Diagnosis of Multisystem Inflammatory Syndrome in Children by a Whole-Blood Transcriptional Signature.

BACKGROUND: To identify a diagnostic blood transcriptomic signature that distinguishes multisystem inflammatory syndrome in children (MIS-C) from Kawasaki disease (KD), bacterial infections, and viral infections. METHODS: Children presenting with MIS-C to participating hospitals in the United Kingdom and the European Union between April 2020 and April 2021 were prospectively recruited. Whole-blood RNA Sequencing was performed, contrasting the transcriptomes of children with MIS-C (n = 38) to those from children with KD (n = 136), definite bacterial (DB; n = 188) and viral infections (DV; n = 138). Genes significantly differentially expressed (SDE) between MIS-C and comparator groups were identified. Feature selection was used to identify genes that optimally distinguish MIS-C from other diseases, which were subsequently translated into RT-qPCR assays and evaluated in an independent validation set comprising MIS-C (n = 37), KD (n = 19), DB (n = 56), DV (n = 43), and COVID-19 (n = 39). RESULTS: In the discovery set, 5696 genes were SDE between MIS-C and combined comparator disease groups. Five genes were identified as potential MIS-C diagnostic biomarkers (HSPBAP1, VPS37C, TGFB1, MX2, and TRBV11-2), achieving an AUC of 96.8% (95% CI: 94.6%-98.9%) in the discovery set, and were translated into RT-qPCR assays. The RT-qPCR 5-gene signature achieved an AUC of 93.2% (95% CI: 88.3%-97.7%) in the independent validation set when distinguishing MIS-C from KD, DB, and DV. CONCLUSIONS: MIS-C can be distinguished from KD, DB, and DV groups using a 5-gene blood RNA expression signature. The small number of genes in the signature and good performance in both discovery and validation sets should enable the development of a diagnostic test for MIS-C.

Neonatal sepsis and transient immunodeficiency: Potential for novel immunoglobulin therapies?

Neonates, especially preterm neonates, have the highest risk of sepsis of all age groups. Transient immaturity of the neonatal immune system is an important risk factor. Neonates suffer from hypogammaglobulinemia as nor IgA nor IgM is transferred over the placenta and IgG is only transferred over the placenta late in gestation. In addition, neutrophil numbers and complement function are also decreased. This mini-review focuses on strategies to improve neonatal host-defense. Both clinical and preclinical studies have attempted to boost neonatal immunity to lower the incidence of sepsis and improve outcome. Recent advances in the development of (monoclonal) antibodies show promising results in preclinical studies but have yet to be tested in clinical trials. Strategies to increase complement activity seem efficient in vitro but potential disadvantages such as hyperinflammation have held back further clinical development. Increase of neutrophil numbers has been tested extensively in clinical trials but failed to show improvement in mortality. Future research should focus on clinical applicability of promising new prevention strategies for neonatal sepsis.

Monoclonal antibodies effectively potentiate complement activation and phagocytosis of Staphylococcus epidermidis in neonatal human plasma.

Central line associated bloodstream infections (CLABSI) with Staphylococcus epidermidis are a major cause of morbidity in neonates, who have an increased risk of infection because of their immature immune system. As especially preterm neonates suffer from antibody deficiency, clinical studies into preventive therapies have thus far focused on antibody supplementation with pooled intravenous immunoglobulins from healthy donors (IVIG) but with little success. Here we study the potential of monoclonal antibodies (mAbs) against S. epidermidis to induce phagocytic killing by human neutrophils. Nine different mAbs recognizing Staphylococcal surface components were cloned and expressed as human IgG1s. In binding assays, clones rF1, CR5133 and CR6453 showed the strongest binding to S. epidermidis ATCC14990 and CR5133 and CR6453 bound the majority of clinical isolates from neonatal sepsis (19 out of 20). To study the immune-activating potential of rF1, CR5133 and CR6453, bacteria were opsonized with mAbs in the presence or absence of complement. We observed that activation of the complement system is essential to induce efficient phagocytosis of S. epidermidis. Complement activation and phagocytic killing could be enhanced by Fc-mutations that improve IgG1 hexamerization on cellular surfaces. Finally, we studied the ability of the mAbs to activate complement in r-Hirudin neonatal plasma conditions. We show that classical pathway complement activity in plasma isolated from neonatal cord blood is comparable to adult levels. Furthermore, mAbs could greatly enhance phagocytosis of S. epidermidis in neonatal plasma. Altogether, our findings provide insights that are crucial for optimizing anti-S. epidermidis mAbs as prophylactic agents for neonatal CLABSI.