Deletion of Wiskott-Aldrich syndrome protein triggers Rac2 activity and increased cross-presentation by dendritic cells

Wiskott-Aldrich syndrome (WAS) is caused by loss-of-function mutations in the WASp gene. Decreased cellular responses in WASp-deficient cells have been interpreted to mean that WASp directly regulates these responses in WASp-sufficient cells. Here, we identify an exception to this concept and show that WASp-deficient dendritic cells have increased activation of Rac2 that support cross-presentation to CD8(+) T cells. Using two different skin pathology models, WASp-deficient mice show an accumulation of dendritic cells in the skin and increased expansion of IFNγ-producing CD8(+) T cells in the draining lymph node and spleen. Specific deletion of WASp in dendritic cells leads to marked expansion of CD8(+) T cells at the expense of CD4(+) T cells. WASp-deficient dendritic cells induce increased cross-presentation to CD8(+) T cells by activating Rac2 that maintains a near neutral pH of phagosomes. Our data reveals an intricate balance between activation of WASp and Rac2 signalling pathways in dendritic cells.

Lentiviral-mediated gene therapy restores B cell tolerance in Wiskott-Aldrich syndrome patients

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency characterized by microthrombocytopenia, eczema, and high susceptibility to developing tumors and autoimmunity. Recent evidence suggests that B cells may be key players in the pathogenesis of autoimmunity in WAS. Here, we assessed whether WAS protein deficiency (WASp deficiency) affects the establishment of B cell tolerance by testing the reactivity of recombinant antibodies isolated from single B cells from 4 WAS patients before and after gene therapy (GT). We found that pre-GT WASp-deficient B cells were hyperreactive to B cell receptor stimulation (BCR stimulation). This hyperreactivity correlated with decreased frequency of autoreactive new emigrant/transitional B cells exiting the BM, indicating that the BCR signaling threshold plays a major role in the regulation of central B cell tolerance. In contrast, mature naive B cells from WAS patients were enriched in self-reactive clones, revealing that peripheral B cell tolerance checkpoint dysfunction is associated with impaired suppressive function of WAS regulatory T cells. The introduction of functional WASp by GT corrected the alterations of both central and peripheral B cell tolerance checkpoints. We conclude that WASp plays an important role in the establishment and maintenance of B cell tolerance in humans and that restoration of WASp by GT is able to restore B cell tolerance in WAS patients.

Lentiviral-mediated gene therapy leads to improvement of B-cell functionality in a murine model of Wiskott-Aldrich syndrome

BACKGROUND

Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency characterized by thrombocytopenia, eczema, infections, autoimmunity, and lymphomas. Transplantation of hematopoietic stem cells from HLA-identical donors is curative, but it is not available to all patients. We have developed a gene therapy (GT) approach for WAS by using a lentiviral vector encoding for human WAS promoter/cDNA (w1.6W) and demonstrated its preclinical efficacy and safety.

OBJECTIVE

To evaluate B-cell reconstitution and correction of B-cell phenotype in GT-treated mice.

METHODS

We transplanted Was(-/-) mice sublethally irradiated (700 rads) with lineage marker-depleted bone marrow wild-type cells, Was(-/-) cells untransduced or transduced with the w1.6W lentiviral vector and analyzed B-cell reconstitution in bone marrow, spleen, and peritoneum.

RESULTS

Here we show that WAS protein(+) B cells were present in central and peripheral B-cell compartments from GT-treated mice and displayed the strongest selective advantage in the splenic marginal zone and peritoneal B1 cell subsets. After GT, splenic architecture was improved and B-cell functions were restored, as demonstrated by the improved antibody response to pneumococcal antigens and the reduction of serum IgG autoantibodies.

CONCLUSION

WAS GT leads to improvement of B-cell functions, even in the presence of a mixed chimerism, further validating the clinical application of the w1.6W lentiviral vector.

Ten years of gene therapy for primary immune deficiencies

Gene therapy with hematopoietic stem cells (HSC) is an attractive therapeutic strategy for several forms of primary immunodeficiencies. Current approaches are based on ex vivo gene transfer of the therapeutic gene into autologous HSC by vector-mediated gene transfer. In the past decade, substantial progress has been achieved in the treatment of severe combined immundeficiencies (SCID)-X1, adenosine deaminase (ADA)-deficient SCID, and chronic granulomatous disease (CGD). Results of the SCID gene therapy trials have shown long-term restoration of immune competence and clinical benefit in over 30 patients. The inclusion of reduced-dose conditioning in the ADA-SCID has allowed the engraftment of multipotent gene-corrected HSC at substantial level. In the CGD trial significant engraftment and transgene expression were observed, but the therapeutic effect was transient. The occurrence of adverse events related to insertional mutagenesis in the SCID-X1 and CGD trial has highlighted the limitations of current retroviral vector technology. For future applications the risk-benefit evaluation should include the type of vector employed, the disease background and the nature of the transgene. The use of self-inactivating lentiviral vectors will provide significant advantages in terms of natural gene regulation and reduction in the potential for adverse mutagenic events. Following recent advances in preclinical studies, lentiviral vectors are now being translated into new clinical approaches, such as Wiskott-Aldrich Syndrome.

Large granular lymphocyte proliferation and revertant mosaicism: two rare events in a Wiskott-Aldrich syndrome patient

We report on a 6 year old patient with an unusual clinical presentation of WAS and oligoclonal proliferation of TCR+ large granular lymphocytes (LGL). Flow cytometry demonstrated two distinct populations of lymphocytes with strongly decreased (WASP-) or normal expression levels of WASP (WASP+), respectively. Molecular analysis confirmed a splice site mutation in intron 2 of the WASP gene in the WASP- cells but not in WASP+ cells. LGL cells were WASP+, suggesting that two independent rare events, somatic revertant mosaicism and LGL expansion, have occurred in a child with WAS. Our report points to diagnostic difficulties in the presence of partial WASP reversions and LGL.

Lymphocyte-dependent and Th2 cytokine-associated colitis in mice deficient in Wiskott-Aldrich syndrome protein

BACKGROUND & AIMS

Controversy exists as to whether patients with inflammatory bowel disease have an underlying immunodeficiency. We have focused on a murine model of the Wiskott-Aldrich syndrome, an immunodeficiency in which autoimmunity can manifest in the form of an inflammatory bowel disease-like illness. Wiskott-Aldrich syndrome protein (WASP) deficiency in mice results in similar clinical features. Herein, we characterized the colitis in WASP-deficient mice.

METHODS

WASP-deficient mice were followed clinically and histologically. Immunologic studies were performed to determine the pathogenic cell population(s), the predominant cytokine expression pattern, and the role of cytokine(s) in colitis pathogenesis.

RESULTS

All WASP-deficient mice develop colitis by 6 months of age. Lymphocytes are required for disease induction, and CD4(+) T cells from WASP-deficient mice are sufficient to induce disease in lymphocyte-deficient hosts. Lamina propria preparations from WASP-deficient mice demonstrated elevations in interferon-gamma, interleukin (IL)-4, and IL-13 levels but decreased IL-6 and no difference in IL-17 expression in comparison with wild-type controls. Treatment with neutralizing antibody to IL-4, but not to interferon-gamma, abrogated colitis development. However, mice deficient in both WASP and IL-4 showed no difference in histologic colitis scores at 24 weeks of age compared with WASP-deficient mice.

CONCLUSIONS

These results demonstrate a critical role for lymphocytes and a relative T helper 2 cytokine predominance in the colitis associated with WASP-deficient mice. This is the only model of colitis with elevated T helper 2 cytokines and aberrant natural regulatory T cell function and is unique in having a human disease counterpart with similar defects.

CD44 and beta3 integrin organize two functionally distinct actin-based domains in osteoclasts

The actin cytoskeleton of mature osteoclasts (OCs) adhering to nonmineralized substrates is organized in a belt of podosomes reminiscent of the sealing zone (SZ) found in bone resorbing OCs. In this study, we demonstrate that the belt is composed of two functionally different actin-based domains: podosome cores linked with CD44, which are involved in cell adhesion, and a diffuse cloud associated with beta3 integrin, which is involved in cell adhesion and contraction. Wiskott Aldrich Syndrome Protein (WASp) Interacting Protein (WIP)-/- OCs were devoid of podosomes, but they still exhibited actin clouds. Indeed, WIP-/- OCs show diminished expression of WASp, which is required for podosome formation. CD44 is a novel marker of OC podosome cores and the first nonintegrin receptor detected in these structures. The importance of CD44 is revealed by showing that its clustering restores podosome cores and WASp expression in WIP-/- OCs. However, although CD44 signals are sufficient to form a SZ, the presence of WIP is indispensable for the formation of a fully functional SZ.

The Phenomenon of Spontaneous Genetic Reversions in the Wiskott-Aldrich Syndrome: A Report of the Workshop of the ESID Genetics Working Party at the XIIth Meeting of the European Society for Immunodeficiencies (ESID). Budapest, Hungary October 4–7, 2006

The Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disease caused by mutations in the Wiskott-Aldrich Protein (WASP) gene, which typically leads to absent WASP protein expression in WAS leukocytes. However, some patients have been found with small populations of WASP-expressing cells caused by reverse or second-site mutations that allow protein expression. An international consortium was established to further investigate these phenomena. This paper summarizes data collected by this consortium that was presented at a workshop held during the XIIth Meeting of the European Society for Immunodeficiencies (ESID), October, 2006. WASP reversions were noted in approximately 11% of 272 patients tested. Many different cell lineages showed reversions. These data form the foundation for further investigation into this phenomenon, which has implications for therapy of this disease.

Impaired T-cell priming in vivo resulting from dysfunction of WASp-deficient dendritic cells

The Wiskott-Aldrich syndrome (WAS) is characterized by defective cytoskeletal dynamics affecting multiple immune cell lineages, and leading to immunodeficiency and autoimmunity. The contribution of dendritic cell (DC) dysfunction to the immune dysregulation has not been defined, although both immature and mature WAS knockout (KO) DCs exhibit significant abnormalities of chemotaxis and migration. To exclude environmental confounders as a result of WAS protein (WASp) deficiency, we studied migration and priming activity of WAS KO DCs in vivo after adoptive transfer into wild-type recipient mice. Homing to draining lymph nodes was reduced and WAS KO DCs failed to localize efficiently in T-cell areas. Priming of both CD4(+) and CD8(+) T lymphocytes by WAS KO DCs preloaded with antigen was significantly decreased. At low doses of antigen, activation of preprimed wild-type CD4(+) T lymphocytes by WAS KO DCs in vitro was also abrogated, suggesting that there is a threshold-dependent impairment even if successful DC-T cell colocalization is achieved. Our data indicate that intrinsic DC dysfunction due to WASp deficiency directly impairs the T-cell priming response in vivo, most likely as a result of inefficient migration, but also possibly influenced by suboptimal DC-mediated cognate interaction.

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.

Requirement for a complex of Wiskott-Aldrich syndrome protein (WASP) with WASP interacting protein in podosome formation in macrophages

Chemotactic migration of macrophages is critical for the recruitment of leukocytes to inflamed tissues. Macrophages use a specialized adhesive structure called a podosome to migrate. Podosome formation requires the Wiskott-Aldrich syndrome protein (WASP), which is a product of the gene defective in an X-linked inherited immunodeficiency disorder, the Wiskott-Aldrich syndrome. Macrophages from WASP-deficient Wiskott-Aldrich syndrome patients lack podosomes, resulting in defective chemotactic migration. However, the molecular basis for podosome formation is not fully understood. I have shown that the WASP interacting protein (WIP), a binding partner of WASP, plays an important role in podosome formation in macrophages. I showed that WASP bound WIP to form a complex at podosomes and that the knockdown of WIP impairs podosome formation. When WASP binding to WIP was blocked, podosome formation was also impaired. When WASP expression was reduced by small interfering RNA transfection, the amount of the complex of WASP with WIP decreased, resulting in reduced podosome formation. Podosomes were restored by reconstitution of the WASP-WIP complex in WASP knockdown cells. These results indicate that the WASP-WIP complex is required for podosome formation in macrophages. When podosome formation was reduced by blocking WASP binding to WIP, transendothelial migration of macrophages, the most crucial process in macrophage trafficking, was impaired. These results suggest that a complex of WASP with WIP plays a critical role in podosome formation, thereby mediating efficient transendothelial migration of macrophages.

The Wiskott-Aldrich syndrome protein is required for the function of CD4(+)CD25(+)Foxp3(+) regulatory T cells

The Wiskott-Aldrich syndrome, a primary human immunodeficiency, results from defective expression of the hematopoietic-specific cytoskeletal regulator Wiskott-Aldrich syndrome protein (WASP). Because CD4⁺CD25⁺Foxp3⁺ naturally occurring regulatory T (nTreg) cells control autoimmunity, we asked whether colitis in WASP knockout (WKO) mice is associated with aberrant development/function of nTreg cells. We show that WKO mice have decreased numbers of CD4⁺CD25⁺Foxp3⁺ nTreg cells in both the thymus and peripheral lymphoid organs. Moreover, we demonstrate that WKO nTreg cells are markedly defective in both their ability to ameliorate the colitis induced by the transfer of CD45RB^hi T cells and in functional suppression assays in vitro. Compared with wild-type (WT) nTreg cells, WKO nTreg cells show significantly impaired homing to both mucosal (mesenteric) and peripheral sites upon adoptive transfer into WT recipient mice. Suppression defects may be independent of antigen receptor–mediated actin rearrangement because both WT and WKO nTreg cells remodeled their actin cytoskeleton inefficiently upon T cell receptor stimulation. Preincubation of WKO nTreg cells with exogenous interleukin (IL)-2, combined with antigen receptor–mediated activation, substantially rescues the suppression defects. WKO nTreg cells are also defective in the secretion of the immunomodulatory cytokine IL-10. Overall, our data reveal a critical role for WASP in nTreg cell function and implicate nTreg cell dysfunction in the autoimmunity associated with WASP deficiency.

Wiskott-Aldrich syndrome protein is required for regulatory T cell homeostasis

Wiskott-Aldrich syndrome protein (WASp) is essential for optimal T cell activation. Patients with WAS exhibit both immunodeficiency and a marked susceptibility to systemic autoimmunity. We investigated whether alterations in Treg function might explain these paradoxical observations. While WASp-deficient (WASp(-/-)) mice exhibited normal thymic Treg generation, the competitive fitness of peripheral Tregs was severely compromised. The total percentage of forkhead box P3-positive (Foxp3(+)) Tregs among CD4(+) T cells was reduced, and WASp(-/-) Tregs were rapidly outcompeted by WASp(+) Tregs in vivo. These findings correlated with reduced expression of markers associated with self-antigen-driven peripheral Treg activation and homing to inflamed tissue. Consistent with these findings, WASp(-/-) Tregs showed a reduced ability to control aberrant T cell activation and autoimmune pathology in Foxp3(-/-)Scurfy (sf) mice. Finally, WASp(+) Tregs exhibited a marked selective advantage in vivo in a WAS patient with a spontaneous revertant mutation, indicating that altered Treg fitness likely explains the autoimmune features in human WAS.

Impaired integrin-dependent function in Wiskott-Aldrich syndrome protein-deficient murine and human neutrophils

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency that manifests as increased susceptibility to many pathogens. Although the spectrum of infections suffered by WAS patients is consistent with defects in neutrophil (PMN) function, the consequences of WAS protein (WASp) deficiency on this innate immune cell have been unclear. We report that deficiency of WASp in both human and murine PMNs resulted in profound defects in clustering of beta2 integrins, leading to defective adhesion and transendothelial migration under conditions of physiologic shear flow. Wild-type PMNs redistributed clustered beta2 integrins to the uropod of the cell during active migration, whereas WASp-deficient cells remain unpolarized. The WASp-deficient PMNs also showed reduced integrin-dependent activation of degranulation and respiratory burst. PMNs from a WAS patient manifested similar defects in integrin clustering and signaling. These results suggest that impaired beta2 integrin function in WASp-deficient PMNs may contribute substantially to the clinical immunodeficiency suffered by WAS patients.

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.

WIP and WASP play complementary roles in T cell homing and chemotaxis to SDF-1α

Homing of lymphocytes to tissues is a biologically important multistep process that involves selectin-dependent rolling, integrin-dependent adhesion and chemokine-directed chemotaxis. The actin cytoskeleton plays a central role in lymphocyte adhesion and motility. Wiskott-Aldrich syndrome protein (WASP), the product of the gene mutated in Wiskott-Aldrich syndrome, and its partner, the Wiskott-Aldrich syndrome protein-interacting protein (WIP), play important roles in actin re-organization in T lymphocytes. We used mice with disruption of the WASP and WIP genes to examine the role of WASP and WIP in T cell homing. T cell homing to spleen and lymph nodes in vivo was deficient in WASP-/- and WIP-/- mice and severely impaired in WASP-/-WIP-/- double knockout (DKO) mice. Deficiency of WASP, WIP or both did not interfere with selectin-dependent rolling or integrin-dependent adhesion of T cells in vitro. Chemotaxis to stromal cell-derived factor-1alpha (SDF-1alpha) in vitro was mildly reduced in T cells from WASP-/- mice. In contrast, it was significantly impaired in T cells from WIP-/- mice and severely reduced in T cells from DKO mice. Cellular F-actin increase following SDF-1alpha stimulation was normal in WASP-/- and WIP-/- T cells, but severely reduced in T cells from DKO mice. Actin re-organization and polarization in response to SDF-1alpha was abnormal in T cells from all knockout mice. Early biochemical events following SDF-1alpha stimulation that are important for chemotaxis and that included phosphorylation of Lck, cofilin, PAK1 and extracellular regulated kinase (Erk) and GTP loading of Rac-1 were examined in T cells from DKO mice and found to be normal. These results suggest that WASP and WIP are not essential for T lymphocyte rolling and adhesion, but play important and partially redundant roles in T cell chemotaxis in vitro and homing in vivo and function downstream of small GTPases.