Preclinical correction of human Fanconi anemia complementation group A bone marrow cells using a safety-modified lentiviral vector.

One of the major hurdles for the development of gene therapy for Fanconi anemia (FA) is the increased sensitivity of FA stem cells to free radical-induced DNA damage during ex vivo culture and manipulation. To minimize this damage, we have developed a brief transduction procedure for lentivirus vector-mediated transduction of hematopoietic progenitor cells from patients with Fanconi anemia complementation group A (FANCA). The lentiviral vector FancA-sW contains the phosphoglycerate kinase promoter, the FANCA cDNA, and a synthetic, safety-modified woodchuck post transcriptional regulatory element (sW). Bone marrow mononuclear cells or purified CD34(+) cells from patients with FANCA were transduced in an overnight culture on recombinant fibronectin peptide CH-296, in low (5%) oxygen, with the reducing agent, N-acetyl-L-cysteine (NAC), and a combination of growth factors, granulocyte colony-stimulating factor (G-CSF), Flt3 ligand, stem cell factor, and thrombopoietin. Transduced cells plated in methylcellulose in hypoxia with NAC showed increased colony formation compared with 21% oxygen without NAC (P<0.03), showed increased resistance to mitomycin C compared with green fluorescent protein (GFP) vector-transduced controls (P<0.007), and increased survival. Thus, combining short transduction and reducing oxidative stress may enhance the viability and engraftment of gene-corrected cells in patients with FANCA.

Lentiviral vectors with amplified beta cell-specific gene expression.

An important goal of gene therapy is to be able to deliver genes, so that they express in a pattern that recapitulates the expression of an endogenous cellular gene. Although tissue-specific promoters confer selectivity, in a vector-based system, their activity may be too weak to mediate detectable levels in gene-expression studies. We have used a two-step transcriptional amplification system to amplify gene expression from lentiviral vectors using the human insulin promoter. In this system, the human insulin promoter drives expression of a potent synthetic transcription activator (the yeast GAL4 DNA-binding domain fused to the activation domain of the Herpes simplex virus-1 VP16 activator), which in turn activates a GAL4-responsive promoter, driving the enhanced green fluorescent protein reporter gene. Vectors carrying the human insulin promoter did not express in non-beta-cell lines, but expressed in murine insulinoma cell lines, indicating that the human insulin promoter was capable of conferring cell specificity of expression. The insulin-amplifiable vector was able to amplify gene expression five to nine times over a standard insulin-promoter vector. In primary human islets, gene expression from the insulin-promoted vectors was coincident with insulin staining. These vectors will be useful in gene-expression studies that require a detectable signal and tissue specificity.

Tissue-specific restriction of cyclophilin A-independent HIV-1- and SIV-derived lentiviral vectors.

The host factor alpha isoform of the tripartite motif 5 (TRIM5alpha) restricts human immunodeficiency virus type 1 (HIV-1) infection in certain non-human primate species. Restriction of HIV-1 is enhanced by binding of the viral capsid to cyclophilin A (CypA) in target cells, although CypA is not absolutely required for restriction in rhesus macaque cells. Simian immunodeficiency virus (SIV) is not restricted by rhesus macaque TRIM5alpha and its capsid does not bind to CypA. Here, the effect of lentiviral CypA dependence on restriction in different tissues was examined by engineering an HIV-1 capsid quadruple mutant (V(86)P/H(87)Q/I(91)V/M(96)I) lentiviral vector (HIV(quad)) that is CypA-independent. Whereas HIV-1 was restricted in rhesus macaque and owl monkey epithelial cells, infection with the HIV(quad) vector was efficient at high viral concentrations. In contrast, HIV(quad) was largely restricted in primary rhesus macaque CD34(+) cells. Human epithelial and primary CD34(+) cells were permissive for HIV-1, HIV(quad) and SIV, whereas transduction of human T cells by HIV(quad) or SIV was impaired. The restrictive human cells did not express increased levels of TRIM5alpha, and restriction was not relieved by abolishing CypA, consistent with HIV(quad) and SIV being CypA-independent. Pseudotyping of lentiviral vectors with the gibbon ape leukemia virus envelope altered their sensitivity to perturbations of the virus-CypA interaction compared to pseudotyping with vesicular stomatitis virus glycoproteins, suggesting that the viral entry pathway modulates restriction. Together, these studies reveal that an HIV-1 capsid quadruple mutant can partially overcome lentiviral restriction in non-human primate epithelial cells, but not in hematopoietic cells. Similarly, human cells vary in their permissiveness for CypA-independent lentiviruses, and suggest the presence of tissue-specific factor(s) that can inhibit lentiviral transduction independently of viral interaction with TRIM5alpha and CypA.

Gene therapy for childhood immunological diseases.

Gene therapy using autologous hematopoietic stem cells (HSC) that are corrected with the normal gene may have a beneficial effect on blood cell production or function, without the immunologic complications of allogeneic HSC transplantation. Childhood immunological diseases are highly favorable candidates for responses to gene therapy using HSC. Hemoglobinopathies, lysosomal and metabolic disorders and defects of hematopoietic stem and progenitor cells should also be ameliorated by gene therapy using autologous HSC. At present, gene therapy has been beneficial for patients with XSCID, ADA-deficient SCID and chronic granulomatous disease. The principle that partial marrow conditioning increases engraftment of gene-corrected HSC has been demonstrated. Clinical trials are being developed in Europe and the United States to treat several other genetic blood cell disorders. This progress is tempered by the serious complication observed in XSCID patients developing T lymphoproliferative disease. New methods for gene transfer (lentiviral and foamy viral vectors, semi-viral systems and gene correction) may retain or further increase the efficacy and decrease the risks from gene therapy using HSC. Ultimately, the relative benefits and risks of autologous gene therapy will be weighed against other available options (for example, allogeneic HSCT) to determine the treatment of choice.

The woodchuck hepatitis virus post-transcriptional regulatory element reduces readthrough transcription from retroviral vectors.

The woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) increases transgene expression from a variety of viral vectors, although the precise mechanism is not known. WPRE is most effective when placed downstream of the transgene, proximal to the polyadenylation signal. We hypothesized that WPRE likely reduces viral mRNA readthrough transcription by improving transcript termination, which in turn would increase viral titers and expression. Using a Cre-lox-mediated plasmid-based assay, we found significant readthrough transcription from gamma-retroviral vector (RV) long terminal repeat (wt RV-LTR) and RV LTR with a self-inactivating deletion (SIN RV-LTR). WPRE, when placed upstream of the RV LTRs, significantly reduced readthrough transcription. Readthrough, present at much lower levels with the SIN HIV-1 LV-LTR, was also reduced with WPRE. When placed in RV vectors, WPRE increased total RV genomic mRNA; and increased viral titers from transiently transfected 293T cells and stable PG13 producer cells by 7- to 15-fold. The mechanism of increased titers and expression was not due to increased nuclear mRNA export, increased rate of viral transcription or a significant increase in viral mRNA half-life. Our results showed that WPRE improved vector genomic transcript termination to increase titers and expression from RVs.

Gene therapy to inhibit xenoantibody production using lentiviral vectors in non-human primates.

Xenoantibodies to the gal alpha1,3 gal (gal) epitope impede the use of pig tissues for xenotransplantation, a procedure that may help overcome the shortage of human organ donors. Stable gal chimerism and tolerance to gal(+) hearts could be achieved in alpha1,3-galactosyltransferase (alpha1,3GT)(-/-) mice using lentiviral vectors expressing porcine alpha1,3GT, the enzyme that synthesizes the gal carbohydrate. In this study, we evaluated whether chimerism sufficient to inhibit anti-gal xenoantibody responses can be achieved using lentivectors in non-human primates. Rhesus macaques were transplanted with autologous, alpha1,3GT-transduced bone marrow (BM) following sublethal irradation. Simian immunodeficiency virus (SIV)- and human immunodeficiency virus (HIV)-1-derived lentiviral constructs were compared. Chimerism was observed in several hematopoietic lineages in all monkeys. Engraftment in animals receiving SIV-based alpha1,3GT constructs was similar to that achieved using the HIV-1-derived lentivector for the first 2 months post-transplantation, but increased thereafter to reach higher levels by 5 months. Upon immunization with porcine hepatocytes, the production of anti-gal immunoglobulin M xenoantibody was substantially reduced in the gal(+) BM recipients compared to controls. This study is the first to report the application of gene therapy to achieve low-level, long-term gal chimerism sufficient to inhibit production of anti-gal antibodies after immunization with porcine cells in rhesus macaques.

HIV-1-derived lentiviral vectors and fetal route of administration on transgene biodistribution and expression in rhesus monkeys.

The gene transfer efficiency of lentiviral vectors pseudotyped with vesicular stomatitis virus-glycoprotein (VSV-G) driven by the MND or CMV promoters and expressing the enhanced green fluorescent protein (EGFP) was investigated in fetal rhesus monkeys (Macaca mulatta) (N=21). Fetuses (50+/-10 days gestation; term 165+/-10 days) were injected under ultrasound guidance using an intraperitoneal (i.p.) or intrahepatic (i.h.) approach with a range of 1 x 10(7)-2 x 10(8) infectious particles/fetus. Analysis of transgene biodistribution and expression was performed in multiple tissues at 3-7 months postgene delivery using quantitative techniques. Overall, results indicated the following: (1) i.p. gene transfer at 40 days gestation resulted in a more diffuse distribution of the vector compared to administration at 60 days gestation; (2) vector biodistribution was similar after administration by the i.p. or i.h. routes; and (3) gene expression analysis in transduced tissues showed the presence of mRNA transcripts that correlated with the level of gene transfer. These studies suggest that fetal gene transfer using the i.p. and i.h. routes results in prolonged transduction and expression of the transgene in multiple tissues.

Time course of bioluminescent signal in orthotopic and heterotopic brain tumors in nude mice.

In vivo bioluminescence imaging is becoming increasingly popular. Quantification of bioluminescence signals requires knowledge of the variability and reproducibility of this technique. The objective of this study was to analyze the time course of luminescent signal emitted from firefly luciferase-expressing tumors in two locations, following luciferin injection and at different times after tumor cell implantation. Knowledge of the kinetics of the bioluminescent signals is required for the reliable quantification and comparison of signal during longitudinal studies. The kinetics of bioluminescence was evaluated in orthotopic and heterotopic brain tumors in mice using a human brain tumor cell line constitutively expressing luciferase. Tumor cells were implanted in the brains and flanks of the animals, and whole-body images revealing tumor location were obtained. Tumor burden was monitored over time by the quantitation of photon emission. The magnitude of bioluminescence measured in vivo varied with time after the injection of luciferin, as well as with dose, which necessitated that the comparison of the quantitative results take into consideration the time after injection. Heterotopic and orthotopic tumors exhibited significantly different time courses; however, time after implantation as characterized by kinetic studies performed on days 4 and 14 after cell implantation revealed no significant differences in orthotopic tumors. Future quantitative longitudinal studies must take into account the differences in the kinetics of different models.

Comparison of gene transfer efficiencies and gene expression levels achieved with equine infectious anemia virus- and human immunodeficiency virus type 1-derived lentivirus vectors.

This report compares gene transfer efficiencies as well as durations and levels of gene expression for human immunodeficiency virus (HIV) and equine infectious anemia virus (EIAV) lentiviral vectors in a variety of human cell types in vitro. EIAV and HIV vectors transduced equivalent numbers of proliferating and G1/S- and G2/M-arrested cells, and both had very low efficiencies of transduction into G0-arrested cells. Analysis of the levels of both the enhanced green fluorescent protein (EGFP) and mRNA demonstrated that the HIV-transduced cells expressed greater levels of EGFP protein and RNA than the EIAV-transduced cells. Measurements of vector-derived EGFP RNA half-lives were fourfold higher with the HIV vector than with the EIAV vector. Long-term culture of EIAV-transduced human cells showed a significant decrease in the number of cells expressing the transgene; however, no corresponding loss was found in EIAV-transduced equine cells. In contrast, only a moderate decrease in the number of transgene-expressing cells was seen with the HIV vectors. Taken together, these results demonstrate that the EIAV vectors transduced human cells with efficiencies similar to those of the HIV vectors. However, our data indicate that transgene expression from EIAV vectors is limited by the instability of vector-derived RNA transcripts and silencing of the EIAV vectors over time.

Lentiviral vector gene transfer into fetal rhesus monkeys (Macaca mulatta): lung-targeting approaches.

We previously reported the efficiency of gene transfer in fetal monkeys using retroviral vectors and an intraperitoneal (IP) approach. Here, we explored intrapulmonary administration to determine whether gene transfer can be limited to the developing lung. The HIV-1-derived lentiviral vector (VSV-G pseudotyped; 1 x 10(7) infectious particles/fetus), using the enhanced green fluorescent protein (EGFP) as a reporter, was directly injected into fetal lung with ultrasound guidance (n=4; 55 or 70 days gestation; term 165+/-10 days). Fetuses were monitored sonographically, fetal/maternal blood samples collected during gestation, and four of four healthy newborns were delivered at term. All lung lobes were positive for the transgene (< or = 1%) when assessed by PCR, and transgene expression was observed by direct fluorescence microscopy and flow cytometry. The results of this study show the following: (1) successful gene transfer in fetal monkeys using an intrapulmonary approach; (2) less transduction of non-pulmonary tissues with gene transfer at 70 days gestation compared with 55 days gestation or use of an IP approach; (3) that the pulmonary epithelium was EGFP-positive by immunohistochemistry; and (4) no evidence of transplacental transport of vector sequences or antibody responses in the dams. The results of these investigations indicate the efficiency of fetal gene transfer by intrapulmonary delivery, and emphasize the importance of the fetal monkey as a preclinical model system for exploring in utero genetic treatment strategies for pulmonary disorders.

Gene therapy for genetic haematological disorders and immunodeficiencies.

Gene transfer and autologous transplantation of haematopoietic stem cells (HSCs) from patients with genetic haematological disorders and immunodeficiencies could provide the same benefits as allogeneic HSC transplantation, without the attendant immunological complications. Inefficient gene delivery to human HSCs has imposed the major limitation to successful application of gene therapy. A recently reported clinical trial of gene transfer into HSCs of infants with X-linked severe combined immunodeficiency (SCID) has achieved immune restoration because of the selective outgrowth of the gene-corrected lymphocytes. Newer methods for manipulating HSCs may lead to efficacy for other disorders. The problems and progress in this area are reviewed herein.

Rhesus monkey model for fetal gene transfer: studies with retroviral- based vector systems.

Many life-threatening conditions that can be diagnosed early in gestation may be treatable in utero using gene therapy. In order to determine in utero gene transfer efficiency and safety, studies were conducted with fetal rhesus monkeys as a model for the human. Included in these studies were Moloney murine leukemia virus (MLV)-based amphotropic retrovirus, vesicular stomatitis virus-G (VSV-G) pseudotyped MLV, and a VSV-G pseudotyped HIV-1-based vector, all expressing the enhanced green fluorescent protein (EGFP) as a reporter gene and driven by a cytomegalovirus-immediate early promoter (N = 16). Rhesus monkey fetuses were administered viral vector supernatant preparations by the intraperitoneal (ip) (N = 14) or intrahepatic (ih) (N = 2) routes via ultrasound guidance at 55 +/- 5 days gestation (late first trimester; term 165 +/- 10 days). Fetuses were monitored sonographically, specimens were collected prenatally and postnatally, and tissue harvests were performed at birth or 3 or 6 months postnatal age (3-10 months post-gene transfer). PCR analyses demonstrated that transduced cells were present at approximately 1.2% in peripheral blood mononuclear cells from fetuses administered amphotropic MLV, <0.5% in fetuses receiving MLV/VSV-G, and approximately 4.2% for the lentiviral vector, which decreased to 2% at birth. Hematopoietic progenitors showed that overall (mean of all time points assessed), approximately 25% of the collected colonies were positive for the EGFP transgene with the lentiviral vector, which was significantly greater than results achieved with the MLV-based vector systems (4-9%; P < or = 0.001-0.016). At necropsy, 0.001-10% of the total genomic DNA was positive for EGFP in most tissues for all groups. EGFP-positive fluorescent cells were found in cell suspensions of thymus, liver, spleen, lymph nodes, cerebral cortex, and bone marrow (0.5-6%). Overall, the results of these studies have shown: (1) healthy infants expressing vector sequences up to 10 months post-gene transfer, (2) fetal primate administration of retroviral vectors results in gene transfer to multiple organ systems, (3) the highest level of gene transfer to hematopoietic progenitors was observed with the lentiviral vector system, and (4) there was no evidence of transplacental transfer of vector sequences into the dams. The rhesus monkey is an important preclinical primate model system for exploring gene transfer approaches for future applications in humans.

Hematopoietic stem cell transplantation for severe combined immune deficiency.

Hematopoietic stem cell transplantation (HSCT) has been the definitive therapy for severe combined immune deficiency (SCID) since the first successful transplant for SCID in 1968. Improvements in the use of HSCT to treat patients with SCID are continuing. For example, during the last 5 years, the first successful in-utero HSCT, and the first success with gene therapy have occurred in patients with SCID. Debate still continues about the role of pretransplantation therapy for SCID patients, and the biology of post-HSCT immune reconstitution is under investigation.

Gene therapy for pediatric AIDS.

Gene therapy is an experimental treatment modality under investigation for applications to HIV-1 infection. We have developed retroviral vectors carrying anti-HIV-1 genes, demonstrated that these genes cause significant suppression of HIV-1 replication in cultures of primary hematopoietic cells, and performed a clinical trial in pediatric AIDS patients. Four HIV-1-infected children and adolescents underwent bone marrow harvest from which CD34+ cells were isolated and transduced by a retroviral vector carrying an RRE decoy gene. The cells were re-infused into the subjects, without complications, showing that gene transfer in pediatric AIDS patients in safe and feasible. However, gene-containing leukocytes in the peripheral blood were seen only at a low level and only in the first months following cell infusion. To attain some degree of efficacy, it will be necessary to achieve a higher level of gene transfer and to obtain sustained gene expression. We are currently developing new gene transfer methods and vectors designed to improve the results in future trials. If it becomes possible to reach the ideal goal of producing high percentages of T lymphocytes and monocytic cells that are resistant to HIV-1 infection, gene therapy could serve as a complement to antiretroviral drug therapy and help to sustain immunologic function.

Lentiviral vectors for efficient delivery of CD80 and granulocyte-macrophage- colony-stimulating factor in human acute lymphoblastic leukemia and acute myeloid leukemia cells to induce antileukemic immune responses.

Cell vaccines engineered to express immunomodulators have shown feasibility in eliminating leukemia in murine models. Vectors for efficient gene delivery to primary human leukemia cells are required to translate this approach to clinical trials. In this study, second-generation lentiviral vectors derived from human immunodeficiency virus 1 were evaluated, with the cytomegalovirus (CMV) promoter driving expression of granulocyte-macrophage-colony-stimulating factor (GM-CSF) and CD80 in separate vectors or in a bicistronic vector. The vectors were pseudotyped with vesicular stomatitis virus G glycoprotein and concentrated to high titers (10(8)-10(9) infective particles/mL). Human acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic myeloid leukemia cell lines transduced with the monocistronic pHR-CD80 vector or the bicistronic pHR-GM/CD vector became 75% to 95% CD80 positive (CD80(+)). More important, transduction of primary human ALL and AML blasts with high-titer lentiviral vectors was consistently successful (40%-95% CD80(+)). The average amount of GM-CSF secretion by the leukemia cell lines transduced with the pHR-GM-CSF monocistronic vector was 2182.9 pg/10(6) cells per 24 hours. Secretion was markedly lower with the bicistronic pHR-GM/CD vector (average, 225.7 pg/10(6) cells per 24 hours). Lower amounts of CMV-driven messenger RNA were detected with the bicistronic vector, which may account for its poor expression of GM-CSF. Primary ALL cells transduced to express CD80 stimulated T-cell proliferation in an autologous mixed lymphocyte reaction. This stimulation was specifically blocked with monoclonal antibodies reactive against CD80 or by recombinant cytotoxic T-lymphocyte antigen 4-immunoglobulin fusion protein. These results show the feasibility of efficiently transducing primary leukemia cells with lentiviral vectors to express immunomodulators to elicit antileukemic immune responses. (Blood. 2000;96:1317-1326)

Intrakines--evidence for a trans-cellular mechanism of action.

Human CXCR4 is the receptor for the CXC chemokine SDF-1alpha and also acts as a coreceptor for T lymphotropic HIV-1 strains. Blocking the surface expression of this receptor via an intrakine approach has recently been shown to efficiently prevent HIV-1 infection of T cells. The CXC-chemokine gene is fused to an endoplasmic reticulum retention signal (KDEL) that retains the newly synthesized chemokine and its receptor within the cell, where both are subsequently degraded. We constructed MoMuLV-based vectors containing the SDF-KDEL construct driven by the "MND" long terminal repeat, using eGFP as a marker gene (MND-SDF-KDEL-IRES-eGFP) and a control vector (MND-X-IRES-eGFP). CEM human T lymphoblastic leukemia cells were transduced with the intrakine vector or the control vector. We detected a marked downregulation of CXCR4 expression in the cells transduced with the intrakine vectors as opposed to the cells transduced with the control vector. However, the eGFP-negative fraction of the cells transduced with the intrakine vector displayed the same CXCR4 downregulation as the eGFP-positive fraction, suggesting an effect in trans. The possibility of this being due to eGFP being silenced while SDF-KDEL was still expressed was excluded by Southern and Northern blot analyses. Upon cultivating the control cells with supernatant of the cells transduced with the intrakine vector, we observed a downregulation of CXCR4 expression on the control cells. Experiments using rhSDF-1alpha showed downregulation by the supernatant to be comparable to that achieved by the exogenous addition of 30 ng/ml SDF-1alpha. To assess the bioactivity of the secreted substance in the supernatant, a chemotaxis assay was performed. The transmigration observed was, once again, within the range of that achieved by the addition of 30 ng/ml SDF-1alpha. We conclude that the intrakine SDF-KDEL, apart from acting within the cell, is also in part secreted and causes the downregulation of the receptor by acting like a secreted chemokine.

Critical factors influencing stable transduction of human CD34(+) cells with HIV-1-derived lentiviral vectors.

Lentiviral vectors have been proposed as a more efficient alternative to Moloney murine leukemia virus-based retroviral vectors for transduction of human hematopoietic progenitors and stem cells. These studies were designed to evaluate the conditions that influence transduction frequency of CD34(+) progenitors, with the goal of optimizing efficiency of stable gene transfer with lentiviral vectors. CD34(+) human cord blood cells and 293 cells were transduced with a human immunodeficiency virus (HIV)-1 derived lentiviral vector pseudotyped with vesicular stomatitis virus glycoprotein and carrying an internal human cytomegalovirus promoter driving enhanced green fluorescent protein (eGFP) expression. Using fluorescence-activated cell sorting analysis of eGFP, we observed pseudotransduction beginning at the time of vector addition and lasting up to 24 h in CD34(+) cells and up to 72 h in 293 cells. Integrase-defective lentiviral vector caused transient eGFP expression for up to 10 days in CD34(+) cells and for up to 14 days in 293 cells. Protamine sulfate conferred no increase in transduction efficiency of CD34(+) cells on fibronectin-coated plates. Transduction frequency was related directly to vector concentration and not to multiplicity of infection across the ranges tested. First- and second-generation lentiviral vectors transduced CD34(+) cells equally, demonstrating a lack of dependence on HIV-1 accessory proteins. These findings will be useful for the optimal utilization of this new class of vectors for transduction of human hematopoietic stem cells.

BTK mediated apoptosis, a possible mechanism for failure to generate high titer retroviral producer clones.

BACKGROUND: It has been shown previously that mutations in the cytoplasmic protein kinase, Bruton's tyrosine kinase (BTK) lead to X-linked agammaglobulinemia, an inherited primary immunodeficiency, thus making it a potential candidate for gene therapy. METHODS: Producer cell lines using retroviral BTK constructs were generated and retroviral titers determined. Southern blot analysis was performed to check for pro-viral integrity in the respective clones. Furthermore, cotransfection of green fluorescent protein (GFP) with BTK expression plasmids was used in HeLa cells to establish and characterize the role of BTK in apoptosis. RESULTS: Following the attempt to generate retroviral producer clones by conventional methods, we observed that the BTK gene is deleted from neomycin-resistant high titer clones. We show that BTK mediated apoptosis in GP#E86 and HeLa cells. Furthermore, membrane targeting and kinase activity are required for this effect. In addition, BTK induced apoptosis could be inhibited by using a specific inhibitor for p38 mitogen-activated protein kinase (MAPK), SB203580. CONCLUSION: Failure to generate retroviral producer clones may be caused by the induction of apoptosis mediated by the therapeutic gene product.