Genetic diseases of blood cells are prime candidates for treatment through ex vivo gene editing of CD34
hematopoietic stem/progenitor cells (HSPCs), and a variety of technologies have been proposed ...to treat these disorders. Sickle cell disease (SCD) is a recessive genetic disorder caused by a single-nucleotide polymorphism in the β-globin gene (HBB). Sickle hemoglobin damages erythrocytes, causing vasoocclusion, severe pain, progressive organ damage, and premature death. We optimize design and delivery parameters of a ribonucleoprotein (RNP) complex comprising Cas9 protein and unmodified single guide RNA, together with a single-stranded DNA oligonucleotide donor (ssODN), to enable efficient replacement of the SCD mutation in human HSPCs. Corrected HSPCs from SCD patients produced less sickle hemoglobin RNA and protein and correspondingly increased wild-type hemoglobin when differentiated into erythroblasts. When engrafted into immunocompromised mice, ex vivo treated human HSPCs maintain SCD gene edits throughout 16 weeks at a level likely to have clinical benefit. These results demonstrate that an accessible approach combining Cas9 RNP with an ssODN can mediate efficient HSPC genome editing, enables investigator-led exploration of gene editing reagents in primary hematopoietic stem cells, and suggests a path toward the development of new gene editing treatments for SCD and other hematopoietic diseases.
Targeted genome editing technology can correct the sickle cell disease mutation of the β-globin gene in hematopoietic stem cells. This correction supports production of red blood cells that ...synthesize normal hemoglobin proteins. Here, we demonstrate that Transcription Activator-Like Effector Nucleases (TALENs) and the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 nuclease system can target DNA sequences around the sickle-cell mutation in the β-globin gene for site-specific cleavage and facilitate precise correction when a homologous donor template is codelivered. Several pairs of TALENs and multiple CRISPR guide RNAs were evaluated for both on-target and off-target cleavage rates. Delivery of the CRISPR/Cas9 components to CD34+ cells led to over 18% gene modification in vitro. Additionally, we demonstrate the correction of the sickle cell disease mutation in bone marrow derived CD34+ hematopoietic stem and progenitor cells from sickle cell disease patients, leading to the production of wild-type hemoglobin. These results demonstrate correction of the sickle mutation in patient-derived CD34+ cells using CRISPR/Cas9 technology.
Sickle cell disease (SCD) is characterized by a single point mutation in the seventh codon of the β-globin gene. Site-specific correction of the sickle mutation in hematopoietic stem cells would ...allow for permanent production of normal red blood cells. Using zinc-finger nucleases (ZFNs) designed to flank the sickle mutation, we demonstrate efficient targeted cleavage at the β-globin locus with minimal off-target modification. By codelivering a homologous donor template (either an integrase-defective lentiviral vector or a DNA oligonucleotide), high levels of gene modification were achieved in CD34+ hematopoietic stem and progenitor cells. Modified cells maintained their ability to engraft NOD/SCID/IL2rγnull mice and to produce cells from multiple lineages, although with a reduction in the modification levels relative to the in vitro samples. Importantly, ZFN-driven gene correction in CD34+ cells from the bone marrow of patients with SCD resulted in the production of wild-type hemoglobin tetramers.
•Delivery of ZFNs and donor templates results in high levels of gene correction in human CD34+ cells from multiple sources, including SCD BM.•Modified CD34+ cells are capable of engrafting immunocompromised NSG mice and produce cells from multiple lineages.
We show that lentiviral delivery of human γ-globin gene under β-globin regulatory control elements in hematopoietic stem cells (HSCs) results in sufficient postnatal fetal hemoglobin (HbF) expression ...to correct sickle cell anemia (SCA) in the Berkeley “humanized” sickle mouse. Upon de-escalating the amount of transduced HSCs in transplant recipients, using reduced-intensity conditioning and varying gene transfer efficiency and vector copy number, we assessed critical parameters needed for correction. A systematic quantification of functional and hematologic red blood cell (RBC) indices, organ pathology, and life span was used to determine the minimal amount of HbF, F cells, HbF/F-cell, and gene-modified HSCs required for correcting the sickle phenotype. We show that long-term amelioration of disease occurred (1) when HbF exceeded 10%, F cells constituted two-thirds of the circulating RBCs, and HbF/F cell was one-third of the total hemoglobin in sickle RBCs; and (2) when approximately 20% gene-modified HSCs repopulated the marrow. Moreover, we show a novel model using reduced-intensity conditioning to determine genetically corrected HSC threshold that corrects a hematopoietic disease. These studies provide a strong preclinical model for what it would take to genetically correct SCA and are a foundation for the use of this vector in a human clinical trial.
Autologous hematopoietic stem cell (HSC) gene therapy for sickle cell disease has the potential to treat this illness without the major immunological complications associated with allogeneic ...transplantation. However, transduction efficiency by β‐globin lentiviral vectors using CD34‐enriched cell populations is suboptimal and large vector production batches may be needed for clinical trials. Transducing a cell population more enriched for HSC could greatly reduce vector needs and, potentially, increase transduction efficiency. CD34+/CD38− cells, comprising ∼1%–3% of all CD34+ cells, were isolated from healthy cord blood CD34+ cells by fluorescence‐activated cell sorting and transduced with a lentiviral vector expressing an antisickling form of beta‐globin (CCL‐βAS3‐FB). Isolated CD34+/CD38− cells were able to generate progeny over an extended period of long‐term culture (LTC) compared to the CD34+ cells and required up to 40‐fold less vector for transduction compared to bulk CD34+ preparations containing an equivalent number of CD34+/CD38− cells. Transduction of isolated CD34+/CD38− cells was comparable to CD34+ cells measured by quantitative PCR at day 14 with reduced vector needs, and average vector copy/cell remained higher over time for LTC initiated from CD34+/38− cells. Following in vitro erythroid differentiation, HBBAS3 mRNA expression was similar in cultures derived from CD34+/CD38− cells or unfractionated CD34+ cells. In vivo studies showed equivalent engraftment of transduced CD34+/CD38− cells when transplanted in competition with 100‐fold more CD34+/CD38+ cells. This work provides initial evidence for the beneficial effects from isolating human CD34+/CD38− cells to use significantly less vector and potentially improve transduction for HSC gene therapy. Stem Cells 2015;33:1532–1542
The use of retroviral vectors in gene therapy has raised safety concerns for the genotoxic risk associated with their uncontrolled insertion into the human genome. We have analyzed the consequences ...of retroviral transduction in T cells from leukemic patients treated with allogeneic stem cell transplantation and donor lymphocytes genetically modified with a suicide gene (HSV-TK). Retroviral vectors integrate preferentially within or near transcribed regions of the genome, with a preference for sequences around promoters and for genes active in T cells at the time of transduction. Quantitative transcript analysis shows that one fifth of these integrations affect the expression of nearby genes. However, transduced T cell populations maintain remarkably stable gene expression profiles, phenotype, biological functions, and immune repertoire in vivo, with no evidence of clonal selection up to 9 yr after administration. Analysis of integrated proviruses in transduced cells before and after transplantation indicates that integrations interfering with normal T cell function are more likely to lead to clonal ablation than expansion in vivo. Despite the potentially dangerous interactions with the T cell genome, retroviral integration has therefore little consequence on the safety and efficacy of T cell transplantation.
Friedreich’s ataxia (FRDA) is an autosomal-recessive disorder primarily attributed to biallelic GAA repeat expansions that reduce expression of the mitochondrial protein frataxin (FXN). FRDA is ...characterized by progressive neurodegeneration, with many patients developing cardiomyopathy that progresses to heart failure and death. The potential to reverse or prevent progression of the cardiac phenotype of FRDA was investigated in a mouse model of FRDA, using an adeno-associated viral vector (AAV8) containing the coding sequence of the FXN gene. The Fxnflox/null::MCK-Cre conditional knockout mouse (FXN-MCK) has an FXN gene ablation that prevents FXN expression in cardiac and skeletal muscle, leading to cardiac insufficiency, weight loss, and morbidity. FXN-MCK mice received a single intravenous injection of an AAV8 vector containing human (hFXN) or mouse (mFXN) FXN genes under the control of a phosphoglycerate kinase promoter. Compared to vehicle-treated FXN-MCK control mice, AAV-treated FXN-MCK mice displayed increases in body weight, reversal of cardiac deficits, and increases in survival without apparent toxicity in the heart or liver for up to 12 weeks postdose. FXN protein expression in heart tissue was detected in a dose-dependent manner, exhibiting wide distribution throughout the heart similar to wild type, but more speckled. These results support an AAV8-based approach to treat FRDA-associated cardiomyopathy.
Display omitted
Fonck and colleagues report that AAV8-mediated systemic administration of FXN transgene significantly improved survival, body weight, heart morphology, cardiac function, cardiac injury biomarkers, and expression of mitochondrial electron transport chain complexes of Friedreich’s ataxia without toxicity observed in the heart and liver of a FXN conditional knockout mouse model.
We examined the efficiency, specificity, and mutational signatures of zinc finger nucleases (ZFNs), transcriptional activator-like effector nucleases (TALENs), and clustered regularly interspaced ...short palindromic repeat (CRISPR)/Cas9 systems designed to target the gene encoding the transcriptional repressor BCL11A, in human K562 cells and human CD34+ progenitor cells. ZFNs and TALENs were delivered as in vitro transcribed mRNA through electroporation; CRISPR/Cas9 was codelivered by Cas9 mRNA with plasmid-encoded guideRNA (gRNA) (pU6.g1) or in vitro transcribed gRNA (gR.1). Analyses of efficacy revealed that for these specific reagents and the delivery methods used, the ZFNs gave rise to more allelic disruption in the targeted locus compared to the TALENs and CRISPR/Cas9, which was associated with increased levels of fetal hemoglobin in erythroid cells produced in vitro from nuclease-treated CD34+ cells. Genome-wide analysis to evaluate the specificity of the nucleases revealed high specificity of this specific ZFN to the target site, while specific TALENs and CRISPRs evaluated showed off-target cleavage activity. ZFN gene-edited CD34+ cells had the capacity to engraft in NOD-PrkdcSCID-IL2Rγnull mice, while retaining multi-lineage potential, in contrast to TALEN gene-edited CD34+ cells. CRISPR engraftment levels mirrored the increased relative plasmid-mediated toxicity of pU6.g1/Cas9 in hematopoietic stem/progenitor cells (HSPCs), highlighting the value for the further improvements of CRISPR/Cas9 delivery in primary human HSPCs.
Chromatin insulators separate active transcriptional domains and block the spread of heterochromatin in the genome. Studies on the chicken hypersensitive site-4 (cHS4) element, a prototypic ...insulator, have identified CTCF and USF-1/2 motifs in the proximal 250 bp of cHS4, termed the "core", which provide enhancer blocking activity and reduce position effects. However, the core alone does not insulate viral vectors effectively. The full-length cHS4 has excellent insulating properties, but its large size severely compromises vector titers. We performed a structure-function analysis of cHS4 flanking lentivirus-vectors and analyzed transgene expression in the clonal progeny of hematopoietic stem cells and epigenetic changes in cHS4 and the transgene promoter. We found that the core only reduced the clonal variegation in expression. Unique insulator activity resided in the distal 400 bp cHS4 sequences, which when combined with the core, restored full insulator activity and open chromatin marks over the transgene promoter and the insulator. These data consolidate the known insulating activity of the canonical 5' core with a novel 3' 400 bp element with properties similar to the core. Together, they have excellent insulating properties and viral titers. Our data have important implications in understanding the molecular basis of insulator function and design of gene therapy vectors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Sickle cell disease (SCD) is caused by a mutation (E6V) in the hemoglobin (Hb) β-chain that induces polymerization of Hb tetramers, red blood cell deformation, ischemia, anemia, and multiple organ ...damage. Gene therapy is a potential alternative to human leukocyte antigen (HLA)-matched allogeneic hematopoietic stem cell transplantation, available to a minority of patients. We developed a lentiviral vector expressing a β-globin carrying three anti-sickling mutations (T87Q, G16D, and E22A) inhibiting axial and lateral contacts in the HbS polymer, under the control of the β-globin promoter and a reduced version of the β-globin locus-control region. The vector (GLOBE-AS3) transduced 60%-80% of mobilized CD34
hematopoietic stem-progenitor cells (HSPCs) and drove βAS3-globin expression at potentially therapeutic levels in erythrocytes differentiated from transduced HSPCs from SCD patients. Transduced HSPCs were transplanted in NOD.Cg-Prkdc
Il2rg
/SzJ (NSG)-immunodeficient mice to analyze biodistribution, chimerism, and transduction efficiency in bone marrow (BM), spleen, thymus, and peripheral blood 12-14 weeks after transplantation. Vector integration site analysis, performed in pre-transplant HSPCs and post-transplant BM cells from individual mice, showed a normal lentiviral integration pattern and no evidence of clonal dominance. An
immortalization (IVIM) assay showed the low genotoxic potential of GLOBE-AS3. This study enables a phase I/II clinical trial aimed at correcting the SCD phenotype in juvenile patients by transplantation of autologous hematopoietic stem cells (HSC) transduced by GLOBE-AS3.
PDF
