Kinetics of peripheral blood neutrophils in severe coronavirus disease 2019.

OBJECTIVES: Emerging evidence of dysregulation of the myeloid cell compartment urges investigations on neutrophil characteristics in coronavirus disease 2019 (COVID-19). We isolated neutrophils from the blood of COVID-19 patients receiving general ward care and from patients hospitalised at intensive care units (ICUs) to explore the kinetics of circulating neutrophils and factors important for neutrophil migration and activation. METHODS: Multicolour flow cytometry was exploited for the analysis of neutrophil differentiation and activation markers. Multiplex and ELISA technologies were used for the quantification of protease, protease inhibitor, chemokine and cytokine concentrations in plasma. Neutrophil polarisation responses were evaluated microscopically. Gelatinolytic and metalloproteinase activity in plasma was determined using a fluorogenic substrate. Co-culturing healthy donor neutrophils with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) allowed us to investigate viral replication in neutrophils. RESULTS: Upon ICU admission, patients displayed high plasma concentrations of granulocyte-colony-stimulating factor (G-CSF) and the chemokine CXCL8, accompanied by emergency myelopoiesis as illustrated by high levels of circulating CD10-, immature neutrophils with reduced CXCR2 and C5aR expression. Neutrophil elastase and non-metalloproteinase-derived gelatinolytic activity were increased in plasma from ICU patients. Significantly higher levels of circulating tissue inhibitor of metalloproteinase 1 (TIMP-1) in patients at ICU admission yielded decreased total MMP proteolytic activity in blood. COVID-19 neutrophils were hyper-responsive to CXCL8 and CXCL12 in shape change assays. Finally, SARS-CoV-2 failed to replicate inside human neutrophils. CONCLUSION: Our study provides detailed insights into the kinetics of neutrophil phenotype and function in severe COVID-19 patients, and supports the concept of an increased neutrophil activation state in the circulation.

Atypical response to bacterial coinfection and persistent neutrophilic bronchoalveolar inflammation distinguish critical COVID-19 from influenza.

Neutrophils are recognized as important circulating effector cells in the pathophysiology of severe coronavirus disease 2019 (COVID-19). However, their role within the inflamed lungs is incompletely understood. Here, we collected bronchoalveolar lavage (BAL) fluids and parallel blood samples of critically ill COVID-19 patients requiring invasive mechanical ventilation and compared BAL fluid parameters with those of mechanically ventilated patients with influenza, as a non-COVID-19 viral pneumonia cohort. Compared with those of patients with influenza, BAL fluids of patients with COVID-19 contained increased numbers of hyperactivated degranulating neutrophils and elevated concentrations of the cytokines IL-1ß, IL-1RA, IL-17A, TNF-α, and G-CSF; the chemokines CCL7, CXCL1, CXCL8, CXCL11, and CXCL12α; and the protease inhibitors elafin, secretory leukocyte protease inhibitor, and tissue inhibitor of metalloproteinases 1. In contrast, α-1 antitrypsin levels and net proteolytic activity were comparable in COVID-19 and influenza BAL fluids. During antibiotic treatment for bacterial coinfections, increased BAL fluid levels of several activating and chemotactic factors for monocytes, lymphocytes, and NK cells were detected in patients with COVID-19 whereas concentrations tended to decrease in patients with influenza, highlighting the persistent immunological response to coinfections in COVID-19. Finally, the high proteolytic activity in COVID-19 lungs suggests considering protease inhibitors as a treatment option.

Interferons and other cytokines, genetics and beyond in COVID-19 and autoimmunity.

Interferons are the best antiviral agents in vitro against SARS-CoV-2 so far and genetic defects in their signaling cascade or neutralization of alfa-interferons by autoantibodies come with more severe COVID-19. However, there is more, as the SARS-CoV-2 dysregulates not only innate immune mechanisms but also T and B cell repertoires. Most genetic, hematological and immunological studies in COVID-19 are at present phenomenological. However, these and antecedent studies contain the seed grains to resolve many unanswered questions and a whole range of testable hypotheses. What are the links, if existing, between genetics and the occurrence of interferon-neutralizing antibodies? Are NAGGED (neutralizing and generated by gene defect) antibodies involved or not? Is the autoimmune process cause or consequence of virus infection? What are the roles played by cytokine posttranslational modifications, such as proteolysis, glycosylation, citrullination and others? How is systemic autoimmunity linked with type 1 interferons? These questions place cytokines and growth factors at pole positions as keys to unlock basic mechanisms of infection and (auto)immunity. Related to cytokine research, (1) COVID-19 patients develop neutralizing autoantibodies, mainly against alpha interferons and it is not yet established whether this is the consequence or cause of virus replication. (2) The glycosylation of recombinant interferon-beta protects against breaking tolerance and the development of neutralizing antibodies. (3) SARS-CoV-2 induces severe inflammation and release of extracellular proteases leading to remnant epitopes, e.g. of cytokines. (4) In the rare event of homozygous cytokine gene segment deletions, observed neutralizing antibodies may be named NAGGED antibodies. (5) Severe cytolysis releases intracellular content into the extracellular milieu and leads to regulated degradation of intracellular proteins and selection of antibody repertoires, similar to those observed in patients with systemic lupus erythematosus. (6) Systematic studies of novel autoimmune diseases on single cytokines will complement the present picture about interferons. (7) Interferon neutralization in COVID-19 constitutes a preamble of more studies about cytokine-regulated proteolysis in the control of autoimmunity. Here we reformulate these seven conjectures into testable questions for future research.

A single-dose live-attenuated YF17D-vectored SARS-CoV-2 vaccine candidate.

The expanding pandemic of coronavirus disease 2019 (COVID-19) requires the development of safe, efficacious and fast-acting vaccines. Several vaccine platforms are being leveraged for a rapid emergency response1. Here we describe the development of a candidate vaccine (YF-S0) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that uses live-attenuated yellow fever 17D (YF17D) vaccine as a vector to express a noncleavable prefusion form of the SARS-CoV-2 spike antigen. We assess vaccine safety, immunogenicity and efficacy in several animal models. YF-S0 has an excellent safety profile and induces high levels of SARS-CoV-2 neutralizing antibodies in hamsters (Mesocricetus auratus), mice (Mus musculus) and cynomolgus macaques (Macaca fascicularis), and-concomitantly-protective immunity against yellow fever virus. Humoral immunity is complemented by a cellular immune response with favourable T helper 1 polarization, as profiled in mice. In a hamster model2 and in macaques, YF-S0 prevents infection with SARS-CoV-2. Moreover, a single dose conferred protection from lung disease in most of the vaccinated hamsters within as little as 10 days. Taken together, the quality of the immune responses triggered and the rapid kinetics by which protective immunity can be attained after a single dose warrant further development of this potent SARS-CoV-2 vaccine candidate.

STAT2 signaling restricts viral dissemination but drives severe pneumonia in SARS-CoV-2 infected hamsters.

Emergence of SARS-CoV-2 causing COVID-19 has resulted in hundreds of thousands of deaths. In search for key targets of effective therapeutics, robust animal models mimicking COVID-19 in humans are urgently needed. Here, we show that Syrian hamsters, in contrast to mice, are highly permissive to SARS-CoV-2 and develop bronchopneumonia and strong inflammatory responses in the lungs with neutrophil infiltration and edema, further confirmed as consolidations visualized by micro-CT alike in clinical practice. Moreover, we identify an exuberant innate immune response as key player in pathogenesis, in which STAT2 signaling plays a dual role, driving severe lung injury on the one hand, yet restricting systemic virus dissemination on the other. Our results reveal the importance of STAT2-dependent interferon responses in the pathogenesis and virus control during SARS-CoV-2 infection and may help rationalizing new strategies for the treatment of COVID-19 patients.