Infectivity of severe acute respiratory syndrome coronavirus 2 in children compared with adults.

BACKGROUND: The role of children in the transmission and community spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unclear. We aimed to quantify the infectivity of SARS-CoV-2 in nasopharyngeal samples from children compared with adults. METHODS: We obtained nasopharyngeal swabs from adult and pediatric cases of coronavirus disease 2019 (COVID-19) and from their contacts who tested positive for SARS-CoV-2 in Manitoba between March and December 2020. We compared viral growth in cell culture, cycle threshold values from the reverse transcription polymerase chain reaction (RT-PCR) of the SARS-CoV-2 envelope (E) gene and the 50% tissue culture infective dose (TCID50/mL) between adults and children. RESULTS: Among 305 samples positive for SARS-CoV-2 by RT-PCR, 97 samples were from children aged 10 years or younger, 78 were from children aged 11-17 years and 130 were from adults (≥ 18 yr). Viral growth in culture was present in 31% of samples, including 18 (19%) samples from children 10 years or younger, 18 (23%) from children aged 11-17 years and 57 (44%) from adults (children v. adults, odds ratio 0.45, 95% confidence interval [CI] 0.28-0.72). The cycle threshold was 25.1 (95% CI 17.7-31.3) in children 10 years or younger, 22.2 (95% CI 18.3-29.0) in children aged 11-17 years and 18.7 (95% CI 17.9-30.4) in adults (p < 0.001). The median TCID50/mL was significantly lower in children aged 11-17 years (316, interquartile range [IQR] 178-2125) than adults (5620, IQR 1171 to 17 800, p < 0.001). Cycle threshold was an accurate predictor of positive culture in both children and adults (area under the receiver-operator curve, 0.87, 95% CI 0.81-0.93 v. 0.89, 95% CI 0.83-0.96, p = 0.6). INTERPRETATION: Compared with adults, children with nasopharyngeal swabs that tested positive for SARS-CoV-2 were less likely to grow virus in culture, and had higher cycle thresholds and lower viral concentrations, suggesting that children are not the main drivers of SARS-CoV-2 transmission.

γδ T-cell function is inhibited in end-stage renal disease and impacted by latent tuberculosis infection.

Patients with end-stage renal disease (ESRD) are at elevated risk of acquiring infectious diseases, including tuberculosis (TB). Inflammation and uremia negatively impact immune function in this population, but specific pathways involved in TB immunity have not been identified. Although γδ T cells are known to contribute to protection from TB, their phenotype and function in patients with ESRD is relatively unknown. To determine this we recruited 20 patients with and 20 without ESRD (controls), with or without latent TB infection to assess γδ T cell frequency, surface phenotype, and cytokine production by flow cytometry in response to stimulation. γδ T cells derived from patients with ESRD exhibited significantly lower expression of CCR5, CXCR3, and CD26 compared to controls. Furthermore, patients with ESRD, particularly the group with latent TB infection, exhibited poor IFNγ, TNFα, and GMCSF responses to stimulation with either phosphoantigen HMB-PP, IL-12/IL-18, E. coli, or phorbol myristate acetate and ionomycin. Similar dysfunctional responses were observed in patients with active TB. Surprisingly, neither the γδ phenotype nor its function was associated with plasma markers of inflammation or microbial translocation. Thus, there is significant perturbation of the γδ T-cell population in patients with ESRD, particularly in those with latent TB infection.

Maintenance of Mycobacterium tuberculosis-specific T cell responses in End Stage Renal Disease (ESRD) and implications for diagnostic efficacy.

End-stage renal disease (ESRD) patients exhibit elevated risk of tuberculosis (TB) reactivation, but current diagnostics, including the interferon gamma release assay (IGRA), exhibit poor sensitivity in ESRD. We tested 80 ESRD patients and found an 18.75% prevalence of IGRA positivity. A subset of patients was assessed for Mtb-specific expression of 44 cytokines/chemokines, and CD4+ T cell phenotype and function. Similar to non-ESRD IGRA+ individuals, Mtb-specific IFNγ, IL-1RA, IP-10, MCP-3 and IL-2 responses were identified in the ESRD IGRA+ group. 27% of the ESRD IGRA- group exhibited MCP-3 or IL-2 Mtb-specific responses, which may identify cases of latent TB infection in ESRD. Stimulation of PBMC with PPD demonstrated similar CD4+ T cell production of IFNγ, TNFα and GM-CSF by ESRD patients. The reported low sensitivity of the IGRA in ESRD cohorts is therefore unlikely to be due to poor T cell cytokine secretion, and may instead reflect defects in antigen presentation.

Comparaison de l'infectivité du coronavirus du syndrome respiratoire aigu sévère 2 chez les enfants et les adultes.

CONTEXTE: Le rôle des enfants dans la propagation et la transmission communautaire du coronavirus du syndrome respiratoire aigu sévère 2 (SRAS-CoV-2) est encore mal compris. Nous visons à quantifier l'infectivité du SRAS-CoV-2 d'échantillons nasopharyngés provenant d'enfants comparativement à ceux provenant d'adultes. MÉTHODES: Nous avons obtenu des écouvillons nasopharyngés de cas adultes et pédiatriques de la maladie à coronavirus 2019 (COVID-19) ainsi que de leurs contacts qui ont obtenu un résultat positif à la présence du SRAS-CoV-2 lors d'un test de dépistage au Manitoba entre les mois de mars et décembre 2020. Nous avons comparé la croissance virale en culture cellulaire, les valeurs de cycle seuil de test d'amplification en chaîne par polymérase couplé à une transcription inverse (RT-PCR) de l'enveloppe (E) du gène du SRAS-CoV-2 et de la dose infectieuse pour 50 % de la culture tissulaire (DICT50/mL) entre les adultes et les enfants. RÉSULTATS: Parmi les 305 échantillons positifs à la présence du SRAS-CoV-2 validés par RT-PCR, 97 échantillons provenaient d'enfants de 10 ans et moins, 78 échantillons d'enfants de 11­17 ans et 130 échantillons d'adultes (≥ 18 ans). On a observé une croissance virale en culture dans 31 % des échantillons, dont 18 (19 %) échantillons d'enfants de 10 ans et moins, 18 (23 %) d'enfants de 11­17 ans et 57 (44 %) d'adultes (enfants c. adultes, rapport de cotes 0,45; intervalle de confiance [IC] à 95 % 0,28­0,72). Le cycle seuil était de 25,1 (IC à 95 % 17,7­31,3) chez les enfants de 10 ans et moins, 22,2 (IC à 95 % 18,3­29,0) chez les enfants de 11­17 ans et 18,7 (IC à 95 % 17,9­30,4) chez les adultes (p < 0,001). La DICT50/mL médiane était considérablement plus faible chez les enfants de 11­17 ans (316, écart interquartile [EI] 178­2125) que chez les adultes (5620, EI 1171­17 800, p < 0,001). Le cycle seuil était un indicateur exact d'une culture positive chez les enfants et les adultes (aire sous la courbe de la fonction d'efficacité du récepteur, 0,87, IC à 95 % 0,81­0,93 c. 0,89, IC à 95 % 0,83­0,96, p = 0,6). INTERPRÉTATION: Comparés aux adultes, les enfants qui ont obtenu un résultat positif à un test de dépistage du SRAS-CoV-2 à l'aide d'un écouvillon nasopharyngé étaient moins susceptibles de présenter une croissance du virus en culture et obtenaient un cycle seuil plus élevé et une concentration virale moins élevée, indiquant que les enfants ne sont pas les principaux vecteurs de la transmission du SRAS-CoV-2.

Elevated expression of LAG-3, but not PD-1, is associated with impaired iNKT cytokine production during chronic HIV-1 infection and treatment.

BACKGROUND: LAG-3 is a potent negative regulator of the immune response but its impact in HIV infection in poorly understood. Unlike exhaustion markers such as PD-1, Tim-3, 2B4 and CD160, LAG-3 is poorly expressed on bulk and antigen-specific T cells during chronic HIV infection and its expression on innate lymphocyte subsets is not well understood. The aim of this study was to assess LAG-3 expression and association with cellular dysfunction on T cells, NK cells and iNKT cells among a cohort of healthy and HIV-infected female sex workers in Nairobi, Kenya. RESULTS: Ex vivo LAG-3 expression was measured by multiparametric flow cytometry, and plasma cytokine/chemokine concentrations measured by bead array. Although LAG-3 expression on bulk T cells was significantly increased among HIV-infected women, the proportion of cells expressing the marker was extremely low. In contrast, LAG-3 was more highly expressed on NK and iNKT cells and was not reduced among women treated with ART. To assess the functional impact of LAG-3 on iNKT cells, iNKT cytokine production was measured in response to lipid (αGalCer) and PMA/Io stimulation by both flow cytometry and cytokine bead array. iNKT cytokine production is profoundly altered by both HIV infection and treatment, and LAG-3, but not PD-1, expression is associated with a reduction in iNKT IFNγ production. CONCLUSIONS: LAG-3 does not appear to mediate T cell exhaustion in this African population, but is instead expressed on innate lymphocyte subsets including iNKT cells. HIV infection alters iNKT cytokine production patterns and LAG-3 expression is uniquely associated with iNKT dysfunction. The continued expression of LAG-3 during treatment suggests it may contribute to the lack of innate immune reconstitution commonly observed during ART.

Mucosal-Associated Invariant T Cells Are Depleted and Exhibit Altered Chemokine Receptor Expression and Elevated Granulocyte Macrophage-Colony Stimulating Factor Production During End-Stage Renal Disease.

Background: End-stage renal disease (ESRD) is associated with an increased susceptibility to infectious diseases, including infection with Mycobacterium tuberculosis (Mtb). Mucosal-associated invariant T (MAIT) cells recognize vitamin B metabolites produced by many bacterial species, including Mtb, and may play an important role in providing protective immunity against tuberculosis infection in the lung. To date, little is known about MAIT cell frequency, phenotype, or function in ESRD patients. Methods: MAIT cells, identified by surface marker expression or MR1 tetramer binding, were characterized in 20 ESRD and 20 healthy control participants by multicolor flow cytometry. Ex vivo MAIT cell phenotype and cytokine production following PMA/ionomycin, IL-12/IL-18, or Escherichia coli stimulation were determined. Monocyte phenotype and plasma C-reactive protein/inflammatory cytokine levels were quantified by flow cytometry, ELISA, and multiplex bead array. Results: Peripheral blood MAIT cells were significantly depleted among ESRD patients compared to controls by both phenotypic and tetramer analysis and exhibited a loss of CXCR3 expression coupled to increased expression of CCR6 and CXCR6. ESRD was also associated with a shift in MAIT PMA-induced cytokine production away from IFNγ production and toward granulocyte macrophage-colony stimulating factor (GM-CSF) secretion, and a loss of E. coli-stimulated tumor necrosis factor α expression. Loss of IFNγ expression was associated with a combination of age, alterations in Tbet and Eomes expression, and inflammatory plasma cytokine levels. Conclusion: The loss of peripheral blood MAIT cells and associated shifts in tissue homing receptor expression and GM-CSF production may contribute to an immune environment that is permissive to bacterial replication, particularly in the lungs.

Cytokine and chemokine expression profiles in response to Mycobacterium tuberculosis stimulation are altered in HIV-infected compared to HIV-uninfected subjects with active tuberculosis.

Mycobacterium tuberculosis (Mtb) infects nearly 2 million people annually and is the most common cause of death in HIV-infected individuals. Tuberculosis (TB) diagnostics cater to HIV-uninfected individuals in non-endemic countries, are expensive, slow, and lack sensitivity for those most affected. Patterns of soluble immune markers from Mtb-stimulated immune cells are not well defined in HIV co-infection. We assessed immune differences between HIV-infected and HIV-uninfected individuals with active TB utilizing IFNγ-based QuantiFERON®-TB Gold In-Tube (QFT) testing in Nairobi, Kenya. Excess QFT supernatants were used to measure cytokine and chemokine responses by a 17-plex bead array. Mtb/HIV co-infected participants were significantly less likely to be QFT+ (47.2% versus 84.2% in the HIV-uninfected group), and demonstrated lower expression of all cytokines except for IFNα2. Receiver operator characteristic analyses identified IL-1α as a potential marker of co-infection. Among HIV-infected individuals, CD4+ T cell count correlated weakly with the expression of several analytes. Co-expression analysis highlighted differences in immune profiles between the groups. These data suggest that there is a unique and detectable Mtb-specific immune response in co-infection. A better understanding of Mtb immunology can translate into much needed immunodiagnostics with enhanced sensitivity in HIV-infected individuals, facilitating their opportunity to obtain live-saving treatment.

Epitope cross-reactivity frequently differs between central and effector memory HIV-specific CD8+ T cells.

HIV diversity may limit the breadth of vaccine coverage due to epitope sequence differences between strains. Although amino acid substitutions within CD8(+) T cell HIV epitopes can result in complete or partial abrogation of responses, this has primarily been demonstrated in effector CD8(+) T cells. In an HIV-infected Kenyan cohort, we demonstrate that the cross-reactivity of HIV epitope variants differs dramatically between overnight IFN-gamma and longer-term proliferation assays. For most epitopes, particular variants (not the index peptide) were preferred in proliferation in the absence of corresponding overnight IFN-gamma responses and in the absence of the variant in the HIV quasispecies. Most proliferating CD8(+) T cells were polyfunctional via cytokine analyses. A trend to positive correlation was observed between proliferation (but not IFN-gamma) and CD4 counts. We present findings relevant to the assessment of HIV vaccine candidates and toward a better understanding of how viral diversity is tolerated by central and effector memory CD8(+) T cells.