Background The endonuclease ARTEMIS, which is encoded by the DCLRE1C gene, is a component of the nonhomologous end-joining pathway and participates in hairpin opening during the V(D)J recombination ...process and repair of a subset of DNA double-strand breaks. Patients with ARTEMIS deficiency usually present with severe combined immunodeficiency (SCID) and cellular radiosensitivity, but hypomorphic mutations can cause milder phenotypes (leaky SCID). Objective We sought to correlate the functional effect of human DCLRE1C mutations on phenotypic presentation in patients with ARTEMIS deficiency. Methods We studied the recombination and DNA repair activity of 41 human DCLRE1C mutations in Dclre1c −/− v-abl kinase–transformed pro-B cells retrovirally engineered with a construct that allows quantification of recombination activity by means of flow cytometry. For assessment of DNA repair efficacy, resolution of γH2AX accumulation was studied after ionizing radiation. Results Low or absent activity was detected for mutations causing a typical SCID phenotype. Most of the patients with leaky SCID were compound heterozygous for 1 loss-of-function and 1 hypomorphic allele, with significant residual levels of recombination and DNA repair activity. Deletions disrupting the C-terminus result in truncated but partially functional proteins and are often associated with leaky SCID. Overexpression of hypomorphic mutants might improve the functional defect. Conclusions Correlation between the nature and location of DCLRE1C mutations, functional activity, and the clinical phenotype has been observed. Hypomorphic variants that have been reported in the general population can be disease causing if combined in trans with a loss-of-function allele. Therapeutic strategies aimed at inducing overexpression of hypomorphic alleles might be beneficial.
Background Combined immunodeficiency with multiple intestinal atresias (CID-MIA) is a rare hereditary disease characterized by intestinal obstructions and profound immune defects. Objective We sought ...to determine the underlying genetic causes of CID-MIA by analyzing the exomic sequences of 5 patients and their healthy direct relatives from 5 unrelated families. Methods We performed whole-exome sequencing on 5 patients with CID-MIA and 10 healthy direct family members belonging to 5 unrelated families with CID-MIA. We also performed targeted Sanger sequencing for the candidate gene tetratricopeptide repeat domain 7A ( TTC7A ) on 3 additional patients with CID-MIA. Results Through analysis and comparison of the exomic sequence of the subjects from these 5 families, we identified biallelic damaging mutations in the TTC7A gene, for a total of 7 distinct mutations. Targeted TTC7A gene sequencing in 3 additional unrelated patients with CID-MIA revealed biallelic deleterious mutations in 2 of them, as well as an aberrant splice product in the third patient. Staining of normal thymus showed that the TTC7A protein is expressed in thymic epithelial cells, as well as in thymocytes. Moreover, severe lymphoid depletion was observed in the thymus and peripheral lymphoid tissues from 2 patients with CID-MIA. Conclusions We identified deleterious mutations of the TTC7A gene in 8 unrelated patients with CID-MIA and demonstrated that the TTC7A protein is expressed in the thymus. Our results strongly suggest that TTC7A gene defects cause CID-MIA.
To the Editor: Early lymphocyte development requires the orchestrated interplay of pathways to maintain genomic integrity and accurate DNA repair during the proliferative bursts associated with ...antigen receptor rearrangement.1 Inborn errors in replication control or DNA repair can lead to primary immunodeficiency.2 We report the case of a patient with combined immunodeficiency, facial dysmorphisms, and autoimmunity with a novel mutation in the DNA polymerase epsilon subunit 2 (POLE2) gene. POLE3 (17kDa) and POLE4 (12kDa) represent 2 additional subunits in the complex.4,5 The functional role of the POLE holoenzyme includes leading strand synthesis required for DNA replication and proofreading activity required for the repair of DNA damage and for maintenance of sequence (epigenetic) inheritance.4,5 The exact function of the POLE2 subunit is not known, but is thought to involve protein-protein interactions, including dimerization with POLE1 and influencing the C-terminal part of the catalytic subunit.
Defect of regulatory T cells in patients with Omenn syndrome Cassani, Barbara, PhD; Poliani, Pietro Luigi, MD, PhD; Moratto, Daniele, PhD ...
Journal of allergy and clinical immunology,
2010, January 2010, 2010-Jan, 2010-01-00, 20100101, Letnik:
125, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Background Omenn syndrome (OS) is an autosomal-recessive disorder characterized by severe immunodeficiency and T-cell–mediated autoimmunity. The disease is caused by hypomorphic mutations in ...recombination-activating genes that hamper the process of Variable (V) Diversity (D) Joining (J) recombination, leading to the generation of autoreactive T cells. We have previously shown that in OS the expression of autoimmune regulator, a key factor governing central tolerance, is markedly reduced. Objective Here, we have addressed the role of peripheral tolerance in the disease pathogenesis. Methods We have analyzed forkhead box protein P3 (FOXP3) expression in peripheral blood T cells of 4 patients with OS and in lymphoid organs of 8 patients with OS and have tested the suppressive activity of sorted CD4+ CD25high peripheral blood T cells in 2 of these patients. Results We have observed that CD4+ CD25high T cells isolated ex vivo from patients with OS failed to suppress proliferation of autologous or allogenic CD4+ responder T cells. Moreover, despite individual variability in the fraction of circulating FOXP3+ CD4 cells in patients with OS, the immunohistochemical analysis of FOXP3 expression in lymph nodes and thymus of patients with OS demonstrated a severe reduction of this cell subset compared with control tissues. Conclusion Overall, these results suggest a defect of regulatory T cells in OS leading to a breakdown of peripheral tolerance, which may actively concur to the development of autoimmune manifestations in the disease.
Background The novel ability to epigenetically reprogram somatic cells into induced pluripotent stem cells (iPSCs) through the exogenous expression of transcription promises to revolutionize the ...study of human diseases. Objective Here we report on the generation of 25 iPSC lines from 6 patients with various forms of primary immunodeficiencies (PIDs) affecting adaptive immunity, innate immunity, or both. Methods Patients’ dermal fibroblasts were reprogrammed by expression of 4 transcription factors, octamer-binding transcription factor 4 ( OCT4 ), sex determining region Y-box 2 ( SOX2 ), Krueppel-like factor 4 ( KLF4 ), and cellular myelomonocytosis proto-oncogene ( cMYC ), by using a single excisable polycistronic lentiviral vector. Results iPSCs derived from patients with PIDs show a stemness profile that is comparable with that observed in human embryonic stem cells. After in vitro differentiation into embryoid bodies, pluripotency of the patient-derived iPSC lines was demonstrated by expression of genes characteristic of each of the 3 embryonic layers. We have confirmed the patient-specific origin of the iPSC lines and ascertained maintenance of karyotypic integrity. Conclusion By providing a limitless source of diseased stem cells that can be differentiated into various cell types in vitro , the repository of iPSC lines from patients with PIDs represents a unique resource to investigate the pathophysiology of hematopoietic and extrahematopoietic manifestations of these diseases and might assist in the development of novel therapeutic approaches based on gene correction.
Multiple immunologic abnormalities have been identified that might account for immune dysregulation in patients with WAS,5 including impaired function of regulatory T and regulatory B cells, ...defective apoptosis, abnormalities of the distribution and diversity of T and B lymphocytes, and defective function of T and natural killer cells, resulting in impaired clearance of pathogens and persistent inflammation. ...Wiskott-Aldrich syndrome protein (WASP)-deficient plasmacytoid dendritic cells are hyperresponsive to Toll-like receptor 9 stimulation and produce high amounts of type 1 interferon, which might also contribute to autoimmunity.6 More recently, we and others have identified B-cell autonomous effects of WASP deficiency that are likely to play a critical role in the autoimmunity of the disease.7-9 These include (1) hyperresponsiveness of WASP-deficient B cells to stimulation through the B-cell receptor and Toll-like receptors; (2) accumulation of B lymphocytes with a characteristic phenotype (CD21lowCD38low), which is indicative of a type 1 interferon signature and a marker of self-reactivity; (3) preferential use of immunoglobulin variable genes that are enriched in patients with autoimmune disease and decreased somatic hypermutation; (4) increased release of immature B cells from the bone marrow to the periphery; (5) increased levels of B cell-activating factor of the TNF family serum; and (6) decreased regulatory B-cell function. PL Table I Molecular, immunologic, and clinical characteristics of patients Values in boldface are outside of age-matched reference values (shown in parentheses).AIHA, Autoimmune hemolytic anemia; ANA, anti-nuclear antibodies; ANCA, anti-neutrophil cytosplasmic antibodies; ASMA, anti-smooth muscle antibodies; BAFF, B cell-activating factor of the TNF family; IBD, inflammatory bowel disease; NA, not available; ND, not done; PL, anti-phospholipid antibodies; Plt, anti-platelet antibodies; TPO, anti-thyroid peroxidase antibodies.
Complete deficiency of either RAG1 or RAG2 results in classical severe combined immunodeficiency lacking T and B cells, since RAG1 mediates DNA binding and cleavage, while RAG2 is an essential ...cofactor for RAG1 function.1 Hypomorphic missense mutations that preserve residual RAG activity and allow the development of oligoclonal T cells, but virtually no B cells, result in recurrent infections, erythroderma, hepatomegaly, colitis, and αβ T-cell expansion (Omenn syndrome).2RAG1/2 mutations can also cause γδ T-cell expansion and immunodeficiency with granulomas.3 Hyper-IgM syndrome is characterized by normal or increased IgM levels with decreased IgG and IgA levels. Because her phenotype was consistent with Omenn syndrome, RAG1 and RAG2 were sequenced.
Background Mutations in Janus kinase 3 (JAK3) are a cause of severe combined immunodeficiency, but hypomorphic JAK3 defects can result in a milder clinical phenotype, with residual development and ...function of autologous T cells. Maternal T-cell engraftment is a common finding in infants with severe combined immunodeficiency but is not typically observed in patients with residual T-cell development. Objective We sought to study in detail the molecular, cellular, and humoral immune phenotype and function of 3 patients with hypomorphic JAK3 mutations. Methods We analyzed the distribution and function of T and B lymphocytes in 3 patients and studied the in vitro and in vivo responses of maternal T lymphocytes in 1 patient with maternal T-cell engraftment and residual production of autologous T lymphocytes. Results B cells were present in normal numbers but with abnormal distribution of marginal zone–like and memory B cells. B-cell differentiation to plasmablasts in vitro in response to CD40 ligand and IL-21 was abolished. In 2 patients the T-cell repertoire was moderately restricted. Surprisingly, 1 patient showed coexistence of maternal and autologous T lymphocytes. By using an mAb recognizing the maternal noninherited HLA-A2 antigen, we found that autologous cells progressively accumulated in vivo but did not compete with maternal cells in vitro. Conclusion The study of 3 patients with hypomorphic JAK3 mutations suggests that terminal B-cell maturation/differentiation requires intact JAK3 function, even if partially functioning T lymphocytes are present. Maternal T-cell engraftment can occur in patients with JAK3 mutations despite the presence of autologous T cells.
Background Cartilage-hair hypoplasia (CHH) is characterized by metaphyseal dysplasia, bone marrow failure, increased risk of malignancies, and a variable degree of immunodeficiency. CHH is caused by ...mutations in the RNA component of the mitochondrial RNA processing (RMRP) endoribonuclease gene, which is involved in ribosomal assembly, telomere function, and cell cycle control. Objectives We aimed to define thymic output and characterize immune function in a cohort of patients with molecularly defined CHH with and without associated clinical immunodeficiency. Methods We studied the distribution of B and T lymphocytes (including recent thymic emigrants), in vitro lymphocyte proliferation, cell cycle, and apoptosis in 18 patients with CHH compared with controls. Results Patients with CHH have a markedly reduced number of recent thymic emigrants, and their peripheral T cells show defects in cell cycle control and display increased apoptosis, resulting in poor proliferation on activation. Conclusion These data confirm that RMRP mutations result in significant defects of cell-mediated immunity and provide a link between the cellular phenotype and the immunodeficiency in CHH.
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