Lentivirus-mediated gene transfer of gp91phox corrects chronic granulomatous disease (CGD) phenotype in human X-CGD cells

[Advances of lentiviral vectors]

Lentiviral vectors are currently very effective tools in molecular and cell experiment. Lentiviral vector, a kind of retroviral vectors, has a number of unique advantages in target gene transferation, for example, the ability of transfection to the dividing or nondividing cells, its high efficiency of transfection and a capacity of large target gene fragments. This paper describes the sources of lentiviral vectors, molecular characteristics, research progress, etc.

Toxicity of repeated intravenous injection of gene therapeutics for X-CGD in mice

We made gene therapeutics for X-chronic granulomatous disease (CGD) by transducing murine bone marrow-derived stem cells with MT-gp91 retrovirus and evaluated possible toxicity in mice as a prerequisite for human clinical trials. Male C57BL/6 mice were injected intravenously with gene therapeutics for X-CGD twice at an interval of two weeks at 5 × 107 cells/kg and sacrificed 2 weeks after the last administration. Significant changes noted in gene therapeutics for X-CGD-treated animals were an increase in white blood cell counts and a slight decrease in albumin/globulin ratio. The red pulp hyperplasia in the spleen accompanied with an increase in organ weight was considered to result from the accumulation of gene therapeutics for X-CGD, bone marrow-derived stem cells, in the spleen. No anti-gp91 antibody was detected in the sera collected from the animals treated with gene therapeutics for X-CGD. No integration of gp91 DNA from retroviral vector was detected in chromosomal DNA of gonads in animals dosed with the test substance, indicating no potential of genomic integration. In conclusion, the repeated dose of gene therapeutics for X-CGD exerted no toxicity. The splenic red pulp hyperplasia and the increase observed in white blood cell counts and in spleen weights were considered as pharmacological changes induced by the treatment.

Simian immunodeficiency virus lentivector corrects human X-linked chronic granulomatous disease in the NOD/SCID mouse xenograft

X-linked chronic granulomatous disease (X-CGD) is a primary immunodeficiency caused by mutations in the phagocyte nicotinamide dinucleotide phosphate oxidase catalytic subunit gp91(phox). Gene therapy targeting hematopoietic stem cells (HSCs) can correct CGD, but permanent correction remains a challenge. Lentiviral vectors have become attractive tools for gene transfer, and they may have the potential to transduce very primitive HSCs. We used a self-inactivating RD114/TR-pseudotyped simian immunodeficiency virus (SIVmac)-based vector encoding human gp91(phox) for ex vivo transduction of peripheral blood-mobilized stem cells (PBSCs) from patients with X-CGD. In PBSCs from two patients, ex vivo transduction efficiencies of 40.5 and 46% were achieved, and correction of oxidase activity was observed in myeloid cells differentiating in culture. When transduced PBSCs from these patients were transplanted into nonobese diabetic/severe combined immunodeficient mice and compared to normal control, 10.5 and 7.3% of the human myeloid cells in bone marrow developing at 6 weeks from the human xenografts expressed the gp91(phox) transgene. Sustained functional correction of oxidase activity was documented in myeloid cells differentiated from engrafted transduced PBSCs. Transgene marking was polyclonal as assessed by vector integration site analysis. These data suggest that RD114/TR SIVmac-based vectors might be suitable for gene therapy of CGD and other hereditary hematologic diseases.

Gene therapy for chronic granulomatous disease

Chronic granulomatous disease (CGD) is a congenital immune deficiency that is a promising therapeutic target for gene replacement into haematopoietic stem cells (HSCs). CGD results from mutations in any one of four genes encoding subunits of the superoxide-generating NADPH oxidase of phagocytes. Life-threatening, recurrent bacterial and fungal infections, as well as inflammatory granulomas, are the hallmarks of the disease. NADPH oxidase activity can be reconstituted by retroviral- or lentiviral-mediated gene transfer to human CGD marrow in vitro and in xenograft transplant models. Gene transfer studies in knockout mouse models that resemble the human disease suggest that correction of oxidase activity in a minority of phagocytes will be of clinical benefit. Phase I clinical studies in unconditioned CGD patients showed transient expression of small numbers of gene-corrected neutrophils. Areas of research at present include efforts to enhance gene transfer rates into repopulating HSCs using vectors that transduce quiescent cells, and to increase the engraftment of genetically corrected HSCs using non-myeloablative conditioning and drug resistance genes for selection.

Highly efficient lentiviral gene transfer in CD34+ and CD34+/38-/lin- cells from mobilized peripheral blood after cytokine prestimulation

Because mobilized peripheral blood (mPB) represents an attractive source of cells for gene therapy, we investigated lentiviral gene transfer in CD34(+) cells and the stem/progenitor-cell-enriched CD34(+)/38(-)/lin(-) cell subset isolated from mPB. In this study, we used an optimized third-generation self-inactivating lentiviral vector containing both the central polypurine tract and the woodchuck hepatitis posttranscriptional regulatory element sequences and encoding enhanced green fluorescent protein (EGFP) under the control of the elongation factor lalpha promoter. This lentivector was first used to compare multiplicity of infection (MOI)-dependent gene transfer efficiency in cord blood (CB) versus mPB CD34(+)-derived cells, colony-forming cells (CFCs), and long-term culture-initiating cells (LTC-ICs). Results showed a difference in the percentage of transduced cells particularly significant at low MOIs. A plateau was reached where 15% and 25% of CB and mPB cells, respectively, remained refractory to lentiviral trans-duction. Effects of a cytokine prestimulation period (18 hours) with interleukin-3, stem cell factor, Flt-3 ligand, and thrombopoietin were then analyzed in total cells, CFCs, and LTC-ICs derived from mPB CD34(+) cells. Transduction levels in those conditions demonstrated a two- and fourfold increase in CFCs and LTC-ICs, respectively, compared with unstimulated (<3 hours) control cells. Moreover, using the same transduction protocol, we were able to efficiently transduce CD34(+)/38(-)/lin(-) cells isolated from mPB, with up to >85% of colonies derived from LTC-ICs expressing EGFP and gene transfer levels remaining stable for 10 weeks in liquid culture. We therefore demonstrate a highly efficient gene transfer in this therapeutically relevant target cell population.

A bicistronic SIN-lentiviral vector containing G156A MGMT allows selection and metabolic correction of hematopoietic protoporphyric cell lines

BACKGROUND

Erythropoietic protoporphyria (EPP) is an inherited disease characterised by a ferrochelatase (FECH) deficiency, the latest enzyme of the heme biosynthetic pathway, leading to the accumulation of toxic protoporphyrin in the liver, bone marrow and spleen. We have previously shown that a successful gene therapy of a murine model of the disease was possible with lentiviral vectors even in the absence of preselection of corrected cells, but lethal irradiation of the recipient was necessary to obtain an efficient bone marrow engraftment. To overcome a preconditioning regimen, a selective growth advantage has to be conferred to the corrected cells.

METHODS

We have developed a novel bicistronic lentiviral vector that contains the human alkylating drug resistance mutant O(6)-methylguanine DNA methyltransferase (MGMT G156A) and FECH cDNAs. We tested their capacity to protect hematopoietic cell lines efficiently from alkylating drug toxicity and correct enzymatic deficiency.

RESULTS

EPP lymphoblastoid (LB) cell lines, K562 and cord-blood-derived CD34(+) cells were transduced at a low multiplicity of infection (MOI) with the bicistronic constructs. Resistance to O(6)-benzylguanine (BG)/N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) was clearly shown in transduced cells, leading to the survival and expansion of provirus-containing cells. Corrected EPP LB cells were selectively amplified, leading to complete restoration of enzymatic activity and the absence of protoporphyrin accumulation.

CONCLUSIONS

This study demonstrates that a lentiviral vector including therapeutic and G156A MGMT genes followed by BG/BCNU exposure can lead to a full metabolic correction of deficient cells. This vector might form the basis of new EPP mouse gene therapy protocols without a preconditioning regimen followed by in vivo selection of corrected hematopoietic stem cells.

Long-term high-level reconstitution of NADPH oxidase activity in murine X-linked chronic granulomatous disease using a bicistronic vector expressing gp91phox and a Delta LNGFR cell surface marker

A murine model of X-linked chronic granulomatous disease (X-CGD), an inherited immune deficiency with absent phagocyte NADPH oxidase activity caused by defects in the gp91(phox) gene, was used to evaluate a bicistronic retroviral vector in which expression of human gp91(phox) and a linked gene for Delta LNGFR, a truncated form of human low-affinity nerve growth factor receptor, are under the control of a spleen focus-forming virus long-terminal repeat (LTR). Four independent cohorts of 11-Gy irradiated X-CGD mice (total, 22 mice) were transplanted with or without preselection of transduced X-CGD bone marrow (BM). Transplanted mice had high-level correction of neutrophil gp91(phox) expression and reconstitution of NADPH oxidase activity. Expression lasted for at least 14 months in primary transplants, and persisted in secondary and tertiary transplants. Both gp91(phox) and Delta LNGFR were detected on circulating granulocytes, lymphocytes, lymphoid, and (for Delta LNGFR) red blood cells. Mice receiving transduced bone marrow [BM] preselected ex vivo for Delta LNGFR expression had high-level (= 80%) reconstitution with transduced cells, with an improved fraction of oxidase-corrected neutrophils posttransplant. Analysis of secondary and tertiary CFU-S showed that silencing of individual provirus integrants can occur even after preselection for Delta LNGFR prior to transplantation, and that persistent provirus expression was associated with multiple integration sites in most cases. No obvious adverse consequences of transgenic protein expression were observed.

A SIN lentiviral vector containing PIGA cDNA allows long-term phenotypic correction of CD34+-derived cells from patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic stem cell (HSC) disorder in which an acquired somatic mutation of the X-linked PIGA gene results in a deficiency in GPI-anchored surface proteins. Clinically, PNH is dominated by a chronic hemolytic anemia, often associated with recurrent nocturnal exacerbations, neutropenia, thrombocytopenia, and thrombotic tendency. Allogenic bone marrow transplantation is the only potentially curative treatment for severe forms of PNH but is associated with a high treatment-related morbidity and mortality. HSC gene therapy could provide a new therapeutic option, especially when an HLA-matched donor is not available. To develop an efficient gene transfer approach, we have designed a new SIN lentiviral vector (TEPW) that contains the PIGA cDNA driven by the human elongation factor 1 alpha promoter, the central DNA flap of HIV-1, and the WPRE cassette. TEPW transduction led to a complete surface expression of the GPI anchor and CD59 in PIGA-deficient cell lines without any selection procedure. Moreover, efficient gene transfer was achieved in bone marrow and mobilized peripheral blood CD34(+) cells derived from two patients with severe PNH disease. This expression was stable during erythroid, myeloid, and megakaryocytic liquid culture differentiation. CD59 surface cell expression was fully restored during 5 weeks of long-term culture.

High-level expression of hemoglobin A in human thalassemic erythroid progenitor cells following lentiviral vector delivery of an antisense snRNA

Mutations at nucleotides 654, 705, or 745 in intron 2 of the human beta-globin gene activate aberrant 3' and 5' splice sites within the intron and prevent correct splicing of beta-globin pre-mRNA, resulting in inhibition of beta-globin synthesis and in consequence beta-thalassemia. Transfection of HeLa cells expressing the 3 thalassemic mutants with modified U7 snRNA (U7.623), containing a sequence antisense to a region between the aberrant splice sites, reduced the incorrect splicing of pre-mRNA and led to increased levels of the correctly spliced beta-globin mRNA and protein. A lentiviral vector carrying the U7.623 gene was effective in restoration of correct splicing in the model cell lines for at least 6 months. Importantly, the therapeutic value of this system was demonstrated in hematopoietic stem cells and erythroid progenitor cells from a patient with IVS2-745/IVS2-1 thalassemia. Twelve days after transduction of the patient cells with the U7.623 lentiviral vector, the levels of correctly spliced beta-globin mRNA and hemoglobin A were approximately 25-fold over background. These results should be regarded as a proof of principle for lentiviral vector-based gene therapy for beta-thalassemia.

Third-generation, self-inactivating gp91(phox) lentivector corrects the oxidase defect in NOD/SCID mouse-repopulating peripheral blood-mobilized CD34+ cells from patients with X-linked chronic granulomatous disease

HIV-1-derived lentivectors are promising for gene transfer into hematopoietic stem cells but require preclinical in vivo evaluation relevant to specific human diseases. Nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice accept human hematopoietic stem cell grafts, providing a unique opportunity for in vivo evaluation of therapies targeting human hematopoietic diseases. We demonstrate for the first time that hematopoietic stem cells from patients with X-linked chronic granulomatous disease (X-CGD) give rise to X-CGD-phenotype neutrophils in the NOD/SCID model that can be corrected using VSV-G-pseudotyped, 3rd-generation, self-inactivating (SIN) lentivector encoding gp91(phox). We transduced X-CGD patient-mobilized CD34(+) peripheral blood stem cells (CD34(+)PBSCs) with lentivector-gp91(phox) or amphotropic oncoretrovirus MFGS-gp91(phox) and evaluated correction ex vivo and in vivo in NOD/SCID mice. Only lentivector transduced CD34(+)PBSCs under ex vivo conditions nonpermissive for cell division, but both vectors performed best under conditions permissive for proliferation (multiple growth factors). Under the latter conditions, lentivector and MFGS achieved significant ex vivo correction of X-CGD CD34(+)PBSCs (18% and 54% of cells expressing gp91(phox), associated with 53% and 163% of normal superoxide production, respectively). However, lentivector, but not MFGS, achieved significant correction of human X-CGD neutrophils arising in vivo in NOD/SCID mice that underwent transplantation (20% and 2.4%, respectively). Thus, 3rd-generation SIN lentivector-gp91(phox) performs well as assessed in human X-CGD neutrophils differentiating in vivo, and our studies suggest that the NOD/SCID model is generally applicable for in vivo study of therapies evaluated in human blood cells expressing a specific disease phenotype.

Gene therapy of hematopoietic stem cells: strategies for improvement

Gene therapy of hematopoietic stem cells (HSC) is limited by low frequency of the target cells, their quiescent nature, poor engraftment of treated HSC, and lack of a selective growth advantage of genetically modified cells. Lentiviral vectors combined with positive selection strategies using conditional cell-growth switches should allow for improvement.

Correction of genetic blood defects by gene transfer

Recent clinical trials in patients with a severe combined immunodeficiency disease demonstrate that gene therapy is a powerful tool in the treatment of genetic blood defects. Recent identification of the genes involved in the pathogenesis of inherited lymphohemopoietic disorders led to animal models of gene transfer. Extensive preclinical studies have overcome some of the obstacles involved in the transduction of hemopoietic cells. These promising results led to the approval of several clinical trials that are currently underway. This review focuses on the clinical outcome in patients with genetic blood defects treated by gene transfer and examines the progress achieved to date and the problems that have been encountered. Despite the obstacles, improved clinical results for several of these diseases are expected within the next 5 years.