Gene transfer to hematopoietic cells--the clinical experience

Lentiviral Based Gene Transduction and Promoter Studies in Human Hematopoietic Stem Cells (hHSCs)

Human hematopoietic stem cells (hHSCs) have enormous potential for clinical use in cell-based therapies, especially as a gene delivery system. Moreover, lentiviral transduction in stem cells is very often associated with low transduction efficiency and low levels of foreign gene expression. Therefore, it is important to analyze vector and promoter systems that can generate robust foreign gene expression in these cells. In this study, we evaluated and compared the ability of different commercially available promoters to drive the expression of exogenous reporter genes in hHSCs and evaluated the effect of different doses of stem cell growth factors on the expression of transgenes. We used lentivirus based vector system carrying the following promoters: 1) Human cytomegalovirus (CMV) promoter, 2) Simian virus 40 (SV40) promoter, 3) mammalian Ubiquitin C (UBC) promoter and 4) cellular polypeptide chain elongation factor 1 alpha (EF1) promoter. EF1 and CMV promoters robustly drove the expression of green fluorescence protein (GFP) reporter gene, while SV40 and UBC promoters induced very low level of GFP expression. Lentivectors containing EF1 and CMV promoters showed high-level stable GFP expression in human cord blood stem cells for 6 weeks period after post transduction. CD133+ hHSCs stimulated with higher concentration of growth factors exhibited enhancement of transduction rate. Cord blood derived CD133+ hHSCs could be effectively transduced with lentivectors under CMV or EF-1 promoters for the expression of foreign gene

The evolution of gene therapy in X-linked severe combined immunodeficiency

OBJECTIVES

To review the evolution of gene therapy in infants with X-linked severe combined immunodeficiency (XL-SCID) and to evaluate the current challenges facing this evolving field.

DATA SOURCES

The MEDLINE, OVID, CINAHL, and HealthSTAR databases were searched to identify pertinent articles using the following keywords: gene therapy, XL-SCID, bone marrow transplant, and viral vectors.

STUDY SELECTION

Journal articles were selected for their relevance to human gene therapy in patients with XL-SCID.

RESULTS

Gene therapy with a retrovirus-derived vector has been used to treat 20 patients with XL-SCID internationally. Although most patients derived improvements in T- and B-cell immune numbers and function, severe adverse effects have occurred. After gene therapy, 5 of the 20 patients developed leukemia. This outcome has been associated with insertion of the corrected gene near the T-cell proto-oncogene LMO2. One of the 5 patients subsequently died.

CONCLUSIONS

Within the past decade, effective improvements in vectorology and cell culture conditions have resulted in clinical success in some infants with SCID and have revived interest after many years of setbacks. However, clinical success and significant adverse events have been reported in patients with XL-SCID who have undergone gene therapy using a retroviral vector. As extensive research into improving safety through vector development and monitoring of gene therapy continues, further progress in gene therapy development can be anticipated.

Serial transplantations in nonobese diabetic/severe combined immunodeficiency mice of transduced human CD34+ cord blood cells: efficient oncoretroviral gene transfer and ex vivo expansion under serum-free conditions

Stable oncoretroviral gene transfer into hematopoietic stem cells (HSCs) provides permanent genetic disease correction. It is crucial to transplant enough transduced HSCs to compete with and replace the defective host hemopoiesis. To increase the number of transduced cells, the role of ex vivo expansion was investigated. For a possible clinical application, all experiments were carried out in serum-free media. A low-affinity nerve growth factor receptor (LNGFR) pseudotyped murine retroviral vector was used to transduce cord blood CD34(+) cells, which were then expanded ex vivo. These cells engrafted up to three generations of serially transplanted nonobese diabetic/severe combined immunodeficiency mice: 54.26% +/- 5.59%, 19.05% +/- 2.01%, and 6.15% +/- 5.16% CD45(+) cells from primary, secondary, and tertiary recipient bone marrow, respectively, were LNGFR(+). Repopulation in secondary and tertiary recipients indicates stability of transgene expression and long-term self-renewal potential of transduced HSCs, suggesting that retroviral gene transfer into HSCs, followed by ex vivo expansion, could facilitate long-term engraftment of genetically modified HSCs.

Differential response of primitive human CD34- and CD34+ hematopoietic cells to the Notch ligand Jagged-1

Recent reports indicate that activation of the Notch signaling pathway delays the differentiation of hematopoietic progenitors, suggesting that Notch may be used to develop novel ex vivo culture conditions for the expansion of primitive cells to be used in clinical transplantation. Here, we compare Notch expression and the effects of Jagged-1 treatment on highly purified subfractions of primitive CD34+ and CD34- human hematopoietic cells. Unlike response of cultured CD34+ cells, Jagged-1 treatment did not enhance the proliferation of CD34- cells, or promote differentiation of CD34- cells into CD34+ cells. While CD34+ and AC133-CD34- cells were shown to express all known forms of Notch receptors, Notch-3 and Notch-4 were not detected in AC133+CD34- cells. Similarly, CD34+ progeny of differentiated CD34- cells did not upregulate Notch-3 or Notch-4 upon differentiation, although transcripts for these genes were expressed in CD34+ arising from CD34+ CD38- parents, suggesting that the Notch receptor expression is tightly and differentially controlled. Fringe, known to inhibit Notch signaling in response to specific Notch ligands, was expressed in parent CD34- and CD34+ cells as well as their CD34+ progeny. We suggest that the inability of primitive CD34- cells to positively respond to Jagged-1 may be due in part to the absence of Notch-3 and Notch-4. Taken together, our study illustrates functional distinctiveness of the primitive CD34- subsets to CD34+ counterparts in relation to Jagged-1 response, and represents the first demonstration of a molecular difference among de novo isolated CD34+ compared to in vitro generated CD34+ cells arising from primitive CD34- or CD34+ parents.

Stem cell transplantation and gene therapy for HIV-related lymphomas

The treatment of patients with HIV-related non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD) is less successful than in the non-HIV setting, in part due to the aggressive character of these lymphomas but also due to the underlying HIV infection. High-dose therapy with stem cell transplantation has been used with success in the HIV-negative lymphoma setting for high-risk or relapsed disease. However, for patients with HIV-NHL and HIV-HD, ultimately the chance for long-term lymphoma-free survival also depends on successful control of the HIV infection. Gene therapy approaches may provide the opportunity for this long-term control. Herein, we describe the use of high-dose chemotherapy with stem cell rescue in conjunction with current and future gene therapy approaches for the treatment of HIV-associated lymphomas.

Hematologic Aspects of HIV/AIDS

This review addresses various aspects of HIV infection pertinent to hematology, including the consequences of HIV infection on specific aspects of hematopoiesis and an update on the current biologic, epidemiologic and therapeutic aspects of AIDS-related lymphoma and Hodgkin's disease. The results of the expanding use of progenitor cell transplantation in HIV infected patients are also reviewed. In Section I, Dr. Scadden reviews the basis for HIV dysregulation of blood cell production, focusing on the role of the stem cell in HIV disease. T cell production and thymic function are discussed, with emphasis placed upon the mechanisms of immune restoration in HIV infected individuals. Results of clinical and correlative laboratory studies are presented. In Section II, Dr. Levine reviews the recent epidemiologic trends in the incidence of lymphoma, since the widespread availability of highly active anti-retroviral therapy (HAART). The biologic aspects of AIDS-lymphoma and Hodgkin's disease are discussed in terms of pathogenesis of disease. Various treatment options for these disorders and the role of concomitant anti-retroviral and chemotherapeutic intervention are addressed. Drs. Zaia and Krishnan will review the area of stem cell transplantation in patients with AIDS related lymphoma, presenting updated information on clinical results of this procedure. Additionally, they report on the use of gene therapy, with peripheral blood CD34+ cells genetically modified using a murine retrovirus, as a means to treat underlying HIV infection. Results of gene transfer experiments and subsequent gene marking in HIV infected patients are reviewed.

Oncoretroviral gene transfer to NOD/SCID repopulating cells using three different viral envelopes

BACKGROUND

The aim of this study was to investigate gene transfer to human umbilical cord blood (CB) CD34(+)/CD38(low) and NOD/SCID repopulating cells using oncoretroviral vectors and to compare the transduction efficiency using three different viral envelopes.

METHODS

CB cells were transduced on Retronectin using an MSCV-based vector with the gene for GFP (MGIN), which was packaged into three different cell lines giving different envelopes: PG13-MGIN (GALV), 293GPG-MGIN (VSV-G) or AM12-MGIN (amphotropic).

RESULTS

Sorted CD34(+)/CD38(low) cells were efficiently transduced after 3 days of cytokine stimulation and the percentage of GFP-positive cells was 61.8+/-6.6% (PG13-MGIN), 26.9+/-3.5% (293GPG-MGIN), and 39.3+/-4.8% (AM12-MGIN). For transplantation experiments, CD34(+) cells were pre-stimulated for 2 days before transduction on Retronectin preloaded with vector and with the addition of 1/10th volume of viral supernatant on day 3. On day 4, the expanded equivalent of 2.5x10(5) cells was injected into irradiated NOD/SCID mice. All three pseudotypes transduced NOD/SCID repopulating cells (SRCs) equally well in the presence of serum, but engraftment was reduced when compared with freshly thawed cells. Simultaneous transduction with all three vector pseudotypes increased the gene transfer efficiency to SRCs but engraftment was significantly impaired. There were difficulties in producing amphotropic vectors at high titers in serum-free medium and transduction of CD34(+) cells using VSV-G-pseudotyped vectors under serum-free conditions was very inefficient. In contrast, transduction with PG13-MGIN under serum-free conditions resulted in the maintenance of SRCs during transduction, high levels of engraftment (29.3+/-6.6%), and efficient gene transfer to SRCs (46.2+/-4.8%).

CONCLUSIONS

The best conditions for transduction and engraftment of CB SRCs were obtained with GALV-pseudotyped vectors using serum-free conditions.

Correction of cross-linker sensitivity of Fanconi anemia group F cells by CD33-mediated protein transfer

Studies have previously described the feasibility of receptor-mediated protein transfer in a cell culture model of Fanconi anemia (FA) group C. This study explores the versatility of this approach by using an antibody single-chain fusion protein to correct the phenotypic defect in FA group F cells. A 68.5-kd chimeric protein (His-M195FANCF) was expressed, consisting of a His tag, a single-chain antibody to the myeloid antigen CD33, and the FANCF protein, as well as a 43-kd His-FANCF fusion protein lacking the antibody motif, in Escherichia coli. The nickel-agarose-purified His-M195FANCF protein bound specifically to the surface of HeLa cells transfected with CD33 and internalized through vesicular structures. The fusion protein, but not CD33, sorted to the nucleus, consistent with the known nuclear localization of FANCF. No similar binding or internalization was observed with His-FANCF. Pretreatment of the transfected cells with chloroquine abolished nuclear accumulation, but there was little change with brefeldin A, indicating a minimal if any role for the Golgi apparatus in mediating transport from endosomes to the cytosol and the nucleus. The intracellular half-life of His-M195FANCF was approximately 160 minutes. Treatment of CD33-transfected FA group F lymphoblastoid cells with 0.1 mg/mL His-M195FANCF conferred resistance to mitomycin C. No similar protection was noted in CD33(-) parental cells or CD33(+) FA cells belonging to groups A and C. These results demonstrate that antibody-directed, receptor-mediated protein transfer is a versatile method for the delivery of biologically active proteins into hematopoietic cells.

Lentiviral-mediated gene transfer into haematopoietic stem cells

OBJECTIVES

Lentiviral vectors can transduce nondividing cells. As most haematopoietic stem cells (HSCs) are nondividing in vivo, lentiviral vectors are promising viral vectors to transfer genes into HSCs.

DESIGN AND SETTING

We have used HIV-1 based lentiviral vectors containing the green fluorescent protein (GFP) gene to transduce umbilical cord blood CD34+ and CD34+/CD38- cells prior to transplantation into NOD/SCID mice.

RESULTS

High level engraftment of human cells was obtained and transgene expression was seen in both myeloid and lymphoid lineages. Bone marrow from the primary transplant recipients mice was transplanted into secondary recipients. GFP expression was seen in both lymphoid and myeloid cells in the secondary recipients 6 weeks posttransplantation. Human haematopoietic progenitor colonies were grown from both primary and secondary recipients. Over 50% of the haematopoietic colonies in these recipients were positive for the GFP transgene by PCR. Following inverse PCR, amplified fragments were sequenced and integration of the vector into human genomic DNA was demonstrated. Several vectors containing different internal promoters were tested in NOD/SCID mice that had been transplanted with transduced CD34+ and CD34+/CD38- cells. The elongation factor-1alpha (EF-1alpha) promoter gave the highest level of expression, both in the myeloid and lymphoid progeny of the engrafting cells.

CONCLUSIONS

These data collectively indicate that candidate human HSCs can be efficiently transduced with lentiviral vectors and that the transgene is highly expressed in their progeny cells.

Clinical Gene Therapy in Hematology: Past and Future

Gene transfer into hematopoietic cells using viral vectors has focused mostly on lymphocytes and hematopoietic stem cells (HSCs). HSCs have been considered particularly important as target cells because of their pluripotency and ability to reconstitute hematopoiesis after myeloablation and transplantation. HSCs are believed to have the ability to live a long time, perhaps a lifetime, in the recipient following bone marrow transplantation. Genetic correction of HSCs can therefore potentially last a lifetime and permanently cure hematologic disorders in which genetic deficiencies cause the pathology. Oncoretroviral vectors have been the main vectors used for HSCs because of their ability to integrate into the chromosomes of their target cells. Gene-transfer efficiency of murine HSCs is high using oncoretroviral vectors. In contrast, gene-transfer efficiency using the same viral vectors to transduce human HSCs or HSCs from large animals has been much lower. Although these difficulties may have several causes, the main reason for the low efficiency of human HSC transduction with oncoretroviral vectors is probably because of the nondividing nature of HSCs. Murine HSCs can be easily stimulated to divide in culture, whereas it is more problematic to stimulate human HSCs to divide rapidly in vitro. Because oncoretroviral vectors require dividing target cells for successful nuclear import of the preintegration complex and subsequent integration of the provirus, only the dividing fraction of the target cells can be transduced. This review focuses on gene transfer into human hematopoietic cells, particularly human HSCs. We review the clinical studies that have been reported, including the recent successful gene therapy for X-linked severe combined immunodeficiency. We discuss how the gene-transfer efficiency of human HSCs can be improved using oncoretroviral and lentiviral vectors.

Lentiviral gene transfer into primary and secondary NOD/SCID repopulating cells

The ability of lentiviral vectors to transfer genes into human hematopoietic stem cells was studied, using a human immunodeficiency virus 1 (HIV-1)–derived vector expressing the green fluorescence protein (GFP) downstream of the phosphoglycerate kinase (PGK) promoter and pseudotyped with the G protein of vesicular stomatitis virus (VSV). High-efficiency transduction of human cord blood CD34+cells was achieved after overnight incubation with vector particles. Sixteen to 28 percent of individual colony-forming units granulocyte-macrophage (CFU-GM) colonies derived from cord blood CD34+ cells were positive by polymerase chain reaction (PCR) for the GFP gene. The transduction efficiency of SCID-repopulating cells (SRC) within the cord blood CD34+population was assessed by serial transplantation into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. When 400 000 cord blood CD34+ cells were transplanted into primary recipients, all primary and secondary recipients contained and expressed the transgene. Over 50% of CFU-GM colonies derived from the bone marrow of these primary and secondary recipients contained the vector on average as determined by PCR. Transplantation of transduced cells in limiting dilution generated GFP+ lymphoid and myeloid progeny cells that may have arisen from a single SRC. Inverse PCR analysis was used to amplify vector-chromosomal junctional fragments in colonies derived from SRC and confirmed that the vector was integrated. These results show that lentiviral vectors can efficiently transduce very primitive human hematopoietic progenitor and stem cells.

Lentiviral gene transfer into primary and secondary NOD/SCID repopulating cells

The ability of lentiviral vectors to transfer genes into human hematopoietic stem cells was studied, using a human immunodeficiency virus 1 (HIV-1)–derived vector expressing the green fluorescence protein (GFP) downstream of the phosphoglycerate kinase (PGK) promoter and pseudotyped with the G protein of vesicular stomatitis virus (VSV). High-efficiency transduction of human cord blood CD34+cells was achieved after overnight incubation with vector particles. Sixteen to 28 percent of individual colony-forming units granulocyte-macrophage (CFU-GM) colonies derived from cord blood CD34+ cells were positive by polymerase chain reaction (PCR) for the GFP gene. The transduction efficiency of SCID-repopulating cells (SRC) within the cord blood CD34+population was assessed by serial transplantation into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. When 400 000 cord blood CD34+ cells were transplanted into primary recipients, all primary and secondary recipients contained and expressed the transgene. Over 50% of CFU-GM colonies derived from the bone marrow of these primary and secondary recipients contained the vector on average as determined by PCR. Transplantation of transduced cells in limiting dilution generated GFP+ lymphoid and myeloid progeny cells that may have arisen from a single SRC. Inverse PCR analysis was used to amplify vector-chromosomal junctional fragments in colonies derived from SRC and confirmed that the vector was integrated. These results show that lentiviral vectors can efficiently transduce very primitive human hematopoietic progenitor and stem cells.

Retroviral transfer of the glucocerebrosidase gene into CD34+ cells from patients with Gaucher disease: in vivo detection of transduced cells without myeloablation

Retroviral gene transfer of the glucocerebrosidase gene to hematopoietic progenitor and stem cells has shown promising results in animal models and corrected the enzyme deficiency in cells from Gaucher patients in vitro. Therefore, a clinical protocol was initiated to explore the safety and feasibility of retroviral transduction of peripheral blood (PB) or bone marrow (BM) CD34+ cells with the G1Gc vector. This vector uses the viral LTR promoter to express the human glucocerebrosidase cDNA. Three adult patients have been entered with follow-up of 6-15 months. Target cells were G-CSF-mobilized and CD34-enriched PB cells or CD34-enriched steady state BM cells, and were transduced ex vivo for 72 hr. Patient 1 had PB cells transduced in the presence of autologous stromal marrow cells. Patient 2 had PB cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. Patient 3 had BM cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. At the end of transduction, the cells were collected and infused immediately without any preparative treatment of the patients. The transduction efficiency of the CD34+ cells at the end of transduction was approximately 1, 10, and 1 for patients 1, 2, and 3, respectively, as estimated by semiquantitative PCR on bulk samples and PCR analysis of individual hematopoietic colonies. Gene marking in vivo was demonstrated in patients 2 and 3. Patient 2 had vector-positive PB granulocytes and mononuclear bone marrow cells at 1 month postinfusion and positive PB mononuclear cells at 2 and 3 months postinfusion. Patient 3 had a positive BM sample at 1 month postinfusion but was negative thereafter. These results indicate that gene-marked cells can engraft and persist for at least 3 months postinfusion, even without myeloablation. However, the level of corrected cells (<0.02%) is too low to result in any clinical benefit, and glucocerebrosidase enzyme activity did not increase in any patient following infusion of transduced cells. Modifications of vector systems and transduction conditions, along with partial myeloablation to allow higher levels of engraftment, may be necessary to achieve beneficial levels of correction in patients with Gaucher disease.