Human X-linked Severe Combined Immunodeficiency Research Articles

Lentivector cryptic splicing mediates increase in CD34+ clones expressing truncated HMGA2 in human X-linked severe combined immunodeficiency

X-linked Severe Combined Immunodeficiency (SCID-X1) due to IL2RG mutations is potentially fatal in infancy where ‘emergency’ life-saving stem cell transplant may only achieve incomplete immune reconstitution following transplant. Salvage therapy SCID-X1 patients over 2 years old (NCT01306019) is a non-randomized, open-label, phase I/II clinical trial for administration of lentiviral-transduced autologous hematopoietic stem cells following busulfan (6 mg/kg total) conditioning. The primary and secondary objectives assess efficacy in restoring immunity and safety by vector insertion site analysis (VISA). In this ongoing study (19 patients treated), we report VISA in blood lineages from first eight treated patients with longer follow up found a > 60-fold increase in frequency of forward-orientated VIS within intron 3 of the High Mobility Group AT-hook 2 gene. All eight patients demonstrated emergence of dominant HMGA2 VIS clones in progenitor and myeloid lineages, but without disturbance of hematopoiesis. Our molecular analysis demonstrated a cryptic splice site within the chicken β-globin hypersensitivity 4 insulator element in the vector generating truncated mRNA transcripts from many transcriptionally active gene containing forward-oriented intronic vector insert. A two base-pair change at the splice site within the lentiviral vector eliminated splicing activity while retaining vector functional capability. This highlights the importance of functional analysis of lentivectors for cryptic splicing for preclinical safety assessment and a redesign of clinical vectors to improve safety.

Transplantation of human cells into Interleukin-2 receptor gamma gene knockout pigs under several conditions.

IntroductionPreviously, we performed gene knockout (KO) of interleukin-2 receptor gamma (IL2RG) in porcine fetal fibroblasts using zinc finger nuclease-encoding mRNAs, subsequently generating IL2RG KO pigs using these cells through somatic cell nuclear transfer. The IL2RG KO pigs lacked a thymus and were deficient in T lymphocytes and natural killer cells, similar to human X-linked severe combined immunodeficiency (SCID) patients. The present study aimed to evaluate whether pigs can support the growth of xenografted human cells and have the potential to be an effective animal model.MethodsThe IL2RG XKOY pigs used in this study were obtained by mating IL2RG XKOX females with wild-type boars. This permitted the routine production of IL2RG KO pigs via natural breeding without complicated somatic cell cloning procedures; therefore, a sufficient number of pigs could be prepared. We transplanted human HeLa S3 cells expressing the tandem dimer tomato into the ears and pancreas of IL2RG KO pigs. Additionally, a newly developed method for the aseptic rearing of SCID pigs was used in case of necessity.ResultsTumors from the transplanted cells quickly developed in all pigs and were verified by histology and immunohistochemistry. We also transplanted these cells into the pancreas of designated pathogen-free pigs housed in novel biocontainment facilities, and large tumors were confirmed.ConclusionsIL2RG KO pigs have the potential to become useful animal models in a variety of translational biology fields.

Gene therapy studies in a canine model of X-linked severe combined immunodeficiency.

Since the occurrence of T cell leukemias in the original human γ-retroviral gene therapy trials for X-linked severe combined immunodeficiency (XSCID), considerable effort has been devoted to developing safer vectors. This review summarizes gene therapy studies performed in a canine model of XSCID to evaluate the efficacy of γ-retroviral, lentiviral, and foamy viral vectors for treating XSCID and a novel method of vector delivery. These studies demonstrate that durable T cell reconstitution and thymopoiesis with no evidence of any serious adverse events and, in contrast to the human XSCID patients, sustained marking in myeloid cells and B cells with reconstitution of normal humoral immune function can be achieved for up to 5 years without any pretreatment conditioning. The presence of sustained levels of gene-marked T cells, B cells, and more importantly myeloid cells for almost 5 years is highly suggestive of transduction of either multipotent hematopoietic stem cells or very primitive committed progenitors.

Severe Papillomavirus Infection Progressing to Metastatic Squamous Cell Carcinoma in Bone Marrow-Transplanted X-Linked SCID Dogs

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common gamma chain (gammac) gene and is identical clinically and immunologically to human XSCID, making it a true homologue of the human disease. Bone marrow-transplanted (BMT) XSCID dogs not only engraft donor T cells and reconstitute normal T-cell function but, in contrast to the majority of transplanted human XSCID patients, also engraft donor B cells and reconstitute normal humoral immune function. Shortly after our initial report of successful BMT of XSCID dogs, it soon became evident that transplanted XSCID dogs developed late-onset severe chronic cutaneous infections containing a newly described canine papillomavirus. This is analogous to the late-onset cutaneous papillomavirus infection recently described for human XSCID patients following BMT. Of 24 transplanted XSCID dogs followed for at least 1 year post-BMT, 71% developed chronic canine papillomavirus infection. Six of the transplanted dogs that developed cutaneous papillomas were maintained for >3 1/2 years post-BMT for use as breeders. Four of these six dogs (67%) developed invasive squamous cell carcinoma (SCC), with three of the dogs (75%) eventually developing metastatic SCC, an extremely rare consequence of SCC in the dog. This finding raises the question of whether SCC will develop in transplanted human XSCID patients later in life. Canine XSCID therefore provides an ideal animal model with which to study the role of the gammac-dependent signaling pathway in the response to papillomavirus infections and the progression of these viral infections to metastatic SCC.

415. Conditional Expression of a Suicide Gene by the Telomere Reverse Transcriptase Promoter for Post-Therapeutic Deletion of Insertional Mutagenesis

The success of gene therapy for human X-linked severe combined immunodeficiency (X-SCID) has been recently clouded by the occurrence of post-therapeutic cancers caused by vector-associated insertional mutagenesis. Improving the safety feature of integrating vectors becomes imperative and challenging. We demonstrated a gene expression cassette that can be possibly exploited in integrating vector systems to eliminate the rare but existing adverse events. The Herpes simplex virus thymidine kinase (HSV-TK) gene under the transcriptional control of the human telomerase reverse transcriptase (hTERT) promoter was incorporated into a self-inactivating HIV-based lentiviral vector. Theoretically, the hTERT promoter is silent in normal somatic cells and re-activated in tumor cells. Therefore, normal gene-corrected cells should not express HSV-TK. However, if some gene-corrected cells subsequently become tumorigenic and the hTERT promoter is re-activated, application of ganciclovir (GCV), a clinically used anti-virus drug, will achieve selective deletion of the cancerous cells. To prove the principle, we transduced tumor cells, including HT-1080 cells (fibrosarcoma), 293T (transformed human embryonic kidney cells), SCCLSU-1 (primary head and neck squamous cell carcinoma cells), and Jurkat cells (acute T cell leukemia cells), and normal cells, including primary human airway fibroblast cells and human marrow mesenchymal stem cells, with 10 MOIs of the HIV-CMV-EGFP-hTERT-TK vector and the HIV-CMV-EGFP control vector, respectively. GCV application only eradicated the tumor cells transduced with vector containing the hTERT-TK element, but had no effects on the normal cells received an identical treatment, suggesting the hTERT-TK cassette in the lentiviral vector was adequate to differentiate tumor cells from normal, thus destroying tumor cells selectively. HT1080 cells with single HIV-CMV-EGFP-hTERT-TK integration was implanted into left flanks of nu/nu mice and the cells with HIV-CMV-EGFP integration to the right flanks of the same animals. After establishment of tumors, GCV administration ablated the left-side tumors but not the right-side tumors. These results suggest the potential of hTERT-TK cassette in integrating vectors as a safety valve for human gene therapy to control post-therapeutic insertional mutagenesis.

Abnormal development of thymic dendritic and epithelial cells in human X-linked severe combined immunodeficiency

The X-linked form of severe combined immunodeficiency (X-SCID) is caused by mutations in the common cytokine receptor gamma chain and results in lack of T and NK cells and defective B cells. Without immune reconstitution, X-SCID patients typically die from infection during infancy. This report describes thymic epithelial (TE), lymphocyte, and dendritic cell (DC) differentiation in the thymic microenvironment of seven X-SCID patients who died before or after treatment for their immunodeficiency. X-SCID thymus consisted predominately of TE cells without grossly evident corticomedullary distinction. CD3 + and CD1a + developing T cells and CD83 + thymic DC were reduced >50-fold when compared to age- and gender-matched control thymus ( P < 0.001). TE expression of epithelial differentiation markers CK14, involucrin, and high molecular weight cytokeratins also differed in X-SCID versus normal thymus. These histopathologic findings indicate that in addition to T cells, thymic DC development and differentiation of TE cells are also abnormal in X-SCID.

Thymopoiesis and T cell development in common gamma chain-deficient dogs.

Our laboratory has identified an X-linked severe combined immunodeficiency (XSCID) in dogs that is the result of mutations in the common gamma chain (gammac) subunit of the interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21 receptors. Canine XSCID, unlike genetically engineered gammac-deficient mice, has a clinical and immunologic phenotype virtually identical to human XSCID, suggesting species-specific differences exist in the role of the gammac and its associated cytokines in mice in comparison to their role in humans and dogs. This review compares and contrasts thymopoiesis and postnatal T cell development in gammac-deficient (XSCID) dogs raised in a conventional environment, with gammac-deficient dogs raised in a gnotobiotic environment. Therapy to accelerate T cell regeneration following hematopoietic stem cell transplantation or gene therapy is also discussed.

Transplantation of X-linked severe combined immunodeficient dogs with CD34+ bone marrow cells.

X-linked severe combined immunodeficiency (X-SCID) is the most common form of human SCID and is caused by mutations in the common gamma chain (gammac), a shared component of the interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 receptors. BMT for human X-SCID results in engraftment of donor T-cells and reconstitution of normal T-cell function but engraftment of few, if any, donor B-cells and poor reconstitution of humoral immune function. Canine X-SCID is also caused by mutations in the yc and has an immunological phenotype identical to that of human X-SCID. We have previously reported that transplantation of nonconditioned X-SCID dogs with unfractionated histocompatible bone marrow results in engraftment of both donor B- and T-cells and reconstitution of normal T-cell and humoral immune function. In this study, we assessed the ability of purified canine CD34+ bone marrow cells to reconstitute lymphoid populations after histocompatible BMT in 6 nonablated X-SCID dogs. All dogs showed engraftment of donor T-cells, with T-cell regeneration occurring through a thymic-dependent pathway, and had reconstituted normal T-cell function. In contrast to our previous studies, only 3 dogs had engraftment of donor B-cells and reconstituted normal antigen-specific B-cell function post-BMT. The variable donor B-cell engraftment and reconstitution of normal humoral immune function observed in this study are similar to the outcomes observed in the majority of human X-SCID patients following BMT. This study demonstrates that canine CD34+ cells contain progenitors capable of immune reconstitution and is the first study to document the ability of CD34+ bone marrow cells to reconstitute normal B- and T-cell function in a nonablated large-animal model of BMT. This study also demonstrates that the quality of immune reconstitution following CD34+ BMT may be dosage dependent Thus canine X-SCID provides a large-animal preclinical model that can be used not only to determine the optimal conditions for both donor B- and T-cell engraftment following CD34 BMT, but also to develop and evaluate strategies for gene therapy protocols that target CD34 cells.

Comparison of Five Retrovirus Vectors Containing the Human IL-2 Receptor γ Chain Gene for Their Ability to Restore T and B Lymphocytes in the X-Linked Severe Combined Immunodeficiency Mouse Model

X-linked severe combined immunodeficiency (XSCID) is caused by mutations in the IL-2 receptor γ chain (IL2RG) gene, resulting in absent T lymphocytes and nonfunctional B lymphocytes. Recently T lymphocyte production and B lymphocyte function were restored in XSCID patients infused with autologous stem cells transduced with a retrovirus containing the human IL2RG cDNA. To optimize the expression of human IL2RG for future clinical trials, we compared five retroviral vectors expressing human IL2RG from different LTR enhancer–promoter elements in a mouse model. Northern and Southern blot analysis of hematopoietic tissues from repopulated mice revealed that the retroviral vector with the highest expression per copy number was MFG-S-hIL2RG, followed by MND-hIL2RG. All five vectors were capable of restoring lymphopoiesis in irradiated XSCID mice transplanted with transduced IL2RG-deficient hematopoietic stem cells. Transduction of IL2RG-deficient hematopoietic stem cells with all five vectors restored T lymphopoiesis in transplanted stem cell-deficient W/Wv mouse recipients. However, only XSCID stem cells transduced with the MFG-S-hIL2RG vector generated B lymphocytes in W/Wv mice. We conclude that the MFG-S-hIL2RG vector provides the best opportunity for in vivo selection and development of B and T lymphocytes for human XSCID gene therapy.

B-cell function in canine X-linked severe combined immunodeficiency

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common gamma (γc) subunit of the IL-2, IL-4, IL-7, IL-9 and IL-15 receptors and has a similar clinical phenotype to human XSCID. We have previously shown that the block in T-cell development is more profound in XSCID dogs than in genetically engineered γc-deficient mice. In this study we evaluated the B-cell function in XSCID dogs. In contrast to the marked decrease in peripheral B-cells in γc-deficient mice, XSCID dogs have increased proportions and numbers of peripheral B-cells as observed in XSCID boys. Canine XSCID B-cells do not proliferate following stimulation with the T-cell-dependent B-cell mitogen, pokeweed mitogen (PWM); however, they proliferate normally in response to the T-cell-independent B-cell mitogen, formalin-fixed, heat-killed Staphylococcus aureus. Canine XSCID B-cells are capable of producing IgM but are incapable of normal class-switching to IgG antibody production as demonstrated by in vitro stimulation with PWM and immunization with the T-cell-dependent antigen, bacteriophage ΦX174. Similar results have been reported for XSCID boys. Thus, it appears that γc-dependent cytokines have differing roles in human and canine B-cell development than in the mouse making the XSCID dog a valuable model for studying the role of these cytokines in B-cell development and function.

Stable and functional lymphoid reconstitution of common cytokine receptor γ chain deficient mice by retroviral-mediated gene transfer

AbstractMutations in the gene encoding the common cytokine receptor gamma chain (γc) are responsible for human X-linked severe combined immunodeficiency disease (SCIDX1). We have used a γc-deficient mouse model to test the feasibility and potential toxicity of γc gene transfer as a therapy for SCIDX1. A retrovirus harboring the murine γc chain was introduced into γc-deficient bone marrow cells, which were then transplanted into alymphoid RAG2/γcdouble-deficient recipient mice. Circulating lymphocytes appeared 4 weeks postgraft and achieved steady-state levels by 8 weeks. The mature lymphocytes present in the grafted mice had integrated the γc transgene, expressed γc transcripts, and were able to proliferate in response to γc-dependent cytokines. The γc-transduced animals demonstrated (1) normal levels of immunoglobulin subclasses, including immunoglobulin G1 (IgG1) and IgG2a (which are severely decreased in γc- mice); (2) the ability to mount an antigen-specific, T-dependent antibody response showing effective in vivo T-B cell cooperation, and (3) the presence of gut-associated cryptopatches and intraepithelial lymphocytes. Importantly, peripheral B and T cells were still present 47 weeks after a primary graft, and animals receiving a secondary graft of γc-transduced bone marrow cells demonstrated peripheral lymphoid reconstitution. That γc gene transfer to hematopoietic precursor cells can correct the immune system abnormalities in γc- mice supports the feasibility of in vivo retroviral gene transfer as a treatment for human SCIDX1.

Stable and functional lymphoid reconstitution of common cytokine receptor γ chain deficient mice by retroviral-mediated gene transfer

Mutations in the gene encoding the common cytokine receptor gamma chain (γc) are responsible for human X-linked severe combined immunodeficiency disease (SCIDX1). We have used a γc-deficient mouse model to test the feasibility and potential toxicity of γc gene transfer as a therapy for SCIDX1. A retrovirus harboring the murine γc chain was introduced into γc-deficient bone marrow cells, which were then transplanted into alymphoid RAG2/γcdouble-deficient recipient mice. Circulating lymphocytes appeared 4 weeks postgraft and achieved steady-state levels by 8 weeks. The mature lymphocytes present in the grafted mice had integrated the γc transgene, expressed γc transcripts, and were able to proliferate in response to γc-dependent cytokines. The γc-transduced animals demonstrated (1) normal levels of immunoglobulin subclasses, including immunoglobulin G1 (IgG1) and IgG2a (which are severely decreased in γc- mice); (2) the ability to mount an antigen-specific, T-dependent antibody response showing effective in vivo T-B cell cooperation, and (3) the presence of gut-associated cryptopatches and intraepithelial lymphocytes. Importantly, peripheral B and T cells were still present 47 weeks after a primary graft, and animals receiving a secondary graft of γc-transduced bone marrow cells demonstrated peripheral lymphoid reconstitution. That γc gene transfer to hematopoietic precursor cells can correct the immune system abnormalities in γc- mice supports the feasibility of in vivo retroviral gene transfer as a treatment for human SCIDX1.

Bone marrow transplantation for canine X-linked severe combined immunodeficiency

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common γ chain which is a subunit of the receptors of IL-2, IL-4, IL-7, IL-9 and IL-15. Bone marrow transplantation (BMT) of human XSCID patients without pretransplant conditioning (cytoablation) results in engraftment of donor T-cells and reconstitution of T-cell function but engraftment of few, if any, donor B cells with resultant poor reconstitution of humoral immune function. In this study, we show that XSCID dogs can be transplanted with allogeneic bone marrow cells resulting in engraftment of both donor B and T cells and reconstitution of full systemic immune function including normal humoral immune function without the need for cytoablation.

Multiple γc-dependent cytokines regulate T-cell development

Mutations in the common γ chain (γc) of cytokine receptors account for human X-linked severe combined immunodeficiency disease. γc contributes to ligand binding and signaling as a component of five cytokine receptors: interleukin-2-receptor (IL-2R), IL-4R, IL-7R, IL-9R and IL-15R. Here, Thomas Malek and colleagues discuss the contribution of individual γc-dependent cytokines in both conventional and intraepithelial T-cell development.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.This is a US government work. There are no restrictions on its use.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.This is a US government work. There are no restrictions on its use.

Characterization of an MDR1 retroviral bicistronic vector for correction of X-linked severe combined immunodeficiency

X-linked severe combined immunodeficiency (XSCID) is a hereditary disorder characterized by severe T cell lymphopenia and abnormal B cell function. The disease is caused by mutations in IL2RG, the gene encoding the interleukin-2 receptor common gamma chain (gamma c) shared by several interleukin receptors. A Harvey retroviral bicistronic vector containing an IL2RG cDNA and cDNA encoding the multidrug transporter (MDR1) was constructed to investigate the correction of XSCID. Translation of the MDR1 cDNA is achieved from an internal ribosome entry site (IRES). Mouse fibroblasts transfected or transduced with the vector expressed both membrane proteins as detected with specific monoclonal antibodies by fluorescence activated cell sorting. Two human XSCID B cell lines were transduced using a filter concentration method in combination with phosphate depletion. Significant expression of both proteins was detected by Western blot analysis. This construct might be particularly useful if high expression of gamma c is required, as might be achievable through in vivo selection for drug resistance of recipient lymphocytes.

Canine X-linked severe combined immunodeficiency. A model for investigating the requirement for the common gamma chain (gamma c) in human lymphocyte development and function.

Our laboratory has identified and characterized an X-linked severe combined immunodeficiency (XSCID) in dogs that is due to mutations in the common gamma (gamma c) subunit of the interleukin-2 (IL2), IL4, IL7, IL9, and IL15 receptors. Canine XSCID, unlike genetically engineered gamma c-deficient mice, has a clinical and immunologic phenotype virtually identical to human XSCID. It appears that species-specific differences exist in the role of the gamma c and its associated cytokines in mice compared to their role in humans and dogs, suggesting gamma c-deficient dogs may be a more relevant model for studying the role of the gamma c in humans. We are utilizing this model for a variety of studies to address: 1. Fundamental questions concerning the role of the gamma c in cytokine regulation and lymphocyte development. 2. The pathogenesis of XSCID. 3. Strategies for improving bone marrow transplantation outcome. 4. Development and evaluation of strategies for gene therapy. 5. Human hematopoietic stem cell development.

Full Immunologic Reconstitution Following Nonconditioned Bone Marrow Transplantation for Canine X-Linked Severe Combined Immunodeficiency

AbstractBone marrow transplantation in human X-linked severe combined immunodeficiency (XSCID) without pretransplant conditioning results in engraftment of donor T cells and reconstitution of T-cell function but engraftment of few, if any, donor B cells and poor reconstitution of humoral immune function. Since bone marrow transplantation remains the most effective treatment of XSCID patients, better strategies are necessary to achieve optimum long-term results. Canine XSCID, like human XSCID, is due to mutations in the common γ chain (γc) gene and has clinical and immunologic features identical to those of human XSCID, making it a true homolog of the human disease. We have successfully performed bone marrow transplantation in three XSCID dogs without pretransplant conditioning, using untreated bone marrow cells from mixed lymphocyte culture–nonreactive normal littermates. Unlike the experience in human XSCID patients, all three dogs engrafted both donor B and T cells and attained full reconstitution of immunologic function. Normal percentages of T cells and T-cell mitogenic responses were attained by 3 months posttransplant. CD3+ T cells after transplantation expressed the CD45RA isoform indicating that the cells were recent thymic emigrants derived from immature progenitors. Serum IgG levels were within normal range by 5 months posttransplant. Immunization with the T-dependent antigen, bacteriophage φX174, demonstrated normal antibody titers, immunologic memory, and class-switching. Polymerase chain reaction (PCR) analysis of the γc locus showed that 100% of circulating T cells and 30% to 50% of circulating B cells were donor-derived. None of the dogs developed clinically evident graft-versus-host disease (GVHD). Thus, canine XSCID provides a model to determine the optimal conditions for bone marrow transplantation in human patients, and to develop and test strategies for somatic gene therapy.

IL2RGbase: a database of gamma c-chain defects causing human X-SCID.

Abstract X-linked severe combined immunodeficiency (X-SCID) is an immune disorder caused by mutations in the X-linked gene IL2RG, which encodes the common γ chain of the lymphocyte receptors for interleukin 2 (IL-2) and many other cytokines. A database of human X-SCID mutations (IL2RGbase) has been assembled, and this article summarizes the first 136 entries from unrelated patients.