Wiskott-Aldrich syndrome: a comprehensive review

Pathophysiology, causes and genetics of paediatric and adult bronchiectasis

Bronchiectasis has historically been considered to be irreversible dilatation of the airways, but with modern imaging techniques it has been proposed that 'irreversible' be dropped from the definition. The upper limit of normal for the ratio of airway to arterial development increases with age, and a developmental perspective is essential. Bronchiectasis (and persistent bacterial bronchitis, PBB) is a descriptive term and not a diagnosis, and should be the start not the end of the patient's diagnostic journey. PBB, characterized by airway infection and neutrophilic inflammation but without significant airway dilatation may be a precursor of bronchiectasis, and there are many commonalities in the microbiology and the pathology, which are reviewed in this article. A high index of suspicion is essential, and a history of chronic wet or productive cough for more than 4-8 weeks should prompt investigation. There are numerous underlying causes of bronchiectasis, although in many cases no cause is found. Causes include post-infectious, especially after tuberculosis, adenoviral or pertussis infection; aspiration syndromes; defects in host defence, which may solely affect the airways (cystic fibrosis, not considered in this review, and primary ciliary dyskinesia); and primary ciliary dyskinesia or be systemic, such as common variable immunodeficiency; genetic syndromes; and anatomical defects such as intraluminal airway obstruction (e.g. foreign body), intramural obstruction (e.g. complete cartilage rings) and external airway compression (e.g. by tuberculous lymph nodes). Identification of the underlying cause is important, because some of these conditions have specific treatments and others genetic implications for the family.

CRISPR/Cas9-mediated deletion of the Wiskott-Aldrich syndrome locus causes actin cytoskeleton disorganization in murine erythroleukemia cells

Wiskott-Aldrich syndrome (WAS) is a recessive X-linked inmmunodeficiency caused by loss-of-function mutations in the gene encoding the WAS protein (WASp). WASp plays an important role in the polymerization of the actin cytoskeleton in hematopoietic cells through activation of the Arp2/3 complex. In a previous study, we found that actin cytoskeleton proteins, including WASp, were silenced in murine erythroleukemia cells defective in differentiation. Here, we designed a CRISPR/Cas9 strategy to delete a 9.5-kb genomic region encompassing the Was gene in the X chromosome of murine erythroleukemia (MEL) cells. We show that Was-deficient MEL cells have a poor organization of the actin cytoskeleton that can be recovered by restoring Was expression. We found that whereas the total amount of actin protein was similar between wild-type and Was knockout MEL cells, the latter exhibited an altered ratio of monomeric G-actin to polymeric F-actin. We also demonstrate that Was overexpression can mediate the activation of Bruton’s tyrosine kinase. Overall, these findings support the role of WASp as a key regulator of F-actin in erythroid cells.

Wiskott-Aldrich syndrome protein (WASP) is a tumor suppressor in T cell lymphoma

In T lymphocytes, the Wiskott-Aldrich Syndrome protein (WASP) and WASP-interacting-protein (WIP) regulate T cell antigen receptor (TCR) signaling, but their role in lymphoma is largely unknown. Here we show that the expression of WASP and WIP is frequently low or absent in anaplastic large cell lymphoma (ALCL) compared to other T cell lymphomas. In anaplastic lymphoma kinase-positive (ALK+) ALCL, WASP and WIP expression is regulated by ALK oncogenic activity via its downstream mediators STAT3 and C/EBP-β. ALK+ lymphomas were accelerated in WASP- and WIP-deficient mice. In the absence of WASP, active GTP-bound CDC42 was increased and the genetic deletion of one CDC42 allele was sufficient to impair lymphoma growth. WASP-deficient lymphoma showed increased mitogen-activated protein kinase (MAPK) pathway activation that could be exploited as a therapeutic vulnerability. Our findings demonstrate that WASP and WIP are tumor suppressors in T cell lymphoma and suggest that MAP-kinase kinase (MEK) inhibitors combined with ALK inhibitors could achieve a more potent therapeutic effect in ALK+ ALCL.

Epigenetic Deregulation in Human Primary Immunodeficiencies

Primary immunodeficiencies (PIDs) are immune disorders resulting from defects in genes involved in immune regulation, and manifesting as an increased susceptibility to infections, autoimmunity, and cancer. However, the molecular basis of some prevalent entities remains poorly understood. Epigenetic control is essential for immune functions, and epigenetic alterations have been identified in different PIDs, including syndromes such as immunodeficiency-centromeric-instability-facial-anomalies, Kabuki, or Wolf-Hirschhorn, among others. Although the epigenetic changes may differ among these PIDs, the reversibility of epigenetic modifications suggests that they might become potential therapeutic targets. Here, we review recent mechanistic advances in our understanding of epigenetic alterations associated with certain PIDs, propose that a fully epigenetically driven mechanism might underlie some PIDs, and discuss the possible prophylactic and therapeutic implications.

Thrombopoietin receptor agonists in hereditary thrombocytopenias

Hereditary thrombocytopenias (HTPs) constitute a heterogeneous group of diseases characterized by a reduction in platelet count and a potential bleeding risk. As a result of advances in diagnostic methods, HTPs are increasingly being identified, and appear to be less rare than previously thought. Most HTPs do not have effective treatments, except for platelet transfusion when bleeding occurs and in preparation for procedures associated with a risk of bleeding. Preliminary clinical evidence suggests that thrombopoietin receptor agonists (TPO-RAs) with an established use in the treatment of certain acquired thrombocytopenias are well tolerated and provide clinical benefits in patients with some forms of HTP. These drugs may therefore be considered for the treatment of HTPs in clinical practice. However, caution and close monitoring are recommended, owing to the absence of long-term safety data and the potential risks posed by prolonged bone marrow stimulation in certain HTPs. In this review, we summarize the available clinical data on TPO-RAs in the treatment of HTPs, and discuss their use in patients with these disorders. We believe that TPO-RAs will play a major role in the treatment of HTPs, particularly myosin heavy chain 9-related disease, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and thrombocytopenia caused by THPO mutations.

A novel splice site mutation in WAS gene in patient with Wiskott-Aldrich syndrome and chronic colitis: a case report

BACKGROUND

Wiskott-Aldrich syndrome is an X-linked recessive immunodeficiency due to mutations in Wiskott-Aldrich syndrome (WAS) gene. WAS gene is encoded for a multifunctional protein with key roles in actin polymerization, signaling pathways, and cytoskeletal rearrangement. Therefore, the impaired protein or its absence cause phenotypic spectrum of the disease. Since identification of novel mutations in WAS gene can help uncover the exact pathogenesis of Wiskott-Aldrich syndrome, the purpose of this study was to investigate disease causing-mutation in an Iranian male infant suspicious of this disorder.

CASE PRESENTATION

The patient had persistent thrombocytopenia from birth, sepsis, and recurrent gastrointestinal bleeding suggestive of both Wiskott-Aldrich syndrome and chronic colitis in favor of inflammatory bowel disease (IBD). To find mutated gene in the proband, whole exome sequencing was performed for the patient and its data showed a novel, private, hemizygous splice site mutation in WAS gene (c.360 + 1G > C).

CONCLUSIONS

Our study found a novel, splice-site mutation in WAS gene and help consider the genetic counselling more precisely for families with clinical phenotypes of both Wiskott-Aldrich syndrome and inflammatory bowel disease and may suggest linked pathways between these two diseases.

A novel mutation in Wiskott-Aldrich gene manifesting as macrothrombocytopenia and neutropenia

Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder, described as a clinical triad of microthrombocytopenia, eczema and recurrent infections. Different mutations in WAS gene have been identified, resulting in various phenotypes and a broad range of disease severity, ranging from classic WAS to X-linked thrombocytopenia and X-linked neutropenia. WAS in some cases can be fatal without haematopoietic stem cell transplantation early in life. In this particular case, we present a novel mutation with a unique presentation. An 18-year-old man incidentally found to have macrothrombocytopenia and neutropenia at 16 years of age later found to be hemizygous for c. 869T>C (p.Ile290Thr) mutation in WAS gene. The late presentation, absence of other manifestations of WAS and presence of macrothrombocytopenia, rather than microthrombocytopenia, which is usually a characteristic finding in WAS, misled the initial diagnosis. On review of literature, this mutation has not been reported as causing WAS.

Nuclear ARP2/3 drives DNA break clustering for homology-directed repair

DNA double-strand breaks repaired by non-homologous end joining display limited DNA end-processing and chromosomal mobility. By contrast, double-strand breaks undergoing homology-directed repair exhibit extensive processing and enhanced motion. The molecular basis of this movement is unknown. Here, using Xenopus laevis cell-free extracts and mammalian cells, we establish that nuclear actin, WASP, and the actin-nucleating ARP2/3 complex are recruited to damaged chromatin undergoing homology-directed repair. We demonstrate that nuclear actin polymerization is required for the migration of a subset of double-strand breaks into discrete sub-nuclear clusters. Actin-driven movements specifically affect double-strand breaks repaired by homology-directed repair in G2 cell cycle phase; inhibition of actin nucleation impairs DNA end-processing and homology-directed repair. By contrast, ARP2/3 is not enriched at double-strand breaks repaired by non-homologous end joining and does not regulate non-homologous end joining. Our findings establish that nuclear actin-based mobility shapes chromatin organization by generating repair domains that are essential for homology-directed repair in eukaryotic cells.

WASP-mediated regulation of anti-inflammatory macrophages is IL-10 dependent and is critical for intestinal homeostasis

Mutations in Wiskott–Aldrich syndrome protein (WASP) cause autoimmune sequelae including colitis. Yet, how WASP mediates mucosal homeostasis is not fully understood. Here we show that WASP-mediated regulation of anti-inflammatory macrophages is critical for mucosal homeostasis and immune tolerance. The generation and function of anti-inflammatory macrophages are defective in both human and mice in the absence of WASP. Expression of WASP specifically in macrophages, but not in dendritic cells, is critical for regulation of colitis development. Importantly, transfer of WT anti-inflammatory macrophages prevents the development of colitis. DOCK8-deficient macrophages phenocopy the altered macrophage properties associated with WASP deficiency. Mechanistically, we show that both WASP and DOCK8 regulates macrophage function by modulating IL-10-dependent STAT3 phosphorylation. Overall, our study indicates that anti-inflammatory macrophage function and mucosal immune tolerance require both WASP and DOCK8, and that IL-10 signalling modulates a WASP-DOCK8 complex.

Deficiency in Wiskott-Aldrich syndrome protein (WASP) has been associated with autoimmune colitis, but the underlying mechanism is still unclear. Here the authors show that WASP deficiency is associated with defective WASP/DOCK8 complex formation, altered IL-10 signalling, and impaired anti-inflammatory macrophage functions.

Wash exhibits context-dependent phenotypes and, along with the WASH regulatory complex, regulates Drosophila oogenesis

WASH, a Wiskott-Aldrich syndrome (WAS) family protein, has many cell and developmental roles related to its function as a branched actin nucleation factor. Similar to mammalian WASHC1, which is embryonic lethal, Drosophila Wash was found to be essential for oogenesis and larval development. Recently, however, Drosophila wash was reported to be homozygous viable. Here, we verify that the original wash null allele harbors an unrelated lethal background mutation; however, this unrelated lethal mutation does not contribute to any Wash oogenesis phenotypes. Significantly, we find that: (1) the homozygous wash null allele retains partial lethality, leading to non-Mendelian inheritance; (2) the allele's functions are subject to its specific genetic background; and (3) the homozygous stock rapidly accumulates modifications that allow it to become robust. Together, these results suggest that Wash plays an important role in oogenesis via the WASH regulatory complex. Finally, we show that another WAS family protein, SCAR/WAVE, plays a similar role in oogenesis and that it is upregulated as one of the modifications that allows the wash allele to survive in the homozygous state.

Wiskott-Aldrich Syndrome Misdiagnosed as Immune Thrombocytopenic Purpura: A Case Report

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency characterized by various clinical phenotypes. We report the case of a 3-year-old immigrant boy presenting with persistent infant-onset thrombocytopenia treated for refractory immune thrombocytopenic purpura. Sequence analysis confirmed the diagnosis of WAS. The patient responded neither to IV infusions of immunoglobulin (Ig) nor a thrombopoietin receptor agonist and is currently planned for stem cell transplantation. Raised awareness is thus vital of this potentially misdiagnosed and lethal disorder. The diagnosis of WAS should be considered in all males with infant-onset immune thrombocytopenic purpura-like features, especially, if mean platelet volume is decreased (<7 fL) and good increment to platelet transfusions are evident.

Neuropsychological Profile of a Girl with Wiskott-Aldrich Syndrome

We report the neuropsychological profile of a 6-year-old girl with Wiskott-Aldrich syndrome, a rare X-linked immunodeficiency disorder associated with thrombocytopenia, eczema, recurrent infections, and malignancy. Wiskott-Aldrich syndrome occurs almost exclusively in males and is extremely rare in females, with no known research focused on cognitive and academic functioning in this population. Our patient was referred due to concerns about her memory and academic functioning. She had a history of progressive thrombocytopenia and hematopoietic stem cell transplantation at age 15 months. Standardized measures of intellectual ability, language, visual-spatial and visual-motor skills, attention, memory, and academic achievement were administered. The results showed average to above-average performance in multiple areas of cognitive and academic functioning, with weaknesses in phonological awareness and rapid naming. The advent of hematopoietic stem cell transplantation has led to considerable improvement in the long-term prognosis of children with Wiskott-Aldrich syndrome. Although the impact of this syndrome and related conditions on neurocognitive development is presently unknown, this case highlights both the importance of considering base rates for commonly occurring conditions and the significant role neuropsychology can play in identifying cognitive strengths and weaknesses in the context of the developing brain.

Crosstalk between WIP and Rho family GTPases

Through actin-binding proteins such as the neural Wiskott-Aldrich syndrome protein (N-WASP) and WASP-interacting protein (WIP), the Rho family GTPases RhoA, Rac1 and Cdc42 are major modulators of the cytoskeleton. (N-)WASP and WIP control Rho GTPase activity in various cell types, either by direct WIP/(N-)WASP/Cdc42 or potential WIP/RhoA binding, or through secondary links that regulate GTPase distribution and/or transcription levels. WIP helps to regulate filopodium generation and participates in the Rac1-mediated ruffle formation that determines cell motility. In neurons, lack of WIP increases dendritic spine size and filamentous actin content in a RhoA-dependent manner. In contrast, WIP deficiency in an adenocarcinoma cell line significantly reduces RhoA levels. These data support a role for WIP in the GTPase-mediated regulation of numerous actin-related cell functions; we discuss the possibility that this WIP effect is linked to cell proliferative status.

Hereditary thrombocytopenias: a growing list of disorders

The introduction of high throughput sequencing (HTS) techniques greatly improved the knowledge of inherited thrombocytopenias (ITs) over the last few years. A total of 33 different forms caused by molecular defects affecting at least 32 genes have been identified; along with the discovery of new disease-causing genes, pathogenetic mechanisms of thrombocytopenia have been better elucidated. Although the clinical picture of ITs is heterogeneous, bleeding has been long considered the major clinical problem for patients with IT. Conversely, the current scenario indicates that patients with some of the most common ITs are at risk of developing additional disorders more dangerous than thrombocytopenia itself during life. In particular, MYH9 mutations result in congenital macrothrombocytopenia and predispose to kidney failure, hearing loss, and cataracts, MPL and MECOM mutations cause congenital thrombocytopenia evolving into bone marrow failure, whereas thrombocytopenias caused by RUNX1, ANKRD26, and ETV6 mutations are characterized by predisposition to hematological malignancies. Making a definite diagnosis of these forms is crucial to provide patients with the most appropriate treatment, follow-up, and counseling. In this review, the ITs known to date are discussed, with specific attention focused on clinical presentations and diagnostic criteria for ITs predisposing to additional illnesses. The currently available therapeutic options for the different forms of IT are illustrated.

How cells engulf: a review of theoretical approaches to phagocytosis

Phagocytosis is a fascinating process whereby a cell surrounds and engulfs particles such as bacteria and dead cells. This is crucial both for single-cell organisms (as a way of acquiring nutrients) and as part of the immune system (to destroy foreign invaders). This whole process is hugely complex and involves multiple coordinated events such as membrane remodelling, receptor motion, cytoskeleton reorganisation and intracellular signalling. Because of this, phagocytosis is an excellent system for theoretical study, benefiting from biophysical approaches combined with mathematical modelling. Here, we review these theoretical approaches and discuss the recent mathematical and computational models, including models based on receptors, models focusing on the forces involved, and models employing energetic considerations. Along the way, we highlight a beautiful connection to the physics of phase transitions, consider the role of stochasticity, and examine links between phagocytosis and other types of endocytosis. We cover the recently discovered multistage nature of phagocytosis, showing that the size of the phagocytic cup grows in distinct stages, with an initial slow stage followed by a much quicker second stage starting around half engulfment. We also address the issue of target shape dependence, which is relevant to both pathogen infection and drug delivery, covering both one-dimensional and two-dimensional results. Throughout, we pay particular attention to recent experimental techniques that continue to inform the theoretical studies and provide a means to test model predictions. Finally, we discuss population models, connections to other biological processes, and how physics and modelling will continue to play a key role in future work in this area.

Wiskott-Aldrich syndrome protein regulates autophagy and inflammasome activity in innate immune cells

Dysregulation of autophagy and inflammasome activity contributes to the development of auto-inflammatory diseases. Emerging evidence highlights the importance of the actin cytoskeleton in modulating inflammatory responses. Here we show that deficiency of Wiskott-Aldrich syndrome protein (WASp), which signals to the actin cytoskeleton, modulates autophagy and inflammasome function. In a model of sterile inflammation utilizing TLR4 ligation followed by ATP or nigericin treatment, inflammasome activation is enhanced in monocytes from WAS patients and in WAS-knockout mouse dendritic cells. In ex vivo models of enteropathogenic Escherichia coli and Shigella flexneri infection, WASp deficiency causes defective bacterial clearance, excessive inflammasome activation and host cell death that are associated with dysregulated septin cage-like formation, impaired autophagic p62/LC3 recruitment and defective formation of canonical autophagosomes. Taken together, we propose that dysregulation of autophagy and inflammasome activities contribute to the autoinflammatory manifestations of WAS, thereby identifying potential targets for therapeutic intervention.

Approach to a Child with Primary Immunodeficiency Made Simple

Primary immunodeficiency disorders (PIDs) are a group of disorders affecting the capability to fight against infection. These include defects in T cells and B cells affecting cell-mediated and humoral immunity, respectively, combined humoral and cell-mediated immunodeficiency, defects in phagocytosis, complement defects, and defects in cytokine or cytokine signalling pathways which are detrimental for immune function. Depending upon the type and severity, age at onset of symptoms can vary from neonatal period to late childhood. Clinically, this group of disorders can involve any organ system of an individual such as respiratory system, gastrointestinal system, skin and mucous membrane, bone and joints, endocrine organs, and nervous system. Common dermatological manifestations include eczema, warts, molluscum contagiosum, mucocutaneous candidiasis, recurrent nonhealing ulcers, skin abscesses, erythroderma, petechiae, and nail changes. The common skin manifestations of various PIDs include eczema (seen in Wiskott-Aldrich syndrome and autosomal dominant hyper IgE syndrome); erythroderma (in Omen syndrome); viral warts or molluscum contagiosum (in autosomal recessive hyper IgE syndrome); chronic mucocutaneous candidiasis (in hyper IgE syndrome, autoimmune polyendocrinopathy candidiasis ectodermal dysplasia syndrome, Th17 cell defects); recurrent nonhealing ulcers (in leucocyte adhesion defect); skin abscesses (in antibody defects, hyper IgE syndrome, and chronic granulomatous disease); petechial or purpuric spots (in Wiskott-Aldrich syndrome).

Nuclear Wiskott-Aldrich syndrome protein co-regulates T cell factor 1-mediated transcription in T cells

BACKGROUND

The Wiskott-Aldrich syndrome protein (WASp) family of actin-nucleating factors are present in the cytoplasm and in the nucleus. The role of nuclear WASp for T cell development remains incompletely defined.

METHODS

We performed WASp chromatin immunoprecipitation and deep sequencing (ChIP-seq) in thymocytes and spleen CD4⁺ T cells.

RESULTS

WASp was enriched at genic and intergenic regions and associated with the transcription start sites of protein-coding genes. Thymocytes and spleen CD4⁺ T cells showed 15 common WASp-interacting genes, including the gene encoding T cell factor (TCF)12. WASp KO thymocytes had reduced nuclear TCF12 whereas thymocytes expressing constitutively active WASp^L272P and WASp^I296T had increased nuclear TCF12, suggesting that regulated WASp activity controlled nuclear TCF12. We identify a putative DNA element enriched in WASp ChIP-seq samples identical to a TCF1-binding site and we show that WASp directly interacted with TCF1 in the nucleus.

CONCLUSIONS

These data place nuclear WASp in proximity with TCF1 and TCF12, essential factors for T cell development.

BCR-ABL1-induced downregulation of WASP in chronic myeloid leukemia involves epigenetic modification and contributes to malignancy

Chronic myeloid leukemia (CML) is a myeloproliferative disease caused by the BCR–ABL1 tyrosine kinase (TK). The development of TK inhibitors (TKIs) revolutionized the treatment of CML patients. However, TKIs are not effective to those at advanced phases when amplified BCR–ABL1 levels and increased genomic instability lead to secondary oncogenic modifications. Wiskott–Aldrich syndrome protein (WASP) is an important regulator of signaling transduction in hematopoietic cells and was shown to be an endogenous inhibitor of the c-ABL TK. Here, we show that the expression of WASP decreases with the progression of CML, inversely correlates with the expression of BCR–ABL1 and is particularly low in blast crisis. Enforced expression of BCR–ABL1 negatively regulates the expression of WASP. Decreased expression of WASP is partially due to DNA methylation of the proximal WASP promoter. Importantly, lower levels of WASP in CML advanced phase patients correlate with poorer overall survival (OS) and is associated with TKI response. Interestingly, enforced expression of WASP in BCR–ABL1-positive K562 cells increases the susceptibility to apoptosis induced by TRAIL or chemotherapeutic drugs and negatively modulates BCR–ABL1-induced tumorigenesis in vitro and in vivo. Taken together, our data reveal a novel molecular mechanism that operates in BCR–ABL1-induced tumorigenesis that can be used to develop new strategies to help TKI-resistant, CML patients in blast crisis (BC).

Periodontal and other oral manifestations of immunodeficiency diseases

The list of immunodeficiency diseases grows each year as novel disorders are discovered, classified, and sometimes reclassified due to our ever-increasing knowledge of immune system function. Although the number of patients with secondary immunodeficiencies (SIDs) greatly exceeds those with primary immunodeficiencies (PIDs), the prevalence of both appears to be on the rise probably because of scientific breakthroughs that facilitate earlier and more accurate diagnosis. Primary immunodeficiencies in adults are not as rare as once thought. Globally, the main causes of secondary immunodeficiency are HIV infection and nutritional insufficiencies. Persons with acquired immune disorders such as AIDS caused by the human immunodeficiency virus (HIV) are now living long and fulfilling lives as a result of highly active antiretroviral therapy (HAART). Irrespective of whether the patient's immune-deficient state is a consequence of a genetic defect or is secondary in nature, dental and medical practitioners must be aware of the constant potential for infections and/or expressions of autoimmunity in these individuals. The purpose of this review was to study the most common conditions resulting from primary and secondary immunodeficiency states, how they are classified, and the detrimental manifestations of these disorders on the periodontal and oral tissues.

Defective thymic output in WAS patients is associated with abnormal actin organization

Wiskott-Aldrich syndrome protein (WASp) is a key regulator of the actin cytoskeleton. Defective T - cell function is a major cause for immune deficiency in Wiskott-Aldrich syndrome (WAS) patients. T cells originate in the bone marrow and develop in the thymus, and then migrate to peripheral tissues. TCR excision circles (TRECs) present in thymic output cells stably, which is used as a molecular marker for thymic output. We found that CD8⁺ T naïve cells of classic WAS patients were significantly reduced, and TRECs in patients with classic WAS and X-linked thrombocytopenia (XLT) dramatically decreased compared with that of HCs. TRECs were also reduced in WAS (KO) mice. These suggest that defective thymic output partially accounts for T cell lymphopenia in WAS patients. However, the correlation between the defect of thymic output and actin organization still remains elusive. We found that the subcellular location and the levels of of F-actin were altered in T cells from both WAS and XLT patients compared to that of HCs with or without stimulation. Our study shows that WASp plays a critical role in thymic output, which highly correlates with the subcellular location and level of F-actin in T cells.

An Evolutionarily Conserved Pathway Essential for Orsay Virus Infection of Caenorhabditis elegans

Many fundamental biological discoveries have been made in Caenorhabditis elegans. The discovery of Orsay virus has enabled studies of host-virus interactions in this model organism. To identify host factors critical for Orsay virus infection, we designed a forward genetic screen that utilizes a virally induced green fluorescent protein (GFP) reporter. Following chemical mutagenesis, two Viro (virus induced reporter off) mutants that failed to express GFP were mapped to sid-3, a nonreceptor tyrosine kinase, and B0280.13 (renamed viro-2), an ortholog of human Wiskott-Aldrich syndrome protein (WASP). Both mutants yielded Orsay virus RNA levels comparable to that of the residual input virus, suggesting that they are not permissive for Orsay virus replication. In addition, we demonstrated that both genes affect an early prereplication stage of Orsay virus infection. Furthermore, it is known that the human ortholog of SID-3, activated CDC42-associated kinase (ACK1/TNK2), is capable of phosphorylating human WASP, suggesting that VIRO-2 may be a substrate for SID-3 in C. elegans. A targeted RNA interference (RNAi) knockdown screen further identified the C. elegans gene nck-1, which has a human ortholog that interacts with TNK2 and WASP, as required for Orsay virus infection. Thus, genetic screening in C. elegans identified critical roles in virus infection for evolutionarily conserved genes in a known human pathway.

Orsay virus is the only known virus capable of naturally infecting the model organism Caenorhabditis elegans, which shares many evolutionarily conserved genes with humans. We exploited the robust genetic tractability of C. elegans to identify three host genes, sid-3, viro-2, and nck-1, which are essential for Orsay virus infection. Mutant animals that lack these three genes are highly defective in viral replication. Strikingly, the human orthologs of these three genes, activated CDC42-associated kinase (TNK2), Wiskott-Aldrich syndrome protein (WASP), and noncatalytic region of tyrosine kinase adaptor protein 1 (NCK1) are part of a known signaling pathway in mammals. These results suggest that TNK2, WASP, and NCK1 may play important roles in mammalian virus infection.

Biological and functional characterization of bone marrow-derived mesenchymal stromal cells from patients affected by primary immunodeficiency

Mesenchymal stromal cells (MSCs) represent a key component of bone marrow (BM) microenvironment and display immune-regulatory properties. We performed a detailed analysis of biological/functional properties of BM-MSCs derived from 33 pediatric patients affected by primary immune-deficiencies (PID-MSCs): 7 Chronic Granulomatous Disease (CGD), 15 Wiskott-Aldrich Syndrome (WAS), 11 Severe Combined Immunodeficiency (SCID). Results were compared with MSCs from 15 age-matched pediatric healthy-donors (HD-MSCs). Clonogenic and proliferative capacity, differentiation ability, immunophenotype, immunomodulatory properties were analyzed. WB and RT-qPCR for CYBB, WAS and ADA genes were performed. All PID-MSCs displayed clonogenic and proliferative capacity, morphology and immunophenotype comparable with HD-MSCs. PID-MSCs maintained the inhibitory effect on T- and B-lymphocyte proliferation, except for decreased inhibitory ability of SCID-MSCs at MSC:PBMC ratio 1:10. While HD- and CGD-MSCs were able to inhibit monocyte maturation into immature dendritic cells, in SCID- and WAS-MSCs this ability was reduced. After Toll-like Receptor priming, PID-MSCs displayed in vitro an altered gene expression profile of pro- and anti-inflammatory soluble factors. PID-MSCs displayed lower PPARγ levels and WAS- and SCID-MSCs higher levels of key osteogenic markers, as compared with HD-MSCs. Our results indicate that PID-MSCs may be defective in some functional abilities; whether these defects contribute to disease pathophysiology deserves further investigation.

Wiskott-Aldrich syndrome: Two case reports with a novel mutation

BACKGROUND

The Wiskott-Aldrich syndrome (WAS) is X-linked recessive disorder associated with microplatelet thrombocytopenia, eczema, infections, and an increased risk of autoimmunity and lymphoid neoplasia. The originally described features of WAS include susceptibility to infections, microthrombocytopenia, and eczema.

AIM

In this case report, we present our experience about two cases diagnosed with a new mutation.

METHODS

We report phenotypical and laboratory description of two cases with WAS.

RESULTS

We, for the first time, detected a new hemizygote mutation of WAS gene (NM_000377.2 p.M393lfs^*102 (c.1178dupT)) in two patients. The first case was an 11-month-old boy presenting with complaints of recurrent soft tissue infection, ear infection, anemia, and thrombocytopenia with a low platelet volume. The second case was a 2-month-old boy presenting with thrombocytopenia and a low platelet volume. Both cases were the first-degree relatives: they were cousins and their mothers were sisters.

CONCLUSION

Herein, we report two cases of WAS and a new gene mutation which would disrupt the WAS protein function within the Polyproline (PPP) domain. This report adds to the growing number of mutations which cause complex clinical manifestations associated with WAS.

The contribution of mouse models to the understanding of constitutional thrombocytopenia

Constitutional thrombocytopenias result from platelet production abnormalities of hereditary origin. Long misdiagnosed and poorly studied, knowledge about these rare diseases has increased considerably over the last twenty years due to improved technology for the identification of mutations, as well as an improvement in obtaining megakaryocyte culture from patient hematopoietic stem cells. Simultaneously, the manipulation of mouse genes (transgenesis, total or conditional inactivation, introduction of point mutations, random chemical mutagenesis) have helped to generate disease models that have contributed greatly to deciphering patient clinical and laboratory features. Most of the thrombocytopenias for which the mutated genes have been identified now have a murine model counterpart. This review focuses on the contribution that these mouse models have brought to the understanding of hereditary thrombocytopenias with respect to what was known in humans. Animal models have either i) provided novel information on the molecular and cellular pathways that were missing from the patient studies; ii) improved our understanding of the mechanisms of thrombocytopoiesis; iii) been instrumental in structure-function studies of the mutated gene products; and iv) been an invaluable tool as preclinical models to test new drugs or develop gene therapies. At present, the genetic determinants of thrombocytopenia remain unknown in almost half of all cases. Currently available high-speed sequencing techniques will identify new candidate genes, which will in turn allow the generation of murine models to confirm and further study the abnormal phenotype. In a complementary manner, programs of random mutagenesis in mice should also identify new candidate genes involved in thrombocytopenia.

Gene Therapy Approaches to Immunodeficiency

Transfer of gene-corrected autologous hematopoietic stem cells in patients with primary immunodeficiencies has emerged as a new therapeutic approach. Patients with various conditions lacking a suitable donor have been treated with retroviral vectors and a gene-addition strategy. Initial promising results were shadowed by the occurrence of malignancies in some of these patients. Current trials, developed in the last decade, use safer viral vectors to overcome the risk of genotoxicity and have led to improved clinical outcomes. This review reflects the progresses made in specific disorders, including adenosine deaminase deficiency, X-linked severe combined immunodeficiency, chronic granulomatous disease, and Wiskott-Aldrich syndrome.

Cellular functions of WASP family proteins at a glance

Proteins of the Wiskott-Aldrich syndrome protein (WASP) family function as nucleation-promoting factors for the ubiquitously expressed Arp2/3 complex, which drives the generation of branched actin filaments. Arp2/3-generated actin regulates diverse cellular processes, including the formation of lamellipodia and filopodia, endocytosis and/or phagocytosis at the plasma membrane, and the generation of cargo-laden vesicles from organelles including the Golgi, endoplasmic reticulum (ER) and the endo-lysosomal network. Recent studies have also identified roles for WASP family members in promoting actin dynamics at the centrosome, influencing nuclear shape and membrane remodeling events leading to the generation of autophagosomes. Interestingly, several WASP family members have also been observed in the nucleus where they directly influence gene expression by serving as molecular platforms for the assembly of epigenetic and transcriptional machinery. In this Cell Science at a Glance article and accompanying poster, we provide an update on the subcellular roles of WHAMM, JMY and WASH (also known as WASHC1), as well as their mechanisms of regulation and emerging functions within the cell.

Invadosomes are coming: new insights into function and disease relevance

Invadopodia and podosomes are discrete, actin-based molecular protrusions that form in cancer cells and normal cells, respectively, in response to diverse signaling pathways and extracellular matrix cues. Although they participate in a host of different cellular processes, they share a common functional theme of controlling pericellular proteolytic activity, which sets them apart from other structures that function in migration and adhesion, including focal adhesions, lamellipodia, and filopodia. In this review, we highlight research that explores the function of these complex structures, including roles for podosomes in embryonic and postnatal development, in angiogenesis and remodeling of the vasculature, in maturation of the postsynaptic membrane, in antigen sampling and recognition, and in cell-cell fusion mechanisms, as well as the involvement of invadopodia at multiple steps of the metastatic cascade, and how all of this may apply in the treatment of human disease states. Finally, we explore recent research that implicates a novel role for exosomes and microvesicles in invadopodia-dependent and invadopodia-independent mechanisms of invasion, respectively.

Multiparametric Whole Blood Dissection: A one-shot comprehensive picture of the human hematopoietic system

Human hematopoiesis is a complex and dynamic system where morphologically and functionally diverse mature cell types are generated and maintained throughout life by bone marrow (BM) Hematopoietic Stem/Progenitor Cells (HSPC). Congenital and acquired hematopoietic disorders are often diagnosed through the detection of aberrant frequency or composition of hematopoietic cell populations. We here describe a novel protocol, called “Whole Blood Dissection” (WBD), capable of analyzing in a single test‐tube, hematopoietic progenitors and all major mature cell lineages composing either BM or peripheral blood (PB) through a multiparametric flow‐cytometry analysis. WBD allows unambiguously identifying in the same tube up to 23 different blood cell types including HSPC subtypes and all the major myeloid and lymphoid lineage compartments at different stages of maturation, through a combination of 17 surface and 1 viability cell markers. We assessed the efficacy of WBD by analyzing BM and PB samples from adult (n = 8) and pediatric (n = 9) healthy donors highlighting age‐related shift in cell composition. We also tested the capability of WBD on detecting aberrant hematopoietic cell composition in clinical samples of patients with primary immunodeficiency or leukemia unveiling expected and novel hematopoietic unbalances. Overall, WBD allows unambiguously identifying >99% of the cell subpopulations composing a blood sample in a reproducible, standardized, cost‐, and time‐efficient manner. This tool has a wide range of potential pre‐clinical and clinical applications going from the characterization of hematopoietic disorders to the monitoring of hematopoietic reconstitution in patients after transplant or gene therapy. © 2017 The Authors. Cytometry Part A Published by Wiley Periodicals, Inc. on behalf of ISAC.

How I manage children with neutropenia

Neutropenia, usually defined as a blood neutrophil count <1·5 × 10⁹ /l, is a common medical problem for children and adults. There are many causes for neutropenia, and at each stage in life the clinical pattern of causes and consequences differs significantly. I recommend utilizing the age of the child and clinical observations for the preliminary diagnosis and primary management. In premature infants, neutropenia is quite common and contributes to the risk of sepsis with necrotizing enterocolitis. At birth and for the first few months of life, neutropenia is often attributable to isoimmune or alloimmune mechanisms and predisposes to the risk of severe bacterial infections. Thereafter when a child is discovered to have neutropenia, often associated with relatively minor symptoms, it is usually attributed to autoimmune disorder or viral infection. The congenital neutropenia syndromes are usually recognized when there are recurrent infections, the neutropenia is severe and there are congenital anomalies suggesting a genetic disorder. This review focuses on the key clinical finding and laboratory tests for diagnosis with commentaries on treatment, particularly the use of granulocyte colony-stimulating factor to treat childhood neutropenia.

Loss of the Arp2/3 complex component ARPC1B causes platelet abnormalities and predisposes to inflammatory disease

Human actin-related protein 2/3 complex (Arp2/3), required for actin filament branching, has two ARPC1 component isoforms, with ARPC1B prominently expressed in blood cells. Here we show in a child with microthrombocytopenia, eosinophilia and inflammatory disease, a homozygous frameshift mutation in ARPC1B (p.Val91Trpfs*30). Platelet lysates reveal no ARPC1B protein and greatly reduced Arp2/3 complex. Missense ARPC1B mutations are identified in an unrelated patient with similar symptoms and ARPC1B deficiency. ARPC1B-deficient platelets are microthrombocytes similar to those seen in Wiskott–Aldrich syndrome that show aberrant spreading consistent with loss of Arp2/3 function. Knockout of ARPC1B in megakaryocytic cells results in decreased proplatelet formation, and as observed in platelets from patients, increased ARPC1A expression. Thus loss of ARPC1B produces a unique set of platelet abnormalities, and is associated with haematopoietic/immune symptoms affecting cell lineages where this isoform predominates. In agreement with recent experimental studies, our findings suggest that ARPC1 isoforms are not functionally interchangeable.

ARPC1B is a component of the actin-related protein 2/3 complex (Arp2/3), which is required for actin filament branching. Kahr et al. show that ARPC1B deficiency in humans is associated with severe multisystem disease that includes platelet abnormalities, eosinophilia, eczema and other indicators of immune disease.

[Advances in research on childhood neutropenia]

Neutrophils, an important type of human immune cells, are involved in host defense against infections. Neutropenia refers to a group of diseases manifesting as a reduction in the absolute value of mature neutrophils and is often accompanied by an increased risk of bacterial infection. According to etiology and pathogenesis, neutropenia is classified into congenital and acquired neutropenia. This article reviews the current research status and advances in the etiology of neutropenia in children. A deep understanding of the etiology of neutropenia helps to improve the diagnosis and treatment of this disease.

A risk factor analysis of outcomes after unrelated cord blood transplantation for children with Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome is a severe X-linked recessive immune deficiency disorder. A scoring system of Wiskott-Aldrich syndrome severity (0.5–5) distinguishes two phenotypes: X-linked thrombocytopenia and classic Wiskott-Aldrich syndrome. Hematopoietic cell transplantation is curative for Wiskott-Aldrich syndrome; however, the use of unrelated umbilical cord blood transplantation has seldom been described. We analyzed umbilical cord blood transplantation outcomes for 90 patients. The median age at umbilical cord blood transplantation was 1.5 years. Patients were classified according to clinical scores [2 (23%), 3 (30%), 4 (23%) and 5 (19%)]. Most patients underwent HLA-mismatched umbilical cord blood transplantation and myeloablative conditioning with anti-thymocyte globulin. The cumulative incidence of neutrophil recovery at day 60 was 89% and that of grade II–IV acute graft-versus-host disease at day 100 was 38%. The use of methotrexate for graft-versus-host disease prophylaxis delayed engraftment (P=0.02), but decreased acute graft-versus-host disease (P=0.03). At 5 years, overall survival and event-free survival rates were 75% and 70%, respectively. The estimated 5-year event-free survival rates were 83%, 73% and 55% for patients with a clinical score of 2, 4–5 and 3, respectively. In multivariate analysis, age <2 years at the time of the umbilical cord blood transplant and a clinical phenotype of X-linked thrombocytopenia were associated with improved event-free survival. Overall survival tended to be better in patients transplanted after 2007 (P=0.09). In conclusion, umbilical cord blood transplantation is a good alternative option for young children with Wiskott-Aldrich syndrome lacking an HLA identical stem cell donor.

Autoinhibition of the Nuclease ARTEMIS Is Mediated by a Physical Interaction between Its Catalytic and C-terminal Domains

The nuclease ARTEMIS is essential for the development of B and T lymphocytes. It is required for opening DNA hairpins generated during antigen receptor gene assembly from variable (V), diversity (D), and joining (J) subgenic elements (V(D)J recombination). As a member of the non-homologous end-joining pathway, it is also involved in repairing a subset of pathological DNA double strand breaks. Loss of ARTEMIS function therefore results in radiosensitive severe combined immunodeficiency (RS-SCID). The hairpin opening activity is dependent on the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), which can bind to and phosphorylate ARTEMIS. The ARTEMIS C terminus is dispensable for cellular V(D)J recombination and in vitro nuclease assays with C-terminally truncated ARTEMIS showing DNA-PKcs-independent hairpin opening activity. Therefore, it has been postulated that ARTEMIS is regulated via autoinhibition by its C terminus. To obtain evidence for the autoinhibition model, we performed co-immunoprecipitation experiments with combinations of ARTEMIS mutants. We show that an N-terminal fragment comprising the catalytic domain can interact both with itself and with a C-terminal fragment. Amino acid exchanges N456A+S457A+E458Q in the C terminus of full-length ARTEMIS resulted in unmasking of the N terminus and in increased ARTEMIS activity in cellular V(D)J recombination assays. Mutations in ARTEMIS-deficient patients impaired the interaction with the C terminus and also affected protein stability. The interaction between the N- and C-terminal domains was not DNA-PKcs-dependent, and phosphomimetic mutations in the C-terminal domain did not result in unmasking of the catalytic domain. Our experiments provide strong evidence that a physical interaction between the C-terminal and catalytic domains mediates ARTEMIS autoinhibition.

Resetting microbiota by Lactobacillus reuteri inhibits T reg deficiency-induced autoimmunity via adenosine A2A receptors

He et al. show that T reg deficiency markedly induces autoimmunity and shifts gut microbiota. Remodeling microbiota by Lactobacillus reuteri was found to inhibit autoimmunity via the metabolite inosine, which interacts with the adenosine A_2A receptor. This finding establishes a link between the gut microbiota, A_2A receptors, and autoimmunity induced by T reg cell deficiency.

Regulatory T (T reg) cell deficiency causes lethal, CD4⁺ T cell–driven autoimmune diseases. Stem cell transplantation is used to treat these diseases, but this procedure is limited by the availability of a suitable donor. The intestinal microbiota drives host immune homeostasis by regulating the differentiation and expansion of T reg, Th1, and Th2 cells. It is currently unclear if T reg cell deficiency–mediated autoimmune disorders can be treated by targeting the enteric microbiota. Here, we demonstrate that Foxp3⁺ T reg cell deficiency results in gut microbial dysbiosis and autoimmunity over the lifespan of scurfy (SF) mouse. Remodeling microbiota with Lactobacillus reuteri prolonged survival and reduced multiorgan inflammation in SF mice. L. reuteri changed the metabolomic profile disrupted by T reg cell deficiency, and a major effect was to restore levels of the purine metabolite inosine. Feeding inosine itself prolonged life and inhibited multiorgan inflammation by reducing Th1/Th2 cells and their associated cytokines. Mechanistically, the inhibition of inosine on the differentiation of Th1 and Th2 cells in vitro depended on adenosine A_2A receptors, which were also required for the efficacy of inosine and of L. reuteri in vivo. These results reveal that the microbiota–inosine–A_2A receptor axis might represent a potential avenue for combatting autoimmune diseases mediated by T reg cell dysfunction.

Corneal ulceration and episcleritis associated with Wiskott–Aldrich syndrome

Purpose

To present anterior segment ophthalmic manifestations of Wiskott–Aldrich syndrome (WAS), a rare X-linked primary immune-deficiency.

Observations

A 15-year old male with WAS presented with multiple corneal ulcers of the left eye. Once resolved, this was followed by separate episodes of episcleritis in the left eye and corneal infiltrates of the right eye. Successful treatment included topical antibiotics and anti-inflammatories.

Conclusions

Ocular manifestations of WAS, due to secondary infection and inflammation, may be severe. This case report emphasizes the importance of prompt ophthalmic evaluation and treatment of these patients.

FOXP3+ Tregs require WASP to restrain Th2-mediated food allergy

In addition to the infectious consequences of immunodeficiency, patients with Wiskott-Aldrich syndrome (WAS) often suffer from poorly understood exaggerated immune responses that result in autoimmunity and elevated levels of serum IgE. Here, we have shown that WAS patients and mice deficient in WAS protein (WASP) frequently develop IgE-mediated reactions to common food allergens. WASP-deficient animals displayed an adjuvant-free IgE-sensitization to chow antigens that was most pronounced for wheat and soy and occurred under specific pathogen-free as well as germ-free housing conditions. Conditional deletion of Was in FOXP3+ Tregs resulted in more severe Th2-type intestinal inflammation than that observed in mice with global WASP deficiency, indicating that allergic responses to food allergens are dependent upon loss of WASP expression in this immune compartment. While WASP-deficient Tregs efficiently contained Th1- and Th17-type effector differentiation in vivo, they failed to restrain Th2 effector responses that drive allergic intestinal inflammation. Loss of WASP was phenotypically associated with increased GATA3 expression in effector memory FOXP3+ Tregs, but not in naive-like FOXP3+ Tregs, an effect that occurred independently of increased IL-4 signaling. Our results reveal a Treg-specific role for WASP that is required for prevention of Th2 effector cell differentiation and allergic sensitization to dietary antigens.

Cancers Related to Immunodeficiencies: Update and Perspectives

The life span of patients with primary and secondary immunodeficiency is increasing due to recent improvements in therapeutic strategies. While the incidence of primary immunodeficiencies (PIDs) is 1:10,000 births, that of secondary immunodeficiencies are more common and are associated with posttransplantation immune dysfunction, with immunosuppressive medication for human immunodeficiency virus or with human T-cell lymphotropic virus infection. After infection, malignancy is the most prevalent cause of death in both children and adults with (PIDs). PIDs more often associated with cancer include common variable immunodeficiency (CVID), Wiskott-Aldrich syndrome, ataxia-telangiectasia, and severe combined immunodeficiency. This suggests that a protective immune response against both infectious non-self-(pathogens) and malignant self-challenges (cancer) exists. The increased incidence of cancer has been attributed to defective elimination of altered or "transformed" cells and/or defective immunity towards cancer cells. The concept of aberrant immune surveillance occurring in PIDs is supported by evidence in mice and from patients undergoing immunosuppression after transplantation. Here, we discuss the importance of PID defects in the development of malignancies and the current limitations associated with molecular pathogenesis of these diseases and emphasize the need for further knowledge of how specific mutations can modulate the immune system to alter immunosurveillance and thereby play a key role in the etiology of malignancies in PID patients.