Mild B-cell lymphocytosis in patients with a CARD11 C49Y mutation

An overview of early genetic predictors of IgA deficiency

INTRODUCTION

Inborn errors of immunity (IEIs) refer to a heterogeneous category of diseases with defects in the number and/or function of components of the immune system. Immunoglobulin A (IgA) deficiency is the most prevalent IEI characterized by low serum level of IgA and normal serum levels of IgG and/or IgM. Most of the individuals with IgA deficiency are asymptomatic and are only identified through routine laboratory tests. Others may experience a wide range of clinical features including mucosal infections, allergies, and malignancies as the most important features. IgA deficiency is a multi-complex disease, and the exact pathogenesis of it is still unknown.

AREAS COVERED

This review compiles recent research on genetic and epigenetic factors that may contribute to the development of IgA deficiency. These factors include defects in B-cell development, IgA class switch recombination, synthesis, secretion, and the long-term survival of IgA switched memory B cells and plasma cells.

EXPERT OPINION

A better and more comprehensive understanding of the cellular pathways involved in IgA deficiency could lead to personalized surveillance and potentially curative strategies for affected patients, especially those with severe symptoms.

Allergen-specific B cell responses in oral immunotherapy-induced desensitization, remission, and natural outgrowth in cow's milk allergy

BACKGROUND

Antigen-specific memory B cells play a key role in the induction of desensitization and remission to food allergens in oral immunotherapy and in the development of natural tolerance (NT). Here, we characterized milk allergen Bos d 9-specific B cells in oral allergen-specific immunotherapy (OIT) and in children spontaneously outgrowing cow's milk allergy (CMA) due to NT.

METHODS

Samples from children with CMA who received oral OIT (before, during, and after), children who naturally outgrew CMA (NT), and healthy individuals were received from Stanford biobank. Bos d 9-specific B cells were isolated by flow cytometry and RNA-sequencing was performed. Protein profile of Bos d 9-specific B cells was analyzed by proximity extension assay.

RESULTS

Increased frequencies of circulating milk allergen Bos d 9-specific B cells were observed after OIT and NT. Milk-desensitized subjects showed the partial acquisition of phenotypic features of remission, suggesting that desensitization is an earlier stage of remission. Within these most significantly expressed genes, IL10RA and TGFB3 were highly expressed in desensitized OIT patients. In both the remission and desensitized groups, B cell activation-, Breg cells-, BCR-signaling-, and differentiation-related genes were upregulated. In NT, pathways associated with innate immunity characteristics, development of marginal zone B cells, and a more established suppressor function of B cells prevail that may play a role in long-term tolerance. The analyses of immunoglobulin heavy chain genes in specific B cells demonstrated that IgG2 in desensitization, IgG1, IgA1, IgA2, IgG4, and IgD in remission, and IgD in NT were predominating. Secreted proteins from allergen-specific B cells revealed higher levels of regulatory cytokines, IL-10, and TGF-β after OIT and NT.

CONCLUSION

Allergen-specific B cells are essential elements in regulating food allergy towards remission in OIT-received and naturally resolved individuals.

Lymphoid clonal hematopoiesis: implications for malignancy, immunity, and treatment

Clonal hematopoiesis (CH) is the age-related expansion of hematopoietic stem cell clones caused by the acquisition of somatic point mutations or mosaic chromosomal alterations (mCAs). Clonal hematopoiesis caused by somatic mutations has primarily been associated with increased risk of myeloid malignancies, while mCAs have been associated with increased risk of lymphoid malignancies. A recent study by Niroula et al. challenged this paradigm by finding a distinct subset of somatic mutations and mCAs that are associated with increased risk of lymphoid malignancy. CH driven by these mutations is termed lymphoid clonal hematopoiesis (L-CH). Unlike myeloid clonal hematopoiesis (M-CH), L-CH has the potential to originate at both stem cells and partially or fully differentiated progeny stages of maturation. In this review, we explore the definition of L-CH in the context of lymphocyte maturation and lymphoid malignancy precursor disorders, the evidence for L-CH in late-onset autoimmunity and immunodeficiency, and the development of therapy-related L-CH following chemotherapy or hematopoietic stem cell transplantation.

CARD11 gain-of-function mutation drives cell-autonomous accumulation of PD-1+ ICOShigh activated T cells, T-follicular, T-regulatory and T-follicular regulatory cells

Introduction

Germline CARD11 gain-of-function (GOF) mutations cause B cell Expansion with NF-κB and T cell Anergy (BENTA) disease, whilst somatic GOF CARD11 mutations recur in diffuse large B cell lymphoma (DLBCL) and in up to 30% of the peripheral T cell lymphomas (PTCL) adult T cell leukemia/lymphoma (ATL), cutaneous T cell lymphoma (CTCL) and Sezary Syndrome. Despite their frequent acquisition by PTCL, the T cell-intrinsic effects of CARD11 GOF mutations are poorly understood.

Methods

Here, we studied B and T lymphocytes in mice with a germline Nethyl-N-nitrosourea (ENU)-induced Card11^M365K mutation identical to a mutation identified in DLBCL and modifying a conserved region of the CARD11 coiled-coil domain recurrently mutated in DLBCL and PTCL.

Results and discussion

Our results demonstrate that CARD11.M365K is a GOF protein that increases B and T lymphocyte activation and proliferation following antigen receptor stimulation. Germline Card11^M365K mutation was insufficient alone to cause B or T-lymphoma, but increased accumulation of germinal center (GC) B cells in unimmunized and immunized mice. Card11^M365K mutation caused cell-intrinsic over-accumulation of activated T cells, T regulatory (T_REG), T follicular (T_FH) and T follicular regulatory (T_FR) cells expressing increased levels of ICOS, CTLA-4 and PD-1 checkpoint molecules. Our results reveal CARD11 as an important, cell-autonomous positive regulator of T_FH, T_REG and T_FR cells. They highlight T cell-intrinsic effects of a GOF mutation in the CARD11 gene, which is recurrently mutated in T cell malignancies that are often aggressive and associated with variable clinical outcomes.

A familial case of B-cell expansion with NF-κB and T-cell anergy caused by a G123D heterozygous missense mutation in the CARD11 gene

B-cell expansion with NF-κB (nuclear factor-kappa B) and T-cell anergy (BENTA) is a rare congenital lymphoproliferative disorder caused by germline gain-of-function mutations in the CARD11 gene. We herein report a familial case of BENTA due to a G123D heterozygous missense mutation in CARD11 inherited by a male from his mother. The mother's clinical course was characterized by polyarthritis and encephalitis in young adulthood, suggesting that autoimmune-like manifestations can occur in BENTA. The B-cell lymphocytosis and splenomegaly seen in her child have been managed with prednisolone and tacrolimus. Further investigations are needed to evaluate the efficacy of calcineurin inhibitors for BENTA.

CARD11 mutation and HBZ expression induce lymphoproliferative disease and adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATL) is caused by human T-cell leukemia virus type 1 (HTLV-1). In addition to HTLV-1 bZIP factor (HBZ), a leukemogenic antisense transcript of HTLV-1, abnormalities of genes involved in TCR-NF-κB signaling, such as CARD11, are detected in about 90% of patients. Utilizing mice expressing CD4⁺ T cell-specific CARD11(E626K) and/or CD4⁺ T cell-specific HBZ, namely CARD11(E626K)^CD4-Cre mice, HBZ transgenic (Tg) mice, and CARD11(E626K)^CD4-Cre;HBZ Tg double transgenic mice, we clarify these genes' pathogenetic effects. CARD11(E626K)^CD4-Cre and HBZ Tg mice exhibit lymphocytic invasion to many organs, including the lungs, and double transgenic mice develop lymphoproliferative disease and increase CD4⁺ T cells in vivo. CARD11(E626K) and HBZ cooperatively activate the non-canonical NF-κB pathway, IRF4 targets, BATF3/IRF4/HBZ transcriptional network, MYC targets, and E2F targets. Most KEGG and HALLMARK gene sets enriched in acute-type ATL are also enriched in double transgenic mice, indicating that these genes cooperatively contribute to ATL development.

Expanding spectrum, intrafamilial diversity, and therapeutic challenges from 15 patients with heterozygous CARD11-associated diseases: A single center experience

CARD11-associated diseases are monogenic inborn errors of immunity involving immunodeficiency, predisposition to malignancy and immune dysregulation such as lymphoproliferation, inflammation, atopic and autoimmune manifestations. Defects in CARD11 can present as mutations that confer a complete or a partial loss of function (LOF) or contrarily, a gain of function (GOF) of the affected gene product. We report clinical characteristics, immunophenotypes and genotypes of 15 patients from our center presenting with CARD11-associated diseases. Index cases are pediatric patients followed in our immunology division who had access to next generation sequencing studies. Variant significance was defined by functional analysis in cultured cells transfected with a wild type and/or with mutated hCARD11 constructs. Cytoplasmic aggregation of CARD11 products was evaluated by immunofluorescence. Nine index patients with 9 unique heterozygous CARD11 variants were identified. At the time of the identification, 7 variants previously unreported required functional validation. Altogether, four variants showed a GOF effect as well a spontaneous aggregation in the cytoplasm, leading to B cell expansion with NF-κB and T cell anergy (BENTA) diagnosis. Additional four variants showing a LOF activity were considered as causative of CARD11-associated atopy with dominant interference of NF-kB signaling (CADINS). The remaining variant exhibited a neutral functional assay excluding its carrier from further analysis. Family segregation studies expanded to 15 individuals the number of patients presenting CARD11-associated disease. A thorough clinical, immunophenotypical, and therapeutic management evaluation was performed on these patients (5 BENTA and 10 CADINS). A remarkable variability of disease expression was clearly noted among BENTA as well as in CADINS patients, even within multiplex families. Identification of novel CARD11 variants required functional studies to validate their pathogenic activity. In our cohort BENTA phenotype exhibited a more severe and expanded clinical spectrum than previously reported, e.g., severe hematological and extra hematological autoimmunity and 3 fatal outcomes. The growing number of patients with dysmorphic facial features strengthen the inclusion of extra-immune characteristics as part of the CADINS spectrum. CARD11-associated diseases represent a challenging group of disorders from the diagnostic and therapeutic standpoint, especially BENTA cases that can undergo a more severe progression than previously described.

A novel CARD11 germline mutation in a Chinese patient of B cell expansion with NF-κB and T cell anergy (BENTA) and literature review

Germline gain-of-function (GOF) mutations in the CARD11 gene lead to a rare primary immunodeficiency disease known as B cell expansion with NF-κB and T cell anergy (BENTA). Affected patients present with a polyclonal expansion of B cells, lymphadenopathy, and splenomegaly. Herein, we report a novel germline in-frame three base-pair deletion (c.1030_1032del, p.K344del) in the CARD11 gene in a patient with atypical BENTA, presenting with a recurrent fever and B cell lymphocytosis. This mutation was inherited from his mother, who is clinically asymptomatic and had a recurrent respiratory tract infection in her childhood. In vitro functional analysis demonstrated that this variant decreased the expression level of the CARD11 protein and activated the NF-κB signal pathway, leading to a higher expression of several NF-κB target gene transcripts in HCT116 cells transfected with mutant CARD11 (K344del-CARD11) as revealed by RNA sequencing analysis. To our knowledge, only 23 BENTA patients have been identified and carried seven distinct GOF mutations in CARD11. The clinical manifestations of patients are highly heterogeneous and there was no significant correlation between genotype and phenotype. In summary, we identified a novel in-frame three base-pair deletion that may be responsible for the pathogenesis of atypical BENTA in a Chinese family. Our study expands the mutational spectrum of the CARD11 gene and may be helpful in the understanding of diseases caused by CARD11 mutations and the clinical management of BENTA.

Mechanistic impact of oligomer poisoning by dominant-negative CARD11 variants

The CARD11 scaffold controls antigen receptor signaling to NF-κB, JNK, and mTOR. Three classes of germline mutations in CARD11 cause Primary Immunodeficiency, including homozygous loss-of-function (LOF) mutations in CARD11 deficiency, heterozygous gain-of-function (GOF) mutations in BENTA disease, and heterozygous dominant-negative LOF mutations in CADINS. Here, we characterize LOF CARD11 mutants with a range of dominant-negative activities to identify the mechanistic properties that cause these variants to exert dominant effects when heterozygous. We find that strong dominant negatives can poison signaling from mixed wild-type:mutant oligomers at two steps in the CARD11 signaling cycle, at the Opening Step and at the Cofactor Association Step. Our findings provide evidence that CARD11 oligomer subunits cooperate in at least two steps during antigen receptor signaling and reveal how different LOF mutations in the same oligomeric signaling hub may cause disease with different inheritance patterns.

Monogenic Adult-Onset Inborn Errors of Immunity

Inborn errors of immunity (IEI) are a heterogenous group of disorders driven by genetic defects that functionally impact the development and/or function of the innate and/or adaptive immune system. The majority of these disorders are thought to have polygenic background. However, the use of next-generation sequencing in patients with IEI has led to an increasing identification of monogenic causes, unravelling the exact pathophysiology of the disease and allowing the development of more targeted treatments. Monogenic IEI are not only seen in a pediatric population but also in adulthood, either due to the lack of awareness preventing childhood diagnosis or due to a delayed onset where (epi)genetic or environmental factors can play a role. In this review, we discuss the mechanisms accounting for adult-onset presentations and provide an overview of monogenic causes associated with adult-onset IEI.

Identification of a genetic signature enriching for response to ibrutinib in relapsed/refractory follicular lymphoma in the DAWN phase 2 trial

Background

The single‐arm DAWN trial (NCT01779791) of ibrutinib monotherapy in patients with relapsed/refractory follicular lymphoma (FL) showed an overall response rate (ORR) of 20.9% and a median response duration of 19.4 months. This biomarker analysis of the DAWN dataset sought to determine genetic classifiers for prediction of response to ibrutinib treatment.

Methods

Whole exome sequencing was performed on baseline tumor samples. Potential germline variants were excluded; a custom set of 1216 cancer‐related genes was examined. Responder‐ versus nonresponder‐associated variants were identified using Fisher's exact test. Classifiers with increasing numbers of genes were created using a greedy algorithm that repeatedly selected genes, adding the most nonresponders to the existing “predicted nonresponders” set and were evaluated with 10‐fold cross‐validation.

Results

Exome data were generated from 88 patient samples and 13,554 somatic mutation variants were inferred. Response data were available for 83 patients (17 responders, 66 nonresponders). Each sample showed 100 to >500 mutated genes, with greater variance across nonresponders. The overall variant pattern was consistent with previous FL studies; 75 genes had mutations in >10% of patients, including genes previously reported as associated with FL. Univariate analysis yielded responder‐associated genes FANCA, HISTH1B, ANXA6, BTG1, and PARP10, highlighting the importance of functions outside of B‐cell receptor signaling, including epigenetic processes, DNA damage repair, cell cycle/proliferation, and cell motility/invasiveness. While nonresponder‐associated genes included well‐known TP53 and CARD11, genetic classifiers developed using nonresponder‐associated genes included ATP6AP1, EP400, ARID1A, SOCS1, and TBL1XR1, suggesting resistance to ibrutinib may be related to broad biological functions connected to epigenetic modification, telomere maintenance, and cancer‐associated signaling pathways (mTOR, JAK/STAT, NF‐κB).

Conclusion

The results from univariate and genetic classifier analyses provide insights into genes associated with response or resistance to ibrutinib in FL and identify a classifier developed using nonresponder‐associated genes, which warrants further investigation.

Trial registration: NCT01779791.

Hyper-IgE syndrome, 2021 update

Clinically and pathologically, the patients with hyper-IgE syndrome present similar skin manifestations to common atopic dermatitis. The original hyper-IgE syndrome is characterized by diminished inflammatory response, in combination with Staphylococcus aureus skin abscess and pneumonia followed by pneumatocele formation. These immunological manifestations are frequently associated with skeletal and connective tissue abnormalities. We previously identified that major causal variants of the hyper-IgE syndrome are dominant negative variants in the STAT3. In addition to the identification of new causative variants for the disorders similar to the original hyper-IgE syndrome, causative variants for new types of hyper-IgE syndrome centered only on atopy, high serum IgE levels, and susceptibility to infection, but not associated with diminished inflammatory response, pneumatocele formation, and connective tissue manifestations, have been identified. Recent discovery identified a novel zinc finger protein that regulates STAT3 transcription. Investigation of IL6ST variants disclosed that IL6ST/IL6R cytokine receptor plays a crucial role for the signal transduction upstream of STAT3 in the pathogenesis of the original hyper-IgE syndrome. Even if the same IL6ST variants are used for the signal transduction of IL-6 family cytokines, the signaling defect is more severe in IL-6/IL-11 and milder in LIF. The fact that the non-immune manifestations of the gain-of-function mutations of TGFBR1 and TGFBR2 are similar to the those of dominant negative mutations of STAT3 provide a clue to elucidate molecular mechanisms of non-immune manifestations of hyper-IgE syndrome. Research on this hereditary atopic syndrome is being actively conducted to elucidate the molecular mechanisms and to develop new therapeutic approaches.

Identification and Characterization of a Germline Mutation in CARD11 From a Chinese Case of B Cell Expansion With NF-κB and T Cell Anergy

B cell expansion with NF-κB and T cell anergy (BENTA) is a rare primary immunodeficiency disorder caused by gain-of-function (GOF) mutations in the CARD11 gene. Affected patients present with persistent B cell lymphocytosis in early childhood paired with lymphadenopathy and splenomegaly. Until now only six activating mutations from 14 patients have been reported in CARD11. Here we report a patient from China with polyclonal B cell lymphocytosis and frequent infections in early life. A heterozygous mutation (c.377G>A, G126D) in exon 5 of CARD11 gene (NM_032415) was identified by whole exome sequencing. In vitro functional studies showed that the G126D mutation is associated with increased expression of CARD11 and NF-κB activation in Hela cells. Flow cytometry analysis indicated NK cell activity and CD107a degranulation of the patient were decreased. RNA sequencing analysis showed that a number of genes in NF-κB pathway increased while those involved in NK cell activity and degranulation were down-regulated. In summary, our work identified a de novo germline GOF mutation in CARD11 with functional evidence of BENTA.

NF-κB: At the Borders of Autoimmunity and Inflammation

The transcription factor NF-κB regulates multiple aspects of innate and adaptive immune functions and serves as a pivotal mediator of inflammatory response. In the first part of this review, we discuss the NF-κB inducers, signaling pathways, and regulators involved in immune homeostasis as well as detail the importance of post-translational regulation by ubiquitination in NF-κB function. We also indicate the stages of central and peripheral tolerance where NF-κB plays a fundamental role. With respect to central tolerance, we detail how NF-κB regulates medullary thymic epithelial cell (mTEC) development, homeostasis, and function. Moreover, we elaborate on its role in the migration of double-positive (DP) thymocytes from the thymic cortex to the medulla. With respect to peripheral tolerance, we outline how NF-κB contributes to the inactivation and destruction of autoreactive T and B lymphocytes as well as the differentiation of CD4⁺-T cell subsets that are implicated in immune tolerance. In the latter half of the review, we describe the contribution of NF-κB to the pathogenesis of autoimmunity and autoinflammation. The recent discovery of mutations involving components of the pathway has both deepened our understanding of autoimmune disease and informed new therapeutic approaches to treat these illnesses.

Mechanistic understanding of the combined immunodeficiency in complete human CARD11 deficiency

BACKGROUND

Germline pathogenic variants impairing the caspase recruitment domain family member 11 (CARD11)-B cell chronic lymphocytic leukemia/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) (CBM) complex are associated with diverse human diseases including combined immunodeficiency (CID), atopy, and lymphoproliferation. However, the impact of CARD11 deficiency on human B-cell development, signaling, and function is incompletely understood.

OBJECTIVES

This study sought to determine the cellular, immunological, and biochemical basis of disease for 2 unrelated patients who presented with profound CID associated with viral and fungal respiratory infections, interstitial lung disease, and severe colitis.

METHODS

Patients underwent next-generation sequencing, immunophenotyping by flow cytometry, signaling assays by immunoblot, and transcriptome profiling by RNA-sequencing.

RESULTS

Both patients carried identical novel pathogenic biallelic loss-of-function variants in CARD11 (c.2509C>T; p.Arg837∗) leading to undetectable protein expression. This variant prevented CBM complex formation, severely impairing the activation of nuclear factor-κB, c-Jun N-terminal kinase, and MALT1 paracaspase activity in B and T cells. This functional defect resulted in a developmental block in B cells at the naive and type 1 transitional B-cell stage and impaired circulating T follicular helper cell (cT_FH) development, which was associated with impaired antibody responses and absent germinal center structures on lymph node histology. Transcriptomics indicated that CARD11-dependent signaling is essential for immune signaling pathways involved in the development of these cells. Both patients underwent hematopoietic stem cell transplantations, which led to functional normalization.

CONCLUSIONS

Complete human CARD11 deficiency causes profound CID by impairing naive/type 1 B-cell and cT_FH cell development and abolishing activation of MALT1 paracaspase, NF-κB, and JNK activity. Hematopoietic stem cell transplantation functionally restores impaired signaling pathways.

Inborn errors of immunity with atopic phenotypes: A practical guide for allergists

Inborn errors of immunity (IEI) are a heterogeneous group of disorders, mainly resulting from mutations in genes associated with immunoregulation and immune host defense. These disorders are characterized by different combinations of recurrent infections, autoimmunity, inflammatory manifestations, lymphoproliferation, and malignancy. Interestingly, it has been increasingly observed that common allergic symptoms also can represent the expression of an underlying immunodeficiency and/or immune dysregulation.

Very high IgE levels, peripheral or organ-specific hypereosinophilia, usually combined with a variety of atopic symptoms, may sometimes be the epiphenomenon of a monogenic disease. Therefore, allergists should be aware that severe and/or therapy-resistant atopic disorders might be the main clinical phenotype of some IEI. This could pave the way to target therapies, leading to better quality of life and improved survival in affected patients.

Targeting NF-κB pathway for the therapy of diseases: mechanism and clinical study

NF-κB pathway consists of canonical and non-canonical pathways. The canonical NF-κB is activated by various stimuli, transducing a quick but transient transcriptional activity, to regulate the expression of various proinflammatory genes and also serve as the critical mediator for inflammatory response. Meanwhile, the activation of the non-canonical NF-κB pathway occurs through a handful of TNF receptor superfamily members. Since the activation of this pathway involves protein synthesis, the kinetics of non-canonical NF-κB activation is slow but persistent, in concordance with its biological functions in the development of immune cell and lymphoid organ, immune homeostasis and immune response. The activation of the canonical and non-canonical NF-κB pathway is tightly controlled, highlighting the vital roles of ubiquitination in these pathways. Emerging studies indicate that dysregulated NF-κB activity causes inflammation-related diseases as well as cancers, and NF-κB has been long proposed as the potential target for therapy of diseases. This review attempts to summarize our current knowledge and updates on the mechanisms of NF-κB pathway regulation and the potential therapeutic application of inhibition of NF-κB signaling in cancer and inflammatory diseases.

Germline CBM-opathies: From immunodeficiency to atopy

Caspase recruitment domain (CARD) protein-B cell CLL/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) [CBM] complexes are critical signaling adaptors that facilitate immune and inflammatory responses downstream of both cell surface and intracellular receptors. Germline mutations that alter the function of members of this complex (termed CBM-opathies) cause a broad array of clinical phenotypes, ranging from profound combined immunodeficiency to B-cell lymphocytosis. With an increasing number of patients being described in recent years, the clinical spectrum of diseases associated with CBM-opathies is rapidly expanding and becoming unexpectedly heterogeneous. Here we review major discoveries that have shaped our understanding of CBM complex biology, and we provide an overview of the clinical presentation, diagnostic approach, and treatment options for those carrying germline mutations affecting CARD9, CARD11, CARD14, BCL10, and MALT1.

A Novel, Heterozygous Three Base-Pair Deletion in CARD11 Results in B Cell Expansion with NF-κB and T Cell Anergy Disease

Germline gain-of-function mutations in CARD11 lead to the primary immunodeficiency, B cell expansion with NF-κB, and T cell anergy (BENTA). Herein, we report the case of a girl, presenting at 2 years of age with lymphocytosis and splenomegaly in whom a novel, in-frame, three base pair deletion in CARD11 was identified resulting in the deletion of a single lysine residue (K215del) from the coiled-coil domain. In vitro functional assays demonstrated that this variant leads to a subtle increase in baseline NF-κB signaling and impaired proliferative responses following T cell receptor and mitogenic stimulation. Previously reported immunological defects associated with BENTA appear mild in our patient who is now 6 years of age; a B cell lymphocytosis and susceptibility to upper respiratory tract infections persist; however, she has broad, sustained responses to protein-polysaccharide conjugate vaccines and displays normal proliferative responses to ex vivo T cell stimulation.

Coordinated regulation of scaffold opening and enzymatic activity during CARD11 signaling

The activation of key signaling pathways downstream of antigen receptor engagement is critically required for normal lymphocyte activation during the adaptive immune response. CARD11 is a multidomain signaling scaffold protein required for antigen receptor signaling to NF-κB, c-Jun N-terminal kinase, and mTOR. Germline mutations in the CARD11 gene result in at least four types of primary immunodeficiency, and somatic CARD11 gain-of-function mutations drive constitutive NF-κB activity in diffuse large B cell lymphoma and other lymphoid cancers. In response to antigen receptor triggering, CARD11 transitions from a closed, inactive state to an open, active scaffold that recruits multiple signaling partners into a complex to relay downstream signaling. However, how this signal-induced CARD11 conversion occurs remains poorly understood. Here we investigate the role of Inducible Element 1 (IE1), a short regulatory element in the CARD11 Inhibitory Domain, in the CARD11 signaling cycle. We find that IE1 controls the signal-dependent Opening Step that makes CARD11 accessible to the binding of cofactors, including Bcl10, MALT1, and the HOIP catalytic subunit of the linear ubiquitin chain assembly complex. Surprisingly, we find that IE1 is also required at an independent step for the maximal activation of HOIP and MALT1 enzymatic activity after cofactor recruitment to CARD11. This role of IE1 reveals that there is an Enzymatic Activation Step in the CARD11 signaling cycle that is distinct from the Cofactor Association Step. Our results indicate that CARD11 has evolved to actively coordinate scaffold opening and the induction of enzymatic activity among recruited cofactors during antigen receptor signaling.

MALT1 Proteolytic Activity Suppresses Autoimmunity in a T Cell Intrinsic Manner

MALT1 is a central signaling component in innate and adaptive immunity by regulating NF-κB and other key signaling pathways in different cell types. Activities of MALT1 are mediated by its scaffold and protease functions. Because of its role in lymphocyte activation and proliferation, inhibition of MALT1 proteolytic activity is of high interest for therapeutic targeting in autoimmunity and certain lymphomas. However, recent studies showing that Malt1 protease-dead knock-in (Malt1-PD) mice suffer from autoimmune disease have somewhat tempered the initial enthusiasm. Although it has been proposed that an imbalance between immune suppressive regulatory T cells (Tregs) and activated effector CD4+ T cells plays a key role in the autoimmune phenotype of Malt1-PD mice, the specific contribution of MALT1 proteolytic activity in T cells remains unclear. Using T cell-conditional Malt1 protease-dead knock-in (Malt1-PDT) mice, we here demonstrate that MALT1 has a T cell-intrinsic role in regulating the homeostasis and function of thymic and peripheral T cells. T cell-specific ablation of MALT1 proteolytic activity phenocopies mice in which MALT1 proteolytic activity has been genetically inactivated in all cell types. The Malt1-PDT mice have a reduced number of Tregs in the thymus and periphery, although the effect in the periphery is less pronounced compared to full-body Malt1-PD mice, indicating that also other cell types may promote Treg induction in a MALT1 protease-dependent manner. Despite the difference in peripheral Treg number, both T cell-specific and full-body Malt1-PD mice develop ataxia and multi-organ inflammation to a similar extent. Furthermore, reconstitution of the full-body Malt1-PD mice with T cell-specific expression of wild-type human MALT1 eliminated all signs of autoimmunity. Together, these findings establish an important T cell-intrinsic role of MALT1 proteolytic activity in the suppression of autoimmune responses.

Rare copy number variants in the genome of Chinese female children and adolescents with Turner syndrome

Turner syndrome (TS) is a congenital disease caused by complete or partial loss of one X chromosome. Low bone mineral status is a major phenotypic characteristic of TS that can not be fully explained by X chromosome loss, suggesting other autosomal-linked mutations may also exist. Therefore, the present study aimed to detect potential genetic mutations in TS through examination of copy number variation (CNV). Seventeen patients with TS and 15 healthy volunteer girls were recruited. Array-based comparative genomic hybridization (a-CGH) was performed on whole blood genomic DNA (gDMA) from the 17 TS patients and 15 healthy volunteer girls to identify potential CNVs. The abnormal CNV of one identified gene (CARD11) was verified by quantitative PCR. All cases diagnosed had TS based on genotype examination and physical characteristics, including short stature and premature ovarian failure. Three rare CNVs, located individually at 7p22.3, 7p22.2, and Xp22.33, where six genes (TTYH3, AMZ1, GNA12, BC038729, CARD11, and SHOX (stature homeobox)) are located, were found in TS patients. Quantitative PCR confirmed the CNV of CARD11 in the genome of TS patients. Our results indicate that CARD11 gene is one of the mutated genes involved in TS disease. However, this CNV is rare and its contribution to TS phenotype requires further study.

Mechanisms of Regulated and Dysregulated CARD11 Signaling in Adaptive Immunity and Disease

CARD11 functions as a key signaling scaffold that controls antigen-induced lymphocyte activation during the adaptive immune response. Somatic mutations in CARD11 are frequently found in Non-Hodgkin lymphoma, and at least three classes of germline CARD11 mutations have been described as the basis for primary immunodeficiency. In this review, we summarize our current understanding of how CARD11 signals, how its activity is regulated, and how mutations bypass normal regulation to cause disease.

The CBM-opathies-A Rapidly Expanding Spectrum of Human Inborn Errors of Immunity Caused by Mutations in the CARD11-BCL10-MALT1 Complex

The caspase recruitment domain family member 11 (CARD11 or CARMA1)-B cell CLL/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) [CBM] signalosome complex serves as a molecular bridge between cell surface antigen receptor signaling and the activation of the NF-κB, JNK, and mTORC1 signaling axes. This positions the CBM complex as a critical regulator of lymphocyte activation, proliferation, survival, and metabolism. Inborn errors in each of the CBM components have now been linked to a diverse group of human primary immunodeficiency diseases termed "CBM-opathies." Clinical manifestations range from severe combined immunodeficiency to selective B cell lymphocytosis, atopic disease, and specific humoral defects. This surprisingly broad spectrum of phenotypes underscores the importance of "tuning" CBM signaling to preserve immune homeostasis. Here, we review the distinct clinical and immunological phenotypes associated with human CBM complex mutations and introduce new avenues for targeted therapeutic intervention.

Holding All the CARDs: How MALT1 Controls CARMA/CARD-Dependent Signaling

The scaffold proteins CARMA1-3 (encoded by the genes CARD11, -14 and -10) and CARD9 play major roles in signaling downstream of receptors with immunoreceptor tyrosine activation motifs (ITAMs), G-protein coupled receptors (GPCR) and receptor tyrosine kinases (RTK). These receptors trigger the formation of oligomeric CARMA/CARD-BCL10-MALT1 (CBM) complexes via kinases of the PKC family. The CBM in turn regulates gene expression by the activation of NF-κB and AP-1 transcription factors and controls transcript stability. The paracaspase MALT1 is the only CBM component having an enzymatic (proteolytic) activity and has therefore recently gained attention as a potential drug target. Here we review recent advances in the understanding of the molecular function of the protease MALT1 and summarize how MALT1 scaffold and protease function contribute to the transmission of CBM signals. Finally, we will highlight how dysregulation of MALT1 function can cause pathologies such as immunodeficiency, autoimmunity, psoriasis, and cancer.

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.

Clinical, Immunological, and Molecular Findings in Four Cases of B Cell Expansion With NF-κB and T Cell Anergy Disease for the First Time From India

B cell expansion with NF-κB and T cell anergy (BENTA) is a rare primary immunodeficiency disorder caused by mutations in the CARD11 gene and results in constitutive NF-κB activation in B and T cells. Affected patients present with polyclonal expansion of B cells at an early age with splenomegaly, lymphadenopathy, and mild autoimmunity. Here, we discuss four BENTA cases with unusual clinical manifestations not previously reported. All patients showed previously reported gain-of-function mutations (G123S, G123D, and C49Y) in the CARD11 gene. Severe autoimmune manifestations were noted for the first time in all our patients.

"Immune TOR-opathies," a Novel Disease Entity in Clinical Immunology

Primary immunodeficiencies (PIDs) represent a group of mostly monogenic disorders caused by loss- or gain-of-function mutations in over 340 known genes that lead to abnormalities in the development and/or the function of the immune system. However, mutations in different genes can affect the same cell-signaling pathway and result in overlapping clinical phenotypes. In particular, mutations in the genes encoding for members of the phosphoinositide3-kinase (PI3K)/AKT/mTOR/S6 kinase (S6K) signaling cascade or for molecules interacting with this pathway have been associated with different PIDs that are often characterized by the coexistence of both immune deficiency and autoimmunity. The serine/threonine kinase mechanistic/mammalian target of rapamycin (mTOR), which acts downstream of PI3K and AKT, is emerging as a key regulator of immune responses. It integrates a variety of signals from the microenvironment to control cell growth, proliferation, and metabolism. mTOR plays therefore a central role in the regulation of immune cells’ differentiation and functions. Here, we review the different PIDs that share an impairment of the PI3K/AKT/mTOR/S6K pathway and we propose to name them “immune TOR-opathies” by analogy with a group of neurological disorders that has been originally defined by PB Crino and that are due to aberrant mTOR signaling (1). A better understanding of the role played by this complex intracellular cascade in the pathophysiology of “immune TOR-opathies” is crucial to develop targeted therapies.

Impaired Control of Epstein-Barr Virus Infection in B-Cell Expansion with NF-κB and T-Cell Anergy Disease

B-cell expansion with NF-κB and T-cell anergy (BENTA) disease is a B-cell-specific lymphoproliferative disorder caused by germline gain-of-function mutations in CARD11. These mutations force the CARD11 scaffold into an open conformation capable of stimulating constitutive NF-κB activation in lymphocytes, without requiring antigen receptor engagement. Many BENTA patients also suffer from recurrent infections, with 7 out of 16 patients exhibiting chronic, low-grade Epstein–Barr virus (EBV) viremia. In this mini-review, we discuss EBV infection in the pathogenesis and clinical management of BENTA disease, and speculate on mechanisms that could explain inadequate control of viral infection in BENTA patients.

Assembly mechanism of the CARMA1-BCL10-MALT1-TRAF6 signalosome

The CARMA1-BCL10-MALT1 (CBM) signalosome is a central mediator of T cell receptor and B cell receptor-induced NF-κB signaling that regulates multiple lymphocyte functions. While caspase-recruitment domain (CARD) membrane-associated guanylate kinase (MAGUK) protein 1 (CARMA1) nucleates B cell lymphoma 10 (BCL10) filament formation through interactions between CARDs, mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a paracaspase with structural similarity to caspases, which recruits TNF receptor-associated factor 6 (TRAF6) for K63-linked polyubiquitination. Here we present cryo-electron microscopy (cryo-EM) structure of the BCL10 CARD filament at 4.0-Å resolution. The structure redefines CARD-CARD interactions compared with the previous EM structure determined from a negatively stained sample. Surprisingly, time-lapse confocal imaging shows that BCL10 polymerizes in a unidirectional manner. CARMA1, the BCL10 nucleator, serves as a hub for formation of star-shaped filamentous networks of BCL10 and significantly decreases the lag period of BCL10 polymerization. Cooperative MALT1 interaction with BCL10 filaments observed under EM suggests immediate dimerization of MALT1 in the BCL10 filamentous scaffold. In addition, TRAF6 cooperatively decorates CBM filaments to form higher-order assemblies, likely resulting in all-or-none activation of the downstream pathway. Collectively, these data reveal biophysical mechanisms in the assembly of the CARMA1-BCL10-MALT1-TRAF6 complex for signal transduction.

Role of the CARMA1/BCL10/MALT1 complex in lymphoid malignancies

Purpose of review

The CARMA1/BCL10/MALT1 (CBM) complex is a multimeric signaling complex controlling several important aspects of lymphocyte activation. Gain-of-function mutations in the genes encoding CBM proteins or their upstream regulators are associated with lymphoid malignancies, whereas loss-of-function mutations lead to immunodeficiency. This review reports on recent findings advancing our understanding of how CBM proteins contribute to malignant and nonmalignant hematological diseases in humans.

Recent findings

Somatic gain-of-function mutations of CARMA1 (also known as CARD11), originally described for patients with diffuse large B-cell lymphoma, have recently been identified in patients with acute T-cell leukemia/lymphoma or Sézary syndrome, and in patients with a B-cell lymphoproliferative disorder known as BENTA. Loss-of-function mutations of CARMA1 and MALT1, on the other hand, have been reported to underlie human immunodeficiency. Lately, it has become clear that CBM-dependent signaling promotes lymphomagenesis not only via NF-κB activation, but also via the AP-1 family of transcription factors. The identification of new substrates of the protease MALT1 and the characterization of mice expressing catalytically inactive MALT1 have deepened our understanding of how the CBM complex controls lymphocyte proliferation through promoting MALT1's protease activity.

Summary

The discovery of CARMA1 gain-of-function mutations in T-cell malignancies and BENTA patients, as well as the association of CARMA1 and MALT1 mutations with human immunodeficiency highlight the importance of CBM proteins in the regulation of lymphocyte functions, and suggest that the protease activity of MALT1 might be targeted to treat specific lymphoid malignancies.

Intrinsic Plasma Cell Differentiation Defects in B Cell Expansion with NF-κB and T Cell Anergy Patient B Cells

B cell Expansion with NF-κB and T cell Anergy (BENTA) disease is a novel B cell lymphoproliferative disorder caused by germline, gain-of-function mutations in the lymphocyte scaffolding protein CARD11, which drives constitutive NF-κB signaling. Despite dramatic polyclonal expansion of naive and immature B cells, BENTA patients also present with signs of primary immunodeficiency, including markedly reduced percentages of class-switched/memory B cells and poor humoral responses to certain vaccines. Using purified naive B cells from our BENTA patient cohort, here we show that BENTA B cells exhibit intrinsic defects in B cell differentiation. Despite a profound in vitro survival advantage relative to normal donor B cells, BENTA patient B cells were severely impaired in their ability to differentiate into short-lived IgD^loCD38^hi plasmablasts or CD138⁺ long-lived plasma cells in response to various stimuli. These defects corresponded with diminished IgG antibody production and correlated with poor induction of specific genes required for plasma cell commitment. These findings provide important mechanistic clues that help explain both B cell lymphocytosis and humoral immunodeficiency in BENTA disease.

Lymphocyte signaling and activation by the CARMA1-BCL10-MALT1 signalosome

The CARMA1-BCL10-MALT1 (CBM) signalosome triggers canonical NF-κB signaling and lymphocyte activation upon antigen-receptor stimulation. Genetic studies in mice and the analysis of human immune pathologies unveiled a critical role of the CBM complex in adaptive immune responses. Great progress has been made in elucidating the fundamental mechanisms that dictate CBM assembly and disassembly. By bridging proximal antigen-receptor signaling to downstream signaling pathways, the CBM complex exerts a crucial scaffolding function. Moreover, the MALT1 subunit confers a unique proteolytic activity that is key for lymphocyte activation. Deregulated 'chronic' CBM signaling drives constitutive NF-κB signaling and MALT1 activation, which contribute to the development of autoimmune and inflammatory diseases as well as lymphomagenesis. Thus, the processes that govern CBM activation and function are promising targets for the treatment of immune disorders. Here, we summarize the current knowledge on the functions and mechanisms of CBM signaling in lymphocytes and how CBM deregulations contribute to aberrant signaling in malignant lymphomas.

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.

Advances in clinical immunology in 2015

Advances in clinical immunology in the past year included the report of practice parameters for the diagnosis and management of primary immunodeficiencies to guide the clinician in the approach to these relatively uncommon disorders. We have learned of new gene defects causing immunodeficiency and of new phenotypes expanding the spectrum of conditions caused by genetic mutations such as a specific regulator of telomere elongation (RTEL1) mutation causing isolated natural killer cell deficiency and mutations in ras-associated RAB (RAB27) resulting in immunodeficiency without albinism. Advances in diagnosis included the increasing use of whole-exome sequencing to identify gene defects and the measurement of serum free light chains to identify secondary hypogammaglobulinemias. For several primary immunodeficiencies, improved outcomes have been reported after definitive therapy with hematopoietic stem cell transplantation and gene therapy.

Gain-of-function mutations and immunodeficiency: at a loss for proper tuning of lymphocyte signaling

PURPOSE OF REVIEW

To present recent advances in the discovery and characterization of new immunodeficiency disorders linked to gain-of-function (GOF) mutations in immune signaling molecules. (Figure is included in full-text article.)

RECENT FINDINGS

In the past 2 years, extensive cellular and molecular studies have illuminated the root causes of pathogenesis for several new monogenic primary immunodeficiency disorders (PIDs) linked to GOF mutations in signaling molecules. Here we discuss on two disorders (BENTA and APDS/PASLI) featuring shared clinical presentation (e.g. lymphoproliferation, selective antibody deficiencies, recurrent sinopulmonary infections). These findings highlight an emerging theme: both loss-of-function and gain-of-function mutations in key molecules can disrupt finely tuned immunoreceptor signaling modalities, resulting in the dysregulation of lymphocyte differentiation and impaired adaptive immunity.

SUMMARY

Continued research on the molecular pathogenesis of PIDs defined by hyperactive signaling molecules will better distinguish these and related disorders, and pinpoint tailored therapeutic interventions for 'retuning' the immune response in these patients.

Cooperative Control of Caspase Recruitment Domain-containing Protein 11 (CARD11) Signaling by an Unusual Array of Redundant Repressive Elements

Several classes of signaling proteins contain autoinhibitory domains that prevent unwarranted signaling and coordinate the induction of activity in response to external cues. CARD11, a scaffold protein critical for antigen receptor signaling to NF-κB, undergoes autoregulation by a poorly understood inhibitory domain (ID), which keeps CARD11 inactive in the absence of receptor triggering through inhibitory intramolecular interactions. This autoinhibitory strategy makes CARD11 highly susceptible to gain-of-function mutations that are frequently observed in diffuse large B cell lymphoma (DLBCL) and that disrupt ID-mediated autoinhibition, leading to constitutive NF-κB activity, which can promote lymphoma proliferation. Although DLBCL-associated CARD11 mutations in the caspase recruitment domain (CARD), LATCH domain, and coiled coil have been shown to disrupt intramolecular ID binding, surprisingly, no gain-of-function mutations in the ID itself have been reported and validated. In this study, we solve this paradox and report that the CARD11 ID contains an unusual array of four repressive elements that function cooperatively with redundancy to prevent spontaneous NF-κB activation. Our quantitative analysis suggests that potent oncogenic CARD11 mutations must perturb autoinhibition by at least three repressive elements. Our results explain the lack of ID mutations in DLBCL and reveal an unusual autoinhibitory domain structure and strategy for preventing unwarranted scaffold signaling to NF-κB.