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Adenosine deaminase 2 deficiency (DADA2) is a rare inherited disorder that is caused by autosomal recessive mutations in the ADA2 gene. Clinical manifestations include early-onset lacunar strokes, vasculitis/vasculopathy, systemic inflammation, immunodeficiency, and hematologic defects. Anti–tumor necrosis factor therapy reduces strokes and systemic inflammation. Allogeneic hematopoietic stem/progenitor cell (HSPC) transplantation can ameliorate most disease manifestations, but patients are at risk for complications. Autologous HSPC gene therapy may be an alternative curative option for patients with DADA2. We designed a lentiviral vector encoding ADA2 (LV-ADA2) to genetically correct HSPCs. Lentiviral transduction allowed efficient delivery of the functional ADA2 enzyme into HSPCs from healthy donors. Supranormal ADA2 expression in human and mouse HSPCs did not affect their multipotency and engraftment potential in vivo. The LV-ADA2 induced stable ADA2 expression and corrected the enzymatic defect in HSPCs derived from DADA2 patients. Patients’ HSPCs re-expressing ADA2 retained their potential to differentiate into erythroid and myeloid cells. Delivery of ADA2 enzymatic activity in patients’ macrophages led to a complete rescue of the exaggerated inflammatory cytokine production. Our data indicate that HSPCs ectopically expressing ADA2 retain their multipotent differentiation ability, leading to functional correction of macrophage defects. Altogether, these findings support the implementation of HSPC gene therapy for DADA2.

BACKGROUND. The human bone marrow (BM) niche contains a population of mesenchymal stromal cells (MSCs) that provide physical support and regulate hematopoietic stem cell (HSC) homeostasis. β-Thalassemia (BT) is a hereditary disorder characterized by altered hemoglobin beta-chain synthesis amenable to allogeneic HSC transplantation and HSC gene therapy. Iron overload (IO) is a common complication in BT patients affecting several organs. However, data on the BM stromal compartment are scarce. METHODS. MSCs were isolated and characterized from BM aspirates of healthy donors (HDs) and BT patients. The state of IO was assessed and correlated with the presence of primitive MSCs in vitro and in vivo. Hematopoietic supportive capacity of MSCs was evaluated by transwell migration assay and 2D coculture of MSCs with human CD34+ HSCs. In vivo, the ability of MSCs to facilitate HSC engraftment was tested in a xenogenic transplant model, whereas the capacity to sustain human hematopoiesis was evaluated in humanized ossicle models. RESULTS. We report that, despite iron chelation, BT BM contains high levels of iron and ferritin, indicative of iron accumulation in the BM niche. We found a pauperization of the most primitive MSC pool caused by increased ROS production in vitro which impaired MSC stemness properties. We confirmed a reduced frequency of primitive MSCs in vivo in BT patients. We also discovered a weakened antioxidative response and diminished expression of BM niche–associated genes in BT-MSCs. This caused a functional impairment in MSC hematopoietic supportive capacity in vitro and in cotransplantation models. In addition, BT-MSCs failed to form a proper BM niche in humanized ossicle models. CONCLUSION. Our results suggest an impairment in the mesenchymal compartment of BT BM niche and highlight the need for novel strategies to target the niche to reduce IO and oxidative stress before transplantation. FUNDING. This work was supported by the SR-TIGET Core grant from Fondazione Telethon and by Ricerca Corrente.

Hematopoietic stem cell gene therapy has become a successful therapeutic strategy for some inherited genetic disorders. Pre-clinical toxicity studies performed to support the human clinical trials using viral-mediated gene transfer and autologous hematopoietic stem and progenitor cell (HSPC) transplantation are complex and the use of mouse models of human diseases makes interpretation of the results challenging. In addition, they rely on the use of conditioning agents that must induce enough myeloablation to allow engraftment of transduced and transplanted HSPC. Busulfan and total body irradiation (TBI) are the most commonly used conditioning regimens in the mouse. Lenticular degeneration and atrophy of reproductive organs are expected histopathological changes. Proliferative and nonproliferative lesions can be observed with different incidence and distribution across strains and mouse models of diseases. The occurrence of these lesions can interfere with the interpretation of pre-clinical toxicity and tumorigenicity studies performed to support the human clinical studies. As such, it is important to be aware of the background incidence of lesions induced by different conditioning regimens. We review the histopathology results from seven long-term studies, five using TBI and two using busulfan.

Chronic granulomatous disease (CGD) is a rare inherited disorder due to loss-of-function mutations in genes encoding the NADPH oxidase subunits. Hematopoietic stem and progenitor cell (HSPC) gene therapy (GT) using regulated lentiviral vectors (LVs) has emerged as a promising therapeutic option for CGD patients. We performed non-clinical Good Laboratory Practice (GLP) and laboratory-grade studies to assess the safety and genotoxicity of LV targeting myeloid-specific Gp91phox expression in X-linked chronic granulomatous disease (XCGD) mice. We found persistence of gene-corrected cells for up to 1 year, restoration of Gp91phox expression and NADPH oxidase activity in XCGD phagocytes, and reduced tissue inflammation after LV-mediated HSPC GT. Although most of the mice showed no hematological or biochemical toxicity, a small subset of XCGD GT mice developed T cell lymphoblastic lymphoma (2.94%) and myeloid leukemia (5.88%). No hematological malignancies were identified in C57BL/6 mice transplanted with transduced XCGD HSPCs. Integration pattern analysis revealed an oligoclonal composition with rare dominant clones harboring vector insertions near oncogenes in mice with tumors. Collectively, our data support the long-term efficacy of LV-mediated HSPC GT in XCGD mice and provide a safety warning because the chronic inflammatory XCGD background may contribute to oncogenesis., Graphical Abstract, In a GLP study, Jofra Hernández and colleagues demonstrate that lentiviral vector-mediated HSPC gene therapy effectively corrects long-term X-linked chronic granulomatous disease in a mouse model of the disease. A small proportion of mice develops hematopoietic tumors originating from rare dominant clones harboring vector insertions near oncogenes.

Adenosine deaminase 2 deficiency (DADA2) is a recently defined inborn error of immunity caused by loss-of-function mutations in the ADA2 gene. Patients suffer from severe manifestations, including early-onset lacunar strokes, intracranial hemorrhages, vasculitis/vasculopathy, systemic inflammation, immunodeficiency, and hematologic abnormalities. The therapeutic benefit of the current treatments is unsatisfactory. Anti-tumor necrosis factor therapy reduces strokes and systemic inflammation but does not correct cytopenia and bone marrow failure. Allogeneic hematopoietic stem/progenitor cell (HSPC) transplantation can ameliorate most disease manifestations, but patients are at risk for complications. Therefore, we proposed that autologous HSPC gene therapy may be an alternative curative option for patients who has no compatible donor or cannot receive intense chemotherapy. We performed an in-depth study, using multiparametric flow cytometry, of the bone marrow (BM) cell composition of three adult patients with the hematological phenotype of DADA2. Compared with healthy donors (HDs), patients' BM exhibited a reduced number of mature and immature populations belonging to different hematopoietic lineages. Patients exhibited a substantial reduction in circulating neutrophils and hematopoietic stem cells and progenitor pools in the BM. Severe neutropenia and HSPC defects are direct causes of DADA2. Indeed, ADA2 knock-down in zebrafish - as rodents do not harbor an ADA2 orthologue gene - caused a significant decrease in neutrophil and HSPC numbers, reminiscent of patients' phenotype. Administration of human recombinant ADA2 effectively corrected both neutropenia and defective hematopoiesis in the zebrafish embryo. We used a third-generation LV to restore constitutive ADA2 expression in HSPCs. Transduction of healthy donors' HSPCs allowed efficient delivery of the functional ADA2 enzyme with no toxicity. Supranormal ADA2 expression in healthy donors' and patients' HSPCs was well-tolerated and did not impact HSPC multilineage differentiation potential in vitro and in vivo. We also assessed whether LV-derived ADA2 could correct the hyperinflammatory M1 macrophage phenotype characteristic of DADA2. ADA2 reconstitution in patients' macrophages led to the normalization of IL-6 and TNF release. Similar results were obtained using M1 macrophages differentiated from ADA2-transduced HSPCs. Altogether, our findings indicate that HSPC gene therapy is a promising approach to re-establish stable ADA2 activity and correct the hematological and inflammatory manifestations in patients with DADA2. Disclosures Aiuti: Orchard Therapeutics: Other: PI of clinical trials sponsored by company.

GSK2696273 (autologous CD34+ cells transduced with retroviral vector that encodes for the human adenosine deaminase [ADA] enzyme) is a gamma-retroviral ex vivo gene therapy of bone marrow-derived CD34+ cells for the treatment of adenosine deaminase deficiency severe combined immunodeficiency (ADA-SCID). ADA-SCID is a severe monogenic disease characterized by immunologic and nonimmunologic symptoms. Bone-marrow transplant from a matched related donor is the treatment of choice, but it is available for only a small proportion of patients. Ex vivo gene therapy of patient bone-marrow CD34+ cells is an alternative treatment. In order to prepare for a marketing authorization application in the European Union, preclinical safety studies in mice were requested by the European Medicines Agency (EMA). A pilot study and a main biodistribution study were performed according to Good Laboratory Practice (GLP) at the San Raffaele Telethon Institute for Gene Therapy test facility. In the main study, human umbilical cord blood (UCB)-derived CD34+ cells were transduced with gamma-retroviral vector used in the production of GSK2696273. Groups of 10 male and 10 female NOD-SCID gamma (NSG) mice were injected intravenously with a single dose of transduced- or mock-transduced UCB CD34+ cells, and they were observed for 4 months. Engraftment and multilineage differentiation of blood cells was observed in the majority of animals in both groups. There was no significant difference in the level of chimerism between the two groups. In the gene therapy group, vector was detectable in lymphohemopoietic and nonlymphohemopoietic tissues, consistent with the presence of gene-modified human hematopoietic donor cells. Given the absence of relevant safety concerns in the data, the nonclinical studies and the clinical experience with GSK2696273 supported a successful application for market authorization in the European Union for the treatment of ADA-SCID patients, for whom no suitable human leukocyte antigen-matched related donor is available.

Chronic granulomatous disease (CGD) is a primary immunodeficiency due to a deficiency in one of the subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. CGD patients are characterized by an increased susceptibility to bacterial and fungal infections, and to granuloma formation due to the excessive inflammatory responses. Several gene therapy approaches with lentiviral vectors have been proposed but there is a lack of in vivo data on the ability to control infections and inflammation. We set up a mouse model of acute infection that closely mimic the airway infection in CGD patients. It involved an intratracheal injection of a methicillin-sensitive reference strain of S. aureus . Gene therapy, with hematopoietic stem cells transduced with regulated lentiviral vectors, restored the functional activity of NADPH oxidase complex (with 20–98% of dihydrorhodamine positive granulocytes and monocytes) and saved mice from death caused by S. aureus , significantly reducing the bacterial load and lung damage, similarly to WT mice even at low vector copy number. When challenged, gene therapy-treated XCGD mice showed correction of proinflammatory cytokines and chemokine imbalance at levels that were comparable to WT. Examined together, our results support the clinical development of gene therapy protocols using lentiviral vectors for the protection against infections and inflammation.

Adenosine Deaminase (ADA) deficiency is an autosomal recessive variant of severe combined immunodeficiency (SCID) caused by systemic accumulation of ADA substrates. Neurological and behavioral abnormalities observed in ADA-SCID patients surviving after stem cell transplantation or gene therapy represent an unresolved enigma in the field. We found significant neurological and cognitive alterations in untreated ADA-SCID patients as well as in two groups of patients after short- and long-term enzyme replacement therapy with PEG-ADA. These included motor dysfunction, EEG alterations, sensorineural hypoacusia, white matter and ventricular alterations in MRI as well as a low mental development index or IQ. Ada-deficient mice were significantly less active and showed anxiety-like behavior. Molecular and metabolic analyses showed that this phenotype coincides with metabolic alterations and aberrant adenosine receptor signaling. PEG-ADA treatment corrected metabolic adenosine-based alterations, but not cellular and signaling defects, indicating an intrinsic nature of the neurological and behavioral phenotype in ADA deficiency.

Hereditary genetic disorders have been shown to be effectively treated by re-introduction of the wild-type gene product via viral modification of autologous CD34+ progenitor cells. However, current manufacturing processes are performed manually or at best by using semi-automated procedures. A standardized production of cellular therapeutic agents and their genetic modification is a major requirement to move cellular and gene therapies from their current translational setting into routine clinical use. A closed and highly automated manufacturing procedure would lead to large improvements in product performance, product safety and operator safety. We have recently developed a functionally closed and fully automated cell processing device, the CliniMACS Prodigy®, which enables complex cellular products to be manufactured.In this functionally closed system, the following steps have been automated: concentration and washing of blood products, magnetic labeling and enrichment of CD34+ cells, cultivation and pre-activation of the enriched CD34+ cells, transduction with lentiviral vectors and resuspension of the final cell product in buffer for infusion.Automated cell preparation, cell labeling and magnetic CD34+ cell separation was achieved from both mobilized and non-mobilized apheresis samples as well as bone marrow aspirates. CD34+ cells were enriched to purities exceeding 90%. Small scale experiments (10e5-10e7 purified CD34+ cells) performed with a newly developed automated transduction process, incorporating a single transduction cycle, resulted in high transduction efficiencies (up to 90%). A scale-up of the procedure was performed using larger numbers of cells (>10e7) enriched from mobilized apheresis material. CD34+ cells were transduced with a clinical-grade lentiviral vector using a two hit protocol already described in a clinical setting and used as standard for a control experiment run in parallel (Scaramuzza et al. 2013, Mol. Ther). Equivalent gene marking efficiencies were obtained. Moreover, gene modified cells maintained full engraftment potential as demonstrated by biodistribution studies in NSG mice.These preliminary data demonstrate that automated cell processing and genetic manipulation of haematopoetic progenitor cells can be efficiently performed in a closed system. Work in progress aims to further optimize this procedure and improve the efficiency of CD34+ cell transduction to levels superior to those currently achieved by manual protocols.

Adenosine deaminase (ADA) deficiency is caused by a purine metabolic dysfunction, leading to severe combined immunodeficiency (SCID) and multiple organ damage. To investigate the efficacy of ex vivo gene therapy with self-inactivating lentiviral vectors (LVs) in correcting this complex phenotype, we used an ADA(-/-) mouse model characterized by early postnatal lethality. LV-mediated ADA gene transfer into bone marrow cells combined with low-dose irradiation rescued mice from lethality and restored their growth, as did transplantation of wild-type bone marrow. Mixed chimerism with multilineage engraftment of transduced cells was detected in the long term in animals that underwent transplantation. ADA activity was normalized in lymphocytes and partially corrected in red blood cells (RBCs), resulting in full metabolic detoxification and prevention of severe pulmonary insufficiency. Moreover, gene therapy restored normal lymphoid differentiation and immune functions, including antigen-specific antibody production. Similar degrees of detoxification and immune reconstitution were obtained in mice treated early after birth or after 1 month of enzyme-replacement therapy, mimicking 2 potential applications for ADA-SCID. Overall, this study demonstrates the efficacy of LV gene transfer in correcting both the immunological and metabolic phenotypes of ADA-SCID and supports the future clinical use of this approach. Adenosine deaminase (ADA) deficiency is caused by a purine metabolic dysfunction, leading to severe combined immunodeficiency (SCID) and multiple organ damage. To investigate the efficacy of ex vivo gene therapy with self-inactivating lentiviral vectors (LVs) in correcting this complex phenotype, we used an ADA(-/-) mouse model characterized by early postnatal lethality. LV-mediated ADA gene transfer into bone marrow cells combined with low-dose irradiation rescued mice from lethality and restored their growth, as did transplantation of wild-type bone marrow. Mixed chimerism with multilineage engraftment of transduced cells was detected in the long term in animals that underwent transplantation. ADA activity was normalized in lymphocytes and partially corrected in red blood cells (RBCs), resulting in full metabolic detoxification and prevention of severe pulmonary insufficiency. Moreover, gene therapy restored normal lymphoid differentiation and immune functions, including antigen-specific antibody production. Similar degrees of detoxification and immune reconstitution were obtained in mice treated early after birth or after 1 month of enzyme-replacement therapy, mimicking 2 potential applications for ADA-SCID. Overall, this study demonstrates the efficacy of LV gene transfer in correcting both the immunological and metabolic phenotypes of ADA-SCID and supports the future clinical use of this approach.

To improve maintenance and gene transfer of human lymphoid progenitors for clinical use in gene therapy of adenosine deaminase (ADA)-deficient SCID we investigated several gene transfer protocols using various stem cell-enriched sources. The lymphoid differentiation potential was measured by an in vitro clonal assay for B/NK cells and in the in vivo SCID-hu mouse model. Ex vivo culture with the cytokines TPO, FLT3-ligand, and SCF (T/F/S) plus IL-3 or IL-7 substantially increased the yield of transduced bone marrow (BM) CD34(+) cells purified from ADA-SCID patients or healthy donors, compared to T/F/S alone. Moreover, the use of IL-3 or IL-7 significantly improved the maintenance of in vitro B cell progenitors from ADA-SCID BM cells and allowed the efficient transduction of B and NK cell progenitors. Under these optimized conditions transduced CD34(+) cells were efficiently engrafted into SCID-hu mice and gave rise to B and T cell progeny, demonstrating the maintenance of in vivo lymphoid reconstitution capacity. The protocol based on the T/F/S + IL-3 combination was included in a gene therapy clinical trial for ADA-SCID, resulting in long-term engraftment of stem/progenitor cells. Remarkably, gene-corrected BM CD34(+) cells obtained from one patient 4 and 11 months after gene therapy were capable of repopulating the lymphoid compartment of SCID-hu hosts.

"Gene therapy with ex vivo-transduced hematopoietic stem/progenitor cells may represent a valid therapeutic option for monogenic immunohematological disorders such as Wiskott-Aldrich syndrome (WAS), a primary immunodeficiency associated with thrombocytopenia. We evaluated the preclinical safety and efficacy of human CD34+ cells transduced with lentiviral vectors (LV) encoding WAS protein (WASp). We first set up and validated a transduction protocol for CD34+ cells derived from bone marrow (BM) or mobilized peripheral blood (MPB) using a clinical grade, highly purified LV. Robust transduction of progenitor cells was obtained in normal donors and WAS patients' cells, without evidence of toxicity. To study biodistribution of human cells and exclude vector release in vivo, LV-transduced CD34+ cells were transplanted in immunodeficient mice, showing a normal engraftment and differentiation ability towards transduced lymphoid and myeloid cells in hematopoietic tissues. Vector mobilization to host cells and transmission to germline cells of the LV were excluded by different molecular assays. Analysis of vector integrations showed polyclonal integration patterns in vitro and in human engrafted cells in vivo. In summary, this work establishes the preclinical safety and efficacy of human CD34+ cells gene therapy for the treatment of WAS."

Gene therapy with ex vivo-transduced hematopoietic stem/progenitor cells may represent a valid therapeutic option for monogenic immunohematological disorders such as Wiskott-Aldrich syndrome (WAS), a primary immunodeficiency associated with thrombocytopenia. We evaluated the preclinical safety and efficacy of human CD34(+) cells transduced with lentiviral vectors (LV) encoding WAS protein (WASp). We first set up and validated a transduction protocol for CD34(+) cells derived from bone marrow (BM) or mobilized peripheral blood (MPB) using a clinical grade, highly purified LV. Robust transduction of progenitor cells was obtained in normal donors and WAS patients' cells, without evidence of toxicity. To study biodistribution of human cells and exclude vector release in vivo, LV-transduced CD34(+) cells were transplanted in immunodeficient mice, showing a normal engraftment and differentiation ability towards transduced lymphoid and myeloid cells in hematopoietic tissues. Vector mobilization to host cells and transmission to germline cells of the LV were excluded by different molecular assays. Analysis of vector integrations showed polyclonal integration patterns in vitro and in human engrafted cells in vivo. In summary, this work establishes the preclinical safety and efficacy of human CD34(+) cells gene therapy for the treatment of WAS.

Adenosine acts as anti-inflammatory mediator on the immune system and has been described in regulatory T cell (Treg)-mediated suppression. In the absence of adenosine deaminase (ADA), adenosine and other purine metabolites accumulate, leading to severe immunodeficiency with recurrent infections (ADA-SCID). Particularly ADA-deficient patients with late-onset forms and after enzyme replacement therapy (PEG-ADA) are known to manifest immune dysregulation. Herein we provide evidence that alterations in the purine metabolism interfere with Treg function, thereby contributing to autoimmune manifestations in ADA deficiency. Tregs isolated from PEG-ADA-treated patients are reduced in number and show decreased suppressive activity, whereas they are corrected after gene therapy. Untreated murine ADA(-/-) Tregs show alterations in the plasma membrane CD39/CD73 ectonucleotidase machinery and limited suppressive activity via extracellular adenosine. PEG-ADA-treated mice developed multiple autoantibodies and hypothyroidism in contrast to mice treated with bone marrow transplantation or gene therapy. Tregs isolated from PEG-ADA-treated mice lacked suppressive activity, suggesting that this treatment interferes with Treg functionality. The alterations in the CD39/CD73 adenosinergic machinery and loss of function in ADA-deficient Tregs provide new insights into a predisposition to autoimmunity and the underlying mechanisms causing defective peripheral tolerance in ADA-SCID. Trials were registered at www.clinicaltrials.gov as NCT00598481/NCT00599781. (Blood. 2012; 119(6): 1428-1439) Adenosine acts as anti-inflammatory mediator on the immune system and has been described in regulatory T cell (Treg)-mediated suppression. In the absence of adenosine deaminase (ADA), adenosine and other purine metabolites accumulate, leading to severe immunodeficiency with recurrent infections (ADA-SCID). Particularly ADA-deficient patients with late-onset forms and after enzyme replacement therapy (PEG-ADA) are known to manifest immune dysregulation. Herein we provide evidence that alterations in the purine metabolism interfere with Treg function, thereby contributing to autoimmune manifestations in ADA deficiency. Tregs isolated from PEG-ADA-treated patients are reduced in number and show decreased suppressive activity, whereas they are corrected after gene therapy. Untreated murine ADA(-/-) Tregs show alterations in the plasma membrane CD39/CD73 ectonucleotidase machinery and limited suppressive activity via extracellular adenosine. PEG-ADA-treated mice developed multiple autoantibodies and hypothyroidism in contrast to mice treated with bone marrow transplantation or gene therapy. Tregs isolated from PEG-ADA-treated mice lacked suppressive activity, suggesting that this treatment interferes with Treg functionality. The alterations in the CD39/CD73 adenosinergic machinery and loss of function in ADA-deficient Tregs provide new insights into a predisposition to autoimmunity and the underlying mechanisms causing defective peripheral tolerance in ADA-SCID.

Adenosine deaminase (ADA) deficiency is a disorder of the purine metabolism leading to combined immunodeficiency and systemic alterations, including skeletal abnormalities. We report that ADA deficiency in mice causes a specific bone phenotype characterized by alterations of structural properties and impaired mechanical competence. These alterations are the combined result of an imbalanced receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin axis, causing decreased osteoclastogenesis and an intrinsic defect of osteoblast function with subsequent low bone formation. In vitro, osteoblasts lacking ADA displayed an altered transcriptional profile and growth reduction. Furthermore, the bone marrow microenvironment of ADA-deficient mice showed a reduced capacity to support in vitro and in vivo hematopoiesis. Treatment of ADA-deficient neonatal mice with enzyme replacement therapy, bone marrow transplantation, or gene therapy resulted in full recovery of the altered bone parameters. Remarkably, untreated ADA–severe combined immunodeficiency patients showed a similar imbalance in RANKL/osteoprotegerin levels alongside severe growth retardation. Gene therapy with ADA-transduced hematopoietic stem cells increased serum RANKL levels and children's growth. Our results indicate that the ADA metabolism represents a crucial modulatory factor of bone cell activities and remodeling. The trials were registered at www.clinicaltrials.gov as #NCT00598481 and #NCT00599781.

Wiskott-Aldrich syndrome (WAS) is a severe X-linked immunodeficiency characterized by recurrent infections, thrombocytopenia, eczema and increased risk of autoimmune disorders and lymphomas. Hematopoietic stem cell (HSC) transplantation from HLA-identical sibling donors is a resolutive treatment, but it is available only for a minority of patients. Transplantation of genetically corrected autologous HSC could represent an alternative treatment, potentially applicable to all patients. In a murine model of WAS (WAS|[minus]|/|[minus]|), we recently demonstrated correction of the T cell defect 4 months after lentiviral vector-mediated gene therapy [Dupr|[eacute]|, Marangoni, et al. Hum Gene Ther. 2006, 17]. The aim of the present study was to investigate the long-term efficacy and safety of our gene therapy approach in WAS|[minus]|/|[minus]| mice.

Adenosine deaminase (ADA) deficiency is a severe combined immunodeficiency (SCID) characterized by systemic toxicity and profoundly impaired lymphoid cell development and functions due to the accumulation of purine metabolites. ADA-deficient (ADA KO) mice die within 3 weeks of age due to metabolic toxicity and can be rescued by enzyme replacement therapy with PEG-ADA. The aim of our study was to investigate the efficacy of gene therapy (GT) in comparison to bone marrow transplantation (BMT) in the ADA KO mouse model. A SIN HIV-1-based lentiviral vector encoding human ADA cDNA under the control of PGK promoter was constructed. ADA KO mice were maintained short-term on PEG-ADA and then transplanted, after non-myeloablative conditioning either with WT BM cells or with ADA KO BM cells transduced ex vivo. We first showed that BMT with donor WT cells rescued mice from lethality, restored T-cell and B-cell counts in the peripheral blood and led to normal proliferation after T or B cells specific stimulation. Similarly, GT with transduced BM cells rescued ADA KO mice from lethality and restored their growth to normal levels. Quantitative PCR for donor cells (Y chromosome in sex-mismatched transplant) and vector-positive cells showed the presence of ADA transduced cells in the peripheral circulation of transplanted ADA KO mice (30|[ndash]|40% 5 months post-GT). Two months after GT, ADA activity in red blood cells reached normal levels and dAXP toxic metabolites decreased to undetectable levels. GT resulted in normal lymphoid differentiation in primary and secondary lymphoid organs, as well as restoration of T-cell and B-cell in vitro proliferative responses after stimulation with anti-CD3/anti-CD28 and anti-IgM antibody, respectively. Finally, serum levels of IgM and IgG were comparable between GT and BMT mice. These studies demonstrate that lentiviral-mediated ADA gene transfer associated with non-myeloablative conditioning corrects both the metabolic and the immunological defects in the ADA KO animal model. We are currently evaluating the long-term safety related to the use of hematopoietic stem/progenitor cells transduced with lentiviral vectors.

Wiskott-Aldrich syndrome (WAS) is a life-threatening X-linked primary immunodeficiency characterized by infections, hemorrhages, autoimmune disorders, and lymphomas. Transplantation of genetically corrected autologous hematopoietic stem cells (HSCs) could represent an alternative treatment to allogeneic HSC transplantation, the latter being often associated with severe complications. We used WAS(-/-) mice to test the efficacy of a gene therapy approach based on nonlethal irradiation followed by transplantation of WAS(-/-) HSCs transduced with lentiviral vectors encoding the WAS protein (WASP) from either the ubiquitous PGK promoter or the tissue-specific WAS promoter. The procedure resulted in significant levels of engraftment of WASP-expressing T cells, B cells, platelets, and myeloid cells. T cells harbored one or two vector copies and displayed partial to full correction of T cell receptor-driven interleukin- 2 production and proliferation. In addition, polymerization of F-actin and localization of WASP at the site of the immunological synapse were restored. The treatment was well tolerated and no pathology was detected by systematic blood analysis and autopsy. The efficacy of WAS gene transfer into HSCs, using the WAS promoter-containing lentiviral vector, combined with nonlethal irradiation provides a strong rationale for the development of gene therapy for WAS patients. Wiskott-Aldrich syndrome (WAS) is a life-threatening X-linked primary immunodeficiency characterized by infections, hemorrhages, autoimmune disorders, and lymphomas. Transplantation of genetically corrected autologous hematopoietic stem cells (HSCs) could represent an alternative treatment to allogeneic HSC transplantation, the latter being often associated with severe complications. We used WAS-/- mice to test the efficacy of a gene therapy approach based on nonlethal irradiation followed by transplantation of WAS-/- HSCs transduced with lentiviral vectors encoding the WAS protein (WASP) from either the ubiquitous PGK promoter or the tissue- specific WAS promoter. The procedure resulted in significant levels of engraftment of WASP-expressing T cells, B cells, platelets, and myeloid cells. T cells harbored one or two vector copies and displayed partial to full correction of T cell receptor-driven interleukin-2 production and proliferation. In addition, polymerization of F-actin and localization of WASP at the site of the immunological synapse were restored. The treatment was well tolerated and no pathology was detected by systematic blood analysis and autopsy. The efficacy of WAS gene transfer into HSCs, using the WAS promoter-containing lentiviral vector, combined with nonlethal irradiation provides a strong rationale for the development of gene therapy for WAS patients

Regulated transgene expression may improve the safety and efficacy of hematopoietic stem cell (HSC) gene therapy. Clinical trials for X-linked chronic granulomatous disease (X-CGD) employing gammaretroviral vectors were limited by insertional oncogenesis or lack of persistent engraftment. Our novel strategy, based on regulated lentiviral vectors (LV), targets gp91(phox) expression to the differentiated myeloid compartment while sparing HSC, to reduce the risk of genotoxicity and potential perturbation of reactive oxygen species levels. Targeting was obtained by a myeloid-specific promoter (MSP) and posttranscriptional, microRNA-mediated regulation. We optimized both components in human bone marrow (BM) HSC and their differentiated progeny in vitro and in a xenotransplantation model, and generated therapeutic gp91(phox) expressing LVs for CGD gene therapy. All vectors restored gp91(phox) expression and function in human X-CGD myeloid cell lines, primary monocytes, and differentiated myeloid cells. While unregulated LVs ectopically expressed gp91(phox) in CD34(+) cells, transcriptionally and posttranscriptionally regulated LVs substantially reduced this off-target expression. X-CGD mice transplanted with transduced HSC restored gp91(phox) expression, and MSP-driven vectors maintained regulation during BM development. Combining transcriptional (SP146.gp91-driven) and posttranscriptional (miR-126-restricted) targeting, we achieved high levels of myeloid-specific transgene expression, entirely sparing the CD34(+) HSC compartment. This dual-targeted LV construct represents a promising candidate for further clinical development.