Activated phosphoinositde 3-kinase (PI3Kδ) syndrome: an Italian point of view on diagnosis and new advances in treatment.

Activated phosphoinositide 3-kinase (PI3Kδ) Syndrome (APDS) is an inborn error of immunity (IEI) with a variable clinical presentation, characterized by infection susceptibility and immune dysregulation that may overlaps with other Primary Immune Regulatory Disorders (PIRDs). The rarity of the disease, its recent discovery, and the multiform /multifaced clinical presentation make it difficult to establish a correct diagnosis, especially at an early stage. As a result, the true prevalence of the pathology remains unknown. There is no treatment protocol for APDS, and drug therapy is primarily focused on treating symptoms. The most common therapies include immunoglobulin replacement therapy, antimicrobial prophylaxis, and immunosuppressive drugs. Hematopoietic stem cell transplantation (HSCT) has been used in some cases, but the risk-benefit balance remains unclear. With the upcoming introduction of specific medications, such as selective inhibitors for PI3Kδ, clinicians are shifting their attention towards target therapy.This review provides a comprehensive overview of APDS with a focus on diagnostic and treatments procedures available. This review may be useful in implementing strategies for a more efficient patients' management and therapeutic interventions.Main Text.

Prurigo-like atopic dermatitis in a child with CARD11-associated severe combined immunodeficiency successfully treated with dupilumab.

A 12-year-old boy affected by severe combined immunodeficiency due to a heterozygous variant in the CARD domain of CARD11, c.169G>A; p.Glu57Lys, developed severe atopic dermatitis and alopecia areata. After failure of conventional systemic therapy, dupilumab was administered at a dose of 400 mg subcutaneously, followed by 200 mg every 14 days. The patient had an excellent clinical response after 1 month and complete remission after a year, with the absence of side effects, demonstrating good efficacy and safety profile.

Interim analysis: Open-label extension study of leniolisib for patients with APDS.

BACKGROUND: Activated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS; or p110δ-activating mutations causing senescent T cells, lymphadenopathy, and immunodeficiency) is an inborn error of immunity caused by PI3Kδ hyperactivity. Resultant immune deficiency and dysregulation lead to recurrent sinopulmonary infections, herpes viremia, autoimmunity, and lymphoproliferation. OBJECTIVE: Leniolisib, a selective PI3Kδ inhibitor, demonstrated favorable impact on immune cell subsets and lymphoproliferation over placebo in patients with APDS over 12 weeks. Here, we report results from an interim analysis of an ongoing open-label, single-arm extension study. METHODS: Patients with APDS aged 12 years or older who completed NCT02435173 or had previous exposure to PI3Kδ inhibitors were eligible. The primary end point was safety, assessed via investigator-reported adverse events (AEs) and clinical/laboratory evaluations. Secondary and exploratory end points included health-related quality of life, inflammatory markers, frequency of infections, and lymphoproliferation. RESULTS: Between September 2016 and August 2021, 37 patients (median age, 20 years; 42.3% female) were enrolled. Of these 37 patients, 26, 9, and 2 patients had previously received leniolisib, placebo, or other PI3Kδ inhibitors, respectively. At the data cutoff date (December 13, 2021), median leniolisib exposure was 102 weeks. Overall, 32 patients (87%) experienced an AE. Most AEs were grades 1 to 3; none were grade 4. One patient with severe baseline comorbidities experienced a grade 5 AE, determined as unrelated to leniolisib treatment. While on leniolisib, patients had reduced annualized infection rates (P = .004), and reductions in immunoglobulin replacement therapy occurred in 10 of 27 patients. Other observations include reduced lymphadenopathy and splenomegaly, improved cytopenias, and normalized lymphocyte subsets. CONCLUSIONS: Leniolisib was well tolerated and maintained durable outcomes with up to 5 years of exposure in 37 patients with APDS. CLINICALTRIALS: gov identifier: NCT02859727.

Allergy and autoimmunity in children: non-mutually exclusive diseases. A narrative review.

In last decades a simultaneous increase in the prevalence of atopic and autoimmune disorders in pediatric population has been observed. Despite the Th1-Th2 paradigm, supporting the polarization of the immune system with Th1 response involved in autoimmune diseases and Th2 response leading to hypersensitivity reactions, recent evidence suggests a possible coexistence of common pathogenic pathways as result of shared immune dysregulation. Similar genes and other mechanisms such as epithelial barrier damage, gut microbiota dysbiosis and reduced number of T regs and IL-10 contribute to the onset of allergy and autoimmunity. IgA deficiency is also hypothesized to be the crosslink between celiac disease and allergy by lowering gut mucous membrane protection from antigens and allergens. The present narrative review aims to give an overview of the co-occurrence of allergic and autoimmune disorders (celiac disease, inflammatory bowel diseases, type 1 diabetes mellitus, thyroid disease, juvenile idiopathic arthritis) in pediatric population, based on the available evidence. We also highlighted the common pathogenic pathways that may underpin both. Our findings confirm that allergic and autoimmune diseases are commonly associated, and clinicians should therefore be aware of the possible coexistence of these conditions in order to ameliorate disease management and patient care. Particular attention should be paid to the association between atopic dermatitis or asthma and celiac disease or type 1 diabetes and vice versa, for therapeutic interventions. Further studies are needed to better clarify mechanisms involved in the pathogenesis and eventually identify new therapeutic strategies.

Unbiased assessment of genome integrity and purging of adverse outcomes at the target locus upon editing of CD4+ T-cells for the treatment of Hyper IgM1.

Hyper IgM1 is an X-linked combined immunodeficiency caused by CD40LG mutations, potentially treatable with CD4+ T-cell gene editing with Cas9 and a "one-size-fits-most" corrective template. Contrary to established gene therapies, there is limited data on the genomic alterations following long-range gene editing, and no consensus on the relevant assays. We developed drop-off digital PCR assays for unbiased detection of large on-target deletions and found them at high frequency upon editing. Large deletions were also common upon editing different loci and cell types and using alternative Cas9 and template delivery methods. In CD40LG edited T cells, on-target deletions were counter-selected in culture and further purged by enrichment for edited cells using a selector coupled to gene correction. We then validated the sensitivity of optical genome mapping for unbiased detection of genome wide rearrangements and uncovered on-target trapping of one or more vector copies, which do not compromise functionality, upon editing using an integrase defective lentiviral donor template. No other recurring events were detected. Edited patient cells showed faithful reconstitution of CD40LG regulated expression and function with a satisfactory safety profile. Large deletions and donor template integrations should be anticipated and accounted for when designing and testing similar gene editing strategies.

Rituximab Monotherapy Is Effective as First-Line Treatment for Granulomatous Lymphocytic Interstitial Lung Disease (GLILD) in CVID Patients.

Granulomatous lymphocytic interstitial lung disease (GLILD) represents a fatal immune dysregulatory complication in common variable immunodeficiency (CVID). Evidence-based diagnostic guidelines are lacking, and GLILD treatment consists in immunosuppressive drugs; nonetheless, therapeutical strategies are heterogeneous and essentially based on experts' opinions and data from small case series or case reports.We aimed to evaluate the efficacy and safety of first-line Rituximab monotherapy for CVID-related GLILD, by assessing symptoms and quality of life alterations, immunological parameters, pulmonary function tests, and lung computed tomography.All six GLILD patients received Rituximab infusions as a first-line treatment. Rituximab was administered at 375 mg/m2 monthly for six infusions followed by maintenance every 3 months; none of the patients experienced severe adverse events. Symptom burden and quality of life significantly improved in treated patients compared to a control group of CVID patients without GLILD. Rituximab treatment indirectly caused a trend toward reduced T-cell activation and exhaustion markers sCD25 and sTIM-3. Lung function improved in treated patients, with statistically significant increases in TLC and DLCO. Lung CT scan findings expressed by means of Baumann scoring system displayed a reduction in the entire cohort.In conclusion, first-line monotherapy with Rituximab displayed high efficacy in disease remission in all treated patients, with improvement of symptoms and amelioration of quality of life, as well as restoration of PFTs and lung CT scan findings.

Scalable GMP-compliant gene correction of CD4+ T cells with IDLV template functionally validated in vitro and in vivo.

Hyper-IgM1 is a rare X-linked combined immunodeficiency caused by mutations in the CD40 ligand (CD40LG) gene with a median survival of 25 years, potentially treatable with in situ CD4+ T cell gene editing with Cas9 and a one-size-fits-most corrective donor template. Here, starting from our research-grade editing protocol, we pursued the development of a good manufacturing practice (GMP)-compliant, scalable process that allows for correction, selection and expansion of edited cells, using an integrase defective lentiviral vector as donor template. After systematic optimization of reagents and conditions we proved maintenance of stem and central memory phenotypes and expression and function of CD40LG in edited healthy donor and patient cells recapitulating the physiological CD40LG regulation. We then documented the preserved fitness of edited cells by xenotransplantation into immunodeficient mice. Finally, we transitioned to large-scale manufacturing, and developed a panel of quality control assays. Overall, our GMP-compliant process takes long-range gene editing one step closer to clinical application with a reassuring safety profile.

Monogenic forms of common variable immunodeficiency and implications on target therapeutic approaches.

PURPOSE OF REVIEW: Common variable immunodeficiency (CVID) is the most common symptomatic inborn error of immunity. The disorder is characterized by variable clinical and immunological manifestations, and, in a small minority of patients, a monogenic cause may be identified. In this review, we focalized on three different monogenic forms of CVID-like disease. RECENT FINDINGS: Activated phosphoinositide 3-kinase delta syndrome (APDS) is a rare disorder characterized by hyperactivated class I phosphatidylinositol-3 kinase (PI3K) pathway. Affected patients present with respiratory infectious episodes, impaired viral clearance and lymphoproliferation. Recently, a direct PI3K inhibitor has been approved and it showed encouraging results both in controlling clinical and immunological manifestations of the disease. On the other hand, patients with defects in CTLA-4 or LRBA gene present with life-threatening immune dysregulation, autoimmunity and lymphocytic infiltration of multiple organs. Abatacept, a soluble cytotoxic T lymphocyte antigen 4 (CTLA-4) fusion protein that acts as a costimulation modulator, has been widely implemented for affected patients with good results as bridge treatment. SUMMARY: Understanding the biological basis of CVID is important not only for enriching our knowledge of the human immune system, but also for setting the basis for potential targeted treatments in this disorder.

Common and Uncommon CT Findings in CVID-Related GL-ILD: Correlations with Clinical Parameters, Therapeutic Decisions and Potential Implications in the Differential Diagnosis.

PURPOSE: To investigate computed tomography (CT) findings of Granulomatous Lymphocytic Interstitial Lung Disease (GL-ILD) in Common Variable Immunodeficiency (CVID), also in comparison with non-GL-ILD abnormalities, correlating GL-ILD features with functional/immunological parameters and looking for GL-ILD therapy predictive elements. METHODS: CT features of 38 GL-ILD and 38 matched non-GL-ILD subjects were retrospectively described. Correlations of GL-ILD features with functional/immunological features were assessed. A logistic regression was performed to find a predictive model of GL-ILD therapeutic decisions. RESULTS: Most common GL-ILD CT findings were bronchiectasis, non-perilymphatic nodules, consolidations, Ground Glass Opacities (GGO), bands and enlarged lymphnodes. GL-ILD was usually predominant in lower fields. Multiple small nodules (≤10 mm), consolidations, reticulations and fibrotic ILD are more indicative of GL-ILD. Bronchiectasis, GGO, Reticulations and fibrotic ILD correlated with decreased lung performance. Bronchiectasis, GGO and fibrotic ILD were associated with low IgA levels, whereas high CD4+ T cells percentage was related to GGO. Twenty out of 38 patients underwent GL-ILD therapy. A model combining Marginal Zone (MZ) B cells percentage, IgA levels, lower field consolidations and lymphnodes enlargement showed a good discriminatory capacity with regards to GL-ILD treatment. CONCLUSIONS: GL-ILD is a lower field predominant disease, commonly characterized by bronchiectasis, non-perilymphatic small nodules, consolidations, GGO and bands. Multiple small nodules, consolidations, reticulations and fibrotic ILD may suggest the presence of GL-ILD in CVID. MZ B cells percentage, IgA levels at diagnosis, lower field consolidations and mediastinal lymphnodes enlargement may predict the need of a specific GL-ILD therapy.

CARD11 dominant negative mutation leads to altered human Natural Killer cell homeostasis.

Dominant negative mutations in CARD11 have been reported in patients with immune dysregulation, severe atopic features, and variable T cell alterations. Data on Natural killer (NK) cells from affected patients are lacking. We report on a 12-year-old boy with severe atopic dermatitis, food induced anaphylaxis and hypogammaglobulinemia harbouring a novel de novo heterozygous variant c.169G > A; p.Glu57Lys in CARD11. The dominant negative effect of this mutation was confirmed on both CD4+ and CD8+. CTLA4+Foxp3+CD4+ Tregs were severely reduced. Patient's NK cells showed reduced expression of NKp46, NKG2D and CD69. Patient's CD56bright NK cells showed in vitro impaired production of IFN-γ. Steady state pS6 levels on patient's NK cells were increased and remained elevated upon IL2 + IL12 + IL18 overnight stimulation. Overall, the effect of CARD11 mutation on mTORC1 differs between T and NK cells. These findings may explain the increased susceptibility to viral infections and the reduced immune surveillance in affected patients.

Immune tolerance breakdown in inborn errors of immunity: Paving the way to novel therapeutic approaches.

Up to 25% of the patients with inborn errors of immunity (IEI) also exhibit immunodysregulatory features. The association of immune dysregulation and immunodeficiency may be explained by different mechanisms. The understanding of mechanisms underlying immune dysregulation in IEI has paved the way for the development of targeted treatments. In this review article, we will summarize the mechanisms of immune tolerance breakdown and the targeted therapeutic approaches to immune dysregulation in IEI.

A randomized, placebo-controlled phase 3 trial of the PI3Kδ inhibitor leniolisib for activated PI3Kδ syndrome.

Activated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS) is an inborn error of immunity with clinical manifestations including infections, lymphoproliferation, autoimmunity, enteropathy, bronchiectasis, increased risk of lymphoma, and early mortality. Hyperactive PI3Kδ signaling causes APDS and is selectively targeted with leniolisib, an oral, small molecule inhibitor of PI3Kδ. Here, 31 patients with APDS aged ≥12 years were enrolled in a global, phase 3, triple-blinded trial and randomized 2:1 to receive 70 mg leniolisib or placebo twice daily for 12 weeks. Coprimary outcomes were differences from baseline in the index lymph node size and the percentage of naïve B cells in peripheral blood, assessed as proxies for immune dysregulation and deficiency. Both primary outcomes were met: the difference in the adjusted mean change (95% confidence interval [CI]) between leniolisib and placebo for lymph node size was -0.25 (-0.38, -0.12; P = .0006; N = 26) and for percentage of naïve B cells, was 37.30 (24.06, 50.54; P = .0002; N = 13). Leniolisib reduced spleen volume compared with placebo (adjusted mean difference in 3-dimensional volume [cm3], -186; 95% CI, -297 to -76.2; P = .0020) and improved key immune cell subsets. Fewer patients receiving leniolisib reported study treatment-related adverse events (AEs; mostly grades 1-2) than those receiving placebo (23.8% vs 30.0%). Overall, leniolisib was well tolerated and significant improvement over placebo was notable in the coprimary endpoints, reducing lymphadenopathy and increasing the percentage of naïve B cells, reflecting a favorable impact on the immune dysregulation and deficiency seen in patients with APDS. This trial was registered at www.clinicaltrials.gov as #NCT02435173.

CVID-Associated B Cell Activating Factor Receptor Variants Change Receptor Oligomerization, Ligand Binding, and Signaling Responses.

PURPOSE: Binding of the B cell activating factor (BAFF) to its receptor (BAFFR) activates in mature B cells many essential pro-survival functions. Null mutations in the BAFFR gene result in complete BAFFR deficiency and cause a block in B cell development at the transition from immature to mature B cells leading therefore to B lymphopenia and hypogammaglobulinemia. In addition to complete BAFFR deficiency, single nucleotide variants encoding BAFFR missense mutations were found in patients suffering from common variable immunodeficiency (CVID), autoimmunity, or B cell lymphomas. As it remained unclear to which extent such variants disturb the activity of BAFFR, we performed genetic association studies and developed a cellular system that allows the unbiased analysis of BAFFR variants regarding oligomerization, signaling, and ectodomain shedding. METHODS: In addition to genetic association studies, the BAFFR variants P21R, A52T, G64V, DUP92-95, P146S, and H159Y were expressed by lentiviral gene transfer in DG-75 Burkitt's lymphoma cells and analyzed for their impacts on BAFFR function. RESULTS: Binding of BAFF to BAFFR was affected by P21R and A52T. Spontaneous oligomerization of BAFFR was disturbed by P21R, A52T, G64V, and P146S. BAFF-dependent activation of NF-κB2 was reduced by P21R and P146S, while interactions between BAFFR and the B cell antigen receptor component CD79B and AKT phosphorylation were impaired by P21R, A52T, G64V, and DUP92-95. P21R, G64V, and DUP92-95 interfered with phosphorylation of ERK1/2, while BAFF-induced shedding of the BAFFR ectodomain was only impaired by P21R. CONCLUSION: Although all variants change BAFFR function and have the potential to contribute as modifiers to the development of primary antibody deficiencies, autoimmunity, and lymphoma, P21R is the only variant that was found to correlate positively with CVID.

Vasculitis and vasculopathy associated with inborn errors of immunity: an overview.

Systemic autoinflammatory diseases (SAIDs) are disorders of innate immunity, which are characterized by unprovoked recurrent flares of systemic inflammation often characterized by fever associated with clinical manifestations mainly involving the musculoskeletal, mucocutaneous, gastrointestinal, and nervous systems. Several conditions also present with varied, sometimes prominent, involvement of the vascular system, with features of vasculitis characterized by variable target vessel involvement and organ damage. Here, we report a systematic review of vasculitis and vasculopathy associated with inborn errors of immunity.

Lymphocyte alterations in patients with Common Variable Immunodeficiency (CVID) and autoimmune manifestations.

INTRODUCTION: Autoimmunity is a common feature in CVID patients. To date the mechanisms leading to the development of such complications are not fully elucidated. MATERIALS AND METHODS: Data from 122 CVID patients subdivided in three groups based on the absence of autoimmunity (n-AI) or the presence of hematologic autoimmune phenomena (Cy-AI) or non-hematologic autoimmune phenomena (n-Cy-AI) were evaluated. RESULTS: We identified a total of 128 autoimmune manifestations in 55/122 patients (45.1%). 30/122 (24.6%) patients presented hematologic autoimmune phenomena while 29/122 (23.8%) presented gastrointestinal autoimmune involvement. Immune thrombocytopenia was the most common manifestation (27/122; 22.1%), followed by autoimmune hemolytic anemia (18/122; 14.8%) and autoimmune enteropathy (17/122; 13.9%). Cy-AI patients displayed higher CD4+ effector memory and terminally differentiated CD8+ cells with lower percentages of naïve and recent thymic emigrants (RTEs) CD4+ cells and a significant expansion of the CD19hiCD21low population. CONCLUSIONS: CVID patients developing autoimmune cytopenias display characteristic immune phenotypic features.

Follicular helper T cell signature of replicative exhaustion, apoptosis, and senescence in common variable immunodeficiency.

Common variable immunodeficiency (CVID) is the most frequent primary antibody deficiency whereby follicular helper T (Tfh) cells fail to establish productive responses with B cells in germinal centers. Here, we analyzed the frequency, phenotype, transcriptome, and function of circulating Tfh (cTfh) cells in CVID patients displaying autoimmunity as an additional phenotype. A group of patients showed a high frequency of cTfh1 cells and a prominent expression of PD-1 and ICOS as well as a cTfh mRNA signature consistent with highly activated, but exhausted, senescent, and apoptotic cells. Plasmatic CXCL13 levels were elevated in this group and positively correlated with cTfh1 cell frequency and PD-1 levels. Monoallelic variants in RTEL1, a telomere length- and DNA repair-related gene, were identified in four patients belonging to this group. Their blood lymphocytes showed shortened telomeres, while their cTfh were more prone to apoptosis. These data point toward a novel pathogenetic mechanism in CVID, whereby alterations in DNA repair and telomere elongation might predispose to antibody deficiency. A Th1, highly activated but exhausted and apoptotic cTfh phenotype was associated with this form of CVID.

Pathogenesis of Autoimmune Cytopenias in Inborn Errors of Immunity Revealing Novel Therapeutic Targets.

Autoimmune diseases are usually associated with environmental triggers and genetic predisposition. However, a few number of autoimmune diseases has a monogenic cause, mostly in children. These diseases may be the expression, isolated or associated with other symptoms, of an underlying inborn error of immunity (IEI). Autoimmune cytopenias (AICs), including immune thrombocytopenic purpura (ITP), autoimmune hemolytic anemia (AIHA), autoimmune neutropenia (AN), and Evans' syndrome (ES) are common presentations of immunological diseases in the pediatric age, with at least 65% of cases of ES genetically determined. Autoimmune cytopenias in IEI have often a more severe, chronic, and relapsing course. Treatment refractoriness also characterizes autoimmune cytopenia with a monogenic cause, such as IEI. The mechanisms underlying autoimmune cytopenias in IEI include cellular or humoral autoimmunity, immune dysregulation in cases of hemophagocytosis or lymphoproliferation with or without splenic sequestration, bone marrow failure, myelodysplasia, or secondary myelosuppression. Genetic characterization of autoimmune cytopenias is of fundamental importance as an early diagnosis improves the outcome and allows the setting up of a targeted therapy, such as CTLA-4 IgG fusion protein (Abatacept), small molecule inhibitors (JAK-inhibitors), or gene therapy. Currently, gene therapy represents one of the most attractive targeted therapeutic approaches to treat selected inborn errors of immunity. Even in the absence of specific targeted therapies, however, whole exome genetic testing (WES) for children with chronic multilineage cytopenias should be considered as an early diagnostic tool for disease diagnosis and genetic counseling.

The Impact of SARS-CoV-2 Infection in Patients with Inborn Errors of Immunity: the Experience of the Italian Primary Immunodeficiencies Network (IPINet).

COVID-19 manifestations range from asymptomatic to life-threatening infections. The outcome in different inborn errors of immunity (IEI) is still a matter of debate. In this retrospective study, we describe the experience of the of the Italian Primary Immunodeficiencies Network (IPINet). Sixteen reference centers for adult or pediatric IEI were involved. One hundred fourteen patients were enrolled including 35 pediatric and 79 adult patients. Median age was 32 years, and male-to-female ratio was 1.5:1. The most common IEI were 22q11.2 deletion syndrome in children (26%) and common variable immunodeficiency (CVID) in adults (65%). Ninety-one patients did not require hospital admission, and among these, 33 were asymptomatic. Hospitalization rate was 20.17%. Older age (p 0.004) and chronic lung disease (p 0.0008) represented risk factors for hospitalization. Hospitalized patients mainly included adults suffering from humoral immunodeficiencies requiring immunoglobulin replacement therapy and as expected had lower B cell counts compared to non-hospitalized patients. Infection fatality rate in the whole cohort was 3.5%. Seroconversion was observed is 86.6% of the patients evaluated and in 83.3% of CVID patients. 16.85% of the patients reported long-lasting COVID symptoms. All but one patient with prolonged symptoms were under IgRT. The fatality rate observed in IEI was slightly similar to the general population. The age of the patients who did not survive was lower compared to the general population, and the age stratified mortality in the 50-60 age range considerable exceeded the mortality from 50 to 60 age group of the Italian population (14.3 vs 0.6%; p < 0.0001). We hypothesize that this is due to the fact that comorbidities in IEI patients are very common and usually appear early in life.

Lack of DOCK8 impairs the primary biologic functions of human NK cells and abrogates CCR7 surface expression in a WASP-independent manner.

Dedicator of Cytokinesis 8 (DOCK8) deficiency is a rare form of autosomal recessive combined immunodeficiency. The effect of DOCK8 deficiency on Natural Killer cell biology has not been fully elucidated yet. Thus, we undertook a detailed phenotypic and functional evaluation of NK cells from seven patients with DOCK8 deficiency. Patients' immature CD56bright NK cells were defective in IFN-γ secretion, while their mature CD56dim NK cells showed impaired cytotoxicity, partially rescued upon rIL-2 addition. Cross-linking of NK cell receptors revealed a specific defect in the CD3 zeta chain-dependent activation pathway in DOCK8 deficiency. Lack of DOCK8, but not of WASP, impaired CCR7 expression on human CD56bright NK cells, a critical receptor for their migration to secondary lymph nodes. Evaluation of a patient's lymph node showed a severe reduction in NK cells that showed increased intracellular expression of CCR7. Our data suggest that DOCK8 deficiency variably affects NK cell homeostasis in humans.