Germline mutations in NFKB2 implicate the noncanonical NF-κB pathway in the pathogenesis of common variable immunodeficiency

Early B cell developmental impairment with progressive B cell deficiency in NFKB2 mutated CVID disease without autoimmunity

This study provides evidence for a novel role for NFKB2 in human B cell development in the bone marrow and in the periphery, leading to progressive peripheral B cell deficiency not always combined with autoimmune phenomena, broadening thus the clinical spectrum of NFKB2 mutated CVID disease and implying an essential role for NFKB2 in early human B cell development.

Primary B-cell immunodeficiencies

Primary B-cell immunodeficiencies refer to diseases resulting from impaired antibody production due to either molecular defects intrinsic to B-cells or a failure of interaction between B-cells and T-cells. Patients typically have recurrent infections and can vary with presentation and complications depending upon where the defect has occurred in B-cell development or the degree of functional impairment. In this review, we describe B-cell specific immune defects categorized by presence or absence of peripheral B-cells, immunoglobulins isotypes and evidence of antibody impairment.

Loss-of-function nuclear factor κB subunit 1 (NFKB1) variants are the most common monogenic cause of common variable immunodeficiency in Europeans

BACKGROUND

The genetic cause of primary immunodeficiency disease (PID) carries prognostic information.

OBJECTIVE

We conducted a whole-genome sequencing study assessing a large proportion of the NIHR BioResource-Rare Diseases cohort.

METHODS

In the predominantly European study population of principally sporadic unrelated PID cases (n = 846), a novel Bayesian method identified nuclear factor κB subunit 1 (NFKB1) as one of the genes most strongly associated with PID, and the association was explained by 16 novel heterozygous truncating, missense, and gene deletion variants. This accounted for 4% of common variable immunodeficiency (CVID) cases (n = 390) in the cohort. Amino acid substitutions predicted to be pathogenic were assessed by means of analysis of structural protein data. Immunophenotyping, immunoblotting, and ex vivo stimulation of lymphocytes determined the functional effects of these variants. Detailed clinical and pedigree information was collected for genotype-phenotype cosegregation analyses.

RESULTS

Both sporadic and familial cases demonstrated evidence of the noninfective complications of CVID, including massive lymphadenopathy (24%), unexplained splenomegaly (48%), and autoimmune disease (48%), features prior studies correlated with worse clinical prognosis. Although partial penetrance of clinical symptoms was noted in certain pedigrees, all carriers have a deficiency in B-lymphocyte differentiation. Detailed assessment of B-lymphocyte numbers, phenotype, and function identifies the presence of an increased CD21low B-cell population. Combined with identification of the disease-causing variant, this distinguishes between healthy subjects, asymptomatic carriers, and clinically affected cases.

CONCLUSION

We show that heterozygous loss-of-function variants in NFKB1 are the most common known monogenic cause of CVID, which results in a temporally progressive defect in the formation of immunoglobulin-producing B cells.

Diagnosis and management of chronic and refractory immune cytopenias in children, adolescents, and young adults

Children, adolescents, and young adults with chronic refractory autoimmune cytopenias represent a rare but challenging group of patients, who are managed frequently by pediatric hematologists. Novel diagnostic tests and genomic discoveries are refining historical diagnoses of Evans syndrome and common variable immunodeficiency, while also elucidating the cellular and molecular basis for these disorders. Genetic characterization of chronic and refractory autoimmune cytopenias has led to targeted therapies with improved clinical outcomes and fewer off-target toxicities. In this review, we focus on the appropriate diagnostic workup, expanded genetic testing, and novel treatment opportunities that are available for these challenging patients.

Lessons learned from the study of human inborn errors of innate immunity

Innate immunity contributes to host defense through all cell types and relies on their shared germline genetic background, whereas adaptive immunity operates through only 3 main cell types, αβ T cells, γδ T cells, and B cells, and relies on their somatic genetic diversification of antigen-specific responses. Human inborn errors of innate immunity often underlie infectious diseases. The range and nature of infections depend on the mutated gene, the deleteriousness of the mutation, and other ill-defined factors. Most known inborn errors of innate immunity to infection disrupt the development or function of leukocytes other than T and B cells, but a growing number of inborn errors affect cells other than circulating and tissue leukocytes. Here we review inborn errors of innate immunity that have been recently discovered or clarified. We highlight the immunologic implications of these errors.

Central adrenal insufficiency in children and adolescents

Central adrenal insufficiency (CAI) is a life-threatening condition caused by either pituitary disease (secondary adrenal insufficiency) or impaired hypothalamic function with inadequate CRH production (tertiary adrenal insufficiency). ACTH deficiency may be isolated or, more frequently, occur in conjunction with other pituitary hormone deficiencies and midline defects. Genetic mutations of the TBX19 causing isolated CAI are rare but a number of genes encoding transcription factors involved in hypothalamic-pituitary gland development, as well as other genes including POMC and PC1, are associated with ACTH deficiency. CAI is frequently identified in congenital, malformative, genetic, and epigenetic syndromes as well as in several acquired conditions of different etiologies. The signs and symptoms vary considerably and depend on the age of onset and the number and severity of associated pituitary defects. They may include hypoglycemia, lethargy, apnea, poor feeding, prolonged cholestatic jaundice, jitteriness, seizures, and sepsis in the neonate, or nonspecific signs such as fatigue, hypotension, vomiting and hyponatremia without hyperkalemia in children. The diagnosis of CAI relies on the measurement of morning cortisol concentrations along with dynamic test for cortisol release with different stimulating agents. Early recognition of CAI and its correct management are mandatory in order to avoid both morbidity and mortality in affected neonates, children and adolescents.

Th1-skewed profile and excessive production of proinflammatory cytokines in a NFKB1-deficient patient with CVID and severe gastrointestinal manifestations

Monoallelic loss-of-function mutations in NFKB1 were recently recognized as the most common monogenic cause of common variable immunodeficiency (CVID). The prototypic clinical phenotype of NFKB1-deficient patients includes common CVID features, such as hypogammaglobulinaemia and sinopulmonary infections, plus other highly variable individual manifestations. Here, we describe a patient with a profound CVID phenotype and severe gastrointestinal manifestations, including chronic and recurrent diarrhoea. Using an NGS customized panel of 323 genes related to primary immunodeficiencies, we identified a novel monoallelic loss-of-function mutation in NFKB1 leading to a truncated protein (c.1149delT/p.Gly384Glu ∗ 48). Interestingly, we also found a rare variant in NOD2 previously associated with Crohn's disease (p.His352Arg). Our patient had hypogammaglobulinaemia with a small number of B cells, most of which were naïve. The most noteworthy findings included marked skewing towards a Th1 phenotype in peripheral blood T cells and excessive production of proinflammatory cytokines (IL-1β, TNFα). The patient's 6-year-old daughter, a carrier of the NFKB1 mutation, is clinically asymptomatic, but has started to show cellular and molecular changes. This case of NFKB1 deficiency appears to be a combination of immunodeficiency and a hyperinflammatory state. The current situation of the patient's daughter provides a glimpse of the preclinical phase of the condition.

Bacille Calmette-Guerin Complications in Newly Described Primary Immunodeficiency Diseases: 2010-2017

Bacille Calmette–Guerin (BCG) vaccine is widely used as a prevention strategy against tuberculosis. BCG is a live vaccine, usually given early in life in most countries. While safe to most recipients, it poses a risk to immunocompromised patients. Several primary immunodeficiency diseases (PIDD) have been classically associated with complications related to BCG vaccine. However, a number of new inborn errors of immunity have been described lately in which little is known about adverse reactions following BCG vaccination. The aim of this review is to summarize the existing data on BCG-related complications in patients diagnosed with PIDD described since 2010. When BCG vaccination status or complications were not specifically addressed in those manuscripts, we directly contacted the corresponding authors for further clarification. We also analyzed data on other mycobacterial infections in these patients. Based on our analysis, around 8% of patients with gain-of-function mutations in STAT1 had mycobacterial infections, including localized complications in 3 and disseminated disease in 4 out of 19 BCG-vaccinated patients. Localized BCG reactions were also frequent in activated PI3Kδ syndrome type 1 (3/10) and type 2 (2/18) vaccinated children. Also, of note, no BCG-related complications have been described in either CTLA4 or LRBA protein-deficient patients; and not enough information on BCG-vaccinated NFKB1 or NFKB2-deficient patients was available to drive any conclusions about these diseases. Despite the high prevalence of environmental mycobacterial infections in GATA2-deficient patients, only one case of BCG reaction has been reported in a patient who developed disseminated disease. In conclusion, BCG complications could be expected in some particular, recently described PIDD and it remains a preventable risk factor for pediatric PIDD patients.

Common Variable Immunodeficiency and Gastric Malignancies

Common variable immunodeficiency (CVID) is an immunodeficiency disorder with a high incidence of gastrointestinal manifestations and an increased risk of gastric carcinoma and lymphoma. This review discusses the latest advancements into the immunological, clinical and diagnostic aspects of gastric malignancies in patients with CVID. The exact molecular pathways underlying the relationships between CVID and gastric malignancies remain poorly understood. These include genetics, immune dysregulation and chronic infections by Helicobacter pylori. Further studies are needed to better stratify the risk for cancer in these patients, to elaborate surveillance programs aimed at preventing these complications, and to develop new and more effective therapeutic approaches.

Human NF-κB1 Haploinsufficiency and Epstein-Barr Virus-Induced Disease-Molecular Mechanisms and Consequences

Nuclear factor kappa-light-chain-enhancer of activated B cells 1 (NF-κB1)-related human primary immune deficiencies have initially been characterized as defining a subgroup of common variable immunodeficiencies (CVIDs), representing intrinsic B-cell disorders with antibody deficiency and recurrent infections of various kind. Recent evidence indicates that NF-κB1 haploinsufficiency underlies a variable type of combined immunodeficiency (CID) affecting both B and T lymphocyte compartments, with a broadened spectrum of disease manifestations, including Epstein–Barr virus (EBV)-induced lymphoproliferative disease and immediate life-threatening consequences. As part of this review series focused on EBV-related primary immunodeficiencies, we discuss the current clinical and molecular understanding of monoallelic NFKB1 germline mutations with special focus on the emerging context of EBV-associated disease. We outline mechanistic implications of dysfunctional NF-κB1 in B and T cells and discuss the fatal relation of impaired T-cell function with the inability to clear EBV infections. Finally, we compare common and suggested treatment angles in the context of this complex disease.

Nuclear Factor-kappaB in Autoimmunity: Man and Mouse

NF-κB (nuclear factor-kappa B) is a transcription complex crucial for host defense mediated by innate and adaptive immunity, where canonical NF-κB signaling, mediated by nuclear translocation of RelA, c-Rel, and p50, is important for immune cell activation, differentiation, and survival. Non-canonical signaling mediated by nuclear translocation of p52 and RelB contributes to lymphocyte maturation and survival and is also crucial for lymphoid organogenesis. We outline NF-κB signaling and regulation, then summarize important molecular contributions of NF-κB to mechanisms of self-tolerance. We relate these mechanisms to autoimmune phenotypes described in what is now a substantial catalog of immune defects conferred by mutations in NF-κB pathways in mouse models. Finally, we describe Mendelian autoimmune syndromes arising from human NF-κB mutations, and speculate on implications for understanding sporadic autoimmune disease.

NF-κB and the Transcriptional Control of Inflammation

The NF-κB transcription factor was discovered 30 years ago and has since emerged as the master regulator of inflammation and immune homeostasis. It achieves this status by means of the large number of important pro- and antiinflammatory factors under its transcriptional control. NF-κB has a central role in inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease, and autoimmunity, as well as diseases comprising a significant inflammatory component such as cancer and atherosclerosis. Here, we provide an overview of the studies that form the basis of our understanding of the role of NF-κB subunits and their regulators in controlling inflammation. We also describe the emerging importance of posttranslational modifications of NF-κB in the regulation of inflammation, and highlight the future challenges faced by researchers who aim to target NF-κB transcriptional activity for therapeutic benefit in treating chronic inflammatory diseases.

Novel nonsense gain-of-function NFKB2 mutations associated with a combined immunodeficiency phenotype

NF-κB signaling through its NFKB1-dependent canonical and NFKB2-dependent noncanonical pathways plays distinctive roles in a diverse range of immune processes. Recently, mutations in these 2 genes have been associated with common variable immunodeficiency (CVID). While studying patients with genetically uncharacterized primary immunodeficiencies, we detected 2 novel nonsense gain-of-function (GOF) NFKB2 mutations (E418X and R635X) in 3 patients from 2 families, and a novel missense change (S866R) in another patient. Their immunophenotype was assessed by flow cytometry and protein expression; activation of canonical and noncanonical pathways was examined in peripheral blood mononuclear cells and transfected HEK293T cells through immunoblotting, immunohistochemistry, luciferase activity, real-time polymerase chain reaction, and multiplex assays. The S866R change disrupted a C-terminal NF-κΒ2 critical site affecting protein phosphorylation and nuclear translocation, resulting in CVID with adrenocorticotropic hormone deficiency, growth hormone deficiency, and mild ectodermal dysplasia as previously described. In contrast, the nonsense mutations E418X and R635X observed in 3 patients led to constitutive nuclear localization and activation of both canonical and noncanonical NF-κΒ pathways, resulting in a combined immunodeficiency (CID) without endocrine or ectodermal manifestations. These changes were also found in 2 asymptomatic relatives. Thus, these novel NFKB2 GOF mutations produce a nonfully penetrant CID phenotype through a different pathophysiologic mechanism than previously described for mutations in NFKB2.

Autoimmunity/inflammation in a monogenic primary immunodeficiency cohort

Primary immunodeficiencies (PIDs) are rare inborn errors of immunity that have a heterogeneous phenotype that can include severe susceptibility to life-threatening infections from multiple pathogens, unique sensitivity to a single pathogen, autoimmune/inflammatory (AI/I) disease, allergies and/or malignancy. We present a diverse cohort of monogenic PID patients with and without AI/I diseases who underwent clinical, genetic and immunological phenotyping. Novel pathogenic variants were identified in IKBKG, CTLA4, NFKB1, GATA2, CD40LG and TAZ as well as previously reported pathogenic variants in STAT3, PIK3CD, STAT1, NFKB2 and STXBP2. AI/I manifestations were frequently encountered in PIDs, including at presentation. Autoimmunity/inflammation was multisystem in those effected, and regulatory T cell (Treg) percentages were significantly decreased compared with those without AI/I manifestations. Prednisolone was used as the first-line immunosuppressive agent in all cases, however steroid monotherapy failed long-term control of autoimmunity/inflammation in the majority of cases and additional immunosuppression was required. Patients with multisystem autoimmunity/inflammation should be investigated for an underlying PID, and in those with PID early assessment of Tregs may help to assess the risk of autoimmunity/inflammation.

The non-canonical NF-κB pathway in immunity and inflammation

The nuclear factor-κB (NF-κB) family of transcription factors is activated by canonical and non-canonical signalling pathways, which differ in both signalling components and biological functions. Recent studies have revealed important roles for the non-canonical NF-κB pathway in regulating different aspects of immune functions. Defects in non-canonical NF-κB signalling are associated with severe immune deficiencies, whereas dysregulated activation of this pathway contributes to the pathogenesis of various autoimmune and inflammatory diseases. Here we review the signalling mechanisms and the biological function of the non-canonical NF-κB pathway. We also discuss recent progress in elucidating the molecular mechanisms regulating non-canonical NF-κB pathway activation, which may provide new opportunities for therapeutic strategies.

Reduced numbers of circulating group 2 innate lymphoid cells in patients with common variable immunodeficiency

Recent studies identified an emerging role of group 2 and 3 innate lymphoid cells (ILCs) as key players in the generation of T-dependent and T-independent antibody production. In this retrospective case-control study, CD117⁺ ILCs (including the majority of ILC2 and ILC3) were reduced in patients with common variable immunodeficiency (CVID). The reduction in CD117⁺ ILCs was distinctive to CVID and could not be observed in patients with X-linked agammaglobulinemia. Patients with a more pronounced reduction in CD117⁺ ILC numbers showed significantly lower numbers of peripheral MZ-like B cells and an increased prevalence of chronic, non-infectious enteropathy. Subsequent phenotyping of ILC subsets in CVID revealed that the reduction in CD117⁺ ILC numbers is due to a reduction in ILC2 numbers. In vitro expansion of CVID ILC2 in response to IL-2, IL-7, IL-25 and IL-33 was impaired. Furthermore, upregulation of MHCII and IL-2RA in response to IL-2, IL-7, IL-25 and IL-33 was impaired in CVID ILC2. Thus, our results indicate a dysregulation of ILC subsets with a reduction in ILC2 numbers in CVID, however, further studies are needed to explore whether ILC abnormalities are a primary finding or secondary to disease complications encountered in CVID.

Immune defects caused by mutations in the ubiquitin system

The importance of the ubiquitin system in health and disease has been widely recognized in recent decades, with better understanding of the various components of the system and their function. Ubiquitination, which is essential to almost all biological processes in eukaryotes, was also found to play an important role in innate and adaptive immune responses. Thus it is not surprising that mutations in genes coding for components of the ubiquitin system cause immune dysregulation. The first defect in the system was described 30 years ago and is due to mutations in the nuclear factor κB (NF-κB) essential modulator, a key regulator of the NF-κB pathway. With use of novel sequencing techniques, many additional mutations in different genes involved in ubiquitination and related to immune system function were identified. This can be clearly illustrated in mutations in the different activation pathways of NF-κB, which result in aberrations in production of various proinflammatory cytokines. The inherited diseases typically manifest with immunodeficiency, autoimmunity, or autoinflammation. In this perspective we provide a short description of the ubiquitin system, with specific emphasis given to its role in the immune system. The various immunodeficiency conditions identified thus far in association with defective ubiquitination are discussed in more detail.

A Case Report of Hypoglycemia and Hypogammaglobulinemia: DAVID Syndrome in a Patient With a Novel NFKB2 Mutation

Context

Deficient anterior pituitary with variable immune deficiency (DAVID) syndrome is a rare disorder in which children present with symptomatic adrenocorticotropic hormone (ACTH) deficiency preceded by hypogammaglobulinemia from B-cell dysfunction with recurrent infections, called common variable immunodeficiency (CVID). Subsequent whole exome sequencing studies have revealed germline heterozygous C-terminal mutations of NFKB2 as a cause of DAVID syndrome or of CVID without clinical hypopituitarism. However, to the best of our knowledge there have been no cases in which the endocrinopathy has presented in the absence of a prior clinical history of CVID.

Case Description

A previously healthy 7-year-old boy with no history of clinical immunodeficiency presented with profound hypoglycemia and seizures. He was found to have secondary adrenal insufficiency and was started on glucocorticoid replacement. An evaluation for autoimmune disease, including for antipituitary antibodies, was negative. Evaluation unexpectedly revealed hypogammaglobulinemia [decreased immunoglobulin G (IgG), IgM, and IgA]. He had moderately reduced serotype-specific IgG responses after pneumococcal polysaccharide vaccine. Subsequently, he was found to have growth hormone deficiency. Six years after initial presentation, whole exome sequencing revealed a de novo heterozygous NFKB2 missense mutation c.2596A>C (p.Ser866Arg) in the C-terminal region predicted to abrogate the processing of the p100 NFKB2 protein to its active p52 form.

Conclusions

Isolated early-onset ACTH deficiency is rare, and C-terminal region NFKB2 mutations should be considered as an etiology even in the absence of a clinical history of CVID. Early immunologic evaluation is indicated in the diagnosis and management of isolated ACTH deficiency.

The non-canonical NF-κB pathway in immunity and inflammation

The nuclear factor-κB (NF-κB) family of transcription factors is activated by canonical and non-canonical signalling pathways, which differ in both signalling components and biological functions. Recent studies have revealed important roles for the non-canonical NF-κB pathway in regulating different aspects of immune functions. Defects in non-canonical NF-κB signalling are associated with severe immune deficiencies, whereas dysregulated activation of this pathway contributes to the pathogenesis of various autoimmune and inflammatory diseases. Here we review the signalling mechanisms and the biological function of the non-canonical NF-κB pathway. We also discuss recent progress in elucidating the molecular mechanisms regulating non-canonical NF-κB pathway activation, which may provide new opportunities for therapeutic strategies.

Damaging heterozygous mutations in NFKB1 lead to diverse immunologic phenotypes

BACKGROUND

The nuclear factor κ light-chain enhancer of activated B cells (NF-κB) signaling pathway is a key regulator of immune responses. Accordingly, mutations in several NF-κB pathway genes cause immunodeficiency.

OBJECTIVE

We sought to identify the cause of disease in 3 unrelated Finnish kindreds with variable symptoms of immunodeficiency and autoinflammation.

METHODS

We applied genetic linkage analysis and next-generation sequencing and functional analyses of NFKB1 and its mutated alleles.

RESULTS

In all affected subjects we detected novel heterozygous variants in NFKB1, encoding for p50/p105. Symptoms in variant carriers differed depending on the mutation. Patients harboring a p.I553M variant presented with antibody deficiency, infection susceptibility, and multiorgan autoimmunity. Patients with a p.H67R substitution had antibody deficiency and experienced autoinflammatory episodes, including aphthae, gastrointestinal disease, febrile attacks, and small-vessel vasculitis characteristic of Behçet disease. Patients with a p.R157X stop-gain experienced hyperinflammatory responses to surgery and showed enhanced inflammasome activation. In functional analyses the p.R157X variant caused proteasome-dependent degradation of both the truncated and wild-type proteins, leading to a dramatic loss of p50/p105. The p.H67R variant reduced nuclear entry of p50 and showed decreased transcriptional activity in luciferase reporter assays. The p.I553M mutation in turn showed no change in p50 function but exhibited reduced p105 phosphorylation and stability. Affinity purification mass spectrometry also demonstrated that both missense variants led to altered protein-protein interactions.

CONCLUSION

Our findings broaden the scope of phenotypes caused by mutations in NFKB1 and suggest that a subset of autoinflammatory diseases, such as Behçet disease, can be caused by rare monogenic variants in genes of the NF-κB pathway.

30 Years of NF-κB: A Blossoming of Relevance to Human Pathobiology

NF-κB was discovered 30 years ago as a rapidly inducible transcription factor. Since that time, it has been found to have a broad role in gene induction in diverse cellular responses, particularly throughout the immune system. Here, we summarize elaborate regulatory pathways involving this transcription factor and use recent discoveries in human genetic diseases to place specific proteins within their relevant medical and biological contexts.

IRAK4 Deficiency in a Patient with Recurrent Pneumococcal Infections: Case Report and Review of the Literature

Primary immunodeficiencies are genetic defects of the innate or adaptive immune system, resulting in a propensity to infections. The innate immune system is the first line of defense against pathogens and is critical to recognize microbes and start the inflammatory cascade. Sensing of microbes occurs by a number of pathogen-recognition receptors, resulting in the activation of inflammatory signal transduction pathways, such as the activation of NF-κB. Herein, we describe a case of IRAK4 deficiency, a key signal transduction molecule of toll-like and IL-1 receptors. We highlight the complexities in diagnosis of these disorders and review genetic defects of the NF-κB pathway.

Primary immunodeficiency diseases: Genomic approaches delineate heterogeneous Mendelian disorders

BACKGROUND

Primary immunodeficiency diseases (PIDDs) are clinically and genetically heterogeneous disorders thus far associated with mutations in more than 300 genes. The clinical phenotypes derived from distinct genotypes can overlap. Genetic etiology can be a prognostic indicator of disease severity and can influence treatment decisions.

OBJECTIVE

We sought to investigate the ability of whole-exome screening methods to detect disease-causing variants in patients with PIDDs.

METHODS

Patients with PIDDs from 278 families from 22 countries were investigated by using whole-exome sequencing. Computational copy number variant (CNV) prediction pipelines and an exome-tiling chromosomal microarray were also applied to identify intragenic CNVs. Analytic approaches initially focused on 475 known or candidate PIDD genes but were nonexclusive and further tailored based on clinical data, family history, and immunophenotyping.

RESULTS

A likely molecular diagnosis was achieved in 110 (40%) unrelated probands. Clinical diagnosis was revised in about half (60/110) and management was directly altered in nearly a quarter (26/110) of families based on molecular findings. Twelve PIDD-causing CNVs were detected, including 7 smaller than 30 Kb that would not have been detected with conventional diagnostic CNV arrays.

CONCLUSION

This high-throughput genomic approach enabled detection of disease-related variants in unexpected genes; permitted detection of low-grade constitutional, somatic, and revertant mosaicism; and provided evidence of a mutational burden in mixed PIDD immunophenotypes.

NFKB2 mutation in common variable immunodeficiency and isolated adrenocorticotropic hormone deficiency: A case report and review of literature

BACKGROUND

Common variable immunodeficiency (CVID) with central adrenal insufficiency is a recently defined clinical syndrome caused by mutations in the nuclear factor kappa-B subunit 2 (NFKB2) gene. We present the first case of NFKB2 mutation in Asian population.

METHODS AND RESULTS

An 18-year-old Chinese female with adrenocorticotropic hormone (ACTH) deficiency was admitted due to adrenal crisis and pneumonia. She had a history of recurrent respiratory infections since childhood and ectodermal abnormalities were noted during physical examination. Immunologic tests revealed panhypogammaglobulinemia and deficient natural killer (NK)-cell function. DNA sequencing of NFKB2 identified a heterozygous nonsense mutation (c.2563 A>T, p.855: Lys>*) in the patient but not her parents.

CONCLUSION

Clinicians should be alert to comorbidities of adrenal insufficiency and ectodermal dysplasia in CVID patients as these might suggest a rare hereditary syndrome caused by NFKB2 mutation.

Tumor-suppressor NFκB2 p100 interacts with ERK2 and stabilizes PTEN mRNA via inhibition of miR-494

Emerging evidence from The Cancer Genome Atlas has revealed that nuclear factor κB2 (nfκb2) gene encoding p100 is genetically deleted or mutated in human cancers, implicating NFκB2 as a potential tumor suppressor. However, the molecular mechanism underlying the antitumorigenic action of p100 remains poorly understood. Here we report that p100 inhibits cancer cell anchorage-independent growth, a hallmark of cellular malignancy, by stabilizing the tumor-suppressor phosphatase and tensin homolog (PTEN) mRNA via a mechanism that is independent of p100's inhibitory role in NFκB activation. We further demonstrate that the regulatory effect of p100 on PTEN expression is mediated by its downregulation of miR-494 as a result of the inactivation of extracellular signal-regulated kinase 2 (ERK2), in turn leading to inhibition of c-Jun/activator protein-1-dependent transcriptional activity. Furthermore, we identify that p100 specifically interacts with non-phosphorylated ERK2 and prevents ERK2 phosphorylation and nuclear translocation. Moreover, the death domain at C-terminal of p100 is identified as being crucial and sufficient for its interaction with ERK2. Taken together, our findings provide novel mechanistic insights into the understanding of the tumor-suppressive role for NFκB2 p100.

NF-κB1 Haploinsufficiency Causing Immunodeficiency and EBV-Driven Lymphoproliferation

Purpose

NF-κB signaling is critically important for regulation of both innate and adaptive immune responses. While activation of NF-κB has been implicated in malignancies such as leukemia and lymphoma, loss-of-function mutations affecting different NF-κB pathway components have been shown to cause primary immunodeficiency disorders. Recently, haploinsufficiency of NF-κB1 has been described in three families with common variable immunodeficiency (CVID).

Methods and Results

We studied a patient with recurrent respiratory infections and bacterial parapharyngeal abscess. Immunological investigations revealed normal total B- cell numbers, but hypogammaglobulinemia, decreased frequencies of class-switched B cells and impaired T-cell proliferation. Targeted next-generation sequencing using a custom-designed panel comprising all known PID genes (IUIS 2014 classification) and novel candidate genes identified a novel heterozygous frameshift mutation in the NFKB1 gene leading to a premature stop codon (c.491delG; p.G165A*31). We could show that the mutation leads to reduced phosphorylation of p105 upon stimulation, resulting in decreased protein levels of p50. The further disease course was mainly characterized by two episodes of severe EBV-associated lymphoproliferative disease responsive to rituximab treatment. Due to disease severity, the patient is considered for allogeneic hematopoietic stem cell transplantation. Interestingly, the father carries the same heterozygous NFKB1 mutation and also shows decreased frequencies of memory B cells but has a much milder clinical phenotype, in line with a considerable phenotypic disease heterogeneity.

Conclusions

Deficiency of NF-κB1 leads to immunodeficiency with a wider phenotypic spectrum of disease manifestation than previously appreciated, including EBV lymphoproliferative diseases as a hitherto unrecognized feature of the disease.

Electronic supplementary material

The online version of this article (doi:10.1007/s10875-016-0306-1) contains supplementary material, which is available to authorized users.

Disturbed canonical nuclear factor of κ light chain signaling in B cells of patients with common variable immunodeficiency

BACKGROUND

Most patients with common variable immunodeficiency (CVID) present with severely reduced switched memory B-cell counts, and some display an increase of CD21^low B-cell counts (CVID 21low), whereas others do not (CVID 21norm). Altered B-cell receptor (BCR) signaling might contribute to the defective memory formation observed in patients with CVID.

OBJECTIVE

We sought to investigate canonical nuclear factor of κ light chain (NF-κB) signaling in B cells from patients with CVID as a central pathway in B-cell differentiation.

METHODS

Degradation of inhibitor of κBα (IκBα) and p65 phosphorylation, nuclear translocation of p65, and regulation of target genes and cell function were investigated after different modes of B-cell stimulation.

RESULTS

BCR-mediated canonical NF-κB signaling was impaired in all mature naive CVID-derived B cells. This impairment was more profound in naive B cells from CVID 21low patients than CVID 21norm patients and most pronounced in CD21^low B cells. The signaling defect translated into reduced induction of Bcl-xL and IκBα, 2 bona fide target genes of the canonical NF-κB pathway. CD40 ligand- and Toll-like receptor 9-mediated signaling were less strongly altered. Signaling in CD21^low B cells but not CD21⁺ B cells of patients with HIV was similarly affected.

CONCLUSION

Combined with the previous description of disturbed Ca²⁺ signaling, the discovery of NF-κB signaling defects, especially in CVID 21low patients, suggests a broad underlying signaling defect affecting especially BCR-derived signals. Given the immune phenotype of monogenic defects affecting Ca²⁺ and NF-κB signaling, the latter is more likely to contribute to the humoral deficiency. The strongly disturbed BCR signaling of CD21^low B cells is characteristic for this cell type and independent of the underlying disease.

Genes associated with common variable immunodeficiency: one diagnosis to rule them all?

Common variable immunodeficiency (CVID) is a primary antibody deficiency characterised by hypogammaglobulinaemia, impaired production of specific antibodies after immunisation and increased susceptibility to infections. CVID shows a considerable phenotypical and genetic heterogeneity. In contrast to many other primary immunodeficiencies, monogenic forms count for only 2-10% of patients with CVID. Genes that have been implicated in monogenic CVID include ICOS, TNFRSF13B (TACI), TNFRSF13C (BAFF-R), TNFSF12 (TWEAK), CD19, CD81, CR2 (CD21), MS4A1 (CD20), TNFRSF7 (CD27), IL21, IL21R, LRBA, CTLA4, PRKCD, PLCG2, NFKB1, NFKB2, PIK3CD, PIK3R1, VAV1, RAC2, BLK, IKZF1 (IKAROS) and IRF2BP2 With the increasing number of disease genes identified in CVID, it has become clear that CVID is an umbrella diagnosis and that many of these genetic defects cause distinct disease entities. Moreover, there is accumulating evidence that at least a subgroup of patients with CVID has a complex rather than a monogenic inheritance. This review aims to discuss current knowledge regarding the molecular genetic basis of CVID with an emphasis on the relationship with the clinical and immunological phenotype.

MECHANISMS IN ENDOCRINOLOGY: An update in the genetic aetiologies of combined pituitary hormone deficiency

Over the last 5 years, new actors involved in the pathogenesis of combined pituitary hormone deficiency in humans have been reported: they included a member of the immunoglobulin superfamily glycoprotein and ciliary G protein-coupled receptors, as well as new transcription factors and signalling molecules. New modes of inheritance for alterations of genes encoding transcription factors have also been described. Finally, actors known to be involved in a very specific phenotype (hypogonadotroph hypogonadism for instance) have been identified in a wider range of phenotypes. These data thus suggest that new mechanisms could explain the low rate of aetiological identification in this heterogeneous group of diseases. Taking into account the fact that several reviews have been published in recent years on classical aetiologies of CPHD such as mutations of POU1F1 or PROP1, we focused the present overview on the data published in the last 5 years, to provide the reader with an updated review on this rapidly evolving field of knowledge.

Autoimmunity and Primary Immunodeficiency Disorders

Advances in DNA sequencing technologies have led to a quickening in the pace at which new genetic immunodeficiency disorders have been identified. Among the newly identified defects are a number of disorders that present primarily with autoimmunity as opposed to recurrent infections. These "immune dysregulation" disorders have begun to cluster together to form an increased understanding of some of the basic molecular mechanisms that underlie the establishment and maintenance of immune tolerance and the development of autoimmunity. This review will present three major themes that have emerged in our understanding of the mechanisms that underlie autoimmunity and immune dysregulation in humans.

60 YEARS OF POMC: Transcriptional and epigenetic regulation of POMC gene expression

Expression of the pro-opiomelanocortin (POMC) gene integrates numerous inputs that reflect the developmental history of POMC-expressing cells of the pituitary and hypothalamus, as well as their critical role in the endocrine system. These inputs are integrated at specific regulatory sequences within the promoter and pituitary or hypothalamic enhancers of the POMC locus. Investigations of developmental mechanisms and transcription factors (TFs) responsible for pituitary activation of POMC transcription led to the discovery of the Pitx factors that have critical roles in pituitary development and striking patterning functions in embryonic development. Terminal differentiation of the two pituitary POMC lineages, the corticotrophs and melanotrophs, is controlled by Tpit; mutations of the human TPIT gene cause isolated adrenocorticotrophic hormone deficiency. Intermediate lobe and melanotroph identity is provided by the pioneer TF Pax7 that remodels chromatin to reveal a new repertoire of enhancers for Tpit action. Many signaling pathways regulate POMC transcription including activation by hypothalamic corticotrophin-releasing hormone acting through the orphan nuclear receptors of the Nur family and feedback repression by glucocorticoids and their glucocorticoid receptor. TFs of the basic helix-loop-helix, Smad, Stat, Etv, and nuclear factor-B families also mediate signals for control of POMC transcription. Whereas most of these regulatory processes are conserved in different species, there are also notable differences between specific targets for regulation of the human compared with mouse POMC genes.

Noncanonical NF-κB Signaling in Health and Disease

Noncanonical NF-κB signaling differs from canonical NF-κB signaling by being activated through different cell surface receptors, cytoplasmic adaptors, and NF-κB dimers. Under normal physiological conditions, this noncanonical pathway has been implicated in diverse biological processes, including lymphoid organogenesis, B cell maturation, osteoclast differentiation, and various functions of other immune cells. Recently, dysfunction of this pathway has also been causally associated with numerous immune-mediated pathologies and human malignancies. Here, we summarize the core elements as well as the recently identified novel regulators of the noncanonical NF-κB signaling pathway. The involvement of this pathway in different pathologies and the potential therapeutic options that are currently envisaged are also discussed.

Loss of B Cells in Patients with Heterozygous Mutations in IKAROS

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by late-onset hypogammaglobulinemia in the absence of predisposing factors. The genetic cause is unknown in the majority of cases, and less than 10% of patients have a family history of the disease. Most patients have normal numbers of B cells but lack plasma cells.

METHODS

We used whole-exome sequencing and array-based comparative genomic hybridization to evaluate a subset of patients with CVID and low B-cell numbers. Mutant proteins were analyzed for DNA binding with the use of an electrophoretic mobility-shift assay (EMSA) and confocal microscopy. Flow cytometry was used to analyze peripheral-blood lymphocytes and bone marrow aspirates.

RESULTS

Six different heterozygous mutations in IKZF1, the gene encoding the transcription factor IKAROS, were identified in 29 persons from six families. In two families, the mutation was a de novo event in the proband. All the mutations, four amino acid substitutions, an intragenic deletion, and a 4.7-Mb multigene deletion involved the DNA-binding domain of IKAROS. The proteins bearing missense mutations failed to bind target DNA sequences on EMSA and confocal microscopy; however, they did not inhibit the binding of wild-type IKAROS. Studies in family members showed progressive loss of B cells and serum immunoglobulins. Bone marrow aspirates in two patients had markedly decreased early B-cell precursors, but plasma cells were present. Acute lymphoblastic leukemia developed in 2 of the 29 patients.

CONCLUSIONS

Heterozygous mutations in the transcription factor IKAROS caused an autosomal dominant form of CVID that is associated with a striking decrease in B-cell numbers. (Funded by the National Institutes of Health and others.).

B-cell survival and development controlled by the coordination of NF-κB family members RelB and cRel

Targeted deletion of BAFF causes severe deficiency of splenic B cells. BAFF-R is commonly thought to signal to nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB)-inducing kinase dependent noncanonical NF-κB RelB. However, RelB-deficient mice have normal B-cell numbers. Recent studies showed that BAFF also signals to the canonical NF-κB pathway, and we found that both RelB and cRel are persistently activated, suggesting BAFF signaling coordinates both pathways to ensure robust B-cell development. Indeed, we report now that combined loss of these 2 NF-κB family members leads to impaired BAFF-mediated survival and development in vitro. Although single deletion of RelB and cRel was dispensable for normal B-cell development, double knockout mice displayed an early B-cell developmental blockade and decreased mature B cells. Despite disorganized splenic architecture in Relb(-/-)cRel(-/-) mice, generation of mixed-mouse chimeras established the developmental phenotype to be B-cell intrinsic. Together, our results indicate that BAFF signals coordinate both RelB and cRel activities to ensure survival during peripheral B-cell maturation.

Impact of loss of NF-κB1, NF-κB2 or c-REL on SLE-like autoimmune disease and lymphadenopathy in Fas(lpr/lpr) mutant mice

Defects in apoptosis can cause autoimmune disease. Loss-of-function mutations in the 'death receptor' FAS impair the deletion of autoreactive lymphocytes in the periphery, leading to progressive lymphadenopathy and systemic lupus erythematosus-like autoimmune disease in mice (Fas(lpr/lpr) (mice homozygous for the lymphoproliferation inducing spontaneous mutation)) and humans. The REL/nuclear factor-κB (NF-κB) transcription factors regulate a broad range of immune effector functions and are also implicated in various autoimmune diseases. We generated compound mutant mice to investigate the individual functions of the NF-κB family members NF-κB1, NF-κB2 and c-REL in the various autoimmune pathologies of Fas(lpr/lpr) mutant mice. We show that loss of each of these transcription factors resulted in amelioration of many classical features of autoimmune disease, including hypergammaglobulinaemia, anti-nuclear autoantibodies and autoantibodies against tissue-specific antigens. Remarkably, only c-REL deficiency substantially reduced immune complex-mediated glomerulonephritis and extended the lifespan of Fas(lpr/lpr) mice. Interestingly, compared with the Fas(lpr/lpr) animals, Fas(lpr/lpr)nfkb2(-/-) mice presented with a dramatic acceleration and augmentation of lymphadenopathy that was accompanied by severe lung pathology due to extensive lymphocytic infiltration. The Fas(lpr/lpr)nfkb1(-/-) mice exhibited the combined pathologies caused by defects in FAS-mediated apoptosis and premature ageing due to loss of NF-κB1. These findings demonstrate that different NF-κB family members exert distinct roles in the development of the diverse autoimmune and lymphoproliferative pathologies that arise in Fas(lpr/lpr) mice, and suggest that pharmacological targeting of c-REL should be considered as a strategy for therapeutic intervention in autoimmune diseases.

Natural killer cell biology illuminated by primary immunodeficiency syndromes in humans

Natural killer (NK) cells are innate immune cytotoxic effector cells well known for their role in antiviral immunity and tumor immunosurveillance. In parts, this knowledge stems from rare inherited immunodeficiency disorders in humans that abrogate NK cell function leading to immune impairments, most notably associated with a high susceptibility to viral infections. Phenotypically, these disorders range from deficiencies selectively affecting NK cells to complex general immune defects that affect NK cells but also other immune cell subsets. Moreover, deficiencies may be associated with reduced NK cell numbers or rather impair specific NK cell effector functions. In recent years, genetic defects underlying the various NK cell deficiencies have been uncovered and have triggered investigative efforts to decipher the molecular mechanisms underlying these disorders. Here we review the associations between inherited human diseases and NK cell development as well as function, with a particular focus on defects in NK cell exocytosis and cytotoxicity. Furthermore we outline how reports of diverse genetic defects have shaped our understanding of NK cell biology.