Omenn Syndrome in Two Infants with Different Hypomorphic Variants in Janus Kinase 3.

Biallelic null or hypomorphic variants in JAK3 cause SCID and less frequently Omenn syndrome. We investigated homozygous hypomorphic JAK3 mutations in two patients, and expression and function of a novel JAK3R431P variant in Omenn syndrome. Immunophenotyping of PBMC from the patient with the novel JAK3R431P variant was undertaken, by flow cytometry and Phosflow after stimulation with IL-2, IL-7, and IL-15. JAK3 expression was investigated by Western blotting. We report two patients with homozygous hypomorphic JAK3 variants and clinical features of Omenn syndrome. One patient had a previously described JAK3R775H variant, and the second had a novel JAK3R431P variant. One patient with a novel JAK3R431P variant had normal expression of JAK3 in immortalised EBV-LCL cells but reduced phosphorylation of STAT5 after stimulation with IL-2, IL-7, and IL-15 consistent with impaired kinase activity. These results suggest the JAK3R431P variant to be hypomorphic. Both patients are alive and well after allogeneic haematopoietic stem cell transplantation. They have full donor chimerism, restitution of thymopoiesis and development of appropriate antibody responses following vaccination. We expand the phenotype of hypomorphic JAK3 deficiency and demonstrate the importance of functional testing of novel variants in disease-causing genes.

Expanding the PRAAS spectrum: De novo mutations of immunoproteasome subunit ß-type 10 in six infants with SCID-Omenn syndrome.

Mutations in proteasome ß-subunits or their chaperone and regulatory proteins are associated with proteasome-associated autoinflammatory disorders (PRAAS). We studied six unrelated infants with three de novo heterozygous missense variants in PSMB10, encoding the proteasome ß2i-subunit. Individuals presented with T-B-NK± severe combined immunodeficiency (SCID) and clinical features suggestive of Omenn syndrome, including diarrhea, alopecia, and desquamating erythematous rash. Remaining T cells had limited T cell receptor repertoires, a skewed memory phenotype, and an elevated CD4/CD8 ratio. Bone marrow examination indicated severely impaired B cell maturation with limited V(D)J recombination. All infants received an allogeneic stem cell transplant and exhibited a variety of severe inflammatory complications thereafter, with 2 peri-transplant and 2 delayed deaths. The single long-term transplant survivor showed evidence for genetic rescue through revertant mosaicism overlapping the affected PSMB10 locus. The identified variants (c.166G>C [p.Asp56His] and c.601G>A/c.601G>C [p.Gly201Arg]) were predicted in silico to profoundly disrupt 20S immunoproteasome structure through impaired ß-ring/ß-ring interaction. Our identification of PSMB10 mutations as a cause of SCID-Omenn syndrome reinforces the connection between PRAAS-related diseases and SCID.

Systemic Inflammation and Normocytic Anemia in DOCK11 Deficiency.

BACKGROUND: Increasing evidence links genetic defects affecting actin-regulatory proteins to diseases with severe autoimmunity and autoinflammation, yet the underlying molecular mechanisms are poorly understood. Dedicator of cytokinesis 11 (DOCK11) activates the small Rho guanosine triphosphatase (GTPase) cell division cycle 42 (CDC42), a central regulator of actin cytoskeleton dynamics. The role of DOCK11 in human immune-cell function and disease remains unknown. METHODS: We conducted genetic, immunologic, and molecular assays in four patients from four unrelated families who presented with infections, early-onset severe immune dysregulation, normocytic anemia of variable severity associated with anisopoikilocytosis, and developmental delay. Functional assays were performed in patient-derived cells, as well as in mouse and zebrafish models. RESULTS: We identified rare, X-linked germline mutations in DOCK11 in the patients, leading to a loss of protein expression in two patients and impaired CDC42 activation in all four patients. Patient-derived T cells did not form filopodia and showed abnormal migration. In addition, the patient-derived T cells, as well as the T cells from Dock11-knockout mice, showed overt activation and production of proinflammatory cytokines that were associated with an increased degree of nuclear translocation of nuclear factor of activated T cell 1 (NFATc1). Anemia and aberrant erythrocyte morphologic features were recapitulated in a newly generated dock11-knockout zebrafish model, and anemia was amenable to rescue on ectopic expression of constitutively active CDC42. CONCLUSIONS: Germline hemizygous loss-of-function mutations affecting the actin regulator DOCK11 were shown to cause a previously unknown inborn error of hematopoiesis and immunity characterized by severe immune dysregulation and systemic inflammation, recurrent infections, and anemia. (Funded by the European Research Council and others.).

Variants in STXBP3 are Associated with Very Early Onset Inflammatory Bowel Disease, Bilateral Sensorineural Hearing Loss and Immune Dysregulation.

BACKGROUND AND AIMS: Very early onset inflammatory bowel disease [VEOIBD] is characterized by intestinal inflammation affecting infants and children less than 6 years of age. To date, over 60 monogenic aetiologies of VEOIBD have been identified, many characterized by highly penetrant recessive or dominant variants in underlying immune and/or epithelial pathways. We sought to identify the genetic cause of VEOIBD in a subset of patients with a unique clinical presentation. METHODS: Whole exome sequencing was performed on five families with ten patients who presented with a similar constellation of symptoms including medically refractory infantile-onset IBD, bilateral sensorineural hearing loss and, in the majority, recurrent infections. Genetic aetiologies of VEOIBD were assessed and Sanger sequencing was performed to confirm novel genetic findings. Western analysis on peripheral blood mononuclear cells and functional studies with epithelial cell lines were employed. RESULTS: In each of the ten patients, we identified damaging heterozygous or biallelic variants in the Syntaxin-Binding Protein 3 gene [STXBP3], a protein known to regulate intracellular vesicular trafficking in the syntaxin-binding protein family of molecules, but not associated to date with either VEOIBD or sensorineural hearing loss. These mutations interfere with either intron splicing or protein stability and lead to reduced STXBP3 protein expression. Knock-down of STXBP3 in CaCo2 cells resulted in defects in cell polarity. CONCLUSION: Overall, we describe a novel genetic syndrome and identify a critical role for STXBP3 in VEOIBD, sensorineural hearing loss and immune dysregulation.

Gain-of-function variants in SYK cause immune dysregulation and systemic inflammation in humans and mice.

Spleen tyrosine kinase (SYK) is a critical immune signaling molecule and therapeutic target. We identified damaging monoallelic SYK variants in six patients with immune deficiency, multi-organ inflammatory disease such as colitis, arthritis and dermatitis, and diffuse large B cell lymphomas. The SYK variants increased phosphorylation and enhanced downstream signaling, indicating gain of function. A knock-in (SYK-Ser544Tyr) mouse model of a patient variant (p.Ser550Tyr) recapitulated aspects of the human disease that could be partially treated with a SYK inhibitor or transplantation of bone marrow from wild-type mice. Our studies demonstrate that SYK gain-of-function variants result in a potentially treatable form of inflammatory disease.

Defective neutrophil development and specific granule deficiency caused by a homozygous splice-site mutation in SMARCD2.

BACKGROUND: SMARCD2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily D, member 2) has recently been shown to have a critical role in granulopoiesis in humans, mice, and zebrafish. Our patient presented with delayed cord separation, failure to thrive, and sepsis. Retrospective whole-exome sequencing confirmed a homozygous splice-site mutation in SMARCD2. OBJECTIVE: We sought to provide the second description of human SMARCD2 deficiency and the first functional analysis of human primary SMARCD2-deficient cells. METHODS: Heparinized venous blood and bone marrow were collected from the patient after obtaining informed consent. Patient leukocytes and CD34+ cells were then isolated, phenotyped, and assessed functionally. RESULTS: Circulating neutrophils appeared phenotypically immature, lacking multilobed nuclei, and neutrophil granules lacked lactoferrin but showed normal levels of myeloperoxidase. Neutrophil oxidative burst was preserved in response to phorbol 12-myristate 13-acetate. Patient bone marrow-derived neutrophils and white blood cells showed a severely impaired chemotactic response. Furthermore, white blood cells showed defective in vitro killing of Staphylococcus aureus, consistent with a specific granule deficiency. Finally, patient bone marrow-derived CD34+ cells showed markedly impaired in vitro expansion and differentiation toward the neutrophil lineage. Before her molecular diagnosis, our patient underwent hematopoietic stem cell transplantation and is well 8 years later. CONCLUSIONS: This report highlights an important role for SMARCD2 in human myelopoiesis and the curative effect of hematopoietic stem cell transplantation for the hematopoietic features of SMARCD2 deficiency.

Germline TET2 loss of function causes childhood immunodeficiency and lymphoma.

Molecular dissection of inborn errors of immunity can help to elucidate the nonredundant functions of individual genes. We studied 3 children with an immune dysregulation syndrome of susceptibility to infection, lymphadenopathy, hepatosplenomegaly, developmental delay, autoimmunity, and lymphoma of B-cell (n = 2) or T-cell (n = 1) origin. All 3 showed early autologous T-cell reconstitution following allogeneic hematopoietic stem cell transplantation. By whole-exome sequencing, we identified rare homozygous germline missense or nonsense variants in a known epigenetic regulator of gene expression: ten-eleven translocation methylcytosine dioxygenase 2 (TET2). Mutated TET2 protein was absent or enzymatically defective for 5-hydroxymethylating activity, resulting in whole-blood DNA hypermethylation. Circulating T cells showed an abnormal immunophenotype including expanded double-negative, but depleted follicular helper, T-cell compartments and impaired Fas-dependent apoptosis in 2 of 3 patients. Moreover, TET2-deficient B cells showed defective class-switch recombination. The hematopoietic potential of patient-derived induced pluripotent stem cells was skewed toward the myeloid lineage. These are the first reported cases of autosomal-recessive germline TET2 deficiency in humans, causing clinically significant immunodeficiency and an autoimmune lymphoproliferative syndrome with marked predisposition to lymphoma. This disease phenotype demonstrates the broad role of TET2 within the human immune system.

Severe type I interferonopathy and unrestrained interferon signaling due to a homozygous germline mutation in STAT2.

Excessive type I interferon (IFNα/ß) activity is implicated in a spectrum of human disease, yet its direct role remains to be conclusively proven. We investigated two siblings with severe early-onset autoinflammatory disease and an elevated IFN signature. Whole-exome sequencing revealed a shared homozygous missense Arg148Trp variant in STAT2, a transcription factor that functions exclusively downstream of innate IFNs. Cells bearing STAT2R148W in homozygosity (but not heterozygosity) were hypersensitive to IFNα/ß, which manifest as prolonged Janus kinase-signal transducers and activators of transcription (STAT) signaling and transcriptional activation. We show that this gain of IFN activity results from the failure of mutant STAT2R148W to interact with ubiquitin-specific protease 18, a key STAT2-dependent negative regulator of IFNα/ß signaling. These observations reveal an essential in vivo function of STAT2 in the regulation of human IFNα/ß signaling, providing concrete evidence of the serious pathological consequences of unrestrained IFNα/ß activity and supporting efforts to target this pathway therapeutically in IFN-associated disease.

Human interleukin-2 receptor ß mutations associated with defects in immunity and peripheral tolerance.

Interleukin-2, which conveys essential signals for immunity, operates through a heterotrimeric receptor. Here we identify human interleukin-2 receptor (IL-2R) ß chain (IL2RB) gene defects as a cause of life-threatening immune dysregulation. We report three homozygous mutations in the IL2RB gene of eight individuals from four consanguineous families that cause disease by distinct mechanisms. Nearly all patients presented with autoantibodies, hypergammaglobulinemia, bowel inflammation, dermatological abnormalities, lymphadenopathy, and cytomegalovirus disease. Patient T lymphocytes lacked surface expression of IL-2Rß and were unable to respond to IL-2 stimulation. By contrast, natural killer cells retained partial IL-2Rß expression and function. IL-2Rß loss of function was recapitulated in a recombinant system in which IL2RB mutations caused reduced surface expression and IL-2 binding. Stem cell transplant ameliorated clinical symptoms in one patient; forced expression of wild-type IL-2Rß also increased the IL-2 responsiveness of patient T lymphocytes in vitro. Insights from these patients can inform the development of IL-2-based therapeutics for immunological diseases and cancer.

An essential role for the Zn2+ transporter ZIP7 in B cell development.

Despite the known importance of zinc for human immunity, molecular insights into its roles have remained limited. Here we report a novel autosomal recessive disease characterized by absent B cells, agammaglobulinemia and early onset infections in five unrelated families. The immunodeficiency results from hypomorphic mutations of SLC39A7, which encodes the endoplasmic reticulum-to-cytoplasm zinc transporter ZIP7. Using CRISPR-Cas9 mutagenesis we have precisely modeled ZIP7 deficiency in mice. Homozygosity for a null allele caused embryonic death, but hypomorphic alleles reproduced the block in B cell development seen in patients. B cells from mutant mice exhibited a diminished concentration of cytoplasmic free zinc, increased phosphatase activity and decreased phosphorylation of signaling molecules downstream of the pre-B cell and B cell receptors. Our findings highlight a specific role for cytosolic Zn2+ in modulating B cell receptor signal strength and positive selection.

ZNF341 controls STAT3 expression and thereby immunocompetence.

Signal transducer and activator of transcription 3 (STAT3) is a central regulator of immune homeostasis. STAT3 levels are strictly controlled, and STAT3 impairment contributes to several diseases including the monogenic autosomal-dominant hyper-immunoglobulin E (IgE) syndrome (AD-HIES). We investigated patients of four consanguineous families with an autosomal-recessive disorder resembling the phenotype of AD-HIES, with symptoms of immunodeficiency, recurrent infections, skeletal abnormalities, and elevated IgE. Patients presented with reduced STAT3 expression and diminished T helper 17 cell numbers, in absence of STAT3 mutations. We identified two distinct homozygous nonsense mutations in ZNF341, which encodes a zinc finger transcription factor. Wild-type ZNF341 bound to and activated the STAT3 promoter, whereas the mutant variants showed impaired transcriptional activation, partly due to nuclear translocation failure. In summary, nonsense mutations in ZNF341 account for the STAT3-like phenotype in four autosomal-recessive kindreds. Thus, ZNF341 is a previously unrecognized regulator of immune homeostasis.

14 Years after Discovery: Clinical Follow-up on 15 Patients with Inducible Co-Stimulator Deficiency.

BACKGROUND: Inducible co-stimulator (ICOS) deficiency was the first monogenic defect reported to cause common variable immunodeficiency (CVID)-like disease in 2003. Since then, 16 patients have been reported worldwide with an increasing range of clinical phenotypes. OBJECTIVE: We sought to compare the clinical and immunological phenotype and provide clinical follow-up and therapeutic approaches for treating ICOS-deficient patients. METHODS: We describe the clinical and laboratory data of 15 patients with available clinical data. Previous publications and clinical assessment were used as data sources. RESULTS: The observed ICOS gene mutations were all deletions leading to undetectable protein expression. The clinical phenotype of ICOS deficiency is much broader than initially anticipated and includes not only CVID-like disease but an increased susceptibility to viral and opportunistic infections, as well as cancer. Impaired B-cell development led to decreased memory B-cells in all patients, and hypogammaglobulinemia in all but one patient. Circulating CXCR5+ CD4+ follicular T-helper-cell numbers were also reduced in all patients. Treatment included immunoglobulin replacement, regular antibiotic prophylaxis, corticosteroids, and steroid-sparing agents. Three patients underwent hematopoietic stem cell transplantation; one of them died due to capillary leak syndrome on day 5 posttransplantation. CONCLUSION: The disease spectrum of ICOS deficiency is expanding from solely B-cell to combined B- and T-cell immunodeficiency, suggesting genetic and environmental modifiers. Genetic diagnosis is the only tool to distinguish ICOS deficiency from other immunological defects. Patients with antibody deficiency, autoimmunity, and combined immunodeficiency should be screened for ICOS mutations.

Identification of Heterozygous Single- and Multi-exon Deletions in IL7R by Whole Exome Sequencing.

PURPOSE: We aimed to achieve a retrospective molecular diagnosis by applying state-of-the-art genomic sequencing methods to past patients with T-B+NK+ severe combined immunodeficiency (SCID). We included identification of copy number variations (CNVs) by whole exome sequencing (WES) using the CNV calling method ExomeDepth to detect gene alterations for which routine Sanger sequencing analysis is not suitable, such as large heterozygous deletions. METHODS: Of a total of 12 undiagnosed patients with T-B+NK+ SCID, we analyzed eight probands by WES, using GATK to detect single nucleotide variants (SNVs) and small insertions and deletions (INDELs) and ExomeDepth to detect CNVs. RESULTS: We found heterozygous single- or multi-exon deletions in IL7R, a known disease gene for autosomal recessive T-B+NK+ SCID, in four families (seven patients). In three families (five patients), these deletions coexisted with a heterozygous splice site or nonsense mutation elsewhere in the same gene, consistent with compound heterozygosity. In our cohort, about a quarter of T-B+NK+ SCID patients (26%) had such compound heterozygous IL7R deletions. CONCLUSIONS: We show that heterozygous IL7R exon deletions are common in T-B+NK+ SCID and are detectable by WES. They should be considered if Sanger sequencing fails to detect homozygous or compound heterozygous IL7R SNVs or INDELs.