Development of an effective immune response in adults with Down Syndrome after SARS-CoV-2 vaccination

Immune dysregulation in individuals with Down syndrome (DS) leads to an increased risk for hospitalization and death due to COVID-19 and may impair the generation of protective immunity after vaccine administration. The cellular and humoral responses of 55 DS patients who received a complete SARS-CoV-2 vaccination regime at one to three (V1) and six (V2) months were characterised. SARS-CoV-2-reactive CD4+ and CD8+ T lymphocytes with a predominant Th1 phenotype were observed at V1, and increased at V2. Likewise, a sustained increase of SARS-CoV-2-specific circulating Tfh (cTfh) cells was observed one to three months after vaccine administration. Specific IgG antibodies against SARS-CoV-2 S protein were detected in 96% and 98% of subjects at V1 and V2, respectively, though IgG titers decreased significantly between both timepoints. SUMMARYThe work shows the cellular and humoral responses to SARS-CoV-2 vaccination of individuals with Down syndrome (DS) after one to three (V1) and six (V2) months. An effective immune response after six months was observed in 98% of DS individuals.

Bead-assisted SARS-CoV-2 multi-antigen serological test allows effective identification of patients

Many new aspects of COVID-19 disease, including different clinical manifestations, have been identified during the pandemic. The wide array of symptoms and variation in disease severity after SARS-CoV-2 infection might be related to heterogeneity in the immune responses of different patients. Here we describe a new method for a simple multi-antigen serological test that generates a full picture of seroconversion in a single reaction. The assay is based on the detection by flow cytometry of multiple immunoglobulin classes (isotypes) specific for four SARS-CoV-2 antigens: the Spike glycoprotein (one of the highly immunogenic proteins), its RBD fragment (the major target for neutralising antibodies), the nucleocapsid protein and the main cysteine-like protease. Until now, most diagnostic serological tests measured antibodies to only one antigen and some patients seemed to not make any antibody response. Our data reveal that while most patients respond against all the viral antigens tested, others show a marked bias to make antibodies against either proteins exposed on the viral particle or those released after cellular infection. Combining all the four antigens and using machine learning techniques, it was possible to clearly discriminate between patients and healthy controls with 100% confidence. Further, combination of antigens and different immunoglobulin isotypes in this multi-antigen assay improved the classification of patients with mild and severe disease. Introduction of this method will facilitate massive screenings of patients to evaluate their immune response. It could also support vaccination campaigns both to select non-immune individuals and to distinguish infected patients from vaccine responders.

SARS-Cov-2 cysteine-like protease (Mpro) is immunogenic and can be detected in serum and saliva of COVID-19-seropositive individuals

Currently, there is a need for reliable tests that allow identification of individuals that have been infected with SARS-CoV-2 even if the infection was asymptomatic. To date, the vast majority of the serological tests for SARS-CoV-2 specific antibodies are based on serum detection of antibodies to either the viral spike glycoprotein (the major target for neutralising antibodies) or the viral nucleocapsid protein that are known to be highly immunogenic in other coronaviruses. Conceivably, exposure of antigens released from infected cells could stimulate antibody responses that might correlate with tissue damage and, hence, they may have some value as a prognostic indicator. We addressed whether other non-structural viral proteins, not incorporated into the infectious viral particle, specifically the viral cysteine-like protease, might also be potent immunogens. Using ELISA tests, coating several SARS-CoV-2 proteins produced in vitro, we describe that COVID-19 patients make high titre IgG, IgM and IgA antibody responses to the Cys-like protease from SARS-CoV-2, also known as 3CLpro or Mpro, and it can be used to identify individuals with positive serology against the coronavirus. Higher antibody titres in these assays associated with more severe disease and no cross-reactive antibodies against prior betacoronavirus were found. Remarkably, IgG antibodies specific for Mpro and other SARS-CoV-2 antigens can also be detected in saliva. In conclusion, Mpro is a potent antigen in infected patients that can be used in serological tests and its detection in saliva could be the basis for a rapid, non-invasive test for COVID-19 seropositivity.

Deregulated cellular circuits driving immunoglobulins and complement consumption associate with the severity of COVID-19

BackgroundSARS-CoV-2 infection causes an abrupt response by the host immune system, which is largely responsible for the pathogenesis and outcome of COVID-19. We aimed to investigate which specific responses from either cellular or humoral immunity associate to severity and progression of COVID-19. MethodsA cohort of 276 patients classified in mild, moderate and severe, was studied. Peripheral blood lymphocyte subpopulations were quantified by flow cytometry, and immunoglobulins and complement proteins by nephelometry. ResultsAt admission, dramatic lymphopenia of T, B and NK cells associated to severity. However, only the proportion of B cells increased, while T and NK cells appeared unaffected. Accordingly, the number of plasma cells and circulating follicular helper T cells (cTfh) increased, but levels of IgM, IgA and IgG were unaffected. When degrees of severity were considered, IgG was lower in severe patients, suggesting an IgG consumption by complement activation or antibody-dependent cellular cytotoxicity (ADCC). Activated CD56-CD16+ NK-cells, which mediate ADCC, were increased. Regarding complement, C3 and C4 protein levels were higher in mild and moderate, but not in severe patients, compared to healthy donors. Moreover, IgG and C4 decreased from day 0 to day 10 in patients who were hospitalized for more than two weeks, but not in patients who were discharged earlier. ConclusionOur study provides important clues to understand the immune response observed in COVID-19 patients, which is probably related to viral clearance, but also underlies its pathogenesis and severity. This study associates for the first time COVID-19 severity with an imbalanced humoral immune response characterized by excessive consumption of IgG and C4, identifying new targets for therapeutic intervention.

Differential Redistribution of Activated Monocyte and Dendritic Cell Subsets to the Lung Associates with Severity of COVID-19

The SARS-CoV-2 is responsible for the pandemic COVID-19 in infected individuals, who can either exhibit mild symptoms or progress towards a life-threatening acute respiratory distress syndrome (ARDS). It is known that exacerbated inflammation and dysregulated immune responses involving T and myeloid cells occur in COVID-19 patients with severe clinical progression. However, the differential contribution of specific subsets of dendritic cells and monocytes to ARDS is still poorly understood. In addition, the role of CD8+ T cells present in the lung of COVID-19 patients and relevant for viral control has not been characterized. With the aim to improve the knowledge in this area, we developed a cross-sectional study, in which we have studied the frequencies and activation profiles of dendritic cells and monocytes present in the blood of COVID-19 patients with different clinical severity in comparison with healthy control individuals. Furthermore, these subpopulations and their association with antiviral effector CD8+ T cell subsets were also characterized in lung infiltrates from critical COVID-19 patients. Collectively, our results suggest that inflammatory transitional and non-classical monocytes preferentially migrate from blood to lungs in patients with severe COVID-19. CD1c+ conventional dendritic cells also followed this pattern, whereas CD141+ conventional and CD123hi plasmacytoid dendritic cells were depleted from blood but were absent in the lungs. Thus, this study increases the knowledge on the pathogenesis of COVID-19 disease and could be useful for the design of therapeutic strategies to fight SARS-CoV-2 infection. Single-sentence summaryDepletion from the blood and differential activation patterns of inflammatory monocytes and CD1c+ conventional dendritic cells associate with development of ARDS in COVID-19 patients.