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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In clinical gene therapy trials for X-linked severe combined immunodeficiency, the development of leukemia has come up as a severe adverse effect. In all five cases, T-cell acute lymphoblastic leukemia (T-ALL) occurred as a direct consequence of insertional mutagenesis by the retrovirus used to deliver the therapeutic gene. Here, we review the mechanisms of insertional mutagenesis, the function of the Il2RG gene and the future developments in the field. New lentiviral and gamma retroviral vectors can significantly improve the safety profile of the tools used but still carry the risk of insertional mutagenesis, as shown in this issue of Leukemia. Finally, the unfortunate side effects of gene therapy have given more insight into the development of human T-ALL.
Leukemia 2008 Oct
PMID:Sola dosis facit venenum. Leukemia in gene therapy trials: a question of vectors, inserts and dosage? 1876 49

The emergence of leukemia following gene transfer to restore common cytokine receptor gamma chain (gammaC) function in X-linked severe combined immunodeficiency (SCID-X1) has raised important questions with respect to gene therapy safety. To explore the risk factors involved, we tested the oncogenic potential of human gammaC in new strains of transgenic mice expressing the gene under the control of the CD2 promoter and locus control region (LCR). These mice demonstrated mildly perturbed T-cell development, with an increased proportion of thymic CD8 cells, but showed no predisposition to tumor development even on highly tumor prone backgrounds or after gamma-retrovirus infection. The human CD2-gammaC transgene rescued T and B-cell development in gammaC(-/-) mice but with an age-related delay, mimicking postnatal reconstitution in SCID-X1 gene therapy subjects. However, we noted that gammaC(-/-) mice are acutely susceptible to murine leukemia virus (MLV) leukemogenesis, and that this trait was not corrected by the gammaC transgene. We conclude that the SCID-X1 phenotype can be corrected safely by stable ectopic expression of gammaC and that the transgene is not significantly oncogenic when expressed in this context. However, an underlying predisposition conferred by the SCID-X1 background appears to collaborate with insertional mutagenesis to increase the risk of tumor development.
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PMID:A novel model of SCID-X1 reconstitution reveals predisposition to retrovirus-induced lymphoma but no evidence of gammaC gene oncogenicity. 1933 36

Five X-linked severe combined immunodeficiency patients (SCID-X1) successfully treated with autologous bone marrow stem cells infected ex vivo with an IL2RG-containing retrovirus subsequently developed T-cell leukemia and four contained insertional mutations at LMO2. Genetic evidence also suggests a role for IL2RG in tumor formation, although this remains controversial. Here, we show that the genes and signaling pathways deregulated in murine leukemias with retroviral insertions at Lmo2 are similar to those deregulated in human leukemias with high LMO2 expression and are highly predictive of the leukemias induced in SCID-X1 patients. We also provide additional evidence supporting the notion that IL2RG and LMO2 cooperate in leukemia induction but are not sufficient and require additional cooperating mutations. The highly concordant nature of the genetic events giving rise to mouse and human leukemias with mutations at Lmo2 are an encouraging sign to those wanting to use mice to model human cancer and may help in designing safer methods for retroviral gene therapy.
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PMID:Murine leukemias with retroviral insertions at Lmo2 are predictive of the leukemias induced in SCID-X1 patients following retroviral gene therapy. 1946 87

Insertional mutagenesis leading to insurgence of leukemia has been shown as a consequence of retroviral (RV)-mediated gene transfer in animal models and in clinical trials of gene therapy for X-linked severe combined immunodeficiency. Aberrant expression of oncogenes neighboring the gamma-RV vector insertion site via induction by the enhancer element of the viral long terminal repeats (LTRs) is thought to have played a role in leukemogenesis. Consequently, RV vectors devoid of LTR enhancer elements could prove as safer tools for gene transfer. To test this hypothesis, we evaluated the immortalization ability of two RV vectors: one carrying the full-length Moloney leukemia virus (MLV) LTR and one with the same LTR in which the enhancer element was deleted [MLV self-inactivating (SIN)]. Unexpectedly, transduction with MLV SIN resulted in an only slightly and not significant decreased immortalization frequency of primary bone marrow (BM) cultures (about 37%) compared to transduction with MLV (about 48%). Similar to MLV, immortalization by MLV SIN is likely caused by insertional activation of oncogenes including Evi1, Mds1, Mef2c, and Hoxa7. Our results indicate that the MLV SIN, devoid of the LTR enhancer element, was still able to immortalize BM cells by activating nearby gene expression, indicating the need of an accurate selection of the internal promoter to obtain safer SIN RV vectors.
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PMID:Self-inactivating retroviral vector-mediated gene transfer induces oncogene activation and immortalization of primary murine bone marrow cells. 1963 58

Therapeutic retroviral vector integration near the oncogene LMO2 is thought to be a cause of leukemia in X-SCID gene therapy trials. However, no published studies have evaluated the frequency of vector integrations near exon 1 of the LMO2 locus. We identified a high incidence region (HIR) of vector integration using PCR techniques in the upstream region close to the LMO2 transcription start site in the TPA-Mat T cell line. The integration frequency of the HIR was one per 4.46 x 10(4) cells. This HIR was also found in Jurkat T cells but was absent from HeLa cells. Furthermore, using human cord blood-derived CD34+ cells we identified a HIR in a similar region as the TPA-Mat T cell line. One of the X-linked severe combined immunodeficiency (X-SCID) patients that developed leukemia after gene therapy had a vector integration site in this HIR. Therefore, the descriptions of the location and the integration frequency of the HIR presented here may help us to better understand vector-induced leukemogenesis.
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PMID:Identification of a high incidence region for retroviral vector integration near exon 1 of the LMO2 locus. 1972 63

The development of leukemia as a consequence of vector-mediated genotoxicity in gene therapy trials for X-linked severe combined immunodeficiency (SCID-X1) has prompted substantial research effort into the design and safety testing of integrating vectors. An important element of vector design is the selection and evaluation of promoter-enhancer elements with sufficient strength to drive reliable immune reconstitution, but minimal propensity for enhancer-mediated insertional mutagenesis. In this study, we set out to explore the effect of promoter-enhancer selection on the efficacy and safety of human immunodeficiency virus-1-derived lentiviral vectors in gammac-deficient mice. We observed incomplete or absent T- and B-cell development in mice transplanted with progenitors expressing gammac from the phosphoglycerate kinase (PGK) and Wiscott-Aldrich syndrome (WAS) promoters, respectively. In contrast, functional T- and B-cell compartments were restored in mice receiving an equivalent vector containing the elongation factor-1-alpha (EF1alpha) promoter; however, 4 of 14 mice reconstituted with this vector subsequently developed lymphoma. Extensive analyses failed to implicate insertional mutagenesis or gammac overexpression as the underlying mechanism. These findings highlight the need for detailed mechanistic analysis of tumor readouts in preclinical animal models assessing vector safety, and suggest the existence of other ill-defined risk factors for oncogenesis, including replicative stress, in gene therapy protocols targeting the hematopoietic compartment.
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PMID:Lymphomagenesis in SCID-X1 mice following lentivirus-mediated phenotype correction independent of insertional mutagenesis and gammac overexpression. 2043 93

After more than 1500 gene therapy clinical trials in the past two decades, the overall conclusion is that for gene therapy (GT) to be successful, the vector systems must still be improved in terms of delivery, expression and safety. The recent development of more efficient and stable vector systems has created great expectations for the future of GT. Impressive results were obtained in three primary immunodeficiencies and other inherited diseases such as congenital blindness, adrenoleukodystrophy or junctional epidermolysis bullosa. However, the development of leukemia in five children included in the GT clinical trials for X-linked severe combined immunodeficiency and the silencing of the therapeutic gene in the chronic granulomatous disease clearly showed the importance of improving safety and efficiency. In this review, we focus on the main strategies available to achieve physiological or tissue-specific expression of therapeutic transgenes and discuss the importance of controlling transgene expression to improve safety. We propose that tissue-specific and/or physiological viral vectors offer the best balance between efficiency and safety and will be the tools of choice for future clinical trials in GT of inherited diseases.
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PMID:Physiological and tissue-specific vectors for treatment of inherited diseases. 2096 71

Virus-based vectors are widely used in hematopoietic stem cell (HSC) gene therapy, and have the ability to integrate permanently into genomic DNA, thus driving long-term expression of corrective genes in all hematopoietic lineages. To date, HSC gene therapy has been successfully employed in the clinic for improving clinical outcomes in small numbers of patients with X-linked severe combined immunodeficiency (SCID-X1), adenosine deaminase deficiency (ADA-SCID), adrenoleukodystrophy (ALD), thalassemia, chronic granulomatous disease (CGD), and Wiskott-Aldrich syndrome (WAS). However, adverse events were observed during some of these HSC gene therapy clinical trials, linked to insertional activation of proto-oncogenes by integrated proviral vectors leading to clonal expansion and eventual development of leukemia. Numerous studies have been performed to understand the molecular basis of vector-mediated genotoxicity, with the aim of developing safer vectors and lower-risk gene therapy protocols. This review will summarize current information on the mechanisms of insertional mutagenesis in hematopoietic stem and progenitor cells due to integrating gene transfer vectors, discuss the available assays for predicting genotoxicity and mapping vector integration sites, and introduce newly-developed approaches for minimizing genotoxicity as a way to further move HSC gene therapy forward into broader clinical application.
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PMID:Stem cell gene therapy: the risks of insertional mutagenesis and approaches to minimize genotoxicity. 2219 47

Four out of 10 patients of X-linked severe combined immunodeficiency (X-SCID) were finally developed leukemia after receiving the treatment of gene therapy delivered by gamma-retroviral vectors. This is due to the vector integrated to the proximity of lmo2 etc proto-oncogene promoters, leading to the activation of onco-gene expression, which raises the concern of the bio-safety of gene therapy vectors. Lentiviral vectors, especially self-inactivating lentiviral vectors, are considered to be much safer than gamma-retroviral vectors. However self-inactivating lentiviral vectors also have encountered with some unsafe factors and one of them is the problem of transcriptional "read-through" . During the past years, achievements have been made to reduce lentiviral vector transcriptional read-through, which are reviewed herein.
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PMID:[Progress in improvement of lentiviral vectors' transcriptional read-through]. 2239 8

Patients with X-linked severe combined immunodeficiency (SCID-X1) were successfully cured following gene therapy with a gamma-retroviral vector (gRV) expressing the common gamma chain of the interleukin-2 receptor (IL2RG). However, 5 of 20 patients developed leukemia from activation of cellular proto-oncogenes by viral enhancers in the long-terminal repeats (LTR) of the integrated vector. These events prompted the design of a gRV vector with self-inactivating (SIN) LTRs to enhance vector safety. Herein we report on the production of a clinical-grade SIN IL2RG gRV pseudotyped with the Gibbon Ape Leukemia Virus envelope for a new gene therapy trial for SCID-X1, and highlight variables that were found to be critical for transfection-based large-scale SIN gRV production. Successful clinical production required careful selection of culture medium without pre-added glutamine, reduced exposure of packaging cells to cell-dissociation enzyme, and presence of cations in wash buffer. The clinical vector was high titer; transduced 68-70% normal human CD34(+) cells, as determined by colony-forming unit assays and by xenotransplantation in immunodeficient NOD.CB17-Prkdc(scid)/J (nonobese diabetic/severe combined immunodeficiency (NOD/SCID)) and NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ (NOD/SCID gamma (NSG))) mice; and resulted in the production of T cells in vitro from human SCID-X1 CD34(+) cells. The vector was certified and released for the treatment of SCID-X1 in a multi-center international phase I/II trial.
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PMID:Critical variables affecting clinical-grade production of the self-inactivating gamma-retroviral vector for the treatment of X-linked severe combined immunodeficiency. 2255 77


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