Immune dysregulation and autoreactivity correlate with disease severity in SARS-CoV-2-associated multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a life-threatening post-infectious complication occurring unpredictably weeks after mild or asymptomatic SARS-CoV-2 infection. We profiled MIS-C, adult COVID-19, and healthy pediatric and adult individuals using single-cell RNA sequencing, flow cytometry, antigen receptor repertoire analysis, and unbiased serum proteomics, which collectively identified a signature in MIS-C patients that correlated with disease severity. Despite having no evidence of active infection, MIS-C patients had elevated S100A-family alarmins and decreased antigen presentation signatures, indicative of myeloid dysfunction. MIS-C patients showed elevated expression of cytotoxicity genes in NK and CD8+ T cells and expansion of specific IgG-expressing plasmablasts. Clinically severe MIS-C patients displayed skewed memory T cell TCR repertoires and autoimmunity characterized by endothelium-reactive IgG. The alarmin, cytotoxicity, TCR repertoire, and plasmablast signatures we defined have potential for application in the clinic to better diagnose and potentially predict disease severity early in the course of MIS-C.

Post-infectious inflammatory disease in MIS-C features elevated cytotoxicity signatures and autoreactivity that correlates with severity

Multisystem inflammatory syndrome in children (MIS-C) is a life-threatening post-infectious complication occurring unpredictably weeks after mild or asymptomatic SARS-CoV2 infection in otherwise healthy children. Here, we define immune abnormalities in MIS-C compared to adult COVID-19 and pediatric/adult healthy controls using single-cell RNA sequencing, antigen receptor repertoire analysis, unbiased serum proteomics, and in vitro assays. Despite no evidence of active infection, we uncover elevated S100A-family alarmins in myeloid cells and marked enrichment of serum proteins that map to myeloid cells and pathways including cytokines, complement/coagulation, and fluid shear stress in MIS-C patients. Moreover, NK and CD8 T cell cytotoxicity genes are elevated, and plasmablasts harboring IgG1 and IgG3 are expanded. Consistently, we detect elevated binding of serum IgG from severe MIS-C patients to activated human cardiac microvascular endothelial cells in culture. Thus, we define immunopathology features of MIS-C with implications for predicting and managing this SARS-CoV2-induced critical illness in children.

Mutation of Tgfbr1 leads to non-hematopoietic defects that drive early onset eosinophilic inflammation in the esophagus

Eosinophilic esophagitis is a chronic disease characterized by tissue-restricted eosinophilia, epithelial basal cell hyperplasia, and esophageal dysfunction. There are three endotypes of eosinophilic esophagitis which are classified based upon the age of disease onset, degree of fibrostenosis, and gene expression patterns. Genetic studies have identified variants that correlate with an increased likelihood to develop eosinophilic esophagitis. Among the top ten variants, nearly all occur in genes expressed by epithelial cells, and approximately one-third encode proteins involved in the transforming growth factor beta (TGFβ) signaling pathway. The pathophysiologic mechanisms underlying these genetic risk factors are poorly understood. Using mice engineered to have an autosomal dominant loss-of-function mutation in the kinase domain of Tgfbr1 we demonstrate that altered TGFβ signaling in non-hematopoietic cells is necessary and sufficient to cause disease that clinically, immunologically, histologically, and transcriptionally recapitulates human eosinophilic esophagitis endotype 2. Tgfbr1 mutation impairs esophageal epithelial cell homeostasis resulting in tissue-restricted increases in proteins that act directly, indirectly, and synergistically to drive accumulation and activation of eosinophils, mast cells, and type 2 innate lymphoid cells (ILC2). These data suggest new ways to approach the prevention and treatment of eosinophilic esophagitis.

The effects of altered TGFβ signaling on human T follicular helper cell development and function

T follicular helper (Tfh) cells are a subset of CD4+ T cells that play a crucial role in the development of memory B cells and plasma cells. T follicular regulatory (Tfr) cells oppose Tfh cells and suppress humoral immune responses. Patients with Loeys-Dietz Syndrome (LDS) type 1 and 2 have an autosomal dominant mutation in the genes encoding TGFβ Receptor 1 or 2, respectively, and have a strong predisposition to develop allergic diseases. We hypothesized that altered development and function of Tfh cells could contribute to increased IgE-mediated allergic phenotypes in LDS. Comparing a cohort of pediatric LDS patients with age-matched healthy volunteers, we found that LDS patients have significantly higher levels of serum IgE and IgG and lower levels of IgM. Congruently, LDS patients have an increased frequency of memory T cells, Th2 cells, and Tfh cells and a significantly lower frequency of Tfr cells. The increase in Tfh cells in LDS was restricted to the CCR4+ CCR6− subset, which has been associated with Th2 immune responses. In vitro, Tfh cells from LDS patients co-cultured with autologous naïve B cells demonstrated a greater ability to induce plasma cell differentiation compared to age-matched healthy volunteers. Additionally, naïve CD4+ T cells from LDS patients cultured in the presence of recombinant TGFβ1 and IL-12 or IL-4 were more likely to differentiate into Tfh cells compared to healthy age-matched controls, suggesting a cell-intrinsic propensity for naïve CD4+ T cells in LDS patients to acquire a Tfh fate. Collectively, our data suggest that LDS mutations alter the development and function of Tfh cells in a manner that promotes IgE-mediated disease.

Reduced TGF‑βR signaling results in increased T cell activation without autoinflammatory disease

Transforming growth factor-β receptor (TGF-βR) signaling is important in regulating the proliferation and differentiation of CD4+ T cells, but how modulating the level of signaling can affect T cell fate remains unclear. We have created a mouse model of Loeys-Dietz syndrome (LDS), an autosomal dominant disease caused by mutations in genes encoding the TGF-βR, by targeting a missense mutation (M318R) to the endogenous murine Tgfbr1 locus. LDS patients exhibit an increased propensity for allergic disease, but no overt immunodeficiency or autoimmune disease. A higher percentage of CD4+ T cells in Tgfbr1M318R/+ mice exhibited a memory phenotype and produced enhanced levels of cytokines including IFN-γ, IL-13, IL-17, and IL-10 upon stimulation, but no autoimmunity was observed. In contrast, mice lacking TGF-βR2 specifically in T cells demonstrate exaggerated IFN-γ production and widespread autoinflammatory disease. While naïve CD4+ T cells from Tgfbr1M318R/+ mice were less likely to upregulate Foxp3 during in vitro culture with recombinant TGF-β, paradoxically, increased percentages and numbers of suppressive Foxp3+ regulatory T cells (Tregs) were observed in vivo, which may indicate a role for increased proliferation or survival of thymically-derived Tregs. The effects of the Tgfbr1M318R/+on T cells appear to be cell intrinsic. We observed no differences in T cells derived from WT bone marrow used to reconstitute irradiated Tgfbr1M318R/+ or WT hosts, while Tgfbr1M318R/+ bone marrow co-transferred with WT bone marrow into WT hosts gave rise to more activated CD4+ T cells and a higher frequency of Foxp3+ cells. These data suggest that partially abrogated TGF-β signaling leads to unexpected effects on T cell development and function.