Multisystem Inflammatory Syndrome in Children (MIS-C) is a new phenomenon reported worldwide with temporal association with Covid-19. The objective of this paper is to evaluate reported cases in children and adolescents. From 1726 papers, 35 documented papers related to MIS-C cases identified 783 individual cases of MIS-C between March-June 2020; with 55% being male ( n = 435) and a median age of 8.6 years (IQR, 7–10 years; range 3 months–20 years). Patients with MIS-C were noted to have a high frequency of gastrointestinal symptoms (71%) including abdominal pain (34%) and diarrhea (27%). Cough and respiratory distress were reported in 4.5% and 9.6% cases respectively. Blood parameters showed neutrophilia in 345/418 (83%) of cases and a high CRP in 587/626 (94%). 362/619 (59%) cases were SARS-CoV-2 infection positive (serology or PCR) however only 41% demonstrated pulmonary changes on chest imaging. Severity of illness was high with 68% cases requiring intensive care admission; 63% requiring inotropic support; 244/783 (28%) cases needing some form of respiratory support (138 mechanically ventilated), and 31 required extra-corporeal membrane oxygenation. Treatment strategies included intravenous immunoglobulin (63%) and intravenous steroids (44%). 29 cases received Infliximab, 47 received IL1 (interleukin) receptor antagonist, and 47 received IL6-receptor antagonist. 12/783 (1.5%) children died. In summary, a higher incidence of gastrointestinal symptoms were noted in MIS-C. In contrast to acute Covid-19 infection in children, MIS-C appears to be a condition of higher severity with 68% of cases having required critical care support.

Data show that children are less severely affected with SARS-Covid-19 than adults; however, there have been a small proportion of children who have been critically unwell. In this systematic review, we aimed to identify and describe which underlying comorbidities may be associated with severe SARS-CoV-2 disease and death. The study protocol was in keeping with Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. A total of 1726 articles were identified of which 28 studies fulfilled the inclusion criteria. The 28 studies included 5686 participants with confirmed SARS-CoV-2 infection ranging from mild to severe disease. We focused on the 108 patients who suffered from severe/critical illness requiring ventilation, which included 17 deaths. Of the 108 children who were ventilated, the medical history was available for 48 patients. Thirty-six of the 48 patients (75%) had documented comorbidities of which 11/48 (23%) had pre-existing cardiac disease. Of the 17 patients who died, the past medical history was reported in 12 cases. Of those, 8/12 (75%) had comorbidities. Conclusion: Whilst only a small number of children suffer from COVID-19 disease compared to adults, children with comorbidities, particularly pre-existing cardiac conditions, represent a large proportion of those that became critically unwell. What is Known:• Children are less severely affected by SARS-CoV-2 than adults.• There are reports of children becoming critically unwell with SARS-CoV-2 and requiring intensive care. What is New:• The majority of children who required ventilation for SARS-CoV-2 infection had underlying comorbidities.• The commonest category of comorbidity in these patients was underlying cardiac disease.

The ontogeny of airway macrophages (AMs) in human lung and their contribution to disease are poorly mapped out. In mice, aging is associated with an increasing proportion of peripherally, as opposed to perinatally derived AMs. We sought to understand AM ontogeny in human lung during healthy aging and after transplant. We characterized monocyte/macrophage populations from the peripheral blood and airways of healthy volunteers across infancy/childhood (2–12 yr), maturity (20–50 yr), and older adulthood (>50 yr). Single-cell RNA sequencing (scRNA-seq) was performed on airway inflammatory cells isolated from sex-mismatched lung transplant recipients. During healthy aging, the proportions of blood and bronchoalveolar lavage (BAL) classical monocytes peak in adulthood and decline in older adults. scRNA-seq of BAL cells from lung transplant recipients indicates that after transplant, the majority of AMs are recipient derived. These data show that during aging, the peripheral monocyte phenotype is consistent with that found in the airways and, furthermore, that the majority of human AMs after transplant are derived from circulating monocytes.

The pediatric lysosomal storage disorder mucopolysaccharidosis type II is caused by mutations in IDS, resulting in accumulation of heparan and dermatan sulfate, causing severe neurodegeneration, skeletal disease, and cardiorespiratory disease. Most patients manifest with cognitive symptoms, which cannot be treated with enzyme replacement therapy, as native IDS does not cross the blood–brain barrier. We tested a brain‐targeted hematopoietic stem cell gene therapy approach using lentiviral IDS fused to ApoEII (IDS.ApoEII) compared to a lentivirus expressing normal IDS or a normal bone marrow transplant. In mucopolysaccharidosis II mice, all treatments corrected peripheral disease, but only IDS.ApoEII mediated complete normalization of brain pathology and behavior, providing significantly enhanced correction compared to IDS. A normal bone marrow transplant achieved no brain correction. Whilst corrected macrophages traffic to the brain, secreting IDS/IDS.ApoEII enzyme for cross‐correction, IDS.ApoEII was additionally more active in plasma and was taken up and transcytosed across brain endothelia significantly better than IDS via both heparan sulfate/ApoE‐dependent receptors and mannose‐6‐phosphate receptors. Brain‐targeted hematopoietic stem cell gene therapy provides a promising therapy for MPS II patients.