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Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a critical regulator of cell death and inflammation, but its relevance for human disease pathogenesis remains elusive. Studies of monogenic disorders might provide critical insights into disease mechanisms and therapeutic targeting of RIPK1 for common diseases. Here, we report on eight patients from six unrelated pedigrees with biallelic loss-of-function mutations in RIPK1 presenting with primary immunodeficiency and/or intestinal inflammation. Mutations in RIPK1 were associated with reduced NF-κB activity, defective differentiation of T and B cells, increased inflammasome activity, and impaired response to TNFR1-mediated cell death in intestinal epithelial cells. The characterization of RIPK1-deficient patients highlights the essential role of RIPK1 in controlling human immune and intestinal homeostasis, and might have critical implications for therapies targeting RIPK1., Competing Interests: The authors declare no conflict of interest.

X-linked severe combined immunodeficiency (X-SCID) leads to a T(-) NK(-) B(+) immunophenotype and is caused by mutations in the gene encoding the IL-2 receptor γ-chain (IL2RG). IL2RG(R222C) leads to atypical SCID with a severe early onset phenotype despite largely normal NK- and T-cell numbers. To address this discrepancy, we performed a detailed analysis of T, B, and NK cells, including quantitative STAT phosphorylation and functional responses to the cytokines IL-2, IL-4, IL-15, and IL-21 in a patient with the IL2RG(R222C) mutation. Moreover, we identified nine additional unpublished patients with the same mutations, all with a full SCID phenotype, and confirmed selected immunological observations. T-cell development was variably affected, but led to borderline T-cell receptor excision circle (TREC) levels and a normal repertoire. T cells showed moderately reduced proliferation, failing enhancement by IL-2. While NK-cell development was normal, IL-2 enhancement of NK-cell degranulation and IL-15-induced cytokine production were absent. IL-2 or IL-21 failed to enhance B-cell proliferation and plasmablast differentiation. These functional alterations were reflected by a differential impact of IL2RG(R222C) on cytokine signal transduction, with a gradient IL-4

Multiple intestinal atresia (MIA) is a rare cause of bowel obstruction that is sometimes associated with a combined immunodeficiency (CID), leading to increased susceptibility to infections. The factors underlying this rare disease are poorly understood. We characterized the immunological and intestinal features of 6 unrelated MIA-CID patients. All patients displayed a profound, generalized lymphocytopenia, with few lymphocytes present in the lymph nodes. The thymus was hypoplastic and exhibited an abnormal distribution of epithelial cells. Patients also had profound disruption of the epithelial barrier along the entire gastrointestinal tract. Using linkage analysis and whole-exome sequencing, we identified 10 mutations in tetratricopeptide repeat domain–7A (TTC7A), all of which potentially abrogate TTC7A expression. Intestinal organoid cultures from patient biopsies displayed an inversion of apicobasal polarity of the epithelial cells that was normalized by pharmacological inhibition of Rho kinase. Our data indicate that TTC7A deficiency results in increased Rho kinase activity, which disrupts polarity, growth, and differentiation of intestinal epithelial cells, and which impairs immune cell homeostasis, thereby promoting MIA-CID development.

There are few reports of clinical presentation, genotype, and HCT outcomes for patients with T-B+NK+ SCID. Between 1981 and 2007, eight of 84 patients with SCID who received and/or were followed after HCT at UCSF had the T-B+NK+ phenotype. One additional patient with T-B+NK+ SCID was identified as the sibling of a patient treated at UCSF. Chart reviews were performed. Molecular analyses of IL7R, IL2RG, JAK3, and the genes encoding the CD3 T-cell receptor components δ (CD3D), ε (CD3E), and ζ (CD3Z) were carried out. IL7R mutations were documented in four patients and CD3D mutations in two others. Three patients had no defects found. Only two of nine patients had an HLA-matched related HCT donor. Both survived, and neither developed GVHD. Five of seven recipients of haploidentical grafts survived. Although the majority of reported cases of T-B+NK+ SCID are caused by defects in IL7R, CD3 complex defects were also found in this series and should be considered when evaluating patients with T-B+NK+ SCID. Additional genes, mutations in which account for T-B+NK+ SCID, remain to be found. Better approaches to early diagnosis and HCT treatment are needed for patients lacking an HLA-matched related donor., (© 2011 John Wiley & Sons A/S.)

FOXN1 deficiency is a primary immunodeficiency characterized by athymia, alopecia totalis, and nail dystrophy. Two infants with FOXN1 deficiency were transplanted with cultured postnatal thymus tissue. Subject 1 presented with disseminated Bacillus Calmette-Guérin infection and oligoclonal T cells with no naive markers. Subject 2 had respiratory failure, human herpes virus 6 infection, cytopenias, and no circulating T cells. The subjects were given thymus transplants at 14 and 9 months of life, respectively. Subject 1 received immunosuppression before and for 10 months after transplantation. With follow up of 4.9 and 2.9 years, subjects 1 and 2 are well without infectious complications. The pretransplantation mycobacterial disease in subject 1 and cytopenias in subject 2 resolved. Subject 2 developed autoimmune thyroid disease 1.6 years after transplantation. Both subjects developed functional immunity. Subjects 1 and 2 have 1053/mm(3) and 1232/mm(3) CD3(+) cells, 647/mm(3) and 868/mm(3) CD4(+) T cells, 213/mm(3) and 425/mm(3) naive CD4(+) T cells, and 10 200 and 5700 T-cell receptor rearrangement excision circles per 100 000 CD3(+) cells, respectively. They have normal CD4 T-cell receptor β variable repertoires. Both subjects developed antigen-specific proliferative responses and have discontinued immunoglobulin replacement. In summary, thymus transplantation led to T-cell reconstitution and function in these FOXN1 deficient infants.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment for severe combined immunodeficiency (SCID). Detailed assessment of the long-term outcome of HSCT, ie, the occurrence of clinical events and the quality and stability of immune reconstitution, is now required. We performed a single-center retrospective analysis of the long-term outcome of HSCT in 90-patient cohort followed for between 2 and 34 years (median, 14 years). Clinical events and immune reconstitution data were collected. Almost half the patients have experienced one or more significant clinical events, including persistent chronic graft-versus-host disease (GVHD), autoimmune and inflammatory manifestations, opportunistic and nonopportunistic infections, chronic human papilloma virus (HPV) infections, and a requirement for nutritional support. With the notable exception of severe HPV infection, these complications tend to become less common 15 years later after HSCT. A multivariate analysis showed that the occurrence of these events correlated with non-genoidentical donors, diagnosis of Artemis SCID, and quality of immune reconstitution. In most cases, HSCT enables long-term survival with infrequent sequelae. However, the occurrence of relatively late-onset complications is a concern that requires specific means of prevention and justifies careful patient follow-up.

Omenn syndrome (OS) is a rare combined immunodeficiency characterized by erythroderma, lymphadenopathy, and autoimmune manifestations. Most cases are due to mutations in the RAG genes. We report a case of OS due to mutations of IL7RA, thus defining Omenn syndrome as a genetically heterogeneous condition.

Purpose of Review: The molecular characterization of inherited T-cell immunodeficiencies has contributed to delineating key factors in human T-cell development. This review reports on the recent description of deleterious mutations in the genes encoding CD3 subunits expressed at the T-lymphocyte membrane in association with the T-cell receptor., Recent Findings: Homozygous mutations in CD3D and CD3E genes lead to a complete block in T-cell development and thus to an early-onset severe combined immunodeficiency phenotype. Thymic studies have shown that the defect in T-cell development occurs at the transition between 'double-negative' and 'double-positive' thymocytes. These results contrast with the partial T-cell immunodeficiency caused by a deficiency in CD3G., Summary: Two new severe combined immunodeficiency conditions have been reported as a consequence of either CD3D or CD3E deficiency. The distinct phenotype of CD3G deficiency sheds light on the differential roles of CD3 subunits in T-lymphocyte development.

Gene therapy has been shown to be a highly effective treatment for infants with typical X-linked severe combined immunodeficiency (SCID-X1, gammac-deficiency). For patients in whom previous allogeneic transplantation has failed, and others with attenuated disease who may present later in life, the optimal treatment strategy in the absence of human leukocyte antigen (HLA)-matched donors is unclear. Here we report the failure of gene therapy in 2 such patients, despite effective gene transfer to bone marrow CD34(+) cells, suggesting that there are intrinsic host-dependent restrictions to efficacy. In particular, there is likely to be a limitation to initiation of normal thymopoiesis, and we therefore suggest that intervention for these patients should be considered as early as possible.

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.

Two siblings with severe combined immune deficiency, one with maternal engraftment and detectable immunologic functions who was alive at the age of 8 years are presented. Both patients had the same JAK3 gene mutation, suggesting that maternal engraftment may result in immune competence leading to long-term survival in patients with severe combined immune deficiency.

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.

Haemopoietic stem-cell transplantation is a life-saving treatment for severe combined immune deficiency. However, there has been little long-term follow-up of this treatment. There is evidence for the persistance of partial immunodeficiency associated with significant infections, including severe human papillomavirus (HPV) disease. We did a retrospective analysis of severe HPV disease in a group of 41 patients with severe combined immune deficiency from one centre who were alive 10 years or longer after haemopoietic stem-cell transplantation. Nine of the 41 patients had extensive chronic HPV disease limited to the skin, with a median onset at 8 years after transplantation. Four had lesions typical of epidermodysplasia verruciformis, a rare genodermatosis. Transplant characteristics, immune status, and chimerism of these nine patients did not differ significantly from those of the other patients. The nine patients with HPV disease had severe combined immune deficiency associated with either common gammac receptor cytokine subunit or Janus kinase-3 (JAK-3) deficiency. By contrast, patients with other forms of severe combined immune deficiency did not have any signs of HPV disease. That genetic causes are the only predisposing factor to be identified for severe combined immune deficiency, suggests that natural-killer cells or gammac/JAK-3-dependent signalling in keratinocytes could have a role in anti-HPV immunity.

We have previously shown correction of X-linked severe combined immunodeficiency [SCID-X1, also known as gamma chain (gamma(c)) deficiency] in 9 out of 10 patients by retrovirus-mediated gamma(c) gene transfer into autologous CD34 bone marrow cells. However, almost 3 years after gene therapy, uncontrolled exponential clonal proliferation of mature T cells (with gammadelta+ or alphabeta+ T cell receptors) has occurred in the two youngest patients. Both patients' clones showed retrovirus vector integration in proximity to the LMO2 proto-oncogene promoter, leading to aberrant transcription and expression of LMO2. Thus, retrovirus vector insertion can trigger deregulated premalignant cell proliferation with unexpected frequency, most likely driven by retrovirus enhancer activity on the LMO2 gene promoter.

Defects of the JAK3-gene are known to cause an autosomal recessive form of severe combined immunodeficiency with almost absent T-cells and functionally defective B-cells (T-B+SCID). The JAK3 protein, an intracellular tyrosine kinase, is crucial for signal-transmission from the common gamma chain to the Signal Transducers and Activators of Transcription (STATs) that drive gene expression in the nucleus. We present nine novel patients with eleven distinct mutations (g.96A>G, g.268G>C, IVS12-1G>A, g.2046C>T, g.2160C>T, g.2175G>A, g.2187G>T, g.2391C>T, g.2406C>T, IVS18+3G>C) among them a mutation in the kinase domain (JH1: g.3167del). The clinical phenotype of the patients shows an unusually broad spectrum ranging from classical SCID to almost normal. In order to understand the complex genotype-phenotype correlation we studied expression and function (by IL-2 induced phosphorylation) of the newly identified and two other alleles with JH1 mutations we recently reported. We found the first mutation in the JH1-domain of JAK3, that precludes kinase activity (L910S). The two other JH1 mutations both caused a premature stop. One of them (C1024fsX1037) also abolished any phosphorylation of JAK3 and expression of the protein. The other mutation (Y1023X), affecting the last JH1 tyrosine, may allow for residual protein expression and phosphorylation. This may indicate that the part of the kinase region downstream Y1023, is not essential for the function of JAK3., (Copyright 2001 Wiley-Liss, Inc.)

During the last 10 years, an increasing number of genes have been identified whose abnormalities account for primary immunodeficiencies, with defects in development and/or function of the immune system. Among them is the JAK3-gene, encoding for a tyrosine kinase that is functionally coupled to cytokine receptors which share the common gamma chain. Defects of this gene cause an autosomal recessive form of severe combined immunodeficiency with almost absent T-cells and functionally defective B-cells (T(-)B(+) SCID). Herewith, we present molecular information on the first 27 unique mutations identified in the JAK3 gene, including clinical data on all of the 23 affected patients reported so far. A variety of mutations scattered throughout all seven functional domains of the protein, and with different functional effects, have been identified. Availability of a molecular screening test, based on amplification of genomic DNA, facilitates the diagnostic approach, and has permitted recognition that JAK3 deficiency may also be associated with atypical clinical and immunological features. Development of a structural model of the JAK3 kinase domain has allowed characterization of the functional effects of the various mutations. Most importantly, molecular analysis at the JAK3 locus results in improved genetic counseling, allows early prenatal diagnosis, and prompts appropriate treatment (currently based on hematopoietic stem cell transplantation) in affected families., (Copyright 2001 Wiley-Liss, Inc.)

Primary immunodeficiency diseases (PID) are attractive candi dates for a gene therapy approach because many of these disorders convey a poor prognosis while a number of the genes mutated in these conditions have been identified. Gene transfer into hematopoietic stem cells (HSC) should, in theory, lead to a cure of the disease. There are, however, a number of limitations mostly related to the failure of clinically available vectors to enable transgene integration into HSC. Nevertheless PID due to a gene defect leading to failure of cell development could be amenable to gene therapy given the selective advantage conferred to transgene expression in progenitor cells. Terminally differentiated cells are, however, long lived, as is the case for T lymphocytes. This concept led to the first gene therapy trials for adenosine deaminase (ADA) deficiency several years ago. Results were in part disappointing mostly because of the concomitant substitutive treatment by polyethylene glycol-ADA. However, recent application to X-linked severe combined immunodeficiency (gamma(c) deficiency) turned out to be efficient at least on a relatively short term basis (i.e. one year so far). These results demonstrate that this concept is valid and can be the basis for the treatment of other forms of severe T-cell immunodeficiencies. Obviously, development of vectors (lentiviruses) able to efficiently target HSC could in the future considerably enlarge the field of PID treatable by gene transfer.

Severe combined immunodeficiency-X1 (SCID-X1) is an X-linked inherited disorder characterized by an early block in T and natural killer (NK) lymphocyte differentiation. This block is caused by mutations of the gene encoding the gammac cytokine receptor subunit of interleukin-2, -4, -7, -9, and -15 receptors, which participates in the delivery of growth, survival, and differentiation signals to early lymphoid progenitors. After preclinical studies, a gene therapy trial for SCID-X1 was initiated, based on the use of complementary DNA containing a defective gammac Moloney retrovirus-derived vector and ex vivo infection of CD34+ cells. After a 10-month follow-up period, gammac transgene-expressing T and NK cells were detected in two patients. T, B, and NK cell counts and function, including antigen-specific responses, were comparable to those of age-matched controls. Thus, gene therapy was able to provide full correction of disease phenotype and, hence, clinical benefit.

In this report, we have analyzed the human T cell repertoire derived in vivo from a single T cell precursor. A unique case of X-linked severe combined immunodeficiency in which a reverse mutation occurred in an early T cell precursor was analyzed to this end. It was determined that at least 1,000 T cell clones with unique T cell receptor-beta sequences were generated from this precursor. This diversity seems to be stable over time and provides protection from infections in vivo. A similar estimation was obtained in an in vitro murine model of T cell generation from a single cell precursor. Overall, our results document the large diversity potential of T cell precursors and provide a rationale for gene therapy of the block of T cell development.

We retrospectively analyzed the B-cell function and leukocyte chimerism of 22 patients with severe combined immunodeficiency with B cells (B(+) SCID) who survived more than 2 years after bone marrow transplantation (BMT) to determine the possible consequences of BMT procedures, leukocyte chimerism, and SCID molecular deficit on B-cell function outcome. Circulating T cells were of donor origin in all patients. In recipients of HLA-identical BMT (n = 5), monocytes were of host origin in 5 and B cells were of host origin in 4 and of mixed origin in 1. In recipients of HLA haploidentical T-cell-depleted BMT (n = 17), B cells and monocytes were of host origin in 14 and of donor origin in 3. Engraftment of B cells was found to be associated with normal B-cell function. In contrast, 10 of 18 patients with host B cells still require Ig substitution. Conditioning regimen (ie, 8 mg/kg busulfan and 200 mg/kg cyclophosphamide) was shown neither to promote B-cell and monocyte engraftment nor to affect B-cell function. Eight patients with B cells of host origin had normal B-cell function. Evidence for functional host B cells was further provided in 3 informative cases by Ig allotype determination and by the detection, in 5 studied cases, of host CD27(+) memory B cells as in age-matched controls. These results strongly suggest that, in some transplanted patients, host B cells can cooperate with donor T cells to fully mature in Ig-producing cells.

X-linked severe combined immunodeficiency (SCID-Xl) is a rare human inherited disorder in which early T and natural killer (NK) lymphocyte development is blocked. The genetic disorder results from mutations in the common gammac chain that participates in several cytokine receptors including the interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. We have shown in a previous report that gammac gene transfer into SCID-Xl bone marrow (BM) cells restores efficient NK cell differentiation. In this study, we have focused on the introduction of the gammac gene into SCID-Xl hematopoietic stem cells with the goal of obtaining differentiation into mature T cells. For this purpose, we used the in vitro hybrid fetal thymic organ culture (FTOC) system in which a combination of cytokines consisting of stem cell factor (SCF), Flt-3L, IL-7, IL-1, and IL-15 is added concomitantly. In this culture system, CD34(+) marrow cells from two SCID-Xl patients were able to mature into double positive CD4(+) CD8(+) cells and to a lesser degree into CD4(+) TCRbeta+ single positive cells after retroviral-mediated gammac gene transfer. In addition, examination of the output cell population at the TCR DJbeta1 locus exhibited multiple rearrangements. These results indicate that restoration of the gammac/JAK/STAT signaling pathway during the early developmental stages of thymocytes can correct the T-cell differentiation block in SCID-Xl hematopoietic progenitor cells and therefore establishes a basis for further clinical gammac gene transfer studies.

Natural killer (NK) cells are characterized by their ability to mediate spontaneous cytotoxicity against susceptible tumor cells and infected cells. They differentiate from hematopoietic progenitor cells. Patients with X-linked severe combined immunodeficiency (SCID X1) carry mutations in the gamma c cytokine receptor gene that result in lack of both T and NK cells. To assess the role of interleukin-2 (IL-2), IL-7, and IL-15 cytokines, which share gamma c receptor subunit, in NK cell differentiation, we have studied NK cell differentiation from cord blood CD34 (+) cells in the presence of either stem cell factor (SCF), IL-2, and IL-7 or SCF and IL-15. The former cytokine combination efficiently induced CD34 (+) CD7 (+) cord blood cells to proliferate and mature into NK cells, while the latter was also able to induce NK cell differentiation from more immature CD34 (+) CD7 (-) cord blood cells. NK cells expressed CD56 and efficiently killed K562 target cells. These results show that IL-15 could play an important role in the maturation of NK cell from cord blood progenitors. Following retroviral-mediated gene transfer of gamma c into SCID X1 bone marrow progenitors, it was possible to reproduce a similar pattern of NK cell differentiation in two SCID-X1 patients with SCF + IL-2 + IL-7 and more efficiently in one of them with SCF + IL-15. These results strongly suggest that the gamma c chain transduces major signal(s) involved in NK cell differentiation from hematopoietic progenitor cells and that IL-15 interaction with gamma c is involved in this process at an earlier step than IL-2/IL-7 interactions of gamma c are. It also shows that gene transfer into hematopoietic progenitor cells could potentially restore NK cell differentiation in SCID X1 patients.

Mutation of the gamma c chain common to interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors has been shown to be responsible for the X chromosome-linked severe combined immune deficiency (SCIDX1). Human SCIDX1 patients are characterized by an absence of T and natural killer cell differentiation. We report the case of a SCIDX1 patient who first had few detectable peripheral T cells, then developed, after haploidentical T-depleted bone marrow transplantation (BMT), up to 2,000/microL autologous T cells. These T cells have persisted over 8 years after BMT and were able to proliferate in the presence of mitogens and of some antigens, although to a lesser extent than control T cells. A stop mutation was identified which predicts that the major part of the cytoplasmic tail of gamma c is truncated. This mutation does not affect high-affinity IL-2 binding, but it partly decreases IL-2 endocytosis and prevents the downmodulation of the IL-2-receptor beta chain and the tyrosine phosphorylation of Jak 3 protein in response to IL-2. This report raises questions concerning the role of the gamma c chain in IL-2 receptor endocytosis and in T-cell development and differentiation.

SCID X1 is characterized by faulty T-cell and natural killer cell differentiation caused by mutation of the gamma-c chain gene encoding a number of multiple cytokine receptors (interleukin-2 [IL-2], IL-4, IL-7, IL-9, and IL-15 receptors). To assess the feasibility of inducing long-term expression and function of the gamma-c chain, Epstein-Barr virus (EBV)-transformed B-cell lines from two patients with SCID X1 were transduced with a Moloney-derived retroviral vector containing the gamma-c chain cDNA. The viral LTR was used as the promoter. Immediately after two cycles of coculture with the psi-crip clone producing the MFG(B2)-gamma-c cDNA vector, gamma-c expression, assessed by detection of the mRNA and membrane protein expression, was found in 15% to 20% of cells. The degree of membrane expression was similar to that in control EBV-B cells. Expression increased steadily over 6 months, becoming detectable in 100% of cells, and remained stable thereafter for a total of 9 months, reflecting positive selection of transduced cells. A study of provirus integration sites showed multiple integration. The expressed gamma-c was functional, because it restored high-affinity IL-2 receptor binding, IL-2 endocytosis, and IL-2-triggered phosphorylation of JAK-3 tyrosine kinase. Similar results were obtained with the two B-cell lines. These results show that efficient gamma-c gene transfer into B-cells lacking functional gamma-c is feasible and results in strong and stable expression of a functional gamma-c chain, apparently conferring a selective growth advantage in culture. Further in vitro studies of gamma-c gene transfer into gamma-c- hematopoietic progenitors are being conducted to assess the feasibility of correcting lymphocyte differentiation defects.

There are numerous inherited immunodeficiencies characterized by either defects in T, B lymphocytes, phagocytic cells or the complement system. About 20 genes involved in inherited immunodeficiencies have now been identified. This opens theorically the possibility to consider gene therapy for the most severe of the diseases. A logical approach consists in attempting gene transfer into hematopoietic stem cells in order to achieve a definitive cure. However, the presently available vectors, i.e. retroviruses induce only stable gene integration and possibly expression into cycling cells while most stem cells are in G0/G1. This precludes at this time efficient gene therapy for many inherited immunodeficiencies. Nevertheless in instances, where there is an early block in cell differentiation like in adenosine desaminase deficiency (ADA) or X-L severe combined immunodeficiency (IL2 R gamma deficiencies), a selective advantage could be provided to the few transduced stem cells enabling progressive lymphocyte differentiation. This hypothesis sets the basis for the ongoing clinical studies in patients with ADA deficiency and will be assessed in available animal model of XL SCID.

X chromosome-linked severe combined immunodeficiency disease (SCIDX1) is characterized by the absence of T-cell and natural killer cell development and results from molecular mutations of the interleukin 2 receptor (IL-2R) gamma chain. The IL-2R gamma chain is a common component of the IL-2, IL-4, and IL-7 receptor systems, which may explain the severe immunophenotype in SCIDX1. We have previously described an atypical SCIDX1 syndrome demonstrating poorly functioning peripheral T cells, which we hypothesized to represent a variant allele at the SCIDX1 locus. We now demonstrate that a splice site mutation in the IL-2R gamma gene is responsible for this atypical SCIDX1. Aberrant RNA splicing resulted in the generation of two IL-2R gamma transcripts: an abundant, nonfunctional isoform containing a small intronic insertion and a second functional isoform with a single amino acid substitution present in limited amounts. Radiolabeled IL-2 binding studies revealed a 5-fold decreased level of expression of functional high-affinity IL-2Rs, which correlated with the quantity of full-length IL-2R gamma transcripts. Further analysis of the T-cell antigen receptor beta-chain repertoire of the patient's T cells demonstrated oligoclonality in multiple V beta families, thus strongly suggesting that the defect in the IL-2R gamma chain generated a limited number of peripheral T-cell clones. This atypical SCIDX1 patient demonstrates that certain IL-2R gamma chain abnormalities can also result in partial immunodeficiency phenotypes, potentially through differential effects on the IL-2, IL-4, or IL-7 receptor systems.

Interactions of interleukin-2 (IL-2) with its high-affinity, heterotrimeric receptor (IL-2R alpha beta gamma) play a pivotal role in the autocrine pathway of T lymphocyte expansion required in an immune response. Mutations in the IL-2R gamma chain-encoding gene have been found in SCIDX1, a primary immunodeficiency characterized by the absence of T cell and NK cell development. We have investigated six unrelated SCIDX1 patients for molecular abnormalities of the IL-2R gamma gene. A variety of defects were identified, including the absence of transcripts, frame-shift deletions and point mutations within canonical cytokine receptor motifs (conserved cysteines and the "WS" box). The ability of these mutated IL-2R gamma chains to participate in the function of a high-affinity IL-2R complex was examined by radiolabeled IL-2 binding studies using Epstein-Barr virus-transformed B lymphoblastoid cell lines (B-LCL) derived from SCIDX1 patients. Although normal control B-LCL express high-affinity IL-2 binding sites (Kd = 60 pM, 150 sites/cell), B-LCL derived from SCIDX1 patients failed to bind IL-2 under high-affinity conditions. These SCIDX1 mutations confirm the critical role of the IL-2R gamma chain in T cell and NK cell development. In addition, these data provide insight into the structure/function relationship of the IL-2R gamma chain by identifying residues required for the formation of a high-affinity IL-2R complex.

We carried out a retrospective analysis of 117 patients with severe combined immunodeficiency who were examined in a single center between Jan. 1, 1970, and Jan. 1, 1992, for the purpose of evaluating disease onset, progression, and outcome. The frequency of case referral increased from 8 from 1970 to 1975 to 56 from 1986 to 1991. The most frequent phenotype was T-/B+ (absence of T lymphocytes and presence of B lymphocytes) (n = 51); there were 36 cases of alymphocytosis, 16 of adenosine deaminase deficiency, 13 of Omenn syndrome, and 1 of reticular dysgenesis. Protracted diarrhea and lung infections were the main infectious complications; infection with bacillus Calmette-Guérin occurred in 10 of 28 vaccinated patients, but none of the six recipients of oral polio vaccine subsequently had poliomyelitis. The presence of maternal T cells was suspected or proved in half the patients with alymphocytosis or T-B+ severe combined immunodeficiency but did not occur in the other forms of the disease. Of the 117 patients, 22 died before transplantation could be performed. Adenosine deaminase deficiency and Omenn syndrome were more frequently associated with death before hematopoietic stem cell transplantation was possible. Fetal liver transplantation was successful in 1 of 10 cases. The survival rate among the 30 recipients of bone marrow with identical human leukocyte antigens (HLA) was 80%, with a median follow-up of 129 months; 23 of 25 patients recovered full immune function. The survival rate among the 50 recipients of HLA-haploidentical T cell-depleted bone marrow was 56%, with a mean follow-up of 35 months. Of the latter patients, 10 (35%) still require immunoglobulin substitution. There has been a trend toward improvement in the survival rate of haploidentical bone marrow recipients, presumably because of more effective infection-control measures and better transplantation strategy.