The Wiskott-Aldrich Syndrome Protein Regulates Nuclear Translocation of NFAT2 and NF-κB (RelA) Independently of Its Role in Filamentous Actin Polymerization and Actin Cytoskeletal Rearrangement

Actin Retrograde Flow Regulated by the Wiskott–Aldrich Syndrome Protein Drives the Natural Killer Cell Response

Understanding the crosstalk between natural killer (NK) cells and the tumor microenvironment (TME) has enhanced the potential of exploiting the interplay between activation and inhibition of NK cells for immunotherapy. This interaction is crucial for understanding how tumor cells escape NK cell immune surveillance. NK cell dysfunction is regulated by two molecular mechanisms, downregulated activating receptor ligand expression on the tumor cells, and upregulated inhibitory signals delivered to NK cells. Recent studies demonstrated the role of mechanotransduction in modulating NK cell responses in the TME. The immunological synapse represents a functional interface between the NK cell and its target, regulated by Actin Retrograde Flow (ARF), which drives the adhesion molecules and receptors toward the central zone of the immunological synapse (IS). Here, we further characterize the role of ARF in controlling the immune response of NK cells, using CRISPR/cas9-mediated Wiskott–Aldrich Syndrome protein (WASp) gene silencing of NK cells. We demonstrate that WASp regulates ARF velocity, affecting the conformation and function of the key NK inhibitory regulator, SH2-domain containing protein tyrosine phosphatase-1 (SHP-1), and consequently, the NK cell response. Our results demonstrate the potential of modulating the biophysical and intracellular regulation of NK activation as a promising approach for improving immunotherapy.

Pyroptosis in host defence against bacterial infection

Pyroptosis, a regulated form of pro-inflammatory cell death, is characterised by cell lysis and by the release of cytokines, damage- and pathogen-associated molecular patterns. It plays an important role during bacterial infection, where it can promote an inflammatory response and eliminate the replicative niche of intracellular pathogens. Recent work, using a variety of bacterial pathogens, has illuminated the versatility of pyroptosis, revealing unexpected and important concepts underlying host defence. In this Review, we overview the molecular mechanisms underlying pyroptosis and discuss their role in host defence, from the single cell to the whole organism. We focus on recent studies using three cellular microbiology paradigms - Mycobacterium tuberculosis, Salmonella Typhimurium and Shigella flexneri - that have transformed the field of pyroptosis. We compare insights discovered in tissue culture, zebrafish and mouse models, highlighting the advantages and disadvantages of using these complementary infection models to investigate pyroptosis and for modelling human infection. Moving forward, we propose that in-depth knowledge of pyroptosis obtained from complementary infection models can better inform future studies using higher vertebrates, including humans, and help develop innovative host-directed therapies to combat bacterial infection.

The Role of the Cytoskeleton in Regulating the Natural Killer Cell Immune Response in Health and Disease: From Signaling Dynamics to Function

Natural killer (NK) cells are innate lymphoid cells, which play key roles in elimination of virally infected and malignant cells. The balance between activating and inhibitory signals derived from NK surface receptors govern the NK cell immune response. The cytoskeleton facilitates most NK cell effector functions, such as motility, infiltration, conjugation with target cells, immunological synapse assembly, and cytotoxicity. Though many studies have characterized signaling pathways that promote actin reorganization in immune cells, it is not completely clear how particular cytoskeletal architectures at the immunological synapse promote effector functions, and how cytoskeletal dynamics impact downstream signaling pathways and activation. Moreover, pioneering studies employing advanced imaging techniques have only begun to uncover the architectural complexity dictating the NK cell activation threshold; it is becoming clear that a distinct organization of the cytoskeleton and signaling receptors at the NK immunological synapse plays a decisive role in activation and tolerance. Here, we review the roles of the actin cytoskeleton in NK cells. We focus on how actin dynamics impact cytolytic granule secretion, NK cell motility, and NK cell infiltration through tissues into inflammatory sites. We will also describe the additional cytoskeletal components, non-muscle Myosin II and microtubules that play pivotal roles in NK cell activity. Furthermore, special emphasis will be placed on the role of the cytoskeleton in assembly of immunological synapses, and how mutations or downregulation of cytoskeletal accessory proteins impact NK cell function in health and disease.

The Common Cytokine Receptor γ Chain Family of Cytokines

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on their sharing the common cytokine receptor γ chain (γc), which was originally discovered as the third receptor component of the IL-2 receptor, IL-2Rγ. The IL2RG gene is located on the X chromosome and is mutated in humans with X-linked severe combined immunodeficiency (XSCID). The breadth of the defects in XSCID could not be explained solely by defects in IL-2 signaling, and it is now clear that γc is a shared receptor component of the six cytokines noted above, making XSCID a disease of defective cytokine signaling. Janus kinase (JAK)3 associates with γc, and JAK3-deficient SCID phenocopies XSCID, findings that served to stimulate the development of JAK3 inhibitors as immunosuppressants. γc family cytokines collectively control broad aspects of lymphocyte development, growth, differentiation, and survival, and these cytokines are clinically important, related to allergic and autoimmune diseases and cancer as well as immunodeficiency. In this review, we discuss the actions of these cytokines, their critical biological roles and signaling pathways, focusing mainly on JAK/STAT (signal transducers and activators of transcription) signaling, and how this information is now being used in clinical therapeutic efforts.

R-loops cause genomic instability in T helper lymphocytes from patients with Wiskott-Aldrich syndrome

BACKGROUND

Wiskott-Aldrich syndrome (WAS), X-linked thrombocytopenia (XLT), and X-linked neutropenia, which are caused by WAS mutations affecting Wiskott-Aldrich syndrome protein (WASp) expression or activity, manifest in immunodeficiency, autoimmunity, genomic instability, and lymphoid and other cancers. WASp supports filamentous actin formation in the cytoplasm and gene transcription in the nucleus. Although the genetic basis for XLT/WAS has been clarified, the relationships between mutant forms of WASp and the diverse features of these disorders remain ill-defined.

OBJECTIVE

We sought to define how dysfunctional gene transcription is causally linked to the degree of T_H cell deficiency and genomic instability in the XLT/WAS clinical spectrum.

METHODS

In human T_H1- or T_H2-skewing cell culture systems, cotranscriptional R-loops (RNA/DNA duplex and displaced single-stranded DNA) and DNA double-strand breaks (DSBs) were monitored in multiple samples from patients with XLT and WAS and in normal T cells depleted of WASp.

RESULTS

WASp deficiency provokes increased R-loops and R-loop-mediated DSBs in T_H1 cells relative to T_H2 cells. Mechanistically, chromatin occupancy of serine 2-unphosphorylated RNA polymerase II is increased, and that of topoisomerase 1, an R-loop preventing factor, is decreased at R-loop-enriched regions of IFNG and TBX21 (T_H1 genes) in T_H1 cells. These aberrations accompany increased unspliced (intron-retained) and decreased spliced mRNA of IFNG and TBX21 but not IL13 (T_H2 gene). Significantly, increased cellular load of R-loops and DSBs, which are normalized on RNaseH1-mediated suppression of ectopic R-loops, inversely correlates with disease severity scores.

CONCLUSION

Transcriptional R-loop imbalance is a novel molecular defect causative in T_H1 immunodeficiency and genomic instability in patients with WAS. The study proposes that cellular R-loop load could be used as a potential biomarker for monitoring symptom severity and prognostic outcome in the XLT-WAS clinical spectrum and could be targeted therapeutically.

Clinical Manifestations and Pathophysiological Mechanisms of the Wiskott-Aldrich Syndrome

The Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder originally described by Dr. Alfred Wiskott in 1937 and Dr. Robert Aldrich in 1954 as a familial disease characterized by infections, bleeding tendency, and eczema. Today, it is well recognized that the syndrome has a wide clinical spectrum ranging from mild, isolated thrombocytopenia to full-blown presentation that can be complicated by life-threatening hemorrhages, immunodeficiency, atopy, autoimmunity, and cancer. The pathophysiology of classic and emerging features is being elucidated by clinical studies, but remains incompletely defined, which hinders the application of targeted therapies. At the same time, progress of hematopoietic stem cell transplantation and gene therapy offer optimistic prospects for treatment options aimed at the replacement of the defective lymphohematopoietic system that have the potential to provide a cure for this rare and polymorphic disease.

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.

WASH overexpression enhances cancer stem cell properties and correlates with poor prognosis of esophageal carcinoma

There is increasing evidence that cytoskeleton remodeling is involved in cancer progression. Wiskott-Aldrich syndrome protein (WASP) family represents a key regulator of actin cytoskeleton remodeling. However, the underlying mechanism of the WASP family in cancer progression remains elusive. Here, we studied the role of WASP and SCAR Homolog (WASH), a recently identified WASP family member, in human esophageal squamous cell carcinoma (ESCC). Using three human ESCC cell lines, we found that WASH expression was significantly elevated in cancer stem-like cells enriched by sphere formation assay. WASH knockdown decreased the sphere-forming capacity of esophageal cancer cells whereas WASH over-expression exhibited the opposite effect. Mechanistically, we identified interleukin-8 (IL-8) as a key downstream target of WASH. IL-8 knockdown completely attenuated tumor sphere formation induced by WASH overexpression. WASH knockdown also delayed the growth of human ESCC xenografts in BALB/c nude mice. Importantly, high WASH levels were associated with poor clinical prognosis in a total of 145 human ESCC tissues. Collectively, our results suggest an essential role of the WASH/IL-8 pathway in human ESCC by maintaining the stemness of cancer cells. Hence, targeting this pathway might represent a promising strategy to control human esophageal carcinoma.

IL-2 in the tumor microenvironment is necessary for Wiskott-Aldrich syndrome protein deficient NK cells to respond to tumors in vivo

To kill target cells, natural killer (NK) cells organize signaling from activating and inhibitory receptors to form a lytic synapse. Wiskott-Aldrich syndrome (WAS) patients have loss-of-function mutations in the actin regulator WASp and suffer from immunodeficiency with increased risk to develop lymphoreticular malignancies. NK cells from WAS patients fail to form lytic synapses, however, the functional outcome in vivo remains unknown. Here, we show that WASp KO NK cells had decreased capacity to degranulate and produce IFNγ upon NKp46 stimulation and this was associated with reduced capacity to kill MHC class I-deficient hematopoietic grafts. Pre-treatment of WASp KO NK cells with IL-2 ex vivo restored degranulation, IFNγ production, and killing of MHC class I negative hematopoietic grafts. Moreover, WASp KO mice controlled growth of A20 lymphoma cells that naturally produced IL-2. WASp KO NK cells showed increased expression of DNAM-1, LAG-3, and KLRG1, all receptors associated with cellular exhaustion and NK cell memory. NK cells isolated from WAS patient spleen cells showed increased expression of DNAM-1 and had low to negative expression of CD56, a phenotype associated with NK cells exhaustion. Finally, in a cohort of neuroblastoma patients we identified a strong correlation between WASp, IL-2, and patient survival.

WASH has a critical role in NK cell cytotoxicity through Lck-mediated phosphorylation

Natural killer (NK) cells are important effector cells of the innate immune system to kill certain virus-infected and transformed cells. Wiskott–Aldrich Syndrome protein (WASP) and SCAR homolog (WASH) has been identified as a member of WASP family proteins implicated in regulating the cytoskeletal reorganization, yet little is known about its function in lymphocytes. Here we demonstrate that WASH is crucial for NK cell cytotoxicity. WASH was found to colocalize with lytic granules upon NK cell activation. Knockdown of WASH expression substantially inhibited polarization and release of lytic granules to the immune synapse, resulting in the impairment of NK cell cytotoxicity. More importantly, our data also define a previously unappreciated mechanism for WASH function, in which Src family kinase Lck can interact with WASH and induce WASH phosphorylation. Mutation of tyrosine residue Y141, identified here as the major site of WASH phosphorylation, partially blocked WASH tyrosine phosphorylation and NK cell cytotoxicity. Taken together, these observations suggest that WASH has a pivotal role for regulation of NK cell cytotoxicity through Lck-mediated Y141 tyrosine phosphorylation.

NKp46 Clusters at the Immune Synapse and Regulates NK Cell Polarization

Natural killer (NK) cells play an important role in first-line defense against tumor and virus-infected cells. The activity of NK cells is tightly regulated by a repertoire of cell surface expressed inhibitory and activating receptors. NKp46 is a major NK cell-activating receptor that is involved in the elimination of target cells. NK cells form different types of synapses that result in distinct functional outcomes: cytotoxic, inhibitory, and regulatory. Recent studies revealed that complex integration of NK receptor signaling controls cytoskeletal rearrangement and other immune synapse-related events. However, the distinct nature by which NKp46 participates in NK immunological synapse formation and function remains unknown. In this study, we determined that NKp46 forms microclusters structures at the immune synapse between NK cells and target cells. Over-expression of human NKp46 is correlated with increased accumulation of F-actin mesh at the immune synapse. Concordantly, knock-down of NKp46 in primary human NK cells decreased recruitment of F-actin to the synapse. Live cell imaging experiments showed a linear correlation between NKp46 expression and lytic granules polarization to the immune synapse. Taken together, our data suggest that NKp46 signaling directly regulates the NK lytic immune synapse from early formation to late function.

SUMOylation-disrupting WAS mutation converts WASp from a transcriptional activator to a repressor of NF-κB response genes in T cells

In Wiskott-Aldrich syndrome (WAS), immunodeficiency and autoimmunity often comanifest, yet how WAS mutations misregulate chromatin-signaling in Thelper (TH) cells favoring development of auto-inflammation over protective immunity is unclear. Previously, we identified an essential promoter-specific, coactivator role of nuclear-WASp in TH1 gene transcription. Here we identify small ubiquitin-related modifier (SUMO)ylation as a novel posttranslational modification of WASp, impairment of which converts nuclear-WASp from a transcriptional coactivator to a corepressor of nuclear factor (NF)-κB response genes in human (TH)1-differentiating cells. V75M, one of many disease-causing mutations occurring in SUMO*motif (72-ψψψψKDxxxxSY-83) of WASp, compromises WASp-SUMOylation, associates with COMMD1 to attenuate NF-κB signaling, and recruits histone deacetylases-6 (HDAC6) to p300-marked promoters of NF-κB response genes that pattern immunity but not inflammation. Consequently, proteins mediating adaptive immunity (IFNG, STAT1, TLR1) are deficient, whereas those mediating auto-inflammation (GM-CSF, TNFAIP2, IL-1β) are paradoxically increased in TH1 cells expressing SUMOylation-deficient WASp. Moreover, SUMOylation-deficient WASp favors ectopic development of the TH17-like phenotype (↑IL17A, IL21, IL22, IL23R, RORC, and CSF2) under TH1-skewing conditions, suggesting a role for WASp in modulating TH1/TH17 plasticity. Notably, pan-histone deacetylase inhibitors lift promoter-specific repression imposed by SUMOylation-deficient WASp and restore misregulated gene expression. Our findings uncovering a SUMOylation-based mechanism controlling WASp's dichotomous roles in transcription may have implications for personalized therapy for patients carrying mutations that perturb WASp-SUMOylation.

B-cell reconstitution after lentiviral vector-mediated gene therapy in patients with Wiskott-Aldrich syndrome

Background

Wiskott-Aldrich syndrome (WAS) is a severe X-linked immunodeficiency characterized by microthrombocytopenia, eczema, recurrent infections, and susceptibility to autoimmunity and lymphomas. Hematopoietic stem cell transplantation is the treatment of choice; however, administration of WAS gene–corrected autologous hematopoietic stem cells has been demonstrated as a feasible alternative therapeutic approach.

Objective

Because B-cell homeostasis is perturbed in patients with WAS and restoration of immune competence is one of the main therapeutic goals, we have evaluated reconstitution of the B-cell compartment in 4 patients who received autologous hematopoietic stem cells transduced with lentiviral vector after a reduced-intensity conditioning regimen combined with anti-CD20 administration.

Methods

We evaluated B-cell counts, B-cell subset distribution, B cell–activating factor and immunoglobulin levels, and autoantibody production before and after gene therapy (GT). WAS gene transfer in B cells was assessed by measuring vector copy numbers and expression of Wiskott-Aldrich syndrome protein.

Results

After lentiviral vector-mediated GT, the number of transduced B cells progressively increased in the peripheral blood of all patients. Lentiviral vector-transduced progenitor cells were able to repopulate the B-cell compartment with a normal distribution of B-cell subsets both in bone marrow and the periphery, showing a WAS protein expression profile similar to that of healthy donors. In addition, after GT, we observed a normalized frequency of autoimmune-associated CD19⁺CD21⁻CD35⁻ and CD21^low B cells and a reduction in B cell–activating factor levels. Immunoglobulin serum levels and autoantibody production improved in all treated patients.

Conclusions

We provide evidence that lentiviral vector-mediated GT induces transgene expression in the B-cell compartment, resulting in ameliorated B-cell development and functionality and contributing to immunologic improvement in patients with WAS.

Actin foci facilitate activation of the phospholipase C-γ in primary T lymphocytes via the WASP pathway

Wiscott Aldrich Syndrome protein (WASP) deficiency results in defects in calcium ion signaling, cytoskeletal regulation, gene transcription and overall T cell activation. The activation of WASP constitutes a key pathway for actin filament nucleation. Yet, when WASP function is eliminated there is negligible effect on actin polymerization at the immunological synapse, leading to gaps in our understanding of the events connecting WASP and calcium ion signaling. Here, we identify a fraction of total synaptic F-actin selectively generated by WASP in the form of distinct F-actin ‘foci’. These foci are polymerized de novo as a result of the T cell receptor (TCR) proximal tyrosine kinase cascade, and facilitate distal signaling events including PLCγ1 activation and subsequent cytoplasmic calcium ion elevation. We conclude that WASP generates a dynamic F-actin architecture in the context of the immunological synapse, which then amplifies the downstream signals required for an optimal immune response.

DOI:http://dx.doi.org/10.7554/eLife.04953.001

The immune system is made up of several types of cells that protect the body against infection and disease. Immune cells such as T cells survey the body and when receptors on their surface encounter infected cells, the receptors activate the T cell by triggering a signaling pathway.

The early stages of T cell receptor signaling lead to the formation of a cell–cell contact zone called the immunological synapse. Filaments of a protein called F-actin—which are continuously assembled and taken apart—make versatile networks and help the immunological synapse to form. F-actin filaments have crucial roles in the later stages of T cell receptor signaling as well, but how they contribute to this is not clear. Whether it is the same F-actin network that participates both in synapse formation and the late stages of T cell receptor signaling, and if so, then by what mechanism, remains unknown.

The answers came from examining the function of a protein named Wiscott-Aldrich Syndrome Protein (WASP), which forms an F-actin network at the synapse. Loss of WASP is known to result in the X-linked Wiscott-Aldrich Syndrome immunodeficiency and bleeding disorder in humans. Although T cells missing WASP can construct immunological synapses, and these synapses do have normal levels of F-actin and early T cell receptor signaling, they still fail to respond to infected cells properly.

Kumari et al. analyzed the detailed structure and dynamics of actin filament networks at immunological synapses of normal and WASP-deficient T cells. Normally, cells had visible foci of newly polymerized F-actin directly above T cell receptor clusters in the immunological synapses, but these foci were not seen in the cells lacking WASP. Kumari et al. found that the F-actin foci facilitate the later stages of the signaling that activates the T cells; this signaling was lacking in WASP-deficient cells.

Altogether, Kumari et al. show that WASP-generated F-actin foci at immunological synapses bridge the early and later stages of T cell receptor signaling, effectively generating an optimal immune response against infected cells. Further work will now be needed to understand whether there are other F-actin substructures that play specialized roles in T cell signaling, and if foci play a related role in other cell types known to be affected in Wiscott-Aldrich Syndrome immunodeficiency.

DOI:http://dx.doi.org/10.7554/eLife.04953.002

Wiskott-Aldrich syndrome in a girl caused by heterozygous WASP mutation and extremely skewed X-chromosome inactivation: a novel association with maternal uniparental isodisomy 6

Wiskott-Aldrich syndrome (WAS) is an X-linked disease characterized by microthrombocytopenia, eczema and immune deficiency, caused primarily by mutations in the WASP (Wiskott-Aldrich syndrome protein) gene. Female carriers are usually asymptomatic because of the preferential activation of the normal, nonmutated X-chromosome in their hematopoietic cells. We report our observations of a female child with WAS, who displayed symptoms of congenital thrombocytopenia. DNA sequencing analysis of the WASP gene revealed a heterozygous nonsense mutation in exon 10. The expressions of WASP and normal WASP mRNA were defective. We found preferential inactivation of the X-chromosome on which wild-type WASP was located. Single-nucleotide polymorphism microarray testing and the analysis of the polymorphic variable number of tandem repeat regions revealed maternal uniparental isodisomy of chromosome 6 (UPD6). Our results underscore the importance of WASP evaluation in females with congenital thrombocytopenia and suggest that UPD6 might be related to the pathophysiology of nonrandom X-chromosome inactivation.

Nuclear role of WASp in gene transcription is uncoupled from its ARP2/3-dependent cytoplasmic role in actin polymerization

Defects in Wiskott-Aldrich Syndrome protein (WASp) underlie development of WAS, an X-linked immunodeficiency and autoimmunity disorder of childhood. Nucleation-promoting factors (NPFs) of the WASp family generate F-actin in the cytosol via the VCA (verprolin-homology, cofilin-homology, and acidic) domain and support RNA polymerase II-dependent transcription in the nucleus. Whether nuclear-WASp requires the integration of its actin-related protein (ARP)2/3-dependent cytoplasmic function to reprogram gene transcription, however, remains unresolved. Using the model of human TH cell differentiation, we find that WASp has a functional nuclear localizing and nuclear exit sequences, and accordingly, its effects on transcription are controlled mainly at the level of its nuclear entry and exit via the nuclear pore. Human WASp does not use its VCA-dependent, ARP2/3-driven, cytoplasmic effector mechanisms to support histone H3K4 methyltransferase activity in the nucleus of TH1-skewed cells. Accordingly, an isolated deficiency of nuclear-WASp is sufficient to impair the transcriptional reprogramming of TBX21 and IFNG promoters in TH1-skewed cells, whereas an isolated deficiency of cytosolic-WASp does not impair this process. In contrast, nuclear presence of WASp in TH2-skewed cells is small, and its loss does not impair transcriptional reprogramming of GATA3 and IL4 promoters. Our study unveils an ARP2/3:VCA-independent function of nuclear-WASp in TH1 gene activation that is uncoupled from its cytoplasmic role in actin polymerization.

The central role of the cytoskeleton in mechanisms and functions of the NK cell immune synapse

Natural killer (NK) cells discriminate between healthy and unhealthy target cells through a balance of activating and inhibitory signals at direct intercellular contacts called immune synapses. Rearrangements in the cellular cytoskeleton have long been known to be critical in assembly of immune synapses. Here, through bringing together the vast literature on this subject, the number of different ways in which the cytoskeleton is important becomes evident. The dynamics of filamentous actin are critical in (i) creating the nanometer-scale organization of NK cell receptors, (ii) establishing cellular polarity, (iii) coordinating immune receptor and integrin-mediated signaling, and (iv) directing secretion of lytic granules and cytokines. The microtubule network also is important in the delivery of lytic granules and vesicles containing cytokines to the immune synapse. Together, these data establish that the cytoskeleton acts as a central regulator of this complex and dynamic process - and an enormous amount of NK cell biology is controlled through the cytoskeleton.

Whole-exome sequencing identifies Coronin-1A deficiency in 3 siblings with immunodeficiency and EBV-associated B-cell lymphoproliferation

BACKGROUND

Primary immunodeficiencies are a rare group of inborn diseases characterized by a broad clinical and genetic heterogeneity. Substantial advances in the identification of the underlying molecular mechanisms can be achieved through the study of patients with increased susceptibility to specific infections and immune dysregulation. We evaluated 3 siblings from a consanguineous family presenting with EBV-associated B-cell lymphoproliferation at an early age (12, 7½, and 14 months, respectively) and profound naive T-cell lymphopenia.

OBJECTIVE

On the basis of the hypothesis of a rare inborn immunodeficiency of autosomal recessive inheritance, we sought to characterize the underlying genetic defect.

METHODS

We performed genome-wide homozygosity mapping, followed by whole-exome sequencing.

RESULTS

We identified a homozygous inherited missense mutation in the gene encoding Coronin-1A (CORO1A) in the 3 siblings. This mutation, p. V134M, results in the substitution of an evolutionarily conserved amino acid within the β-propeller domain, which abrogates almost completely the protein expression in the patients' cells. In addition to a significant diminution of naive T-cell numbers, we found impaired development of a diverse T-cell repertoire, near-to-absent invariant natural killer T cells, and severely diminished mucosal-associated invariant T cell numbers.

CONCLUSIONS

Our findings define a new clinical entity of a primary immunodeficiency with increased susceptibility to EBV-induced lymphoproliferation in patients associated with hypomorphic Coronin-1A mutation.

The bone morphogenetic protein receptor-1A pathway is required for lactogenic differentiation of mammary epithelial cells in vitro

Bone morphogenetic proteins (BMPs) have been implicated in the control of proliferation, tissue formation, and differentiation. BMPs regulate the biology of stem and progenitor cells and can promote cellular differentiation, depending on the cell type and context. Although the BMP pathway is known to be involved in early embryonic development of the mammary gland via mesenchymal cells, its role in later epithelial cellular differentiation has not been examined. The majority of the mammary gland development occurs post-natal, and its final functional differentiation is characterized by the emergence of alveolar cells that produce milk proteins. Here, we tested the hypothesis that bone morphogenetic protein receptor 1A (BMPR1A) function was required for mammary epithelial cell differentiation. We found that the BMPR1A-SMAD1/5/8 pathway was predominantly active in undifferentiated mammary epithelial cells, compared with differentiated cells. Reduction of BMPR1A mRNA and protein, using short hairpin RNA, resulted in a reduction of SMAD1/5/8 phosphorylation in undifferentiated cells, indicating an impact on this pathway. When the expression of the BMPR1A gene knocked down in undifferentiated cells, this also prevented beta-casein production during differentiation of the mammary epithelial cells by lactogenic hormone stimulation. Addition of Noggin, a BMP antagonist, also prevented beta-casein expression. Together, this demonstrated that BMP-BMPR1A-SMAD1/5/8 signal transduction is required for beta-casein production, a marker of alveolar cell differentiation. This evidence functionally identifies BMPR1A as a potential new regulator of mammary epithelial alveolar cell differentiation.

Nuclear role of WASp in the pathogenesis of dysregulated TH1 immunity in human Wiskott-Aldrich syndrome

The clinical symptomatology in the X-linked Wiskott-Aldrich syndrome (WAS), a combined immunodeficiency and autoimmune disease resulting from WAS protein (WASp) deficiency, reflects the underlying coexistence of an impaired T helper 1 (TH1) immunity alongside intact TH2 immunity. This suggests a role for WASp in patterning T(H) subtype immunity, yet the molecular basis for the TH1-TH2 imbalance in human WAS is unknown. We have discovered a nuclear role for WASp in the transcriptional regulation of the TH1 regulator gene TBX21 at the chromatin level. In primary TH1-differentiating cells, a fraction of WASp is found in the nucleus, where it is recruited to the proximal promoter locus of the TBX21 gene, but not to the core promoter of GATA3 (a TH2 regulator gene) or RORc (a TH17 regulator gene). Genome-wide mapping demonstrates association of WASp in vivo with the gene-regulatory network that orchestrates TH1 cell fate choice in the human TH cell genome. Functionally, nuclear WASp associates with H3K4 trimethyltransferase [RBBP5 (retinoblastoma-binding protein 5)] and H3K9/H3K36 tridemethylase [JMJD2A (Jumonji domain-containing protein 2A)] proteins, and their enzymatic activity in vitro and in vivo is required for achieving transcription-permissive chromatin dynamics at the TBX21 proximal promoter in primary differentiating TH1 cells. During TH1 differentiation, the loss of WASp accompanies decreased enrichment of RBBP5 and, in a subset of WAS patients, also of filamentous actin at the TBX21 proximal promoter locus. Accordingly, human WASp-deficient TH cells, from natural mutation or RNA interference-mediated depletion, demonstrate repressed TBX21 promoter dynamics when driven under TH1-differentiating conditions. These chromatin derangements accompany deficient T-BET messenger RNA and protein expression and impaired TH1 function, defects that are ameliorated by reintroducing WASp. Our findings reveal a previously unappreciated role of WASp in the epigenetic control of T-BET transcription and provide a new mechanism for the pathogenesis of WAS by linking aberrant histone methylation at the TBX21 promoter to dysregulated adaptive immunity.

The Wiskott-Aldrich syndrome protein regulates CTL cytotoxicity and is required for efficient killing of B cell lymphoma targets

WAS is a primary immunodeficiency as a result of mutations in the gene encoding the WASP, a key actin regulator of hematopoietic cells. Whether killing defects in CD8(+) CTLs contribute to WAS-associated immunodeficiency and susceptibility to tumor development remains to be explored. CTL lines from WAS patients, generated by repeated stimulation with SAg-loaded B-EBV, displayed reduced production of cytokines (IL-2, IFN-γ, and TNF-α) but almost normal proliferation upon SAg stimulation. Although WAS CTLs killed target B cells in a SAg dose-dependent manner, their efficiency was reduced, especially at a low SAg dose. The cytotoxic efficiency of WAS CTLs was particularly reduced against tumoral B cell lines. WAS CTLs expressed normal levels of lytic molecules and demonstrated efficient exocytosis upon target cell encounter. However, the lytic granules appeared not to fully polarize toward the center of the CTL/tumor target cell contact area. Importantly, the use of a gene therapy lentiviral vector was sufficient to restore efficient cytotoxic activity. Our study suggests that CTL dysfunction contributes to the development of hematological malignancies in WAS patients.

Blockage of Notch1 signaling modulates the T-helper (Th)1/Th2 cell balance in chronic hepatitis B patients

AIM

Chronic hepatitis B virus (HBV) infection is thought to involve the imbalance of T-helper (Th)1/Th2 cells. Many procedures found Notch signaling involved the proliferation and differentiation of T lymphocytes during development and peripheral functions. The aim of this study was to discover the effect of blockage of Notch1 signaling to Th cells and the mechanisms involved in chronic hepatitis B patients.

METHODS

CD4(+) T cells from hepatitis B patients and healthy volunteers were isolated, and Notch1 expression of CD4(+) T cells was determined by reverse transcription polymerase chain reaction (RT-PCR). Blockage of Notch1 signaling of peripheral blood mononuclear cells (PBMC) from chronic hepatitis B patients, Th1- and Th2-type cytokines were assayed by enzyme-linked immunosorbent assay and levels of T-bet, GATA-3 mRNA were measured by RT-PCR.

RESULTS

Notch1 expression of CD4(+) T cells from chronic hepatitis B patients was upregulated, on the contrary to that from acute hepatitis B patients and healthy volunteers. Blockage of Notch1 signaling can strongly inhibit the production of Th2-type cytokines and the expression of GATA-3; the production of Th1-type cytokines and the expression of T-bet, however, were enhanced.

CONCLUSION

Blockage of Notch1 signaling could regulate the immune balance of Th1/Th2 in chronic hepatitis B patients, which may be mediated partly by regulating transcription factors T-bet and GATA-3.

WASP: a key immunological multitasker

The Wiskott-Aldrich syndrome protein (WASP) is an important regulator of the actin cytoskeleton that is required for many haematopoietic and immune cell functions, including effective migration, phagocytosis and immune synapse formation. Loss of WASP activity leads to Wiskott-Aldrich syndrome, an X-linked disease that is associated with defects in a broad range of cellular processes, resulting in complex immunodeficiency, autoimmunity and microthrombocytopenia. Intriguingly, gain of function mutations cause a separate disease that is mainly characterized by neutropenia. Here, we describe recent insights into the cellular mechanisms of these two related, but distinct, human diseases and discuss their wider implications for haematopoiesis, immune function and autoimmunity.

Navigating barriers: the challenge of directed secretion at the natural killer cell lytic immunological synapse

INTRODUCTION

Natural killer (NK) cells have an inherent ability to recognize and destroy a wide array of cells rendered abnormal by stress or disease. NK cells can kill a targeted cell by forming a tight interface-the lytic immunological synapse. This represents a dynamic molecular arrangement that over time progresses through a series of steps to ultimately deliver the contents of specialized organelles known as lytic granules.

DISCUSSION

In order to mediate cytotoxicity, the NK cell faces the challenge of mobilizing the lytic granules, polarizing them to the targeted cell, facilitating their approximation to the NK cell membrane, and releasing their contents.

CONCLUSION

This review is focused upon the final steps in accessing function through the lytic immunological synapse.

SWAP-70-like adapter of T cells: a novel Lck-regulated guanine nucleotide exchange factor coordinating actin cytoskeleton reorganization and Ca2+ signaling in T cells

SWAP-70-like adapter of T cells (SLAT) is a recently identified guanine nucleotide exchange factor (GEF) for Cdc42 and Rac1, which is highly expressed in both thymocytes and peripheral T cells. Here, we present and discuss findings resulting from biochemical and genetic analyses aimed at unveiling the role of SLAT in CD4+ T-cell development, activation, and T-helper (Th) cell differentiation. Slat(-/-) mice display a developmental defect at one of the earliest stages of thymocyte differentiation, the double negative 1 (DN1) stage, leading to decreased peripheral T-cell numbers. Slat(-/-) peripheral CD4+ T cells demonstrate impaired T-cell receptor/CD28-induced proliferation and IL-2 production. Moreover, SLAT positively regulates the development of Th1 and Th2 inflammatory responses by controlling Ca2+/NFAT signaling. SLAT is also a positive regulator of the recently emerging Th subset, i.e., Th17 cells, as evidenced by its critical role in Th17 cell-mediated central nervous system inflammation. Furthermore, TCR engagement induces SLAT translocation to the immunological synapse, a process mediated by its Lck-dependent phosphorylation, which thereafter facilitates the triggering of SLAT GEF activity towards Cdc42 and Rac1, leading to NFAT activation and Th1/Th2 differentiation. Future work will aim to dissect the interacting partners of SLAT and may thus shed light on the poorly understood events that coordinate and link actin cytoskeleton reorganization to Ca2+ signaling and gene transcription in T cells.

Wiskott-Aldrich syndrome protein is required for homeostasis and function of invariant NKT cells

NKT cells comprise a separate T lineage expressing semi-invariant T cell receptors. Canonical invariant NKT (iNKT) cells specifically recognize lipid Ags presented by CD1d, a MHC class I-like molecule. iNKT cells function, in part, as initial responders to bacterial infection and play a role in immune surveillance and tumor rejection. The Wiskott-Aldrich Syndrome protein (WASp) serves as a crucial link between cellular stimuli and cytoskeletal rearrangements. Although we and others have identified a key role for WASp in homeostasis of T-regulatory and marginal zone B cells, little data exist regarding the role for WASp within the iNKT lineage. Analysis of WASp-expressing cell populations in heterozygous female WASp mice revealed a substantial selective advantage for WASp(+) vs WASp(-) iNKT cells. Although adult WASp-deficient (WASp(-/-)) mice had normal thymic and bone marrow iNKT numbers, we observed 2- to 3-fold reduction in the numbers of iNKT cells in the spleen and liver. This peripheral iNKT deficit is manifested, in part, due to defective iNKT homeostasis. WASp(-/-) iNKT cells exhibited reduced levels of integrin surface expression and decreased homing and/or retention within peripheral tissues in a competitive repopulation model. In addition, analysis of young mice showed that WASp is important for both maturation and egress of thymic iNKT cells. WASp(-/-) iNKT cells also exhibited a marked reduction in Ag-induced proliferation and cytokine production. Our findings highlight the crucial role for WASp in iNKT development, homeostasis, and activation, and identify iNKT dysfunction as an additional factor likely to contribute to the clinical features observed in WAS patients.

The Wiskott-Aldrich syndrome protein is required for iNKT cell maturation and function

The Wiskott-Aldrich syndrome (WAS) protein (WASp) is a regulator of actin cytoskeleton in hematopoietic cells. Mutations of the WASp gene cause WAS. Although WASp is involved in various immune cell functions, its role in invariant natural killer T (iNKT) cells has never been investigated. Defects of iNKT cells could indeed contribute to several WAS features, such as recurrent infections and high tumor incidence. We found a profound reduction of circulating iNKT cells in WAS patients, directly correlating with the severity of clinical phenotype. To better characterize iNKT cell defect in the absence of WASp, we analyzed was(-/-) mice. iNKT cell numbers were significantly reduced in the thymus and periphery of was(-/-) mice as compared with wild-type controls. Moreover analysis of was(-/-) iNKT cell maturation revealed a complete arrest at the CD44(+) NK1.1(-) intermediate stage. Notably, generation of BM chimeras demonstrated a was(-/-) iNKT cell-autonomous developmental defect. was(-/-) iNKT cells were also functionally impaired, as suggested by the reduced secretion of interleukin 4 and interferon gamma upon in vivo activation. Altogether, these results demonstrate the relevance of WASp in integrating signals critical for development and functional differentiation of iNKT cells and suggest that defects in these cells may play a role in WAS pathology.

Formation and function of the lytic NK-cell immunological synapse

The natural killer (NK)-cell immunological synapse is the dynamic interface formed between an NK cell and its target cell. Formation of the NK-cell immunological synapse involves several distinct stages, from the initiation of contact with a target cell to the directed delivery of lytic-granule contents for target-cell lysis. Progression through the individual stages is regulated, and this tight regulation underlies the precision with which NK cells select and kill susceptible target cells (including virally infected cells and cancerous cells) that they encounter during their routine surveillance of the body.

New insights into the biology of Wiskott-Aldrich syndrome (WAS)

The Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency disease with a characteristic clinical phenotype that includes thrombocytopenia with small platelets, eczema, recurrent infections due to immunodeficiency, and an increased incidence of autoimmune manifestations and malignancies. The identification of the molecular defect in the WAS gene has broadened the clinical spectrum of disease to include chronic or intermittent X-linked thrombocytopenia (XLT), a relatively mild form of WAS, and X-linked neutropenia (XLN) due to an arrest of myelopoiesis. The pathophysiological mechanisms relate to defective actin polymerization in hematopoietic cells as a result of deficient or dysregulated activity of the WAS protein (WASp). The severity of disease is variable and somewhat predictable from genotype. Treatment strategies therefore range from conservative through to early definitive intervention by using allogeneic hematopoietic stem cell transplantation and potentially somatic gene therapy. All aspects of the condition from clinical presentation to molecular pathology and basic cellular mechanisms have been reviewed recently.

Tyrosine-phosphorylation-dependent translocation of the SLAT protein to the immunological synapse is required for NFAT transcription factor activation

SWAP-70-like adaptor of T cells (SLAT) is a guanine nucleotide exchange factor for Rho GTPases that regulates the development of T helper 1 (Th1) and Th2 cell inflammatory responses by controlling the Ca(2+)-NFAT signaling pathway. However, the mechanism used by SLAT to regulate these events is unknown. Here, we report that the T cell receptor (TCR)-induced translocation of SLAT to the immunological synapse required Lck-mediated phosphorylation of two tyrosine residues located in an immunoreceptor tyrosine-based activation motif-like sequence but was independent of the SLAT PH domain. This subcellular relocalization was coupled to, and necessary for, activation of the NFAT pathway. Furthermore, membrane targeting of the SLAT Dbl-homology (catalytic) domain was sufficient to trigger TCR-mediated NFAT activation and Th1 and Th2 differentiation in a Cdc42-dependent manner. Therefore, tyrosine-phosphorylation-mediated relocalization of SLAT to the site of antigen recognition is required for SLAT to exert its pivotal role in NFAT-dependent CD4(+) T cell differentiation.

Development of lentiviral gene therapy for Wiskott Aldrich syndrome

BACKGROUND

Wiskott Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency. This complex disease is characterised by microthrombocytopenia, recurrent infections, eczema and is associated with a high incidence of autoimmunity and of lymphoid malignancies. WAS is attracting growing attention not only because it highlights the rich cellular and systems biology revolving around cytoskeletal regulation but also because it is candidate for a haematopoietic stem cell gene therapy indication.

OBJECTIVES

As several groups are developing this novel approach, this review discusses the state of the art and challenges in clinical development of gene therapy for WAS, with particular regard to biosafety.

METHODS

In spite of the successes of haematopoietic gene therapy for genetic immune deficiencies, there is a need for more efficient transduction protocols and for vectors with a superior safety profile. Preclinical studies have provided reasonable expectations that haematopoietic gene therapy with a self-inactivated HIV-1-derived vector using the native gene promoter for expression of the WAS transgene will be safe and will lead to the restoration of WAS protein in the haematopoietic and immune system at levels sufficient to provide an improvement in the condition of WAS patients.

CONCLUSIONS

Phase I/II clinical studies will soon be initiated in several European centres to assess the safety and efficacy of this lentiviral vector in WAS patients.

Antiparallel segregation of notch components in the immunological synapse directs reciprocal signaling in allogeneic Th:DC conjugates

Direct T cell allorecognition underlies the development of a vigorous immune response in the clinical setting of acute graft rejection. The Notch pathway is an important regulator of Th immune responses, yet the molecular underpinnings of directional Notch signaling, otherwise critical for binary cell fate decisions, are unknown during autologous or allogeneic Th:DC interactions. Using the development of immune synapses (IS) in the allogeneic, human physiological Th:DC interaction, we demonstrate that Th-Notch1 receptor and DC-Notch ligands (Delta-like1, Jagged1) cluster in their apposed central-supramolecular-activation-clusters (cSMAC), whereas DC-Notch1 receptor and Th-Notch ligands cluster in their apposed peripheral-SMAC (pSMAC). Numb, a negative regulator of Notch, is excluded from the IS-microdomains where Notch1 receptor accumulates. This antiparallel arrangement across the partnering halves of the IS supports reciprocal Notch signal propagation in the DC-to-Th direction via the cSMAC and Th-to-DC direction via the pSMAC. As a result, processed Notch1 receptor (Notch-intracellular-domain, NICD1) and its ligands, as well as their downstream targets, HES-1 and phosphorylated-STAT3, accumulate in the nuclei of both cell-types. There is also enhancement of GLUT1 expression in both cell-types, as well as increased production of Th-IFN-gamma. Significantly, neutralizing Notch1R Ab inhibits NICD1 and HES-1 nuclear translocation, and production of IFN-gamma. In contrast, the IS formed during Ag-nonspecific, autologous Th:DC interaction is immature, resulting in failure of Notch1 receptor segregation and subsequent nuclear translocation of NICD1. Our results provide the first evidence for the asymmetric recruitment of Notch components in the Th:DC immunological synapse, which regulates the bidirectional Notch signal propagation.

Structure-function analysis of the WIP role in T cell receptor-stimulated NFAT activation: evidence that WIP-WASP dissociation is not required and that the WIP NH2 terminus is inhibitory

WASP and its binding partner WIP play important roles in T cells both in actin polymerization and in interleukin-2 transcription. Aberrations thereof contribute to the pathology of Wiskott-Aldrich syndrome (WAS). To directly evaluate the cooperativity of WIP and WASP in interleukin-2 transcription, we investigated how the WIP-WASP complex regulates NF-AT-mediated gene transcription. We developed an improved model system for analysis, using WIP and WASP cotransfection into Jurkat cells, in which strong induction of NFAT reporter activation is observed with anti-T cell receptor (TCR) antibody without the phorbol 12-myristate 13-acetate usually used previously. Using this system, our findings contradict a prevailing conceptual model of TCR-induced WIP-WASP dissociation by showing in three ways that the WIP-WASP complex mediates TCR-induced NFAT activation without dissociation. First, phosphorylation of WIP Ser(488) does not cause dissociation of the WIP-WASP complex. Second, WIP-WASP complexes do not dissociate demonstrably after TCR stimulation. Third, a fusion protein of WIP to WASP efficiently mediates NFAT activation. Next, our studies clarify that WIP stabilization of WASP explains otherwise unexpected results in TCR-induced NFAT activation. Finally, we find that the NH(2) terminus of WIP is a highly inhibitory region for TCR-mediated transcriptional activation in which at least two elements contribute: the NH(2)-terminal polyproline and the NH(2)-terminal actin-binding WH2 domain. This suggests that WIP, like WASP, is subject to autoinhibition. Our data indicate that the WIP-WASP complex plays an important role in WASP stabilization and NFAT activation.

Calcium signalling in lymphocyte activation and disease

Calcium signals in cells of the immune system participate in the regulation of cell differentiation, gene transcription and effector functions. An increase in intracellular levels of calcium ions (Ca2+) results from the engagement of immunoreceptors, such as the T-cell receptor, B-cell receptor and Fc receptors, as well as chemokine and co-stimulatory receptors. The major pathway that induces an increase in intracellular Ca2+ levels in lymphocytes is through store-operated calcium entry (SOCE) and calcium-release-activated calcium (CRAC) channels. This Review focuses on the role of Ca2+ signals in lymphocyte functions, the signalling pathways leading to Ca2+ influx, the function of the recently discovered regulators of Ca2+ influx (STIM and ORAI), and the relationship between Ca2+ signals and diseases of the immune system.

Impaired LPS-induced signaling in microglia overexpressing the Wiskott-Aldrich syndrome protein N-terminal domain

Wiskott-Aldrich syndrome protein (WASP) plays important roles in TCR signaling, but its roles in signal transduction in innate immune cells have not been well characterized. As microglia are the primary immune effector cells in the brain, WASP may possibly have important roles in microglial activation, such as production of inflammatory and anti-inflammatory cytokines and neurotoxic factors. Here, we established a microglial cell line from WASP dominant-negative transgenic (Tg) mice overexpressing the N-terminal enabled/vasodilator-stimulated phosphoprotein homology 1 (EVH1) domain. WASP Tg microglia were impaired in production of inflammatory cytokines such as tumor necrosis factor-alpha, IL-6 and IL-1beta upon LPS stimulation, whereas anti-inflammatory IL-10 production was significantly enhanced. Also, LPS-induced phosphorylation of nuclear factor kappaB was reduced in WASP Tg microglia. Furthermore, WASP Tg microglia exhibited less cytotoxicity against co-cultured neurons after stimulation by LPS and IFN-gamma, with a concordant decrease in nitric oxide production. These results strongly suggest that WASP may have pivotal roles through the EVH1 domain in the LPS signaling cascade, either directly or indirectly, and modulates inflammatory immune responses in microglia.

Disruption of the cortical actin cytoskeleton does not affect store operated Ca2+ channels in human T-cells

Lymphocyte signaling and activation leads to the influx of extracellular Ca(2+) via the activation of Ca(2+) release activated Ca(2+) (CRAC) channels in the plasma membrane. Activation of CRAC channels occurs following emptying of the endoplasmic reticulum intracellular Ca(2+) stores. One model to explain the coupling of store-emptying to CRAC activation is the secretion-like conformational coupling model. This model proposes that store depletion increases junctions between the endoplasmic reticulum and the plasma membrane in a manner that could be regulated by the cortical actin cytoskeleton. Here, we show that stabilization or depolymerization of the actin cytoskeleton failed to affect CRAC activation. We therefore conclude that rearrangement of the actin cytoskeleton is dispensable for store-operated Ca(2+) entry in T-cells.

Detection of 28 novel mutations in the Wiskott–Aldrich syndrome and X-linked thrombocytopenia based on multiplex PCR

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder including microthrombocytopenia, eczema and immunodeficiency. A mild form is known as the X-linked thrombocytopenia (XLT). We screened 150 individuals or families based on a multiplex PCR method. We found 28 novel mutations (7 missense, 1 nonsense, 1 nonstop change, 5 splice site mutations and 14 deletions or insertions). The method relied on the co-synthesis of 5 amplicons and direct sequencing, optimizing the novel protocol proposed by Jones et al. [L.N. Jones, M.I. Lutskiy, J. Cooley, et al. A novel protocol to identify mutations in patients with Wiskott-Aldrich syndrome, Blood Cells Mol. Dis. 28 (2002) 392-398]. It was thus possible to identify faster and at a lower cost the mutations in newly diagnosed patients. The mutation distribution, according to the type, was in keeping with the distribution reported previously. No clear-cut genotype-phenotype correlation was observed.

Impaired in vitro regulatory T cell function associated with Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency characterized by the contradictory coexistence of impaired T-cell function and exaggerated T-cell-mediated pathology, including autoimmunity and eczema. WAS protein (WASp)-deficient mice are also immunodeficient and can develop autoimmune disease. Since defects in regulatory T-cells (Treg) are associated with autoimmunity, we examined the presence and function of these cells in WAS patients and WASp-deficient mice. We found that CD4(+)CD25(+)FOXP3(+) Treg cells can develop in the absence of WASp expression. However, Treg cells both from WASp-deficient mice and from four out of five WAS patients studied showed impaired in vitro suppressor function. In WASp-deficient mice, this defect could be partially rescued by pre-activation with IL-2, suggesting that inadequate cell activation may play a role in WASp-deficient Treg dysfunction. These findings may provide insights into the complex pathophysiology and paradoxical phenotypes of WAS and suggest new therapeutic modalities for autoimmunity in these patients.

Human natural killer cell deficiencies

PURPOSE OF REVIEW

Human natural killer cell deficiencies are a relevant clinical entity that provides insight into the role of natural killer cells in host defense, as well as the basic biology of natural killer cells. Since previously reviewing these disorders, significant developments warrant their reconsideration.

RECENT FINDINGS

Human natural killer cell deficiencies can occur as part of a more pervasive immunodeficiency syndrome or, rarely, in isolation. The most informative examples of the former are in the context of a known genetic defect, because the deficiency of natural killer cell development or activity can be attributed to the specific gene function. Since last reviewed, there are five human gene mutations that are now appreciated to affect natural killer cells, and additional new insights into natural killer cell biology have been obtained through seven others. Six new reports of isolated natural killer cell deficiencies, as well as a suggested classification scheme, are also reviewed.

SUMMARY

Appreciation of human genetic syndromes that include natural killer cell deficiencies, as well as new cases of isolated natural killer cell deficiencies, continue to advance the understanding of natural killer cell biology and solidify the role of natural killer cells in defense against human herpesviral infection.

Current understanding of the Wiskott-Aldrich syndrome and prospects for gene therapy

Gene therapy, based on the transplantation of genetically corrected autologous hematopoietic stem cells (HSCs), has proven to be an effective therapeutic approach as an alternative to allogenic HSC transplantation for the cure of severe combined immunodeficiencies (SCID). In this article, the recent preclinical studies aiming towards gene therapy trials for the Wiskott-Aldrich syndrome (WAS), a life-threatening immunodeficiency characterized by infections, hemorrhages, autoimmune disorders and lymphomas, will be reviewed. An update of the safety and efficacy data obtained in studies performed in murine disease models and in cells from WAS patients will be presented. Based on these data and on the clinical results of the recent trials for SCID, the most critical issues regarding the implementation of a gene therapy approach for WAS will be discussed.

Defective Th1 cytokine gene transcription in CD4+ and CD8+ T cells from Wiskott-Aldrich syndrome patients

Wiskott-Aldrich syndrome (WAS) protein (WASP) plays a key role in TCR-mediated activation and immunological synapse formation. However, the effects of WASP deficiency on effector functions of human CD4+ and CD8+ T cells remain to be determined. In this study, we report that TCR/CD28-driven proliferation and secretion of IL-2, IFN-gamma, and TNF-alpha are strongly reduced in CD8+ T cells from WAS patients, compared with healthy donor CD8+ T cells. Furthermore, WAS CD4+ T cells secrete low levels of IL-2 and fail to produce IFN-gamma and TNF-alpha, while the production of IL-4, IL-5, and IL-10 is only minimally affected. Defective IL-2 and IFN-gamma production persists after culture of naive WAS CD4+ T cells in Th1-polarizing conditions. The defect in Th1 cytokine production by WAS CD4+ and CD8+ T cells is also present at the transcriptional level, as shown by reduced IL-2 and IFN-gamma mRNA transcripts after TCR/CD28 triggering. The reduced transcription of Th1 cytokine genes in WAS CD4+ T cells is associated with a defective induction of T-bet mRNA and a reduction in the early nuclear recruitment of NFAT-1, while the defective activation of WAS CD8+ T cells correlates with reduced nuclear recruitment of both NFAT-1 and NFAT-2. Together, our data indicate that WASP regulates the transcriptional activation of T cells and is required specifically for Th1 cytokine production.

Dual role for RhoA in suppression and induction of cytokines in the human neutrophil

Production of tumor necrosis factor-alpha (TNFalpha) by the neutrophil (PMN) is a pivotal event in innate immunity, but the signals regulating TNFalpha induction in this primary cell are poorly understood. Herein, we use protein transduction to identify novel, opposing anti- and pro-cytokine-inducing roles for RhoA in the resting and lipopolysaccharide (LPS)-stimulated human PMN, respectively. In the resting cell, RhoA suppresses Cdc42 activation, IkappaBalpha degradation, nuclear factor-kappaB (NF-kappaB) activation, and induction of TNFalpha and NF-kappaB-dependent chemokines. Suppression of TNFalpha induction by RhoA is Rho kinase alpha (ROCKalpha) independent, but Cdc42 dependent, because TNFalpha induction by C3 transferase is attenuated by inhibition of Cdc42, and constitutively active Cdc42 suffices to activate NF-kappaB and induce TNFalpha. By contrast, we also place RhoA downstream of p38 mitogen-activated protein kinase and Cdc42 in a novel LPS-activated pathway in which p38, Cdc42, and ROCKalpha all promote TNFalpha protein expression. The p65 subunit of NF-kappaB coprecipitates with RhoA in a manner sensitive to the RhoA activation state. Our findings suggest a new, 2-faced role for RhoA as a checkpoint in innate immunity.

A Partial Down-regulation of WASP Is Sufficient to Inhibit Podosome Formation in Dendritic Cells

The Wiskott Aldrich syndrome protein (WASP) is a hematopoietic-specific cytoskeletal regulator that is necessary for induction of normal immunity. In the context of effective gene therapy for WAS, cellular models of human WASP deficiency are important for definition of the threshold of protein expression required for optimal activity. Using lentiviral vector-mediated RNA interference (RNAi), we were able to down-regulate the levels of human WASP in cell lines and primary cells. In dendritic cells (DC), RNAi-induced WASP deficiency did not impair phenotypic maturation but perturbed cytoskeletal organization. As a result, podosomes, which are actin-rich structures present in immature adherent DC, were formed less efficiently and motility was disturbed. Overall, treatment of cells with RNAi recapitulated the phenotype of cells derived from patients or animals with inactivating mutations of the WAS gene. Interestingly, reduction of the levels of WASP to about 60% of normal was sufficient to inhibit the formation of podosomes in DC, implying that this cell type requires near-normal levels of WASP to sustain physiological cytoskeleton-dependent activities.

WASP and the phenotypic range associated with deficiency

PURPOSE OF REVIEW

This review reports on the range of clinical phenotypes that are caused by mutations in the Wiskott-Aldrich Syndrome Protein (WASP) gene. The basis of genotype-phenotype correlation in Wiskott-Aldrich syndrome (WAS) is discussed, with regard to expression of the WAS protein (WASp) and of the effects of WASP mutations on WASp function. Advances in preclinical models of gene therapy for WAS are presented.

RECENT FINDINGS

Two recent studies have supported genotype-phenotype correlation in WAS and in related X-linked thrombocytopenia. Expression of the WASp was found to be the best predictor of clinical phenotype. Investigation of autoimmune manifestations associated with WAS has shown that autoimmune hemolytic anemia and elevated serum IgM associate with a more severe clinical course. Finally, while results of hematopoietic stem cell transplantation for WAS continue to improve, several studies have shown the potential benefit of novel therapeutic approaches based on gene transfer. In particular, use of lentiviral vector-driven expression of the WASP gene under autologous promoter sequences has been found to result in increased targeting of hematopoietic stem cells, higher levels of WASp expression, and improved reconstitution of immune function.

SUMMARY

Availability of tools that allow analysis of WASp expression has provided evidence for a genotype-phenotype correlation in patients with WASP gene defects. Protein expression is an important prognostic indicator. The molecular and cellular abnormalities of WAS-associated defects are being identified, and significant advances in vector-mediated gene transfer have opened possibilities for the treatment of WAS based on gene therapy.

Lymphocyte calcium signaling from membrane to nucleus

Ca(2+) signals control a variety of lymphocyte responses, ranging from short-term cytoskeletal modifications to long-term changes in gene expression. The identification of molecules and channels that modulate Ca(2+) entry into T and B lymphocytes has both provided details of the molecular events leading to immune responses and raised controversy. Here we review studies of the pathways that allow Ca(2+) entry, the function of Ca(2+) in the regulation of cell polarity and motility and the principles by which Ca(2+)-dependent transcription regulates lymphocyte function.

Structure and function of the Wiskott-Aldrich syndrome protein

PURPOSE OF REVIEW

Mutations of the Wiskott-Aldrich syndrome protein can result in highly variable clinical symptoms that affect the hematopoietic/immunologic system. The responsible gene, WASP, has multiple domains, each with unique functions that were only recently fully recognized.

RECENT FINDINGS

Two new comprehensive studies of patients with mutations of the Wiskott-Aldrich syndrome protein unequivocally demonstrated a strong phenotype-genotype correlation; the most predictive variable was the presence or absence of the Wiskott-Aldrich syndrome protein in the lymphoid cells from patients with X-linked thrombocytopenia or Wiskott-Aldrich syndrome, respectively. A third clinical study revealed a high rate (>70%) of autoimmune disorders in patients with classic Wiskott-Aldrich syndrome, possibly caused by immune dysregulation involving both T and B cell defects. In addition, the Wiskott-Aldrich syndrome protein is required for natural killer cell function by participating in the formation of immunologic synapses and facilitating the nuclear translocation of nuclear factor for activated T cell and nuclear factor-kappaB. Finally, the Wiskott-Aldrich syndrome protein was shown to play an important role in lymphoid development and in the maturation and function of myelomonocytic cells.

SUMMARY

The progress made in dissecting the functions of the Wiskott-Aldrich syndrome protein has direct implications for our understanding of the distinct clinical phenotypes (Wiskott-Aldrich syndrome/X-linked thrombocytopenia; intermittent thrombocytopenia; congenital neutropenia), for making diagnostic and prognostic decisions, and for the selection of therapeutic strategies--from conservative symptomatic treatment to curative hematopoietic stem cell transplantation, or, in the future, gene therapy.