Preterm infants are susceptible to neonatal sepsis, a syndrome of pro-inflammatory activity, organ damage, and altered metabolism following infection. Given the unique metabolic challenges and poor glucose regulatory capacity of preterm infants, their glucose intake during infection may have a high impact on the degree of metabolism dysregulation and organ damage. Using a preterm pig model of neonatal sepsis, we previously showed that a drastic restriction in glucose supply during infection protects against sepsis via suppression of glycolysis-induced inflammation, but results in severe hypoglycemia. Now we explored clinically relevant options for reducing glucose intake to decrease sepsis risk, without causing hypoglycemia and further explore the involvement of the liver in these protective effects. We found that a reduced glucose regime during infection increased survival via reduced pro-inflammatory response, while maintaining normoglycemia. Mechanistically, this intervention enhanced hepatic oxidative phosphorylation and possibly gluconeogenesis, and dampened both circulating and hepatic inflammation. However, switching from a high to a reduced glucose supply after the debut of clinical symptoms did not prevent sepsis, suggesting metabolic conditions at the start of infection are key in driving the outcome. Finally, an early therapy with purified human inter-alpha inhibitor protein, a liver-derived anti-inflammatory protein, partially reversed the effects of low parenteral glucose provision, likely by inhibiting neutrophil functions that mediate pathogen clearance. Our findings suggest a clinically relevant regime of reduced glucose supply for infected preterm infants could prevent or delay the development of sepsis in vulnerable neonates.

Background: Two separate genome-wide association studies demonstrated that polymorphisms in SERPINA1, encoding serine protease inhibitor alpha-1 antitrypsin (A1AT), are associated with increased risk of developing antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) [1, 2]. It has been proposed that the functionality of A1AT is decreased in inflammatory conditions [3]. Objectives: This study aimed to gain insight into function of A1AT in AAV, including the relationships of A1AT genotype, and functional activity of A1AT, with targeted biomarkers and disease activity in AAV. Methods: Clinical data and peripheral blood samples were examined from 250 participants with AAV in a longitudinal cohort, and 80 healthy control individuals. Among those with AAV, 170 with wild-type (WT) A1AT genotype (MM) and 80 with mutant (mut) A1AT genotype (MS, MZ, SS, SZ, or ZZ) with available samples during active disease and remission were selected. Comprehensive analyses were performed, including A1AT total and functional levels, markers of neutrophil activation, and cyto/chemokines. Results: Participants with mut A1AT genotype were younger at diagnosis of AAV than those with WT A1AT genotype (Table 1). Among participants with AAV and WT A1AT genotype, 66.5% were PR3-ANCA positive and 26.5% were MPO-ANCA positive during their disease course, as compared to 73.8% and 17.5%, respectively, among those with mut A1AT genotype. Birmingham Vasculitis Activity Score/WG during active visits, and Disease Extent Index are presented in Table 1. Functional A1AT [4] was higher with WT A1AT genotype than with mut genotype during both active disease (p < 0.01) and remission (p < 0.01), and higher among participants with AAV and WT A1AT genotype than among healthy subjects (p < 0.01). Total and functional A1AT aligned with genotype (Table 1) and were consistently lower among those with Z alleles (data not shown). During active AAV, levels of proinflammatory cytokines IL-8 and IL-6 were similar across the A1AT genotype subgroups. The decline of these cytokines during remission of AAV was more distinct among those with WT A1AT genotype than those with mut genotype. In contrast, levels of IL-1α and IL-13 were more affected among those with mut genotype than those with WT A1AT genotype, resulting in significant increased levels during active disease (p=0.05 and p < 0.01, respectively). Levels of IL-8 and IL-6 among healthy control subjects were lower than those with WT A1AT genotype during remission (p < 0.01 and p < 0.01, respectively), but IL-1α and IL-13 were similar. During active AAV and remission, levels of the anti-inflammatory cytokine IL-10 were slightly higher among those with WT A1AT genotype than those with mut genotype (p=0.07 and p=0.20, respectively). By comparison, mean IL-10 among healthy subjects was lower than among those with WT A1AT genotype in remission (p < 0.01). Conclusion: A1AT genotype among people with AAV is associated with differences in age at diagnosis, inflammatory markers, and several cytokines. Further analyses will explore the relationships among A1AT functional levels and disease characteristics and activity of AAV. REFERENCES: [1] Lyons PA, Rayner TF, Trivedi S, Holle JU, Watts RA, Jayne DR, et al. Genetically distinct subsets within ANCA-associated vasculitis. N Engl J Med. 2012;367(3):214-23. doi: 10.1056/NEJMoa1108735. PubMed PMID: 22808956. [2] Merkel PA, Xie G, Monach PA, Ji X, Ciavatta DJ, Byun J, et al. Identification of Functional and Expression Polymorphisms Associated With Risk for Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis. Arthritis Rheumatol. 2017;69(5):1054-66. Epub 20170406. doi: 10.1002/art.40034. PubMed PMID: 28029757. [3] Mota A, et al. Alpha 1-antitrypsin activity is markedly decreased in Wegener's granulomatosis. Rheumatol Int. 2014 Apr;34(4):553-8. doi: 10.1007/s00296-013-2745-9. [4] Engelmaier A, Weber A. Sensitive and specific measurement of alpha1-antitrypsin activity with an elastase complex formation immunosorbent assay (ECFISA). J Pharm Biomed Anal. 2022;209:114476. Epub 2021 Nov 23. doi: 10.1016/j.jpba.2021.114476. PubMed PMID: 34838346. Acknowledgements: NIL. Disclosure of Interests: Lynn Fussner Amgen, Ivan Bilic Ivan Bilic is a full-time employee of Takeda Pharmaceutical Company, Carol McAlear: None declared, David Cuthbertson: None declared, Jie Cheng Jie Cheng is a full-time employee of Takeda Pharmaceutical Company, Elise Chen Elise Chen is a full-time employee of Takeda Pharmaceutical Company, Markus Weiller Markus Weiller is a full-time employee of Takeda Pharmaceutical Company, Ulrich Specks Consultant: Amgen, Argenix, AstraZeneca, Boehringer Ingelheim, CSL Vifor, Grant/research support: Amgen, AstraZeneca, Bristol Myers Squibb, Genentech, GSK, Northstar Medical Radioisotopes, Takeda., Peter A Merkel Stock options: Kyverna, Q32, Sparrow, Consultant: AbbVie, Amgen, ArGenx, AstraZeneca, Boeringher-Ingelheim, Bristol-Myers Squibb, Cabaletta, CSL Behring, Dynacure, GlaxoSmithKline, HiBio, InflaRx, Janssen, Kyverna, Novartis, NS Pharma, Q32, Regeneron, Sparrow, Takeda. Vistera., Grant/research support: AbbVie, Amgen, AstraZeneca, Boeringher-Ingelheim, Bristol-Myers Squibb, Eicos, Electra, Forbius, Genentech/Roche, Genzyme/Sanofi, GlaxoSmithKline, InflaRx, Neutrolis, Takeda.

Necrotizing enterocolitis (NEC) is a microbiota- and feeding-related gut inflammatory disease in preterm infants. The standard of care (SOC) treatment for suspected NEC is antibiotic treatment and reduced enteral feeding, but how SOC treatment mitigates NEC remains unclear. We explored whether SOC treatment alone or combined with an anti-inflammatory protein (inter-alpha inhibitor protein, IAIP) supplementation improves outcomes in a preterm piglet model of formula-induced NEC. Seventy-one cesarean-delivered preterm piglets were initially fed formula, developing NEC symptoms by day 3, and then randomized into CON (continued feeding) or SOC groups (feeding cessation and antibiotics), each with or without human IAIP (2×2 factorial design). By day 5, IAIP treatment did not significantly influence outcomes, whereas SOC treatment effectively reduced NEC lesions, diarrhea, and bloody stools. Notably, SOC treatment improved gut morphology and function, dampened gut inflammatory responses, altered the colonic microbiota composition, and modulated systemic immune responses. Plasma proteomic analysis revealed the effects of SOC treatment on organ development and systemic inflammatory responses. Collectively, these findings suggest that SOC treatment significantly prevents NEC progression in preterm piglets via effects on gut structure, function, and microbiota, as well as systemic immune and inflammatory responses. Timely feeding cessation and antibiotics are critical factors in preventing NEC progression in preterm infants, while the benefits of additional human IAIP treatment remain to be established.

Immunoglobulin replacement therapy is a life-saving treatment in patients with immunodeficiency and effective in the management of autoimmune disorders. Immunoglobulins are administered intravenously or subcutaneously, with the latter route reducing systemic reactions and providing an option for self-infusion, increasing patient convenience, while decreasing patient burden, healthcare utilization, and costs. A major limitation with subcutaneous administrations is the frequency of infusion due to limited volumes administrable into subcutaneous space, necessitating increased drug concentration, absorption, and dispersion. Increasing the concentration of immunoglobulins from 10 to 20

Abstract The balance of activating and inhibitory signals from the low affinity Fc gamma receptors modulates immune responses triggered by IgG antibody‐immune complexes. In homeostasis, this leads to antigen clearance, while in autoimmune diseases to unwanted immune response. Besides the activating receptors FcɣRIIa, FcɣRIIIa, and the inhibitory FcɣRIIb receptor, a third activating receptor, FcɣRIIc, was shown to be expressed on several immune cell types, however, only in the presence of a functional FCGR2C‐ORF allele. FcɣRIIc expression is associated with autoimmune diseases such as idiopathic thrombocytopenic purpura, systemic lupus erythematosus or systemic sclerosis. Thus, the determination of the functional FCGR2C gene resulting in protein expression on immune cells becomes highly relevant, particularly in the context of unwanted immune responses through inadvertent FcɣRIIc activation by molecules targeting stimulation of the inhibitory receptor FcɣRIIb, currently pursued by several pharmaceutical companies. The high degree of homology within the FCGR2/3 gene cluster complicates development of an accurate method for identification of FcɣRIIc expression. Here we describe a comprehensive approach to characterize genetic status of the FCGR2C gene locus consisting of cDNA sequencing, SNaPshot genotyping and low‐coverage next‐generation sequencing. This might enable Mendelian randomization hypothesis testing across autoimmune diseases to personalize therapies and enhance treatment outcomes.

Gene therapy has the potential to maintain therapeutic blood clotting factor IX (FIX) levels in patients with hemophilia B by delivering a functional human F9 gene into liver cells. This phase 1/2, open-label dose-escalation study investigated BAX 335 (AskBio009, AAV8.sc-TTR-FIXR338Lopt), an adeno-associated virus serotype 8 (AAV8)-based FIX Padua gene therapy, in patients with hemophilia B. This report focuses on 12-month interim analyses of safety, pharmacokinetic variables, effects on FIX activity, and immune responses for dosed participants. Eight adult male participants (aged 20-69 years; range FIX activity, 0.5% to 2.0%) received 1 of 3 BAX 335 IV doses: 2.0 x 10(11); 1.0 x 10(12); or 3.0 x 10(12) vector genomes/kg. Three (37.5%) participants had 4 serious adverse events, all considered unrelated to BAX 335. No serious adverse event led to death. No clinical thrombosis, inhibitors, or other FIX Padua-directed immunity was reported. FIX expression was measurable in 7 of 8 participants; peak FIX activity displayed dose dependence (32.0% to 58.5% in cohort 3). One participant achieved sustained therapeutic FIX activity of similar to 20%, without bleeding or replacement therapy, for 4 years; in others, FIX activity was not sustained beyond 5 to 11 weeks. In contrast to some previous studies, corticosteroid treatment did not stabilize FIX activity loss. We hypothesize that the loss of transgene expression could have been caused by stimulation of innate immune responses, including CpG oligodeoxynucleotides introduced into the BAX 335 coding sequence by codon optimization.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Background Heterozygous point mutations in the GT splice donor consensus sequence of exon 11 of the PIK3R1 gene (coding for p85 alpha, p55 alpha, and p50 alpha regulatory subunits of PI3K) lead to exon skipping and thereby to an aberrant protein that leaves PI3K hyperactivated. Several patients with this particular variant of PI3 kinase delta syndrome (APDS) suffering from sinopulmonary infections and lymphoproliferation have been described.Methods (Whole exome) sequencing, evaluation of cellular and clinical phenotypes.Results We here report a family with a new heterozygous mutation in this gene, a 9 bp deletion (c. 1418_1425 + 1del) that, however, leads to the same skipping of exon 11. The clinical phenotypes of their members partly overlap features of patients of other reports.Conclusions We found a new mutation in PIK3R1 and show how broad the resulting clinical spectrum can be.

Primary immunodeficiencies (PIDs) represent a large group of disorders with an increased susceptibility to infections. Severe combined immunodeficiency (SCID) is the most severe form of primary immunodeficiencies (PIDs) with marked T-cell lymphopenia. Investigation of the genetic aetiology using classical Sanger sequencing is associated with considerable diagnostic delay. We here established a custom-designed, next-generation sequencing (NGS)-based panel to efficiently identify disease-causing genetic defects in PID patients and applied this method in SCID patients of Turkish origin with previously undefined genetic aetiology. We used HaloPlex enrichment technology, a targeted, NGS-based method which was designed to diagnose patients with SCID and other PIDs. Our HaloPlex panel included a total of 356 PID-related genes, and we searched disease-causing mutations in 19 Turkish SCID patients without a genetic diagnosis. The coverage of targeted regions ranged from 97.47% to 99.62% with an average of 98.31% for all patients. All known SCID genes were covered with a percentage of at least 97.3%. We made a genetic diagnosis in six of 19 (33%) patients, including four novel disease-causing mutations identified in RAG1, JAK3 and IL2RG, respectively. We showed that this NGS-based method can provide rapid genetic diagnosis for patients suffering from SCID, potentially facilitating clinical treatment decisions.

RASGRP1 is an important guanine nucleotide exchange factor and activator of the RAS-MAPK pathway following T cell antigen receptor (TCR) signaling. The consequences of RASGRP1 mutations in humans are unknown. In a patient with recurrent bacterial and viral infections, born to healthy consanguineous parents, we used homozygosity mapping and exome sequencing to identify a biallelic stop-gain variant in RASGRP1. This variant segregated perfectly with the disease and has not been reported in genetic databases. RASGRP1 deficiency was associated in T cells and B cells with decreased phosphorylation of the extracellular-signal-regulated serine kinase ERK, which was restored following expression of wild-type RASGRP1. RASGRP1 deficiency also resulted in defective proliferation, activation and motility of T cells and B cells. RASGRP1-deficient natural killer (NK) cells exhibited impaired cytotoxicity with defective granule convergence and actin accumulation. Interaction proteomics identified the dynein light chain DYNLL1 as interacting with RASGRP1, which links RASGRP1 to cytoskeletal dynamics. RASGRP1-deficient cells showed decreased activation of the GTPase RhoA. Treatment with lenalidomide increased RhoA activity and reversed the migration and activation defects of RASGRP1-deficient lymphocytes.

E2A is an essential regulator of early B cell development. Here, we have demonstrated that E2A together with E2-2 controlled germinal center (GC) B cell and plasma cell development. As shown by the identification of regulated E2A, E2-2 target genes in activated B cells, these E-proteins directly activated genes with important functions in GC B cells and plasma cells by inducing and maintaining DNase I hypersensitive sites. Through binding to multiple enhancers in the Igh 3' regulatory region and Aicda locus, E-proteins regulated class switch recombination by inducing both Igh germline transcription and AID expression. By regulating 3' Igk and Igh enhancers and a distal element at the Prdm1 (Blimp1) locus, E-proteins contributed to Igk, Igh, and Prdm1 activation in plasmablasts. Together, these data identified E2A and E2-2 as central regulators of B cell immunity.

To the editor: Biallelic TTC7A mutations have recently been shown to cause early-onset inflammatory bowel disease or multiple intestinal atresias accompanied by severe combined immunodeficiency (MIA-SCID), a disease usually fatal in infancy without curative treatment.1-4 We studied a patient (P1) born in the thirty-third gestational week (to healthy Turkish consanguineous parents) who suffered from combined immunodeficiency and chronic diarrhea. Two older siblings had previously died of severe diarrhea. Within the first 2 months, P1 suffered from constipation followed by watery diarrhea without identifiable cause. Radiographic colonography revealed normal rectum diameter but hypoplastic descending and sigmoid colon and dilated small intestine and ascending and transverse colon (Figure 1A). Duodenal (Figure 1B) and colonic biopsies (supplemental Figure 1A, available online on the Blood Web site) showed graft-versus-host disease (GVHD)–like lesions. P1 experienced several pneumonia episodes (including Klebsiella pneumoniae septicemia) and pyelonephritis. Thymic tissue was hypoplastic (Figure 1C). At 3.5 months, P1 exhibited B lymphopenia and hypogammaglobulinemia (supplemental Table 1) requiring immunoglobulin substitution and trimethoprim/sulfamethoxazole prophylaxis. P1 died at age 15 months of sepsis without an identified causative agent. Figure 1 Identification and intestinal histopathology of TTC7A-mutated patients. (A) Radiograph colonography with barium enema in P1 showing decreased diameter of the descending and sigmoid colon, dilated small intestine segments, and dilation of ascending and ... Given the consanguinity, we assumed an autosomal-recessive inheritance and performed homozygosity mapping (Figure 1D) and exome sequencing. Unexpectedly, we identified a perfectly segregating homozygous missense mutation in TTC7A ({type:entrez-nucleotide,attrs:{text:NM_020458,term_id:572876398,term_text:NM_020458}}NM_020458:c.T1037C;p.L346P) (Figure 1E and supplemental Figure 1B). The substitution of the highly conserved TTC7ALeu346 residue (supplemental Figure 1D) to TTC7APro346 was predicted damaging to TTC7A function by SIFT and PolyPhen-2 prediction algorithms. Concomitantly, we investigated another patient (P2) with classical MIA-SCID manifesting in lymphopenia with near-absent CD8+ T cells, hypogammaglobulinemia, undetectable thymic tissue (supplemental Figures 1F, 2, and 3B), and extended intestinal atresia (Figure 1G). Molecular analysis revealed a large genomic deletion comprising TTC7A exons 6 through 8, causing frameshift and premature transcriptional stop codon ({type:entrez-nucleotide,attrs:{text:NM_020458,term_id:572876398,term_text:NM_020458}}NM_020458:c765_1065del;p.N256Qfs*7) (Figure 1H and supplemental Figure 2B-C). The pronounced immunodeficiency despite mild structural intestinal defects in P1 prompted us to compare the lymphocyte compartments of P1 and P2. Both showed B-cell lymphopenia and hypogammaglobulinemia (supplemental Table 1) despite the presence of naive, marginal zone–like and class-switched memory B cells (supplemental Figure 3A). Increased proportion of transitional B cells in P1 indicated a partial developmental block (supplemental Figure 3A) reminiscent of the tonic BCR- or BAFF-signaling defects resulting in decreased B-cell survival and hypogammaglobulinemia.5,6 TTC7A is required for tethering of phosphatidylinositol 4-kinase, catalytic, alpha (PI4KCA) to the plasma membrane,2 which in turn phosphorylates phosphatidylinositol into phosphatidylinositol(4,5)P2, a second messenger in the phospholipase C gamma-2 (PLCγ2) and phosphatidylinositol 3′-kinase (PI3K) signaling cascades downstream of lymphocyte antigen receptors.7 P1 had unremarkable T-cell counts (supplemental Table 1), CD4+ and/or CD8+ T-cell distribution (supplemental Figure 3B), and T-cell repertoire (supplemental Figure 1E). Maternal cells were absent. A significant proportion of CD4+ T cells in P2 but not in P1 expressed CD25 activation marker, possibly as a compensatory mechanism that would otherwise lead to proliferative expansion8 (supplemental Figure 3B). Cell-surface expression of CD44, CD62L, and CD69 and neutrophil counts and oxidative burst were normal (not shown). Higher TTC7A expression in thymic stroma compared with thymocytes had suggested aberrant thymic (micro)environment as a T-cell extrinsic cause for T-lymphopenia in TTC7A deficiency.1 We challenged this finding by monitoring T-cell proliferation of pulse-labeled patient peripheral blood mononuclear cells after anti-CD3 stimulation. Whereas P2’s T cells showed no proliferative response, proliferation of T cells from P1 was only partially impaired (Figure 1I). TTC7APro346 protein in HEK293 cells was stable and detectable at levels similar to those for TTC7Awildtype (supplemental Figure 3D), implying that TTC7ALeu346Pro represents a hypomorphic variant allowing for residual protein function. Furthermore, T cells from both patients were unable to upregulate CD25 expression after anti-CD3 stimulation, suggesting T-cell receptor (TCR)–signaling defects (Figure 1I). Accordingly, the majority of P1’s T cells had naive CD45RA+ phenotype (supplemental Figure 3C). One possible explanation might be the inability of mutant TTC7A to recruit PI4KCA to the plasma membrane, required for its interaction with CD4-p56lck and downstream signal transduction.9 Because lymphocyte-specific protein tyrosine kinase (LCK) interaction with CD4 and/or CD8 is essential for T-cell development and activation,10 TTC7A might be an integral component of the TCR signalosome. Notably, in contrast to previous observations of defective T-cell proliferation1,4 and our findings, a recent study identified patients with hyperproliferative TTC7A-mutant T cells,11 underlining the phenotypic variability of TTC7A-mutant immunodeficiency. TTC7A deficiency was recently identified as the molecular cause for MIA with or without accompanying SCID.1,3 The hallmark feature of TTC7A deficiency was varying degree of intestinal aberrations. The mildest case presented with intestinal aberrations consisting of bloody diarrhea, apoptotic enterocolitis, and acute GVHD-like symptoms, but no atresias, and the extent of the observed lymphopenia remained unclear.2 P1 had B-lymphopenia, hypogammaglobulinemia, and functional T-cell defects, but intestinal structural aberrations were mild and GVHD-like signs were discrete. Collectively, the clinical spectrum of TTC7A deficiency is considerably more variable than previously appreciated, which should alert physicians to consider TTC7A mutational analysis in (S)CID patients.

Combined immunodeficiencies (CIDs) comprise a heterogeneous group of monogenic disorders manifesting with lymphocyte defects, recurrent infections and dysregulated immune response. Recently, we and others have described clinical and molecular features of the combined immunodeficiency syndromes

Background Combined immunodeficiencies are marked by inborn errors of T-cell immunity in which the T cells that are present are quantitatively or functionally deficient. Impaired humoral immunity is also common. Patients have severe infections, autoimmunity, or both. The specific molecular, cellular, and clinical features of many types of combined immunodeficiencies remain unknown. Methods We performed genetic and cellular immunologic studies involving five unrelated children with early-onset invasive bacterial and viral infections, lymphopenia, and defective T-cell, B-cell, and natural killer (NK)-cell responses. Two patients died early in childhood; after allogeneic hematopoietic stem-cell transplantation, the other three had normalization of T-cell function and clinical improvement. Results We identified biallelic mutations in the dedicator of cytokinesis 2 gene (DOCK2) in these five patients. RAC1 activation was impaired in the T cells. Chemokine-induced migration and actin polymerization were defective in the T cells, B cells, and NK cells. NK-cell degranulation was also affected. Interferon-α and interferon-λ production by peripheral-blood mononuclear cells was diminished after viral infection. Moreover, in DOCK2-deficient fibroblasts, viral replication was increased and virus-induced cell death was enhanced; these conditions were normalized by treatment with interferon alfa-2b or after expression of wild-type DOCK2. Conclusions Autosomal recessive DOCK2 deficiency is a new mendelian disorder with pleiotropic defects of hematopoietic and nonhematopoietic immunity. Children with clinical features of combined immunodeficiencies, especially with early-onset, invasive infections, may have this condition. (Supported by the National Institutes of Health and others.).

CD8 coreceptor expression is dynamically regulated during thymocyte development and is tightly controlled by the activity of at least 5 different cis-regulatory elements. Despite the detailed characterization of the Cd8 loci, the regulation of the complex expression pattern of CD8 cannot be fully explained by the activity of the known Cd8 enhancers. In this study, we revisited the Cd8ab gene complex with bioinformatics and transgenic reporter gene expression approaches to search for additional Cd8 cis-regulatory elements. This led to the identification of an ECR (ECR-4), which in transgenic reporter gene expression assays, directed expression preferentially in CD44(hi)CD62L(+) CD8(+) T cells, including innate-like CD8(+) T cells. ECR-4, designated as Cd8 enhancer E8VI, was bound by Runx/CBFβ complexes and Bcl11b, indicating that E8VI is part of the cis-regulatory network that recruits transcription factors to the Cd8ab gene complex in CD8(+) T cells. Transgenic reporter expression was maintained in LCMV-specific CD8(+) T cells upon infection, although short-term, in vitro activation led to a down-regulation of E8VI activity. Finally, E8VI directed transgene expression also in CD8αα(+) DCs but not in CD8αα-expressing IELs. Taken together, we have identified a novel Cd8 enhancer that directs expression in CD44(hi)CD62L(+) CD8(+) T cells, including innate-like and antigen-specific effector/memory CD8(+) T cells and in CD8αα(+) DCs, and thus, our data provide further insight into the cis-regulatory networks that control CD8 expression.

Background: Alterations of immune homeostasis in the gut can result in development of inflammatory bowel disease (IBD). Recently, Mendelian forms of IBD have been discovered, as exemplified by deficiency of IL-10 or its receptor subunits. In addition, other types of primary immunodeficiency disorders might be associated with intestinal inflammation as one of their leading clinical presentations.Objective: We investigated a large consanguineous family with 3 children who presented with early-onset IBD within the first year of life, leading to death in infancy in 2 of them.Methods: Homozygosity mapping combined with exome sequencing was performed to identify the molecular cause of the disorder. Functional experiments were performed to assess the effect of IL-21 on the immune system.Results: A homozygous mutation in IL21 was discovered that showed perfect segregation with the disease. Deficiency of IL-21 resulted in reduced numbers of circulating CD19(+) B cells, including IgM(+) naive and class-switched IgG memory B cells, with a concomitant increase in transitional B-cell numbers. In vitro assays demonstrated that mutant IL-21(Leu49Pro) did not induce signal transducer and activator of transcription 3 phosphorylation and immunoglobulin class-switch recombination.Conclusion: Our study uncovers IL-21 deficiency as a novel cause of early-onset IBD in human subjects accompanied by defects in B-cell development similar to those found in patients with common variable immunodeficiency. IBD might mask an underlying primary immunodeficiency, as illustrated here with IL-21 deficiency.

Primary immunodeficiency disorders enable identification of genes with crucial roles in the human immune system. Here we study patients suffering from recurrent bacterial, viral and Cryptosporidium infections, and identify a biallelic mutation in the MAP3K14 gene encoding NIK (NF-κB-inducing kinase). Loss of kinase activity of mutant NIK, predicted by in silico analysis and confirmed by functional assays, leads to defective activation of both canonical and non-canonical NF-κB signalling. Patients with mutated NIK exhibit B-cell lymphopenia, decreased frequencies of class-switched memory B cells and hypogammaglobulinemia due to impaired B-cell survival, and impaired ICOSL expression. Although overall T-cell numbers are normal, both follicular helper and memory T cells are perturbed. Natural killer (NK) cells are decreased and exhibit defective activation, leading to impaired formation of NK-cell immunological synapses. Collectively, our data illustrate the non-redundant role for NIK in human immune responses, demonstrating that loss-of-function mutations in NIK can cause multiple aberrations of lymphoid immunity.