Human SARS-CoV-2 challenge resolves local and systemic response dynamics (preprint)

The COVID-19 pandemic is an ongoing global health threat, yet our understanding of the cellular disease dynamics remains limited. In our unique COVID-19 human challenge study we used single cell genomics of nasopharyngeal swabs and blood to temporally resolve abortive, transient and sustained infections in 16 seronegative individuals challenged with preAlpha-SARS-CoV-2. Our analyses revealed rapid changes in cell type proportions and dozens of highly dynamic cellular response states in epithelial and immune cells associated with specific timepoints or infection status. We observed that the interferon response in blood precedes the nasopharynx, and that nasopharyngeal immune infiltration occurred early in transient but later in sustained infection, and thus correlated with preventing sustained infection. Ciliated cells showed an acute response phase, upregulated MHC class II while infected, and were most permissive for viral replication, whilst nasal T cells and macrophages were infected non-productively. We resolve 54 T cell states, including acutely activated T cells that clonally expanded while carrying convergent SARS-CoV-2 motifs. Our novel computational pipeline (Cell2TCR) identifies activated antigen-responding clonotype groups and motifs in any dataset. Together, we show that our detailed time series data (covid19cellatlas.org) can serve as a 'Rosetta stone' for the epithelial and immune cell responses, and reveals early dynamic responses associated with protection from infection.

COVID-19 progression and convalescence in common variable immunodeficiency patients shows incomplete adaptive responses and persistent inflammasome activation (preprint)

Patients with common variable immunodeficiency (CVID), the most prevalent symptomatic primary immunodeficiency, are characterized by hypogammaglobulinemia, poorly protective vaccine titers and increased susceptibility to infections. New pathogens such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), might constitute a particular threat to these immunocompromised patients since many of them experience a slower recovery and do not achieve full response to SARS-CoV-2 vaccines. To define the molecular basis of the altered immune responses caused by SARS-CoV-2 infection in CVID patients, we generated longitudinal single-cell datasets of peripheral blood immune cells along viral infection and recovery. We sampled the same individuals before, during and after SARS-CoV-2 infection to model their specific immune response dynamics while removing donor variability. We observed that COVID-19 CVID patients show defective canonical NF-κB pathway activation and dysregulated expression of BCR-related genes in naïve B cells, as well as enhanced cytotoxic activity but incomplete cytokine response in NK and T cells. Moreover, monocytes from COVID-19 CVID patients show persistent activation of several inflammasome-related genes, including the pyrin and NLRC4 inflammasomes. Our results shed light on the molecular basis of the prolonged clinical manifestations observed in these immunodeficient patients upon SARS-CoV-2 infection, which might illuminate the development of tailored treatments for COVID-19 CVID patients.

A spatial multi-omics atlas of the human lung reveals a novel gland-associated immune niche (preprint)

To (re)define tissue architecture of the lung and airways at the cellular and molecular level, we profiled five proximal-to-distal locations of healthy human lungs in depth using multi-omic single cell/nuclei and Visium Spatial Transcriptomics. Using computational data integration and analysis, we extend beyond the suspension cell paradigm of lung atlases to date, to define and discover macro and micro-anatomical tissue compartments. We describe novel cell types and states in vascular, stromal and nerve bundle microenvironments. From our spatial transcriptomics, we discover and validate a novel survival niche for IgA plasma cells in the airway submucosal glands (SMG). In this niche we define a supporting role for SMG epithelial cells in mucosal immunity through recruitment and maintenance of IgA plasma, B and CD4 T cells locally at the airway SMG. We identify an immune-supporting role for SMG duct and serous cells with distinct signalling circuits to recruit B cells and IgA plasma cells, promoting longevity and antibody secretion through expression of CCL28, APRIL and IL6. We find high expression of MHC-II in SMG duct and serous cells, which are localised closely with memory CD4 T cells, suggesting local modulation of antigen specific immune responses locally at the glands. This new tissue microenvironment, which we term the “gland-associated immune niche” (GAIN) has major implications for respiratory immunity and infection response. Our single cell and spatial data is available for download and query at lungcellatlas.org.

The local and systemic response to SARS-CoV-2 infection in children and adults (preprint)

While a substantial proportion of adults infected with SARS-CoV-2 progress to develop severe disease, children rarely manifest respiratory complications. Therefore, understanding differences in the local and systemic response to SARS-CoV-2 infection between children and adults may provide important clues about the pathogenesis of SARS-CoV-2 infection. To address this, we first generated a healthy reference multi-omics single cell data set from children (n=30) in whom we have profiled triple matched samples: nasal and tracheal brushings and PBMCs, where we track the developmental changes for 42 airway and 31 blood cell populations from infancy, through childhood to adolescence. This has revealed the presence of naive B and T lymphocytes in neonates and infants with a unique gene expression signature bearing hallmarks of innate immunity. We then contrast the healthy reference with equivalent data from severe paediatric and adult COVID-19 patients (total n=27), from the same three types of samples: upper and lower airways and blood. We found striking differences: children with COVID-19 as opposed to adults had a higher proportion of innate lymphoid and non-clonally expanded naive T cells in peripheral blood, and a limited interferon-response signature. In the airway epithelium, we found the highest viral load in goblet and ciliated cells and describe a novel inflammatory epithelial cell population. These cells represent a transitional regenerative state between secretory and ciliated cells; they were found in healthy children and were enriched in pediatric and adult COVID-19 patients. Epithelial cells display an antiviral and neutrophil-recruiting gene signature that is weaker in severe paediatric versus adult COVID-19. Our matched blood and airway samples allowed us to study the spatial dynamics of infection. Lastly, we provide a user-friendly interface for this data as a highly granular reference for the study of immune responses in airways and blood in children.

The cellular immune response to COVID-19 deciphered by single cell multi-omics across three UK centres (preprint)

The COVID-19 pandemic, caused by SARS coronavirus 2 (SARS-CoV-2), has resulted in excess morbidity and mortality as well as economic decline. To characterise the systemic host immune response to SARS-CoV-2, we performed single-cell RNA-sequencing coupled with analysis of cell surface proteins, providing molecular profiling of over 800,000 peripheral blood mononuclear cells from a cohort of 130 patients with COVID-19. Our cohort, from three UK centres, spans the spectrum of clinical presentations and disease severities ranging from asymptomatic to critical. Three control groups were included: healthy volunteers, patients suffering from a non-COVID-19 severe respiratory illness and healthy individuals administered with intravenous lipopolysaccharide to model an acute inflammatory response. Full single cell transcriptomes coupled with quantification of 188 cell surface proteins, and T and B lymphocyte antigen receptor repertoires have provided several insights into COVID-19: 1. a new non-classical monocyte state that sequesters platelets and replenishes the alveolar macrophage pool; 2. platelet activation accompanied by early priming towards megakaryopoiesis in immature haematopoietic stem/progenitor cells and expansion of megakaryocyte-primed progenitors; 3. increased clonally expanded CD8+ effector:effector memory T cells, and proliferating CD4+ and CD8+ T cells in patients with more severe disease; and 4. relative increase of IgA plasmablasts in asymptomatic stages that switches to expansion of IgG plasmablasts and plasma cells, accompanied with higher incidence of BCR sharing, as disease severity increases. All data and analysis results are available for interrogation and data mining through an intuitive web portal. Together, these data detail the cellular processes present in peripheral blood during an acute immune response to COVID-19, and serve as a template for multi-omic single cell data integration across multiple centers to rapidly build powerful resources to help combat diseases such as COVID-19.