The interleukin-7 receptor gene is at 5p13

Severe combined immunodeficiency--an update

Severe combined immunodeficiencies (SCIDs) are a group of inherited disorders responsible for severe dysfunctions of the immune system. These diseases are life-threatening when the diagnosis is made too late; they are the most severe forms of primary immunodeficiency. SCID patients often die during the first two years of life if appropriate treatments to reconstitute their immune system are not undertaken. Conventionally, SCIDs are classified according either to the main pathway affected by the molecular defect or on the basis of the specific immunologic phenotype that reflects the stage where the blockage occurs during the differentiation process. However, during the last few years many new causative gene alterations have been associated with unusual clinical and immunological phenotypes. Many of these novel forms of SCID also show extra-hematopoietic alterations, leading to complex phenotypes characterized by a functional impairment of several organs, which may lead to a considerable delay in the diagnosis. Here we review the biological and clinical features of SCIDs paying particular attention to the most recently identified forms and to their unusual or extra-immunological clinical features.

Interleukin 7 and thymic stromal lymphopoietin: from immunity to leukemia

Cancer is often caused by deregulation of normal developmental processes. Here, we review recent research on the aberrant activation of two hematopoietic cytokine receptors in acute lymphoid leukemias. Somatic events in the genes for thymic stromal lymphopoietin and Interleukin 7 receptors as well as in their downstream JAK kinases result in constitutive ligand-independent activation of survival and proliferation in B and T lymphoid precursors. Drugs targeting these receptors or the signaling pathways might provide effective therapies of these leukemias.

Cell biology of IL-7, a key lymphotrophin

IL-7 is essential for the development and survival of T lymphocytes. This review is primarily from the perspective of the cell biology of the responding T cell. Beginning with IL-7 receptor structure and regulation, the major signaling pathways appear to be via PI3K and Stat5, although the requirement for either has yet to be verified by published knockout experiments. The proliferation pathway induced by IL-7 differs from conventional growth factors and is primarily through posttranslational regulation of p27, a Cdk inhibitor, and Cdc25a, a Cdk-activating phosphatase. The survival function of IL-7 is largely through maintaining a favorable balance of bcl-2 family members including Bcl-2 itself and Mcl-1 on the positive side, and Bax, Bad and Bim on the negative side. There are also some remarkable metabolic effects of IL-7 withdrawal. Studies of IL-7 receptor signaling have yet to turn up unique pathways, despite the unique requirement for IL-7 in T cell biology. There remain significant questions regarding IL-7 production and the major producing cells have yet to be fully characterized.

Interleukin-7 receptor alpha (IL-7Ralpha) deficiency: cellular and molecular bases. Analysis of clinical, immunological, and molecular features in 16 novel patients

Analysis of gene-targeted mice and patients with severe combined immunodeficiency due to mutations of the alpha chain of the interleukin-7 receptor (IL-7Ralpha) has shown important differences between mice and humans in the role played by IL-7 in lymphoid development. More recently, it has been shown that IL-7Ralpha is also shared by the receptor for another cytokine, thymic stromal lymphopoietin (TSLP). In this review, we discuss recent advances in IL-7- and TSLP-mediated signaling. We also report on the clinical and immunological features of 16 novel patients with IL-7Ralpha deficiency and discuss the results of hematopoietic stem cell transplantation.

Severe combined immunodeficiency caused by deficiency in either the delta or the epsilon subunit of CD3

We investigated the molecular mechanism underlying a severe combined immunodeficiency characterized by the selective and complete absence of T cells. The condition was found in 5 patients and 2 fetuses from 3 consanguineous families. Linkage analysis performed on the 3 families revealed that the patients were carrying homozygous haplotypes within the 11q23 region, in which the genes encoding the gamma, delta, and epsilon subunits of CD3 are located. Patients and affected fetuses from 2 families were homozygous for a mutation in the CD3D gene, and patients from the third family were homozygous for a mutation in the CD3E gene. The thymus from a CD3delta-deficient fetus was analyzed and revealed that T cell differentiation was blocked at entry into the double positive (CD4+CD8+) stage with the accumulation of intermediate CD4-single positive cells. This indicates that CD3delta plays an essential role in promoting progression of early thymocytes toward double-positive stage. Altogether, these findings extend the known molecular mechanisms underlying severe combined immunodeficiency to a new deficiency, i.e., CD3epsilon deficiency, and emphasize the essential roles played by the CD3epsilon and CD3delta subunits in human thymocyte development, since these subunits associate with both the pre-TCR and the TCR.

Structure, sequence, and promoter analysis of human disabled-2 gene (DAB2)

Disabled-2 (DAB2 for human and Dab2 for other species) is one of two mammalian orthologues of Drosophila Disabled. DAB2 exhibits properties of a tumor suppressor gene: the expression of DAB2 is eliminated in 85-95% of breast and ovarian tumors; homozygous deletions of the gene have been found in some of these tumors; and reintroduction of DAB2 expression suppresses tumorigenicity of carcinoma cells. To study the mechanisms of loss of expression and to detect possible mutations in tumors, we have investigated the genomic structure of the DAB2 gene. The complete DAB2 gene was identified and sequenced from four overlapping BAC clones found to contain the gene. Complement factor 9 (C9) gene was localized next to the DAB2 gene at the 3'-end of the BAC DNA fragments. The human DAB2 gene is about 35 kb in size and consists of 15 exons and 14 introns, producing an approximately 4-kb message. A spliced variant corresponding to mouse Dab2 p93 and a 3'-end spliced variant were also identified. The translation initiation site resides in the second exon, and the noncoding first exon is separated from the second exon by a 14-kb intron. The 420-bp sequence 5' of exon 1 contains a CpG island (39 CpG sites). This 420-bp putative promoter was found to contain the site for transcription initiation, identified by RNase protection assay, and is sufficient for active transcription in epithelial cells. The information about the gene structure of DAB2 will enable us to analyze possible mutations and the mechanisms of loss of DAB2 expression in tumors.

Expression analysis and characterization of alternatively spliced transcripts of human IL-7Ralpha chain encoding two truncated receptor proteins in relapsed childhood all

In the family of cytokines and cytokine receptors, alternative splicing of pre-mRNA is a frequently observed process that generates different protein isoforms from a single genetic locus. The splicing-derived cytokine receptor protein isoforms are mostly soluble receptors or show alterations in their cytoplasmic domain. It is possible that receptor abnormalities or a pathological ratio of different isoforms may contribute to leukaemia by circumventing normal growth factor control or altering the balance of proliferation and differentiation. IL-7 plays a critical role in early stages of both B and T cell maturation. Moreover, it stimulates the expansion of mature T cells including anti-tumour reactive cells as well as a number of T and B cell malignancies underlining its potential importance for deregulated lymphoid proliferation and leukaemogenesis. Here, we present detailed data on the expression of the interleukin 7 receptor alpha chain (IL-7Ralpha) in leukaemic cells from 210 children with acute lymphoblastic leukaemia (ALL) and describe two novel alternatively spliced transcripts of human IL-7Ralpha coding for truncated receptor proteins which are still capable of binding IL-7. IL-7Ralpha mRNA expression was more frequent in more mature pre-B ALL [91% (30/33)] than in common [81% (81/100)] or pro-B ALL [64% (18/28)], or even in T ALL [64% (29/45)]. These results are in concordance with flow cytometric analyses on the proportion of IL-7Ralpha bearing cells among total blast cell population. Our results lead us to assume that splicing derived IL-7Ralpha isoforms play a potential role in modulating IL-7 signal transduction and might be important for the pathogenesis of leukaemia.

The gene for severe combined immunodeficiency disease in Athabascan-speaking Native Americans is located on chromosome 10p

Severe combined immunodeficiency disease (SCID) consists of a group of heterogeneous genetic disorders. The most severe phenotype, T-B- SCID, is inherited as an autosomal recessive trait and is characterized by a profound deficiency of both T cell and B cell immunity. There is a uniquely high frequency of T-B- SCID among Athabascan-speaking Native Americans (A-SCID). To localize the A-SCID gene, we conducted a genomewide search, using linkage analysis of approximately 300 microsatellite markers in 14 affected Athabascan-speaking Native American families. We obtained conclusive evidence for linkage of the A-SCID locus to markers on chromosome 10p. The maximum pairwise LOD scores 4.53 and 4.60 were obtained from two adjacent markers, D10S191 and D10S1653, respectively, at a recombination fraction of straight theta=.00. Recombination events placed the gene in an interval of approximately 6.5 cM flanked by D10S1664 and D10S674. Multipoint analysis positioned the gene for the A-SCID phenotype between D10S191 and D10S1653, with a peak LOD score of 5.10 at D10S191. Strong linkage disequilibrium was found in five linked markers spanning approximately 6.5 cM in the candidate region, suggesting a founder effect with an ancestral mutation that occurred sometime before 1300 A.D.

Cytokine receptor genes: structure, chromosomal location, and involvement in human disease

Haemopoietic cytokines regulate haemopoietic cell function via specific cell surface receptors. These receptors are members of a large superfamily of transmembrane proteins and are characterised by a 200 amino acid extracellular sequence encoding the ligand binding domain. Several of the genes for members of this superfamily have now been characterised at the molecular level revealing a highly conserved organisation and a number of these genes have been localised cytogenetically. The recent finding that genes for the IL-3 and GM-CSF receptor alpha chain subunits colocalise to a small region of the pseudoautosomal region and the observation that the LIF receptor locus is present in a cluster of receptor genes on chromosome 5 suggest the possibility that subsets of cytokine receptor genes may be organised into clusters. This possibility is discussed and the potential significance of cytokine receptor gene clusters is assessed. Several of the receptor genes are known to be involved in inherited disorders and there is evidence to suggest lesions in cytokine receptor genes could have a role in leukaemia. We review the gene organisation, localisation and involvement in disease for the known cytokine receptor loci. This large family of receptors is expanding with the steady discovery of new members--all of which have the potential to be involved in human disorders.