X-linked Inhibitor Of Apoptosis Protein Deficiency Research Articles

Interleukin-1–mediated hyperinflammation in XIAP deficiency is associated with defective autophagy

AbstractDeficiency of X-linked inhibitor of apoptosis protein (XIAP) is a rare genetic condition that can present with recurrent episodes of hemophagocytic lymphohistiocytosis (HLH), though the exact mechanisms leading to this hyperinflammatory disorder are unclear. Understanding its biology is critical to developing targeted therapies for this potentially fatal disease. Here, we report on a novel multiexonic intragenic duplication leading to XIAP deficiency with recurrent HLH that demonstrated complete response to interleukin (IL)-1β blockade. We further demonstrate using both primary patient cells and genetically modified THP-1 monocyte cell lines that, contrary to what has previously been shown in mouse cells, XIAP-deficient human macrophages do not produce excess IL-1β when stimulated under standard conditions. Instead, nucleotide-binding oligomerization domain–like receptor family pyrin domain containing 3 (NLRP3) inflammasome–mediated hyperproduction of IL-1β is observed only when the XIAP-deficient cells are stimulated under autophagy-promoting conditions and this correlates with defective autophagic flux as measured by decreased accumulation of the early autophagy marker LC3-II. This work, therefore, highlights IL-1β blockade as a therapeutic option for patients with XIAP deficiency experiencing recurrent HLH and identifies a critical role for XIAP in promoting autophagy as a means of limiting IL-1β–mediated hyperinflammation during periods of cellular stress.

Identification of Germline Non-coding Deletions in XIAP Gene Causing XIAP Deficiency Reveals a Key Promoter Sequence

X-linked inhibitor of apoptosis protein (XIAP) deficiency, also known as the X-linked lymphoproliferative syndrome of type 2 (XLP-2), is a rare immunodeficiency characterized by recurrent hemophagocytic lymphohistiocytosis, splenomegaly, and inflammatory bowel disease. Variants inXIAPincluding missense, non-sense, frameshift, and deletions of coding exons have been reported to cause XIAP deficiency. We studied three young boys with immunodeficiency displaying XLP-2-like clinical features. No genetic variation in the coding exons ofXIAPwas identified by whole-exome sequencing (WES), although the patients exhibited a complete loss of XIAP expression. Targeted next-generation sequencing (NGS) of the entire locus ofXIAPwas performed on DNA samples from the three patients. Molecular investigations were assessed by gene reporter expression assays in HEK cells and CRISPR-Cas9 genome editing in primary T cells. NGS ofXIAPidentified three distinct non-coding deletions in the patients that were predicted to be driven by repetitive DNA sequences. These deletions share a common region of 839bp that encompassed the first non-coding exon ofXIAPand contained regulatory elements and marks specific of an active promoter. Moreover, we showed that among the 839bp, the exon was transcriptionally active. Finally, deletion of the exon by CRISPR-Cas9 in primary cells reduced XIAP protein expression. These results identify a key promoter sequence contained in the first non-coding exon ofXIAP. Importantly, this study highlights that sequencing of the non-coding exons that are not currently captured by WES should be considered in the genetic diagnosis when no variation is found in coding exons.

Hematopoietic Cell Transplantation Rescues Inflammatory Bowel Disease and Dysbiosis of Gut Microbiota in XIAP Deficiency

X-linked inhibitor of apoptosis protein (XIAP) deficiency is an infrequent inborn error of immunity that is often associated with refractory inflammatory bowel disease (IBD). The natural course of XIAP deficiency is typically associated with poor prognosis, and hematopoietic cell transplantation (HCT) is the only curative treatment. To study (1) the effect of HCT on patients with XIAP deficiency undergoing HCT, (2) the status of XIAP deficiency-associated IBD after HCT, and (3) the gut microbiota of XIAP deficiency-associated IBD before and after HCT. A nationwide survey of patients with XIAP deficiency was conducted. A spreadsheet questionnaire was collected from the physicians. Feces samples collected from the patients before and after HCT and their healthy family members were analyzed. Twenty-six patients with XIAP deficiency underwent HCT by the end of March 2020, and 22 patients (84.6%) survived. All the survivors underwent a fludarabine-based reduced-intensity condition regimen. Acute graft-versus-host disease was observed in 17 patients (65.4%). Nineteen patients experienced refractory IBD before undergoing HCT. IBD improved remarkably after HCT. After HCT, the colonoscopic and pathological symptoms were restored to normal, and the pediatric ulcerative colitis activity index improved significantly. Gut microbiota indicated dysbiosis before HCT; however, it was improved to resemble that of the healthy family members afterHCT. This study revealed that HCT has a favorable outcome for XIAP deficiency. HCT rescues gut inflammation and dysbiosis in patients with XIAP deficiency.

X-linked inhibitor of apoptosis protein deficiency complicated with Crohn's disease-like enterocolitis and Takayasu arteritis: A case report

X-linked inhibitor of apoptosis protein (XIAP) deficiency results in monogenic inflammatory bowel disease. To date, no vasculitis associated with XIAP deficiency has been reported. A 10-year-old boy was diagnosed with Crohn's disease and he responded poorly to conventional treatment for Crohn's disease. He was dependent on corticosteroids and parenteral nutrition. To manage severe colitis, he underwent ileostomy followed by ileocolectomy for an ileo-sigmoid fistula. At the age of 15 years, he developed IgA vasculitis and at the age of 17 years, he developed refractory Takayasu arteritis (TAK), which was resistant to corticosteroid and immunosuppressive therapy. Whole-exome sequencing revealed a novel mutation of the splice acceptor site in XIAP (c.1057-1G > A) at the age of 19 years. Allogeneic hematopoietic stem cell transplantation was successful with subsequent withdrawal of intensive immunosuppressive therapy and clinical remission of both enterocolitis and TAK. This case suggests that patients with XIAP deficiency could develop intractable inflammatory disease involving the intestinal tract and blood vessels.

Interplay between Caspase 9 and X-linked Inhibitor of Apoptosis Protein (XIAP) in the oocyte elimination during fetal mouse development

Mammalian female fertility is limited by the number and quality of oocytes in the ovarian reserve. The number of oocytes is finite since all germ cells cease proliferation to become oocytes in fetal life. Moreover, 70–80% of the initial oocyte population is eliminated during fetal and neonatal development, restricting the ovarian reserve. Why so many oocytes are lost during normal development remains an enigma. In Meiotic Prophase I (MPI), oocytes go through homologous chromosome synapsis and recombination, dependent on formation and subsequent repair of DNA double strand breaks (DSBs). The oocytes that have failed in DSB repair or synapsis get eliminated mainly in neonatal ovaries. However, a large oocyte population is eliminated before birth, and the cause or mechanism of this early oocyte loss is not well understood. In the current paper, we show that the oocyte loss in fetal ovaries was prevented by a deficiency of Caspase 9 (CASP9), which is the hub of the mitochondrial apoptotic pathway. Furthermore, CASP9 and its downstream effector Caspase 3 were counteracted by endogenous X-linked Inhibitor of Apoptosis (XIAP) to regulate the oocyte population; while XIAP overexpression mimicked CASP9 deficiency, XIAP deficiency accelerated oocyte loss. In the CASP9 deficiency, more oocytes were accumulated at the pachytene stage with multiple γH2AFX foci and high LINE1 expression levels, but with normal levels of synapsis and overall DSB repair. We conclude that the oocytes with LINE1 overexpression were preferentially eliminated by CASP9-dependent apoptosis in balance with XIAP during fetal ovarian development. When such oocytes were retained, however, they get eliminated by a CASP9-independent mechanism during neonatal development. Thus, the oocyte is equipped with multiple surveillance mechanisms during MPI progression to safe-guard the quality of oocytes in the ovarian reserve.

Hematopoietic Stem Cell Transplantation for XIAP Deficiency in Japan.

BackgroundX-linked inhibitor of apoptosis protein (XIAP) deficiency is a rare immunodeficiency that is characterized by recurrent hemophagocytic lymphohistiocytosis (HLH) and splenomegaly and sometimes associated with refractory inflammatory bowel disease (IBD). Although hematopoietic stem cell transplantation (HSCT) is the only curative therapy, the outcomes of HSCT for XIAP deficiency remain unsatisfactory compared with those for SLAM-associated protein deficiency and familial HLH.AimTo investigate the outcomes and adverse events of HSCT for patients with XIAP deficiency, a national survey was conducted.MethodsA spreadsheet questionnaire was sent to physicians who had provided HSCT treatment for patients with XIAP deficiency in Japan.ResultsUp to the end of September 2016, 10 patients with XIAP deficiency had undergone HSCT in Japan, 9 of whom (90%) had survived. All surviving patients had received a fludarabine-based reduced intensity conditioning (RIC) regimen. Although 5 patients developed post-HSCT HLH, 4 of them survived after etoposide administration. In addition, the IBD associated with XIAP deficiency improved remarkably after HSCT in all affected cases.ConclusionThe RIC regimen and HLH control might be important factors for successful HSCT outcomes, with improved IBD, in patients with XIAP deficiency.Electronic supplementary materialThe online version of this article (doi:10.1007/s10875-016-0348-4) contains supplementary material, which is available to authorized users.

Prenatal Findings Leading to Early Diagnosis of X-Linked Inhibitor of Apoptosis Protein (XIAP) Deficiency

X-linked inhibitor of apoptosis protein (XIAP) deficiency is a primary hyperinflammatory immunodeficiency typically diagnosed following an episode of hemophagocytic lymphohistiocytosis (HLH) or in the setting of early onset severe inflammatory bowel disease (IBD). Hematopoietic cell transplant (HCT) is the definitive treatment. We present an infant with prenatal hepatosplenomegaly and hepatic calcifications who was subsequently diagnosed with XIAP deficiency in infancy. Whole exome sequencing (WES) for patient and parents was performed. Clinical course and immunophenotyping were reviewed. Hepatosplenomegaly, hepatic calcifications and large placenta were noted on prenatal ultrasound at 35 weeks performed for maternal pre-eclampsia. Postnatal evaluation revealed thrombocytopenia and direct hyperbilirubinemia, raising concerns for congenital infection, chromosomal abnormality, or a metabolic disorder. However, the abnormalities normalized over 7 days and he had a negative congenital infection work up, and karyotype, microarray, and metabolic evaluation were normal. WES showed a single likely pathogenic variant, a de novo c.1021_1022delAA; p.Asn341Tyr-fs*8 hemizygous deletion in XIAP, predicted to be null. Flow cytometry revealed <1.5% XIAP expression in all peripheral blood mononuclear lineages. After hospitalization at 10 mo for fever and hives, IgG and prophylactic medications were started. At 14 mo he was again hospitalized for fever, neutropenia, and elevated ferritin that spontaneously resolved. Otherwise, his development is progressing normally and HCT is planned. XIAP deficiency presented with prenatal hepatic inflammation and newborn findings mimicking congenital infection. Fever, hives and incomplete HLH occurred before 15 mo. The early diagnosis of XIAP deficiency has allowed for definitive HCT to be undertaken electively.

Inability to resolve specific infection generates innate immunodeficiency syndrome in Xiap−/− mice

AbstractEmerging evidence indicates that innate immunodeficiency syndromes are linked to mutations in innate receptors and to specific infections. X-linked lymphoproliferative syndrome type-2 (XLP-2) is associated with deficiency in X-linked inhibitor of apoptosis protein (XIAP), with poorly understood molecular mechanisms. Here we showed that XIAP deficiency selectively impaired B-cell chronic lymphocytic leukemia/lymphoma 10 (BCL10)-mediated innate responses to dectin-1 ligands but did not affect responses to various Toll-like receptor agonists. Consequently, Xiap−/− mice became highly vulnerable on Candida albicans infection. The compromised early innate responses led to the persistent presence of C albicans and inflammatory cytokines in Xiap−/− mice. Furthermore, priming of Xiap−/− mice with the dectin-1 ligand curdlan alone resulted in XLP-2–like syndromes. Restoration of dectin-1–induced Rac1 activation and phagocytosis by resolvin D1, but not up-regulation of nuclear factor-κB, rescued Xiap−/− mice from C albicans lethal infection. Therefore, development of XLP-2 in XIAP-deficient patients could be partly due to sustained inflammation as a consequence of defective BCL10-dependent innate immunity toward specific pathogens. Importantly, our results suggest the potential therapeutic value of resolvin D1 in the treatment of XLP-2 and innate immunodeficiency syndromes.

Sa1768 Defective Numbers of TH17 Cells With Regulatory Properties in Crohn's Disease

Background and Aims: The genetic contribution to inflammatory bowel disease (IBD) is only partially understood and it has been suggested that rare variants that escape detection by genome-wide association studies contribute to the genetic risk in IBD. To identify novel, rare high-penetrance variants involved in disease etiology, we performed exome sequencing in cases of familial and sporadic early-onset IBD. Methods and Results: Exome sequencing revealed a novel hemizygous nonsense mutation (E99X) in the gene encoding for the Xlinked inhibitor of apoptosis protein (XIAP) in a three-year old patient with a one-year history of colonic, stricturing and fistulizing CD refractory to treatment with corticosteroids, immunosuppressants, and anti-TNFα antibodies. XIAP deficiency is associated with X-linked lymphoproliferative syndrome (XLP), a primary immunodeficiency characterized by severe susceptibility to Epstein-Barr virus (EBV) infection. In accordance with absence of XLPrelated clinical symptoms, EBV-specific antibodies and EBV DNA could not be detected in the CD patient. In addition, while XIAP has been implicated in various immunological pathways related to IBD including T cell apoptosis, Natural Killer T cell homeostasis, and inflammasome activation, relative and absolute numbers of PBMC subsets, stimulationand restimulation-induced T cell proliferation and apoptosis, and NLRP3-dependent IL-1β release were unimpaired in the CD patient. However, while XIAP-deficient PBMCs and monocytes exhibited unaltered responses to toll-like receptor 2, 3, 4, 7, and 9 stimulation, they failed to respond to NOD2 stimulation by muramyl dipeptide. Accordingly, co-immunoprecipitation studies revealed that wildtype but not E99X XIAP associated with NOD2 in a RIP2-dependent manner. Lentiviral reconstitution of XIAP expression in primary monocyte-derived dendritic cells restored NOD2 signaling and confirmed a critical role of XIAP deficiency in the observed NOD2 defects. Conclusion: Our studies reveal a novel XIAP mutation associated with early onset IBD and suggest that XIAP deficiency may contribute to disease pathogenesis via impaired NOD2 signaling. In addition, given the central role of XIAP deficiency in XLP, these results support the concept that at least a subset of IBD cases may result from congenital or acquired immunodeficiency.

P679 X-linked inhibitor of apoptosis protein in early-onset inflammatory bowel disease

Background and Aims: The genetic contribution to inflammatory bowel disease (IBD) is only partially understood and it has been suggested that rare variants that escape detection by genome-wide association studies contribute to the genetic risk in IBD. To identify novel, rare high-penetrance variants involved in disease etiology, we performed exome sequencing in cases of familial and sporadic early-onset IBD. Methods and Results: Exome sequencing revealed a novel hemizygous nonsense mutation (E99X) in the gene encoding for the Xlinked inhibitor of apoptosis protein (XIAP) in a three-year old patient with a one-year history of colonic, stricturing and fistulizing CD refractory to treatment with corticosteroids, immunosuppressants, and anti-TNFα antibodies. XIAP deficiency is associated with X-linked lymphoproliferative syndrome (XLP), a primary immunodeficiency characterized by severe susceptibility to Epstein-Barr virus (EBV) infection. In accordance with absence of XLPrelated clinical symptoms, EBV-specific antibodies and EBV DNA could not be detected in the CD patient. In addition, while XIAP has been implicated in various immunological pathways related to IBD including T cell apoptosis, Natural Killer T cell homeostasis, and inflammasome activation, relative and absolute numbers of PBMC subsets, stimulationand restimulation-induced T cell proliferation and apoptosis, and NLRP3-dependent IL-1β release were unimpaired in the CD patient. However, while XIAP-deficient PBMCs and monocytes exhibited unaltered responses to toll-like receptor 2, 3, 4, 7, and 9 stimulation, they failed to respond to NOD2 stimulation by muramyl dipeptide. Accordingly, co-immunoprecipitation studies revealed that wildtype but not E99X XIAP associated with NOD2 in a RIP2-dependent manner. Lentiviral reconstitution of XIAP expression in primary monocyte-derived dendritic cells restored NOD2 signaling and confirmed a critical role of XIAP deficiency in the observed NOD2 defects. Conclusion: Our studies reveal a novel XIAP mutation associated with early onset IBD and suggest that XIAP deficiency may contribute to disease pathogenesis via impaired NOD2 signaling. In addition, given the central role of XIAP deficiency in XLP, these results support the concept that at least a subset of IBD cases may result from congenital or acquired immunodeficiency.

Intracellular signaling dynamics during apoptosis execution in the presence or absence of X-linked-inhibitor-of-apoptosis-protein

X-linked-inhibitor-of-apoptosis-protein (XIAP) is the most potent intracellular inhibitor of caspases-9, -3 and -7. While highly elevated XIAP levels reduce the apoptotic response to various stimuli, the potency of physiological XIAP expression to control caspase activation and the consequences of XIAP deficiency on apoptosis execution remain controversial. We therefore analyzed parental and XIAP-deficient DLD-1 and HCT-116 colon cancer cells by employing fluorescence-based single-cell imaging of mitochondrial permeabilisation and effector caspase activation. Our results demonstrate that physiological XIAP expression maintains a transient “off”-state for effector caspase activation following mitochondrial permeabilisation. Loss of XIAP expression instead accelerated the caspase activation response, but did not enhance the measured caspase activity. Apoptosis execution kinetics were independent of activating the intrinsic or extrinsic pathway by either staurosporine or TRAIL, and corresponded to computational systems analyses of caspase activation dynamics. We confirmed a protective role of XIAP upstream of mitochondrial permeabilisation during TRAIL-induced apoptosis, however, once mitochondria permeabilised ultimately no cell could escape effector caspase activation, regardless of potential cell-to-cell variability within the populations or the presence of XIAP. Our study provides comprehensive kinetic and mechanistic insight into the rapid molecular dynamics during apoptosis execution in the presence or absence of physiological XIAP expression.

Natural killer T cells and X-linked lymphoproliferative syndrome

Recent progress in elucidating the physiopathology of X-linked lymphoproliferative syndrome (XLP) has raised novel and important issues regarding the biology of natural killer T cells. Here I will review this information and discuss the issues involved. XLP is a rare inherited immunodeficiency characterized by a high susceptibility to severe infection by the Epstein-Barr virus. Mutations in the gene SH2D1A (or alternatively SAP) underlie 80% of familial XLP (XLP-1) cases. Recently the remaining 20% of familial XLP (XLP-2) cases were shown to harbor mutations in the gene XIAP (X-linked inhibitor of apoptosis protein). Both SAP and XIAP deficiencies are associated with a defect in the development and/or homeostasis of natural killer T cells. It can be hypothesized that the susceptibility to Epstein-Barr virus in XLP might result from the defect of natural killer T cells. The role of these cells in viral infection is unclear, but several herpes viruses have developed strategies to escape natural killer T cells. The discovery that SAP and XIAP deficiency leads to a defect in natural killer T cells has also shed light on novel signaling pathways required for natural killer T cell development and/or homeostasis.