Impact of anthracycline-based chemotherapy on RB1 gene methylation in peripheral blood leukocytes and biomarkers of oxidative stress and inflammation in sarcoma patients.

PURPOSE: We investigated the impact of anthracycline-based chemotherapy on methylation status of RB1 gene in peripheral blood leukocytes together with parameters of oxidative stress and inflammation in sarcoma patients. PATIENTS/METHODS: Blood samples were collected from 51 consecutive newly diagnosed sarcoma patients admitted to University Hospital Center Zagreb (Zagreb, Croatia) for first-line chemotherapy before the first cycle and post-chemotherapy. Methylation and copy number variation (CNV) of leukocyte RB1 gene were assessed using MS-MLPA probes. In addition, in blood samples, parameters of oxidative stress (ROS, MDA, SOD, and GSH) and inflammation (CRP, WBC, and NBC) were followed. RESULTS: In pre-chemotherapy samples, no CNVs and aberrant methylation of CpG106 promoter region of RB1 gene were detected; however, one patient had hypermethylation (by approximately 10%) of imprinted locus CpG85 in intron 2 of RB1 gene. In addition, a very good correlation of the tumor burden and CRP and tumor burden and GSH was found. The anthracycline-based chemotherapy reverts methylation of RB1 gene-imprinted locus CpG85 to normal level. Moreover, inflammation and oxidative stress parameters such as CRP, WBC, ROS, and MDA were significantly decreased in post-chemotherapy samples. CONCLUSION: This single-centered study on a cohort of consecutive sarcoma patients indicates that sarcoma patients can have aberrant germline DNA methylation and confirms the relationship of tumor burden with inflammation and oxidative stress. The applied chemotherapy protocols reverted RB1 gene methylation to normal level and decreased the level of inflammation and oxidative damage, thus indicating chemotherapy benefit to the patient's health status.

In-line warming reduces in-line pressure of subcutaneous infusion of concentrated immunoglobulins.

Immunoglobulin replacement therapy is a life-saving treatment in patients with immunodeficiency and effective in the management of autoimmune disorders. Immunoglobulins are administered intravenously or subcutaneously, with the latter route reducing systemic reactions and providing an option for self-infusion, increasing patient convenience, while decreasing patient burden, healthcare utilization, and costs. A major limitation with subcutaneous administrations is the frequency of infusion due to limited volumes administrable into subcutaneous space, necessitating increased drug concentration, absorption, and dispersion. Increasing the concentration of immunoglobulins from 10 to 20% halves the required volume, but leads to higher dynamic viscosity, limiting infusion rate. Recombinant human hyaluronidase increases dispersion and absorption of immunoglobulins allowing administration of ≤ 600 mL per site, but does not change viscosity. Since the viscosity of fluids depends on temperature, we tested the feasibility of in-line warming of immunoglobulin formulations to physiological temperatures. In vitro analysis showed no negative impact of in-line warming to 38 °C on product quality. Subcutaneous infusion studies in pigs confirmed the feasibility of infusion rates of up to 7.5 mL/min with in-line warmed TAK-881, an immunoglobulin 20% facilitated with recombinant human hyaluronidase. In-line pressures were reduced compared with conventional immunoglobulin 20%, and local tolerance was not altered. Reduction of in-line pressures was more pronounced with thinner needle sets, indicating a potential benefit for patients. In summary, an in in-line warming device can circumvent the limitation of high viscosity, while product quality and local tolerance are maintained. The results of the presented studies warrant further testing in a phase 1 clinical study.

DPYD genotyping and predicting fluoropyrimidine toxicity: where do we stand?

Fluoropyrimidines (FPs) are antineoplastic drugs widely used in the treatment of various solid tumors. Nearly 30% of patients treated with FP chemotherapy experience severe FP-related toxicity, and in some cases, toxicity can be fatal. Patients with reduced activity of DPD, the main enzyme responsible for the breakdown of FP, are at an increased risk of experiencing severe FP-related toxicity. While European regulatory agencies and clinical societies recommend pre-treatment DPD deficiency screening for patients starting treatment with FPs, this is not the case with American ones. Pharmacogenomic guidelines issued by several pharmacogenetic organizations worldwide recommend testing four DPD gene (DPYD) risk variants, but these can predict only a proportion of toxicity cases. New evidence on additional common DPYD polymorphisms, as well as identification and functional characterization of rare DPYD variants, could partially address the missing heritability of DPD deficiency and FP-related toxicity.

DPYD polymorphisms c.496A>G, c.2194G>A and c.85T>C and risk of severe adverse drug reactions in patients treated with fluoropyrimidine-based protocols.

AIMS: Cancer patients with reduced dihydropyrimidine dehydrogenase (DPD) activity are at increased risk of severe fluoropyrimidine (FP)-related adverse events (AE). Guidelines recommend FP dosing adjusted to genotype-predicted DPD activity based on four DPYD variants (rs3918290, rs55886062, rs67376798 and rs56038477). We evaluated the relationship between three further DPYD polymorphisms: c.496A>G (rs2297595), *6 c.2194G>A (rs1801160) and *9A c.85T>C (rs1801265) and the risk of severe AEs. METHODS: Consecutive FP-treated adult patients were genotyped for "standard" and tested DPYD variants, and for UGT1A1*28 if irinotecan was included, and were monitored for the occurrence of grade ≥3 (National Cancer Institute Common Terminology Criteria) vs. grade 0-2 AEs. For each of the tested polymorphisms, variant allele carriers were matched to respective wild type controls (optimal full matching combined with exact matching, in respect to: age, sex, type of cancer, type of FP, DPYD activity score, use of irinotecan/UGT1A1, adjuvant therapy, radiotherapy, biological therapy and genotype on the remaining two tested polymorphisms). RESULTS: Of the 503 included patients (82.3% colorectal cancer), 283 (56.3%) developed grade ≥3 AEs, mostly diarrhoea and neutropenia. Odds of grade ≥3 AEs were higher in c.496A>G variant carriers (n = 127) than in controls (n = 376) [OR = 5.20 (95% CI 1.88-14.3), Bayesian OR = 5.24 (95% CrI 3.06-9.12)]. Odds tended to be higher in c.2194G>A variant carriers (n = 58) than in controls (n = 432) [OR = 1.88 (0.95-3.73), Bayesian OR = 1.90 (1.03-3.56)]. c.85T>C did not appear associated with grade ≥3 AEs (206 variant carriers vs. 284 controls). CONCLUSION: DPYD c.496A>G and possibly c.2194G>A variants might need to be considered for inclusion in the DPYD genotyping panel.

BAX 335 hemophilia B gene therapy clinical trial results: potential impact of CpG sequences on gene expression.

Gene therapy has the potential to maintain therapeutic blood clotting factor IX (FIX) levels in patients with hemophilia B by delivering a functional human F9 gene into liver cells. This phase 1/2, open-label dose-escalation study investigated BAX 335 (AskBio009, AAV8.sc-TTR-FIXR338Lopt), an adeno-associated virus serotype 8 (AAV8)-based FIX Padua gene therapy, in patients with hemophilia B. This report focuses on 12-month interim analyses of safety, pharmacokinetic variables, effects on FIX activity, and immune responses for dosed participants. Eight adult male participants (aged 20-69 years; range FIX activity, 0.5% to 2.0%) received 1 of 3 BAX 335 IV doses: 2.0 × 1011; 1.0 × 1012; or 3.0 × 1012 vector genomes/kg. Three (37.5%) participants had 4 serious adverse events, all considered unrelated to BAX 335. No serious adverse event led to death. No clinical thrombosis, inhibitors, or other FIX Padua-directed immunity was reported. FIX expression was measurable in 7 of 8 participants; peak FIX activity displayed dose dependence (32.0% to 58.5% in cohort 3). One participant achieved sustained therapeutic FIX activity of ∼20%, without bleeding or replacement therapy, for 4 years; in others, FIX activity was not sustained beyond 5 to 11 weeks. In contrast to some previous studies, corticosteroid treatment did not stabilize FIX activity loss. We hypothesize that the loss of transgene expression could have been caused by stimulation of innate immune responses, including CpG oligodeoxynucleotides introduced into the BAX 335 coding sequence by codon optimization. This trial was registered at www.clinicaltrials.gov as #NCT01687608.

Breast metastasis as the initial presentation of malignant pleural mesothelioma.

Metastatic involvement of the breast is far less common than primary breast carcinoma, comprising 0.5%-6.6% of all breast malignancies. Malignant pleural mesothelioma (MPM) is a rare and aggressive tumor with higher incidence among men, particularly smokers, strongly associated with asbestos exposure. The epithelioid type of MPM can represent a diagnostic pitfall in this setting, as it shows similar histologic features to primary breast carcinoma as well as other metastatic epithelioid malignancies. We report a rare case of breast metastasis of malignant pleural mesothelioma in a 61-year-old female.

Publisher Correction: Human DEF6 deficiency underlies an immunodeficiency syndrome with systemic autoimmunity and aberrant CTLA-4 homeostasis.

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

Human DEF6 deficiency underlies an immunodeficiency syndrome with systemic autoimmunity and aberrant CTLA-4 homeostasis.

Immune responses need to be controlled tightly to prevent autoimmune diseases, yet underlying molecular mechanisms remain partially understood. Here, we identify biallelic mutations in three patients from two unrelated families in differentially expressed in FDCP6 homolog (DEF6) as the molecular cause of an inborn error of immunity with systemic autoimmunity. Patient T cells exhibit impaired regulation of CTLA-4 surface trafficking associated with reduced functional CTLA-4 availability, which is replicated in DEF6-knockout Jurkat cells. Mechanistically, we identify the small GTPase RAB11 as an interactor of the guanine nucleotide exchange factor DEF6, and find disrupted binding of mutant DEF6 to RAB11 as well as reduced RAB11+CTLA-4+ vesicles in DEF6-mutated cells. One of the patients has been treated with CTLA-4-Ig and achieved sustained remission. Collectively, we uncover DEF6 as player in immune homeostasis ensuring availability of the checkpoint protein CTLA-4 at T-cell surface, identifying a potential target for autoimmune and/or cancer therapy.

Variant PIK3R1 Hypermorphic Mutation and Clinical Phenotypes in a Family with Short Statures, Mild Immunodeficiency and Lymphoma.

Background Heterozygous point mutations in the GT splice donor consensus sequence of exon 11 of the PIK3R1 gene (coding for p85α, p55α, and p50α regulatory subunits of PI3K) lead to exon skipping and thereby to an aberrant protein that leaves PI3K hyperactivated. Several patients with this particular variant of PI3 kinase delta syndrome (APDS) suffering from sinopulmonary infections and lymphoproliferation have been described. Methods (Whole exome) sequencing, evaluation of cellular and clinical phenotypes. Results We here report a family with a new heterozygous mutation in this gene, a 9 bp deletion (c.1418_1425+1del) that, however, leads to the same skipping of exon 11. The clinical phenotypes of their members partly overlap features of patients of other reports. Conclusions We found a new mutation in PIK3R1 and show how broad the resulting clinical spectrum can be.

RASGRP1 deficiency causes immunodeficiency with impaired cytoskeletal dynamics.

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

Molecular functions of the transcription factors E2A and E2-2 in controlling germinal center B cell and plasma cell development.

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

Adverse Reaction to Cetuximab, an Epidermal Growth Factor Receptor Inhibitor.

Dear Editor, Inhibition of the epidermal growth factor receptor (EGFR) is a new strategy in treatment of a variety of solid tumors, such as colorectal carcinoma, non-small cell lung cancer, squamous cell carcinoma of the head and neck, and pancreatic cancer (1). Cetuximab is a chimeric human-murine monoclonal antibody against EGFR. Cutaneous side effects are the most common adverse reactions occurring during epidermal growth factor receptor inhibitors (EGFRI) therapy. Papulopustular rash (acne like rash) develop with 80-86% patients receiving cetuximab, while xerosis, eczema, fissures, teleangiectasiae, hyperpigmentations, and nail and hair changes occur less frequently (2). The mechanism underlying these skin changes has not been established and understood. It seems EGFRI alter cell growth and differentiation, leading to impaired stratum corneum and cell apoptosis (3-5). An abdominoperineal resection of the rectal adenocarcinoma (Dukes C) was performed on a 43-year-old female patient. Following surgery, adjuvant chemo-radiotherapy was applied. After two years, the patient suffered a metastatic relapse. Abdominal lymphadenopathy was detected on multi-slice computer tomography (MSCT) images, with an increased value of the carcinoembryonic antigen (CEA) tumor marker (maximal value 57 ng/mL). Hematological and biochemical tests were within normal limits, so first-line chemotherapy with oxaliplatin and a 5-fluorouracil (FOLFOX4) protocol was introduced. A wild type of the KRAS gene was confirmed in tumor tissue (diagnostic prerequisite for the introduction of EGFRI) and cetuximab (250 mg per m2 of body surface) was added to the treatment protocol. The patient responded well to the treatment with confirmed partial regression of the tumor formations. Three months after the patient started using cetuximab, an anti-EGFR monoclonal antibody, the patient presented with a papulopustular eruption in the seborrhoeic areas (Figure 1) and eczematoid reactions on the extremities with dry, scaly, itchy skin (Figure 2). Furthermore, hair and nail changes gradually developed, culminating with trichomegaly (Figure 3) and paronychia (Figure 4). The patient was treated with oral antibiotics (tetracycline) and a combination of topical steroids with moisturizing emollients due to xerosis, without reduction of EGFRI therapy and with a very good response. Trichomegaly was regularly sniped with scissors. Nail fungal infection was ruled out by native examination and cultivation, so antiseptics and corticosteroid ointments were introduced for paronychia treatment. During the above-mentioned therapy, apart from skin manifestations, iatrogenic neutropenia grade IV occurred, with one febrile episode, and because of this, the dose of cytostatic drugs was reduced. After 10 months of therapy, progression of the disease occurred with lung metastases, so EGFRI therapy was discontinued and the patient was given second-line chemotherapy for metastatic colorectal carcinoma. This led to gradual resolution of all aforementioned cutaneous manifestations. Since the pathogenesis of skin side-effects due to EGFRI is not yet fully understood, there are no strict therapy protocols. Therapy is mainly based on clinical experience and follows the standard treatments for acne, rosacea, xerosis, paronychia, and effluvium. The therapeutic approach for papulopustular exanthema includes topical and systemic antibiotics for their antimicrobial as well as anti-inflammatory effect, sometimes in combination with topical steroids. Topical application of urea cream with K1 vitamin yielded positive results in skin-changes prevention during EGFRI therapy, especially with xerosis, eczema, and pruritus (6). Hair alterations in the form of effluvium are usually tolerable, and if needed a 2% minoxidil solution may be applied. Trichomegaly or abnormal eyelash growth can lead to serious complications, so ophthalmologic examination is needed. At the beginning of the growth, regular lash clipping may reduce possibility of corneal abrasion (7,8). Nail changes can just be a cosmetic problem (pigmentary changes, brittle nails), and in the occurrence of paronychia or onycholysis (of several or all nails) they result in high morbidity and impair daily activities. Nail management should be started as soon as possible because of slow nail growth and the relatively long half-life of EGFRI. Combination of topical iodide, corticosteroids, antibiotics, and antifungals with avoidance of nail traumatization will yield the best results (9). EGFRI are potentially life prolonging therapies, and our goal as dermatovenereologists is to provide optimal patient care and improve their quality of life in a multidisciplinary collaboration with oncologists, radiotherapists, and ophthalmologists.

How polymorphisms of the cytochrome P450 genes affect ibuprofen and diclofenac metabolism and toxicity.

Interindividual variability in drug metabolism is an important cause of adverse drug reactions and variability in drug efficiency. Polymorphisms of cytochrome P450 (CYPs) genes have a significant effect on drug metabolism and toxicity. This review brings an update about how genetic polymorphisms of CYP2C8 and CYP2C9 enzymes affect the disposition and clinical outcomes of ibuprofen and diclofenac, two of the most common pain relievers. The most common side effects associated with the influence of CYP2C8*3 and CYP2C9*2*3 variants on ibuprofen and diclofenac pharmacokinetics are hepatotoxicity and gastrointestinal bleeding. CYP genotyping may therefore identify patients at increased risk of these adverse reactions, and these patients could have their doses adjusted or start receiving another NSAID that does not share the same metabolic pathways with ibuprofen or diclofenac. However, before genotyping is introduced into regular clinical practice, more research is needed to evaluate the effectiveness of this strategy in improving treatment with ibuprofen and diclofenac.

Inherited DOCK2 Deficiency in Patients with Early-Onset Invasive Infections.

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

The Most Common Cutaneous Side Effects of Epidermal Growth Factor Receptor Inhibitors and Their Management.

The use of epidermal growth factor receptor inhibitors (EGFRI) for the treatment of solid tumors is increasing due to elevated expression of epidermal growth factor receptors (EGFR) in the stimulation of tumor development. EGFR inhibitors have shown to be effective in the treatment of neoplasms of the head, neck, colon, and lung. Inhibition of EGFR may cause cutaneous reactions in more than 50% of patients. The most common skin manifestations are papulopustular lesions in the seborrhoeic areas (upper torso, face, neck, and scalp). Other cutaneous side effects include xerosis and hair and nail changes. The onset of eruption is usually within one to three weeks after starting therapy, although in some cases it may occur much later. All dermatologic side effects are reversible and generally resolve after adequate therapy. However, for a minority of patients side effects are severe and intolerable, demanding dose reduction or even interruption of therapy. A positive correlation has been demonstrated between the degree of cutaneous toxicity and the antitumor response. For dermatologists the goal is to provide treatment of symptoms, so that the patient may continue to benefit from the EGFRI therapy. However, frequent cutaneous manifestations, even though related to a better antitumor response, may limit use of the therapy considering the interference with patient quality of life. Early management of cutaneous side effects of EGFRI may prevent severe, extensive symptoms, the need for dose reduction, or antitumor therapy interruption. This indicates a dermatologist should play a role in early stages of treatment.

A novel Cd8-cis-regulatory element preferentially directs expression in CD44hiCD62L+ CD8+ T cells and in CD8αα+ dendritic cells.

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

Biallelic loss-of-function mutation in NIK causes a primary immunodeficiency with multifaceted aberrant lymphoid immunity.

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

Early-onset inflammatory bowel disease and common variable immunodeficiency-like disease caused by IL-21 deficiency.

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