Preferential expansion of cross-reactive pre-existing switched memory B cells that recognize the SARS-CoV-2 Omicron variant Spike protein

In previously unvaccinated and uninfected individuals, non-RBD SARS-CoV-2 spike-specific B cells were prominent in two distinct, durable, resting, cross-reactive, "pre-existing" switched memory B cell compartments. While pre-existing RBD-specific B cells were extremely rare in uninfected and unvaccinated individuals, these two pre-existing switched memory B cell compartments were molded by vaccination and infection to become the primary source of RBD-specific B cells that are triggered by vaccine boosting. The frequency of wild-type RBD-binding memory B cells that cross-react with the Omicron variant RBD did not alter with boosting. In contrast, after a boost, B cells recognizing the full-length Omicron variant spike protein expanded, with pre-existing resting memory B cells differentiating almost quantitatively into effector B cell populations. B cells derived from "ancient" pre-existing memory cells and that recognize the full-length wild-type spike with the highest avidity after boosting are the B cells that also bind the Omicron variant spike protein. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/21268554v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@1de97acorg.highwire.dtl.DTLVardef@b7ab7forg.highwire.dtl.DTLVardef@5c38dcorg.highwire.dtl.DTLVardef@99106c_HPS_FORMAT_FIGEXP M_FIG C_FIG

Neutrophil Profiles of Pediatric COVID-19 and Multisystem Inflammatory Syndrome in Children

Multisystem Inflammatory Syndrome in Children (MIS-C) is a delayed-onset, COVID-19-related hyperinflammatory systemic illness characterized by SARS-CoV-2 antigenemia, cytokine storm and immune dysregulation; however, the role of the neutrophil has yet to be defined. In adults with severe COVID-19, neutrophil activation has been shown to be central to overactive inflammatory responses and complications. Thus, we sought to define neutrophil activation in children with MIS-C and acute COVID-19. We collected samples from 141 children: 31 cases of MIS-C, 43 cases of acute pediatric COVID-19, and 67 pediatric controls. We found that MIS-C neutrophils display a granulocytic myeloid-derived suppressor cell (G-MDSC) signature with highly altered metabolism, which is markedly different than the neutrophil interferon-stimulated gene (ISG) response observed in pediatric patients during acute SARS-CoV-2 infection. Moreover, we identified signatures of neutrophil activation and degranulation with high levels of spontaneous neutrophil extracellular trap (NET) formation in neutrophils isolated from fresh whole blood of MIS-C patients. Mechanistically, we determined that SARS-CoV-2 immune complexes are sufficient to trigger NETosis. Overall, our findings suggest that the hyperinflammatory presentation of MIS-C could be mechanistically linked to persistent SARS-CoV-2 antigenemia through uncontrolled neutrophil activation and NET release in the vasculature. One Sentence SummaryCirculating SARS-CoV-2 antigen:antibody immune complexes in Multisystem Inflammatory Syndrome in Children (MIS-C) drive hyperinflammatory and coagulopathic neutrophil extracellular trap (NET) formation and neutrophil activation pathways, providing insight into disease pathology and establishing a divergence from neutrophil signaling seen in acute pediatric COVID-19.

Expansion of Cytotoxic CD4+ T cells in the lungs in severe COVID-19

The contributions of T cells infiltrating the lungs to SARS-CoV-2 clearance and disease progression are poorly understood. Although studies of CD8+ T cells in bronchoalveolar lavage and blood have suggested that these cells are exhausted in severe COVID-19, CD4+ T cells have not been systematically interrogated within the lung parenchyma. We establish here that cytotoxic CD4+ T cells (CD4+CTLs) are prominently expanded in the COVID-19 lung infiltrate. CD4+CTL numbers in the lung increase with disease severity and progression is accompanied by widespread HLA-DR expression on lung epithelial and endothelial cells, increased apoptosis of epithelial cells and tissue remodeling. Based on quantitative evidence for re-activation in the lung milieu, CD4+ CTLs are as likely to drive viral clearance as CD8+ T cells and may also be contributors to lung inflammation and eventually to fibrosis in severe COVID-19. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=138 SRC="FIGDIR/small/21253885v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@198a382org.highwire.dtl.DTLVardef@16b3cdorg.highwire.dtl.DTLVardef@769032org.highwire.dtl.DTLVardef@1f4cd1c_HPS_FORMAT_FIGEXP M_FIG C_FIG In BriefIn severe COVID-19 cytotoxic CD4+ T cells accumulate in draining lymph nodes and in the lungs during the resolving phase of the disease. Re-activated cytotoxic CD4+ T cells and cytotoxic CD8+ T cells are present in roughly equivalent numbers in the lungs at this stage and these cells likely collaborate to eliminate virally infected cells and potentially induce fibrosis. A large fraction of epithelial and endothelial cells in the lung express HLA class II in COVID-19 and there is temporal convergence between CD4+CTL accumulation and apoptosis in the lung. HighlightsO_LIIn severe COVID-19, activated CD4+ CTLs accumulate in the lungs late in disease C_LIO_LIThese cells likely participate in SARS-CoV-2 clearance, collaborating with CD8+ T cells many of which exhibit an exhausted phenotype C_LIO_LIT cells likely contribute to the late exacerbation of inflammation C_LIO_LICD4+CTLs have been linked to fibrosis in many disorders and could also be responsible for the eventual induction of fibrosis in a subset of COVID-19 patients C_LI SummaryThe contributions of T cells infiltrating the lungs to SARS-CoV-2 clearance and disease progression are poorly understood. Although studies of CD8+ T cells in bronchoalveolar lavage and blood have suggested that these cells are exhausted in severe COVID-19, CD4+ T cells have not been systematically interrogated within the lung parenchyma. We establish here that cytotoxic CD4+ T cells (CD4+CTLs) are prominently expanded in the COVID-19 lung infiltrate. CD4+CTL numbers in the lung increase with disease severity and progression is accompanied by widespread HLA-DR expression on lung epithelial and endothelial cells, increased apoptosis of epithelial cells and tissue remodeling. Based on quantitative evidence for re-activation in the lung milieu, CD4+ CTLs are as likely to drive viral clearance as CD8+ T cells and may also be contributors to lung inflammation and eventually to fibrosis in severe COVID-19.