissue immune and cellular responses associated with COVID-19 infection, symptoms, and lethality. To address this, we collected tissues from 11 organs during the clinical autopsy of 17 individuals who succumbed to COVID-19, resulting in a tissue bank of approximately 420 specimens. We generated comprehensive cellular maps capturing COVID-19 biology related to patients demise through single-cell and single-nucleus RNA-Seq of lung, kidney, liver and heart tissues, and further contextualized our findings through spatial RNA profiling of distinct lung regions. We developed a computational framework that incorporates removal of ambient RNA and automated cell type annotation to facilitate comparison with other healthy and diseased tissue atlases. In the lung, we uncovered significantly altered transcriptional programs within the epithelial, immune, and stromal compartments and cell intrinsic changes in multiple cell types relative to lung tissue from healthy controls. We observed evidence of: alveolar type 2 (AT2) differentiation replacing depleted alveolar type 1 (AT1) lung epithelial cells, as previously seen in fibrosis; a concomitant increase in myofibroblasts reflective of defective tissue repair; and, putative TP63+ intrapulmonary basal-like progenitor (IPBLP) cells, similar to cells identified in H1N1 influenza, that may serve as an emergency cellular reserve for severely damaged alveoli. Together, these findings suggest the activation and failure of multiple avenues for regeneration of the epithelium in these terminal lungs. SARS-CoV-2 RNA reads were enriched in lung mononuclear phagocytic cells and endothelial cells, and these cells expressed distinct host response transcriptional programs. We corroborated the compositional and transcriptional changes in lung tissue through spatial analysis of RNA profiles in situ and distinguished unique tissue host responses between regions with and without viral RNA, and in COVID-19 donor tissues relative to healthy lung. Finally, we analyzed genetic regions implicated in COVID-19 GWAS with transcriptomic data to implicate specific cell types and genes associated with disease severity. Overall, our COVID-19 cell atlas is a foundational dataset to better understand the biological impact of SARS-CoV-2 infection across the human body and empowers the identification of new therapeutic interventions and prevention strategies.