Safe and efficient generation of recombinant retroviruses with amphotropic and ecotropic host ranges

Site-specific integration of targeted DNA into animal cell genomes

Novel genetically engineered retroviral vectors and targeting plasmids are described that enable the site-specific targeting of exogenous DNA into the genomes of cultured animal cells. The protocol involves the transduction of competent cells by a chimeric retroviral vector containing a transcription unit composed of two linked cassettes: an upstream marker gene under the control of the viral 5' LTR; and a downstream reporter trap containing a strong promoter 5' to a 48bp yeast FRT element. When cells containing such integrated units are co-transfected with a plasmid encoding yeast FLP recombinase and a promoterless targeting plasmid containing a reporter cDNA tract 3' to an homologous FRT element, the targeting plasmid recombines at the chromosomally preconfigured FRT site, and a new hemizygous function is introduced into the downstream cassette. These reagents provide a new portable system for site-specific targeting of chemically modified genes into uniform and unique sites in genomically integrated transcription units.

Diminished prohormone convertase 3 expression (PC1/PC3) inhibits progastrin post-translational processing

Gastrin is initially synthesized as a large precursor that requires endoproteolytic cleavage by a prohormone convertase (PC) for bioactivation. Gastric antral G-cells process progastrin at Arg(94)Arg(95) and Lys(74)Lys(75) residues generating gastrin heptadecapeptide (G17-NH(2)). Conversely, duodenal G-cells process progastrin to gastrin tetratriacontapeptide (G34-NH(2)) with little processing at Lys(74)Lys(75). Both tissues express PC1/PC3 and PC2. Previously, we demonstrated that heterologous expression of progastrin in an endocrine cell line that expresses PC1/PC3 and little PC2 (AtT-20) resulted in the formation of G34-NH(2). To confirm that PC1/PC3 was responsible for progastrin processing in AtT-20 cells and capable of processing progastrin in vivo we coexpressed either human wild-type (Lys(74)Lys(75)) or mutant (Arg(74)Arg(75), Lys(74)Arg(75), and Arg(74)Lys(75)) progastrins in AtT-20 cells with two different antisense PC1/PC3 constructs. Coexpression of either antisense construct resulted in a consistent decrease in G34-NH(2) formation. Gastrin mRNA expression and progastrin synthesis were equivalent in each cell line. Although mutation of the Lys(74)Lys(75) site within G34-NH(2) to Lys(74)Arg(75) resulted in the production of primarily G17-NH(2) rather than G34-NH(2), inhibition of PC1/PC3 did not significantly inhibit processing at the Lys(74)Arg(75) site. We conclude that PC1/PC3 is a progastrin processing enzyme, suggesting a role for PC1/PC3 progastrin processing in G-cells.

Progress with retroviral gene vectors

Retroviral vectors have become a standard tool for gene transfer technology. Compared with other gene transfer systems, retroviral vectors have several advantages, including their ability to transduce a variety of cell types, to integrate efficiently into the genomic DNA of the recipient cells and to express the transduced gene at high levels. The relatively well understood biology of retroviruses has made possible the development of packaging cell lines which provide in trans all the viral proteins required for viral particle formation. The design of different types of packaging cells has evolved to reduce the possibility of helper virus production. The host range of retroviruses has been expanded by pseudotyping the vectors with heterologous viral glycoproteins and receptor-specific ligands. The development of lentivirus vectors has allowed efficient gene transfer to quiescent cells. This review describes different strategies adopted for developing vectors to be used in gene therapy applications.

RNase P ribozymes selected in vitro to cleave a viral mRNA effectively inhibit its expression in cell culture

An in vitro selection procedure was used to select RNase P ribozyme variants that efficiently cleaved the sequence of the mRNA encoding thymidine kinase of herpes simplex virus 1. Of the 45 selected variants sequenced, 25 ribozymes carried a common mutation at nucleotides 224 and 225 of RNase P catalytic RNA from Escherichia coli (G(224)G(225) --> AA). These selected ribozymes exhibited at least 10 times higher cleavage efficiency (k(cat)/K(m)) than that derived from the wild type ribozyme. Our results suggest that the mutated A(224)A(225) are in close proximity to the substrate and enhance substrate binding of the ribozyme. When these ribozyme variants were expressed in herpes simplex virus 1-infected cells, the levels of thymidine kinase mRNA and protein were reduced by 95-99%. Our study provides the first direct evidence that RNase P ribozyme variants isolated by the selection procedure can be used for the construction of gene-targeting ribozymes that are highly effective in tissue culture. These results demonstrate the potential for using RNase P ribozymes as gene-targeting agents against any mRNA sequences, and using the selection procedure as a general approach for the engineering of RNase P ribozymes.

The antiangiogenesis effect of interleukin 12 during early growth of human pancreatic cancer in SCID mice

Interleukin 12 (IL-12) is a heterodimeric cytokine that exerts a potent antitumor effect through its pleiotropic actions. It was recently reported that IL-12 has also a potent antiangiogenic effect through the induction of IFN-gamma, which triggers the production of chemokines such as IP-10 that has been shown to have antiangiogenesis properties. In this study we transfected the IL-12 gene into a human pancreatic adenocarcinoma cell line (PK-1). PK-1 cells transfected with the green fluorescence protein (gfp) gene were used as positive controls. The in vitro growth curve and in vivo tumor growth of transfectants (IL-12/PK-1 and gfp/PK-1) were compared with those of parental cells. The SCID mice used in this study were administered antiasialo GM-1 Ab (100 microg, i.p., twice weekly) to deplete the remaining immunoeffector cells, NK cells. Using a skinfold chamber model, we observed and recorded tumor angiogenesis by intravital microscopy. In vitro growth of IL-12/PK-1 and gfp/PK-1 cells was not different from that of wild-type PK-1 cells (wt/PK-1). However, IL-12 transfected PK-1 cells did not develop into tumors as did the wt/PK-1 cells after subcutaneous inoculation in antiasialo GM-1 Ab administered SCID mice. The growth of IL-12/PK-1 tumors was restored in mice treated with anti-IL-12 antibody. We found that IL-12/PK-1, in contrast to gfp/PK-1 and wt/PK-1, failed to initiate an angiogenic response, as observed in the skinfold chamber model. These results indicate that the antiangiogenesis effect of IL-12 alone, without immune system involvement, is sufficient to block the growth of human pancreatic cancer.

Participation of endogenously produced interferon gamma in interleukin 4-mediated tumor rejection

To elucidate the molecular mechanism underlying IL-4-induced tumor rejection, we challenged mice with a mouse adenocarcinoma cell line, colon 26, genetically engineered to express constitutively IL-4 gene (colon 26/IL-4). Immunocompetent BALB/c mice rejected colon 26/IL-4 cells but not parental cells or cells transduced with a control gene (colon 26/control). Moreover, on rechallenge, parental cells and colon 26/control cells were rejected by normal BALB/c mice that had previously rejected colon 26/IL-4. However, both nude and severe combined immunodeficiency (SCID) mice failed to reject colon 26/IL-4 as well as parental or colon 26/control cells. In contrast, nude mice did reject colon 26/IL-4 after transfer of lymphocytes obtained from the draining lymph nodes of BALB/c mice injected with colon 26/IL-4. These results indicate that challenging mice with colon 26/IL-4 tumor cells resulted in the generation of memory cytotoxic T lymphocytes in the draining lymph nodes. At 3 days after the challenge, IFN-gamma, IL-12 p35, and p40 mRNA expression was selectively enhanced in the draining lymph nodes of mice bearing colon 26/IL-4 cells. Finally, mice deficient in the IFN-gamma gene did not reject colon 26/IL-4 cells. These results suggest that IL-4-induced memory cytotoxic T lymphocyte generation requires IFN-gamma production in the draining lymph nodes, in order to generate a protective immune response.

Inhibition of interleukin 7 receptor signaling by antigen receptor assembly

After the productive rearrangement of immunoglobulin (Ig) heavy chain genes, precursor (pre-)B lymphocytes undergo a limited number of cell divisions in response to interleukin (IL)-7. Here, we present evidence that this phase of IL-7-dependent expansion is constrained by an inhibitory signal initiated by antigen receptor assembly. A line of pre-B cells from normal murine bone marrow that expresses a mu heavy chain with a D-proximal V(H)7183.2 region divides continuously in IL-7. IL-7 responsiveness ceases upon differentiation to the mu(1), kappa(1) stage, despite continuing expression of the IL-7 receptor (IL-7R), suggesting that antigen receptor assembly inhibits IL-7 responsiveness. This is confirmed by introduction of a rearranged lambda light chain gene, which inhibits proliferative signaling through the IL-7R. Inhibition is specific to the IL-7R, because it is overcome by replacement of the IL-7R cytoplasmic domain with corresponding sequences from the closely related IL-2Rbeta chain. Alteration of a single tyrosine residue, Tyr410, in the IL-7R cytoplasmic domain to phenylalanine also prevents the inhibition of proliferation after antigen receptor assembly. Thus, the loss of IL-7 responsiveness after antigen receptor assembly may be mediated through the recruitment of an inhibitory molecule to this residue. Our findings identify a novel mechanism that limits cytokine-dependent proliferation during B lymphopoiesis. This mechanism may be essential for the proper regulation of peripheral B lymphocyte numbers.

Inhibition of apoptosis in human tumour cells by the tumour-associated serpin, SCC antigen-1

The squamous cell carcinoma antigen (SCC Ag) is a tumour-associated protein and a member of the serine protease inhibitor (serpin) family. The SCC Ag has been used as a serologic tumour marker for SCC progression, and its elevated serum levels are a risk factor for disease relapse. However, the biologic significance of this intracytoplasmic protein in cancer cells remains unknown. In this report, we demonstrated that apoptosis induced by 7-ethyl-10-hydroxycamptothecin, tumour necrosis factor-alpha (TNF-alpha) or interleukin (IL)-2-activated natural killer (NK) cells was significantly inhibited in tumour cells transduced with the SCC Ag-1 cDNA, as compared to control cells in vitro. Also, inhibition of the SCC Ag-1 expression in tumour cells by transfection of antisense SCC Ag-1 cDNA was accompanied by significantly increased sensitivity of these cells to apoptosis induced by etoposide or TNF-alpha. The mechanism of protection of tumour cells from apoptosis involved inhibition of caspase-3 activity and/or upstream proteases. In vivo, tumour cells overexpressing the SCC Ag-1 formed significantly larger tumours in nude mice than the SCC Ag-1-negative controls. Thus, overexpression of the SCC Ag-1, a member of the serpin family, in human cancer cells contributed to their survival by mediating protection from drug-, cytokine- or effector cell-induced apoptosis.

Bone marrow-derived dendritic cells pulsed with tumor homogenate induce immunity against syngeneic intracerebral glioma

To evaluate the efficacy and toxicity of dendritic cell (DC) based therapy for intracerebral gliomas, we utilized a cell line derived from an astrocytoma that arose spontaneously in a VM/Dk mouse. This astrocytoma mirrors human gliomas phenotypically, morphologically and secretes transforming growth factor (TGF)-betas, immunosuppressive cytokines secreted by human gliomas. Systemic vaccination of mice with DCs pulsed with tumor homogenate followed by intracranial tumor challenge produced a > 160% increase in median survival (p = 0.016) compared with mice vaccinated with PBS or unpulsed DCs (p = 0.083). Fifty percent of mice treated with pulsed DCs survived long-term. Immunologic memory was demonstrated by survival of mice rechallenged with tumor. Both cell-mediated and humoral immunity was induced. On histological examination only focal areas of demyelination at the tumor implantation site were present. There was no evidence that autoimmune encephalomyelitis was induced by DC vaccination. Therefore, in a murine model, vaccination with DCs pulsed with glioma tumor homogenate is a safe and effective therapy against a syngeneic glioma located in the immunologically privileged central nervous system (CNS).

Retrovirally mediated IFN-beta transduction of macrophages induces resistance to HIV, correlated with up-regulation of RANTES production and down-regulation of C-C chemokine receptor-5 expression

Constitutive expression of IFN-beta by HIV target cells may be an alternative or complementary therapeutic approach for the treatment of AIDS. We show that macrophages derived from CD34+ cells from umbilical cord blood can be efficiently transduced by a retroviral vector carrying the IFN-beta coding sequence. This results in resistance to infection by a macrophage-tropic HIV type 1, as shown by the drastic reduction in the HIV DNA copy number per cell and in p24 release. Moreover, IFN-beta transduction totally blocked secretion of proinflammatory cytokines after HIV infection. The constitutive IFN-beta production also resulted in an increased production of IL-12 and IFN-gamma Th1-type cytokines and of the beta-chemokines macrophage-inflammatory protein-1alpha, macrophage-inflammatory protein-1beta, and RANTES. RANTES was found to be involved in the HIV resistance observed, and this was correlated with a down-regulation of the CCR-5 HIV entry coreceptor. These results demonstrate the feasibility and the efficacy of such IFN-beta-mediated gene therapy. In addition to inhibiting HIV replication, IFN-beta transduction could have beneficial immune effects in HIV-infected patients by favoring cellular immune responses.

Improved safety and titre of murine leukaemia virus (MLV)-based retroviral vectors

Many retroviral vectors based on murine leukaemia virus (MLV) contain the first 420 nucleotides of the gag gene, as this was reported to increase vector titre by increasing the efficiency of RNA packaging. In this study, deletion of this gag sequence from its original location did not decrease the titre of two retroviral vectors, pBabe puro and MFG-S-. The two vectors could be improved by replacing the gag sequence with a CTE from Mason-Pfizer monkey virus (MPMV). This substitution improved vector titre, while eliminating a region of homology between vector and packaging constructs. Gene Therapy (2000) 7, 300-305.

Trafficking and proteolytic release of epidermal growth factor receptor ligands are modulated by their membrane-anchoring domains

Ligands that bind to the epidermal growth factor (EGF) receptor are initially synthesized as integral membrane proteins that are released from the cell surface by regulated proteolysis. To study the role of the membrane-anchoring domain in ligand release, we made two artificial ligands. The first possessed the membrane-anchoring domain from EGF whereas the second had the corresponding domain from heparin binding EGF-like growth factor (HB-EGF). Both ligands lacked amino-terminal extensions, and were epitope-tagged at the carboxyl terminus. Following stable expression in human mammary epithelial cells, their cellular localization and rate of proteolytic release were examined. We found that constructs with the membrane-anchoring domain from EGF were found primarily at the cell surface and displayed a relatively high rate of constitutive release. Constructs with the HB-EGF membrane-anchoring domain displayed a higher internalized fraction and a very low rate of constitutive release. The two ligand constructs also displayed different patterns of stimulated release. Proteolysis of the chimera with the HB-EGF membrane-anchoring domain was stimulated by activation of protein kinase C, but release of EGF from constructs with the EGF membrane-anchoring domain was insensitive to this. Calcium ionophores, calmodulin antagonists, and tyrosine phosphatase inhibitors stimulated the release of both ligands. Furthermore, the release of the two constructs showed different sensitivity to metalloprotease inhibitors. Despite a large fold-increase in ligand proteolysis following cell stimulation, only a small fraction of total cell-associated ligand was released per hour. Our results show that the membrane-anchoring domain of EGF-like ligands can specify both their localization and proteolytic processing. The structures of the membrane-anchoring region of this class of ligands can thus regulate their activity.

Genetic modification of cultured skin substitutes by transduction of human keratinocytes and fibroblasts with platelet-derived growth factor-A

Gene therapy promises the potential for improved treatment of cutaneous wounds. This study evaluated whether genetically modified cultured skin substitutes can act as vehicles for gene therapy in an athymic mouse model of wound healing. Human keratinocytes and fibroblasts were genetically engineered by retroviral transduction to overexpress human platelet-derived growth factor-A chain. Three types of skin substitutes were prepared from collagen-glycosaminoglycan substrates populated with fibroblasts and keratinocytes: HF-/HK-, containing both unmodified fibroblasts and keratinocytes; HF-/HK+, containing unmodified fibroblasts and modified keratinocytes; and HF+/HK-, containing modified fibroblasts and unmodified keratinocytes. Skin substitutes were cultured for two weeks before grafting to full-thickness wounds on athymic mice. The modified skin substitutes secreted significantly elevated levels of platelet-derived growth factor throughout the culture period. Expression of retroviral platelet-derived growth factor-A mRNA was maintained after grafting to mice, and was detected in all HF-/HK+ grafts and one HF+/HK- graft at two weeks after surgery. Although no differences were seen between control and modified grafts, the results suggest that genetically modified cultured skin substitutes can be a feasible mechanism for cutaneous gene therapy. The cultured skin model used for these studies has advantages over other skin analogs containing only epidermal cells; because it contains both fibroblasts and keratinocytes, it therefore offers greater opportunities for genetic modification and potential modulation of wound healing.

Avian reticuloendotheliosis virus strain A and spleen necrosis virus do not infect human cells

Spleen necrosis virus (SNV) and Reticuloendotheliosis virus strain A (REV-A) belong to the family of reticuloendotheliosis viruses and are 90% sequence related. SNV-derived retroviral vectors produced by the REV-A-based D17.2G packaging cell line were shown to infect human cells (H.-M. Koo, A. M. C. Brown, Y. Ron, and J. P. Dougherty, J. Virol. 65:4769-4776, 1991), while similar vectors produced by another SNV-based packaging cell line, DSH134G, are not infectious in human cells (reviewed by R. Dornburg, Gene Ther. 2:301-310, 1995). Here we describe a careful reevaluation of the infectivity of vectors produced from the most commonly used REV-A- or SNV-based packaging cells obtained from various sources with, among them, one batch of D17.2G packaging cells obtained from the American Type Culture Collection. None of these packaging cells produced vectors able to infect human cells. Thus, contrary to previously published data, we conclude that REV-based vectors are not infectious in human cells.

CD4(+) T helper cells engineered to produce latent TGF-beta1 reverse allergen-induced airway hyperreactivity and inflammation

T helper 2 (Th2) cells play a critical role in the pathogenesis of asthma, but the precise immunological mechanisms that inhibit Th2 cell function in vivo are not well understood. Using gene therapy, we demonstrated that ovalbumin-specific (OVA-specific) Th cells engineered to express latent TGF-beta abolished airway hyperreactivity and airway inflammation induced by OVA-specific Th2 effector cells in SCID and BALB/c mice. These effects correlated with increased concentrations of active TGF-beta in the bronchoalveolar lavage (BAL) fluid, demonstrating that latent TGF-beta was activated in the inflammatory environment. In contrast, OVA-specific Th1 cells failed to inhibit airway hyperreactivity and inflammation in this system. The inhibitory effect of TGF-beta-secreting Th cells was antigen-specific and was reversed by neutralization of TGF-beta. Our results demonstrate that T cells secreting TGF-beta in the respiratory mucosa can indeed regulate Th2-induced airway hyperreactivity and inflammation and suggest that TGF-beta-producing T cells play an important regulatory role in asthma.

IL-12 Drives IFN-γ-Dependent Autoimmune Kidney Disease in MRL-Fas lpr Mice

IL-12 is secreted by kidney tubular epithelial cells in autoimmune MRL-Faslpr mice before renal injury and increases with advancing disease. Because IL-12 is a potent inducer of IFN-γ, the purpose of this study was to determine whether local provision of IL-12 elicits IFN-γ-secreting T cells within the kidney, which, in turn, incites injury in MRL-Faslpr mice. We used an ex vivo retroviral gene transfer strategy to construct IL-12-secreting MRL-Faslpr tubular epithelial cells (IL-12 “carrier cells”), which were implanted under the kidney capsule of MRL-Faslpr mice before renal disease for a sustained period (28 days). IL-12 “carrier cells” generated intrarenal and systemic IL-12. IL-12 fostered a marked, well-demarcated accumulation of CD4, CD8, and double negative (CD4−CD8− B220+) T cells adjacent to the implant site. We detected more IFN-γ-producing T cells (CD4 > CD8 > CD4−CD8− B220+) at 28 days (73 ± 14%) as compared with 7 days (20 ± 8%) after implanting the IL-12 “carrier cells;” the majority of these cells were proliferating (60–70%). By comparison, an increase in systemic IL-12 resulted in a diffuse acceleration of pathology in the contralateral (unimplanted) kidney. IFN-γ was required for IL-12-incited renal injury, because IL-12 “carrier cells” failed to elicit injury in MRL-Faslpr kidneys genetically deficient in IFN-γ receptors. Furthermore, IFN-γ “carrier cells” elicited kidney injury in wild-type MRL-Faslpr mice. Taken together, IL-12 elicits autoimmune injury by fostering the accumulation of IFN-γ-secreting CD4, CD8, and CD4−CD8− B220+ T cells within the kidney, which, in turn, promote a cascade of events culminating in autoimmune kidney disease in MRL-Faslpr mice.

Retrovirus-mediated transfer of human alpha-galactosidase A gene to human CD34+ hematopoietic progenitor cells

Fabry disease, caused by a deficiency of lysosomal enzyme alpha-galactosidase A (alpha-gal A), is one of the inherited disorders potentially treatable by gene transfer to hematopoietic stem cells. In this study, a high-titer amphotropic retroviral producer cell line, MFG-alpha-gal A, was established. CD34+ cells from normal umbilical cord blood were transduced by centrifugal enhancement. The alpha-gal A activity in transduced cells increased 3.6-fold above the activity in nontransduced cells. Transduction efficiency measured by PCR for the integrated alpha-gal A cDNA in CFU-GM colonies was in the range of 42-88% (average, 63%). The expression of functional enzyme in TFI erythroleukemia was sustained for as long as cells remained in culture (84 days) and for 28 days in LTC-IC cultures of CD34+ cells. The ability of the transduced CD34+ cells to secrete the enzyme and to correct enzyme-deficient Fabry fibroblasts was assessed by cocultivation of these cells. The enzyme was secreted into the medium from transduced CD34+ cells and taken up by Fabry fibroblasts through mannose 6-phosphate receptors. These findings suggest that genetically corrected hematopoietic stem/progenitor cells can be an enzymatic source for neighboring enzyme-deficient cells, and can potentially be useful for gene therapy of Fabry disease.

The HIV Nef protein alters Ca(2+) signaling in myelomonocytic cells through SH3-mediated protein-protein interactions

Human immunodeficiency virus Nef plays an important role in AIDS pathogenesis. In addition to the well known down-regulation of cell surface receptors (CD4, MHCI), Nef is able to alter cellular signaling. Of particular interest for this study is the ability of Nef to bind with a very high affinity to SH3 domains of myelomonocyte-specific protein-tyrosine kinases of the Src family (Src-like PTK). We have therefore investigated Ca(2+) signaling in HL60 cells retrovirally transduced with wild type Nef or with a Nef mutant deficient in the SH3-interacting proline-rich motif (Nef((PXXP)4(-))). In differentiated HL60 cells, Nef markedly altered cellular Ca(2+) signaling; the amount of intracellularly stored Ca(2+) was increased, and as a consequence, store-operated Ca(2+)-influx was decreased. This effect was not observed in undifferentiated HL60 cells or in CEM T-lymphocytes and correlated with the differentiation-induced up-regulation of Src-like PTK. The Nef effect on Ca(2+) signaling depended entirely on the integrity of its PXXP motif. The Src-like PTK p56/59(hck) co-immunoprecipitated with both Nef and with the inositol 1,4,5-trisphosphate receptor, providing a possible mechanistic link between the viral protein and intracellular Ca(2+) stores of the host cell. Collectively, our results demonstrate that the human immunodeficiency virus 1 Nef protein manipulates intracellular Ca(2+) stores through SH3-mediated interactions in myelomonocytic cells.

Differentiation-induced insulin secretion from nonendocrine cells with engineered human proinsulin cDNA

To investigate the effects of differentiation on insulin secretion from engineered nonendocrine cells, modified human proinsulin cDNA (INS/fur) was transfected to THP-1 monocyte and C2C12 myoblast cell lines. When THP-1 was differentiated into macrophages with phorbol ester, the insulin secretion rate was increased by 3.1-fold. This increase in insulin secretion is accompanied by a 17.6-fold increase in the processing efficiency of the modified human proinsulin and by a 3.5-fold increase in the abundance of furin mRNA. In addition, differentiation of C2C12 into myotubes, which can be induced by changing the serum, showed a 9.9-fold increase in insulin secretion and was accompanied by a 1.6-fold increase in the abundance of furin mRNA. The involvement of posttranslational processing and the exocytotic process in differentiation-induced insulin secretion could lead to the possibility of regulation of insulin secretion from genetically engineered cells.

Simultaneous Ex Vivo Expansion of Cytomegalovirus and Epstein-Barr Virus–Specific Cytotoxic T Lymphocytes Using B-Lymphoblastoid Cell Lines Expressing Cytomegalovirus pp65

Cytomegalovirus (CMV) infection and Epstein-Barr virus (EBV)-induced lymphoproliferative disease are serious complications associated with allogeneic stem cell transplantation. Immunotherapy using ex vivo expanded, virus-specific cytotoxic T lymphocytes (CTL) has been explored and proven to be effective in therapeutic or prophylactic regimens for CMV and EBV infections. To generate CTL specific for both CMV and EBV, we engineered EBV-transformed B-lymphoblastoid cell lines (BLCL) to express CMV pp65 for use as antigen-presenting cells (APC). BLCL were transduced with a recombinant retrovirus encoding pp65, the immunodominant CMV polypeptide. Western blot analysis and immunocytochemistry confirmed the expression of pp65 in the transduced cells. Peripheral blood mononuclear cells (PBMC) from healthy CMV seropositive donors were stimulated with autologous pp65-expressing BLCL weekly for 3 weeks. Chromium release assays showed that the resulting CTL cultures possessed specific cytotoxicity against EBV and CMV. Recombinant vaccinia viruses encoding individual CMV peptides were used to demonstrate that this CMV-specific cytotoxicity was specific for pp65. Assays on CD4- and CD8-depleted CTL fractions indicated that CD8+ CTL mediated the pp65-specific cytotoxicity. These CMV/EBV-specific CTL recognized CMV- and EBV-infected targets sharing HLA class I antigens, but not HLA mismatched targets. Our results demonstrate that BLCL can be used as APC to stimulate expansion of EBV- and CMV-specific CTL simultaneously. These findings have potential implications for posttransplant CMV and EBV immunotherapy in recipients of allogeneic stem cell transplants.

Simultaneous Ex Vivo Expansion of Cytomegalovirus and Epstein-Barr Virus–Specific Cytotoxic T Lymphocytes Using B-Lymphoblastoid Cell Lines Expressing Cytomegalovirus pp65

Cytomegalovirus (CMV) infection and Epstein-Barr virus (EBV)-induced lymphoproliferative disease are serious complications associated with allogeneic stem cell transplantation. Immunotherapy using ex vivo expanded, virus-specific cytotoxic T lymphocytes (CTL) has been explored and proven to be effective in therapeutic or prophylactic regimens for CMV and EBV infections. To generate CTL specific for both CMV and EBV, we engineered EBV-transformed B-lymphoblastoid cell lines (BLCL) to express CMV pp65 for use as antigen-presenting cells (APC). BLCL were transduced with a recombinant retrovirus encoding pp65, the immunodominant CMV polypeptide. Western blot analysis and immunocytochemistry confirmed the expression of pp65 in the transduced cells. Peripheral blood mononuclear cells (PBMC) from healthy CMV seropositive donors were stimulated with autologous pp65-expressing BLCL weekly for 3 weeks. Chromium release assays showed that the resulting CTL cultures possessed specific cytotoxicity against EBV and CMV. Recombinant vaccinia viruses encoding individual CMV peptides were used to demonstrate that this CMV-specific cytotoxicity was specific for pp65. Assays on CD4- and CD8-depleted CTL fractions indicated that CD8+ CTL mediated the pp65-specific cytotoxicity. These CMV/EBV-specific CTL recognized CMV- and EBV-infected targets sharing HLA class I antigens, but not HLA mismatched targets. Our results demonstrate that BLCL can be used as APC to stimulate expansion of EBV- and CMV-specific CTL simultaneously. These findings have potential implications for posttransplant CMV and EBV immunotherapy in recipients of allogeneic stem cell transplants.

Gene therapy for Parkinson's disease: review and update

Gene transfer technology is under exploration to find therapies for the treatment of Parkinson's disease (PD) and other neurodegenerative disorders. The technology of genetic transfer can also be used as a neurobiological tool to understand the role of various genes in animal models of neurodegeneration. We describe the general approaches to gene therapy for neurodegeneration, with specific attention to commonly used methodologies. Current gene therapy models for PD are then described in two parts: genetic transfer of the biosynthetic enzymes for dopamine synthesis, and genetic transfer of the genes encoding neurotrophic factors protective for dopaminergic neurones. Future strategies for the genetic treatment of PD, such as the introduction of genes to prevent apoptosis or to detoxify free radical species are also discussed. Limitations of current approaches, such as the length and regulation of transgene expression, as well as strategies to overcome those limitations, are emphasised where possible. Gene therapy remains a promising but as yet theoretical approach to the treatment of PD in humans. However, current results in animal models predict eventual therapeutic applications.

The role of the membrane-spanning domain sequence in glycoprotein-mediated membrane fusion

The role of glycoprotein membrane-spanning domains in the process of membrane fusion is poorly understood. It has been demonstrated that replacing all or part of the membrane-spanning domain of a viral fusion protein with sequences that encode signals for glycosylphosphatidylinositol linkage attachment abrogates membrane fusion activity. It has been suggested, however, that the actual amino acid sequence of the membrane-spanning domain is not critical for the activity of viral fusion proteins. We have examined the function of Moloney murine leukemia virus envelope proteins with substitutions in the membrane-spanning domain. Envelope proteins bearing substitutions for proline 617 are processed and incorporated into virus particles normally and bind to the viral receptor. However, they possess greatly reduced or undetectable capacities for the promotion of membrane fusion and infectious virus particle formation. Our results imply a direct role for the residues in the membrane-spanning domain of the murine leukemia virus envelope protein in membrane fusion and its regulation. They also support the thesis that membrane-spanning domains possess a sequence-dependent function in other protein-mediated membrane fusion events.

Expression of the beta2-subunit and apical localization of Na+-K+-ATPase in metanephric kidney

During kidney organogenesis, the Na+-K+-ATPase pump is not restricted to the basolateral plasma membrane of the renal epithelial cell but is instead either localized to the apical and lateral membrane sites of the early nephron or expressed in a nonpolarized distribution in the newly formed collecting ducts. The importance of Na+-K+-ATPase beta-subunit expression in the translocation of the Na+-K+-ATPase to the plasma membrane raises the question as to which beta-subunit isoform is expressed during kidney organogenesis. Immunocytochemical, Western analysis and RNase protection studies showed that both beta2-subunit protein and beta2 mRNA are expressed in the early gestation to midgestation human metanephric kidney. In contrast, although beta1 mRNA abundance is equivalent to that of the beta2-subunit in the metanephric kidney, the beta1-subunit protein was not detected in early to midgestation metanephric kidney samples. Immunocytochemical analysis revealed that both alpha1- and beta2-subunits were present in the apical epithelial plasma membranes of distal nephron segments of early stage nephrons, maturing loops of Henle, and collecting ducts during kidney development. We also detected a significant increase in alpha1 and beta1 mRNA after birth with a marked reduction in beta2 mRNA abundance associated with an increase in alpha1- and beta1-subunit proteins and loss of beta2 protein expression. These studies support the conclusion that the expression of the beta2-subunit in the fetal kidney may be an important mechanism controlling polarization of the Na+-K+-ATPase pump in the epithelia of the developing nephron during kidney organogenesis.

Retroviral transfer of human MDR1 gene to hematopoietic cells: effects of drug selection and of transcript splicing on expression of encoded P-glycoprotein

Protection of hematopoietic cells of patients undergoing anticancer chemotherapy by MDR1 gene transfer is currently being studied in clinical trials. From animal studies, it has been suggested that aberrant splicing due to cryptic donor and acceptor sites in the MDR1 cDNA could be a major reason for failure to obtain high-level expression of P-glycoprotein in bone marrow. We investigated effects of drug selection on protein expression levels and on splicing of MDR1 transcripts in murine bone marrow cells (BMCs) in vitro. To this end, retroviruses were generated through an identical plasmid, pHaMDR1/A, introduced into different packaging cells. GP + E86- but not PA317-derived producer cells were found to express truncated in addition to full-length message. In BMCs transduced with GP + E86-derived viruses, both messages were increased after treatment with colchicine or daunomycin. Similar results were obtained with NIH 3T3 fibroblasts. However, transduced and drug-selected BMCs displayed the spliced transcript even if the respective PA317-derived producer cells contained no truncated RNA as detected in transduced NIH 3T3 fibroblasts. Short-term drug selection in BMCs transduced with either ecotropic or amphotropic retroviruses resulted in a striking increase in P-glycoprotein expression. Thus, aberrant splicing failed to abrogate P-glycoprotein expression in BMCs. We also studied a vector in which MDR1 was coexpressed with glucocerebrosidase, using an internal ribosomal entry site. Although chemoprotection was less efficient than with pHaMDR1/A, augmentation of protein expression was observed at low selecting drug concentrations. Our study shows that drug selection can partially compensate for inefficient transduction of hematopoietic cells, and may help to develop strategies by which unstable expression of transduced genes can be overcome.

Rat embryonic myoblasts are restricted to forming primary fibres while later myogenic populations are pluripotent

Three populations of myoblasts, embryonic, foetal and adult, appear sequentially during myogenesis. The present study uses retroviruses to mark myoblasts clones in vivo from these populations. Myoblasts labelled at E15 (embryonic) contributed to primary fibres only. The majority of marked primary fibres were slow but a small number of clones contained marked primaries which were no longer slow at E19. Myoblasts labelled at E17 (foetal) fused with both primary and secondary fibres and most clones contained both fast and slow fibres. Similarly, adult myoblasts marked at P0 fused with all fibre types. These results indicate that embryonic myoblasts are restricted to producing only primary fibres which are initially slow but which can convert to being fast. Clones of foetal and adult myoblasts fuse with both primary and secondary fibres which may be either fast or slow.

Activation conditions determine susceptibility of murine primary T-lymphocytes to retroviral infection

BACKGROUND

Genetically modified T-lymphocytes are potential therapeutic agents for the treatment of various disorders. Successful retroviral infection of primary murine T-lymphocytes is a prerequisite to the study of adoptive cell therapies in a small animal model. The definition of factors controlling retroviral infection of T-lymphocytes would also be useful to better understand retroviral diseases. However, retroviral-mediated gene transfer into murine primary T-cells has remained elusive.

METHODS

In order to define the requirements for stable and efficient gene transfer in primary murine T-lymphocytes, we investigated factors capable of affecting retroviral infection. These include activation conditions (using mitogens or monoclonal antibodies), culture conditions (including media composition and cytokine addition), timing of viral exposure, retroviral receptor selection (ecotropic, amphotropic, or vesicular stomatitis virus G (VSV-G) glycoprotein receptor), and viral titer.

RESULTS

We show that efficient gene transfer can be achieved in murine T-lymphocytes, provided that a number of favorable conditions are met, in particular optimized T-cell activation conditions, optimal timing of infection, adequate interleukin-2 concentration and T-cell density, and a high viral titer. On a particulate basis, we find that ecotropic particles are more effective than amphotropic or VSV-G-pseudotyped particles, and recommend the use of a specifically selected retroviral packaging cell line. CD4+ T-cells are equally or more infectible than CD8+ lymphocytes, depending on the activation conditions. The Th1 and Th2 subsets are comparably susceptible to retroviral infection, in contrast to what has been reported in some instances of human T-cell infection by human immunodeficiency virus (HIV).

CONCLUSIONS

We establish conditions that enable efficient retroviral-mediated gene transfer in murine primary T-lymphocytes. T-lymphocytes are not uniformly susceptible to retroviral infection depending on the mode of T-cell activation. These findings have implications for devising approaches to the study of T-cell biology, adoptive cell therapies, and the pathophysiology of retroviral diseases in mouse models.

Contrasting effects of activating mutations of GalphaS and the thyrotropin receptor on proliferation and differentiation of thyroid follicular cells

The cyclic AMP pathway is a major regulator of thyrocyte function and proliferation and, predictably, its inappropriate activation is associated with a sub-set of human thyroid tumours. Activating mutations are, however, more common in the thyrotropin receptor (TSHR) than in its downstream transducer, Galphas. To investigate whether this reflects an inherent difference in their oncogenic potency, we compared the effects of retrovirally-transduced mutant (A623I) TSHR or (Q227L) Galphas (GSP), using the rat thyroid cell line FRTL5 and primary human thyrocytes. In FRTL5, expression of GSP or mutant (m) TSHR induced a 2 - 3-fold increase in basal levels of cAMP. This was associated with TSH-independent proliferation (assessed by both cell number and DNA synthesis) and function (as shown by increased expression of thyroglobulin (Tg) and the sodium/iodide symporter). In primary cultures, expression of mTSHR, but not GSP, consistently induced formation of colonies with epithelial morphology and thyroglobulin expression, capable of 10 - 15 population doublings (PD) compared to less than three in controls. Thus, while mTSHR and GSP exert similar effects in FRTL5, use of primary cultures reveals a major difference in their ability to induce sustained proliferation in normal human thyrocytes, and provides the first direct evidence that mTSHR is sufficient to initiate thyroid tumorigenesis.

Def-2, -3, -6 and -8, novel mouse genes differentially expressed in the haemopoietic system

To identify developmentally regulated genes during myeloid differentiation, a self-inactivating retroviral gene-trap vector carrying a beta-galactosidase-neomycin (SA/lacZ/neo) fusion gene was constructed and used to infect myeloid progenitor cells (FDCP-Mix A4). G418-resistant and beta-galactosidase positive cell lines (gene-trap integration [GTI] clones) were established and induced to differentiate in vitro into either macrophages or granulocytes. Expression of the trapped loci was monitored at a single-cell level by analysing the mature cell types for beta-galactosidase activity. All 37 GTI clones tested showed down-regulation either during granulocyte or both granulocytic and macrophage differentiation. The endogenous coding regions fused to the SA/lacZ/neo reporter gene were isolated from eight clones. Molecular analysis revealed that half of them represented novel mouse genes (def-2, -3, -6 and -8) which we confirmed to be differentially expressed in primary haemopoietic tissues. Database searches revealed no significant similarities for def-2 (associated with haemopoietic progenitors) and def-8 (expressed most strongly in peripheral leucocytes). Def-6, which is down-regulated upon the differentiation into myeloid as well as erythroid lineages, was found to be closely related but not identical with the recently described B-cell-specific switch recombinase SWAP-70. Def-3, which is down-regulated upon differentiation into granulocytes but expressed in progenitor cells and macrophages, defines a novel family of RNA binding proteins.

Acquired constitutive expression of interferon beta after gene transduction enhances human immunodeficiency virus type 1-specific cytotoxic T lymphocyte activity by a RANTES-dependent mechanism

CTL lines directed against HIV-1 antigens were generated from infected individuals and were transduced by the HMB-K(b)HuIFNbeta vector, resulting in low, constitutive expression of interferon beta (IFN-beta). The IFN-beta-transduced cells showed markedly increased HIV-1-specific, MHC class I-restricted CTL activity against HIV-1-LAI Gag, Pol, or Env antigens. This effect of IFN-beta was correlated with an overexpression of RANTES and completely abrogated by RANTES-blocking antibody. The present results provide the first evidence that IFN-beta transduction of CTL lines enhances HIV-specific cytotoxic activities through an upregulation of RANTES production. The efficient elimination of HIV-infected cells by IFN-beta-transduced CTL lines makes this gene therapy approach an attractive treatment for AIDS.

Intramuscular grafts of myoblasts genetically modified to secrete glial cell line-derived neurotrophic factor prevent motoneuron loss and disease progression in a mouse model of familial amyotrophic lateral sclerosis

Effects of ex vivo GDNF gene delivery on the degeneration of motoneurons were studied in the G1H transgenic mouse model of familial ALS carrying a human superoxide dismutase (SOD1) with a Gly93Ala mutation (Gurney et al., 1994). Retroviral vectors were made to produce human GDNF or E. coli beta-galactosidase (beta-Gal) by transient transfection of the Phoenix cell line and used to infect primary mouse myoblasts. In 6-week-old G1H mice, 50,000 myoblasts per muscle were injected bilaterally into two hindlimb muscles. Untreated G1H and wild-type mice served as additional controls. At 17 weeks of age, 1 week before sacrifice, these muscles were injected with fluorogold (FG) to retrogradely label spinal motoneurons that maintained axonal projections to the muscles. There were significantly more large FG-labeled alpha motoneurons at 18 weeks in GDNF-treated G1H mice than in untreated and beta-Gal-treated G1H mice. A morphometric study of motoneuron size distribution showed that GDNF shifted the size distribution of motoneurons toward larger cells compared with control G1H mice, although the average size and number of large motoneurons in GDNF-treated mice were less than that in wild-type mice. GDNF also prolonged the onset of disease, delayed the deterioration of performance in tests of motor behavior, and slowed muscle atrophy. Quantitative, real-time RT-PCR and PCR showed persistence of transgene mRNA and DNA in muscle for up to 12 weeks postgrafting. These observations demonstrate that ex vivo GDNF gene therapy in a mouse model of FALS promotes the survival of functional motoneurons, suggesting that a similar approach might delay the progression of neurodegeneration in ALS.

Complement-protected amphotropic retroviruses from murine packaging cells

The application of retroviruses generated from murine cells for in vivo gene therapy is restricted primarily because of the rapid inactivation of these viruses by the human complement system. To circumvent this disadvantageous property of murine retroviruses we have generated infectious amphotropic retroviruses that exhibit strong protection against human complement attack. The membrane of these viruses contains a fusion protein, DAFF2A, that is composed of the catalytic domain of the human complement regulatory protein (CRP) decay-accelerating factor (DAF) and the envelope protein of the amphotropic murine leukemia virus (MuLV) 4070A (EnvA). The fusion of two other CRPs, MCP and CD59, to the same amphotropic Env moiety did not lead to equivalent results. The fusion protein DAFF2A was stably expressed in mouse NIH 3T3-based helper cells and independently identified with either alpha-DAF MAb or alpha-Env PAb on the cell membrane. Western blot analysis confirmed the expected molecular weight of the fusion protein. Viral titers obtained from NIH 3T3 helper cell pools were 5 x 10(5) CFU for wild-type amphotropic EnvA virus and 1 x 10(5) CFU for DAFF2A virus, respectively. By blocking the catalytic domain of DAF by pretreatment with alpha-DAF MAb DAFF2A, recombinant virions could be converted to wild-type with respect to sensitivity against human serum. Since the method for producing virions that are protected against human serum should be applicable to any cell type it offers a novel tool for human in vivo gene therapy.

Correction of Uroporphyrinogen Decarboxylase Deficiency (Hepatoerythropoietic Porphyria) in Epstein-Barr Virus-Transformed B-Cell Lines by Retrovirus-Mediated Gene Transfer: Fluorescence-Based Selection of Transduced Cells

Hepatoerythropoietic porphyria (HEP) is an inherited metabolic disorder characterized by the accumulation of porphyrins resulting from a deficiency in uroporphyrinogen decarboxylase (UROD). This autosomal recessive disorder is severe, starting early in infancy with no specific treatment. Gene therapy would represent a great therapeutic improvement. Because hematopoietic cells are the target for somatic gene therapy in this porphyria, Epstein-Barr virus-transformed B-cell lines from patients with HEP provide a model system for the disease. Thus, retrovirus-mediated expression of UROD was used to restore enzymatic activity in B-cell lines from 3 HEP patients. The potential of gene therapy for the metabolic correction of the disease was demonstrated by a reduction of porphyrin accumulation to the normal level in deficient transduced cells. Mixed culture experiments demonstrated that there is no metabolic cross-correction of deficient cells by normal cells. However, the observation of cellular expansion in vitro and in vivo in immunodeficient mice suggested that genetically corrected cells have a competitive advantage. Finally, to facilitate future human gene therapy trials, we have developed a selection system based on the expression of the therapeutic gene. Genetically corrected cells are easily separated from deficient ones by the absence of fluorescence when illuminated under UV light.

Correction of Uroporphyrinogen Decarboxylase Deficiency (Hepatoerythropoietic Porphyria) in Epstein-Barr Virus-Transformed B-Cell Lines by Retrovirus-Mediated Gene Transfer: Fluorescence-Based Selection of Transduced Cells

Hepatoerythropoietic porphyria (HEP) is an inherited metabolic disorder characterized by the accumulation of porphyrins resulting from a deficiency in uroporphyrinogen decarboxylase (UROD). This autosomal recessive disorder is severe, starting early in infancy with no specific treatment. Gene therapy would represent a great therapeutic improvement. Because hematopoietic cells are the target for somatic gene therapy in this porphyria, Epstein-Barr virus-transformed B-cell lines from patients with HEP provide a model system for the disease. Thus, retrovirus-mediated expression of UROD was used to restore enzymatic activity in B-cell lines from 3 HEP patients. The potential of gene therapy for the metabolic correction of the disease was demonstrated by a reduction of porphyrin accumulation to the normal level in deficient transduced cells. Mixed culture experiments demonstrated that there is no metabolic cross-correction of deficient cells by normal cells. However, the observation of cellular expansion in vitro and in vivo in immunodeficient mice suggested that genetically corrected cells have a competitive advantage. Finally, to facilitate future human gene therapy trials, we have developed a selection system based on the expression of the therapeutic gene. Genetically corrected cells are easily separated from deficient ones by the absence of fluorescence when illuminated under UV light.

C/EBP Bypasses Granulocyte Colony-Stimulating Factor Signals to Rapidly Induce PU.1 Gene Expression, Stimulate Granulocytic Differentiation, and Limit Proliferation in 32D cl3 Myeloblasts

Within hematopoiesis, C/EBP is expressed only in myeloid cells, and PU.1 is expressed mainly in myeloid and B-lymphoid cells. C/EBP-deficient mice lack the neutrophil lineage and retain monocytes, whereas PU.1-deficient mice lack monocytes and have severely reduced neutrophils. We expressed a C/EBP-estrogen receptor ligand-binding domain fusion protein, C/EBPWT-ER, in 32D cl3 myeloblasts. 32D cl3 cells proliferate in interleukin-3 (IL-3) and differentiate to neutrophils in granulocyte colony-stimulating factor (G-CSF). In the presence of estradiol, C/EBPWT-ER induced morphologic differentiation and the expression of the myeloperoxidase, lactoferrin, and G-CSF receptor mRNAs. C/EBPWT-ER also induced a G1/S cell cycle block, with induction of p27 and Rb hypophosphorylation. bcr-ablp210 prevented 32D cl3 cell differentiation. Activation of C/EBP-ER in 32D-bcr-ablp210 or Ba/F3 B-lymphoid cells induced cell cycle arrest independent of terminal differentiation. C/EBPWT-ER induced endogenous PU.1 mRNA within 8 hours in both 32D cl3 and Ba/F3 cells, even in the presence of cycloheximide, indicating that C/EBP directly activates the PU.1 gene. However, activation of a PU.1-ER fusion protein in 32D cl3 cells induced myeloperoxidase (MPO) RNA but not terminal differentiation. Thus, C/EBP acts downstream of G-CSF and upstream of PU.1, p27, and potentially other factors to induce myeloblasts to undergo granulocytic differentiation and cell cycle arrest.

C/EBP Bypasses Granulocyte Colony-Stimulating Factor Signals to Rapidly Induce PU.1 Gene Expression, Stimulate Granulocytic Differentiation, and Limit Proliferation in 32D cl3 Myeloblasts

Within hematopoiesis, C/EBP is expressed only in myeloid cells, and PU.1 is expressed mainly in myeloid and B-lymphoid cells. C/EBP-deficient mice lack the neutrophil lineage and retain monocytes, whereas PU.1-deficient mice lack monocytes and have severely reduced neutrophils. We expressed a C/EBP-estrogen receptor ligand-binding domain fusion protein, C/EBPWT-ER, in 32D cl3 myeloblasts. 32D cl3 cells proliferate in interleukin-3 (IL-3) and differentiate to neutrophils in granulocyte colony-stimulating factor (G-CSF). In the presence of estradiol, C/EBPWT-ER induced morphologic differentiation and the expression of the myeloperoxidase, lactoferrin, and G-CSF receptor mRNAs. C/EBPWT-ER also induced a G1/S cell cycle block, with induction of p27 and Rb hypophosphorylation. bcr-ablp210 prevented 32D cl3 cell differentiation. Activation of C/EBP-ER in 32D-bcr-ablp210 or Ba/F3 B-lymphoid cells induced cell cycle arrest independent of terminal differentiation. C/EBPWT-ER induced endogenous PU.1 mRNA within 8 hours in both 32D cl3 and Ba/F3 cells, even in the presence of cycloheximide, indicating that C/EBP directly activates the PU.1 gene. However, activation of a PU.1-ER fusion protein in 32D cl3 cells induced myeloperoxidase (MPO) RNA but not terminal differentiation. Thus, C/EBP acts downstream of G-CSF and upstream of PU.1, p27, and potentially other factors to induce myeloblasts to undergo granulocytic differentiation and cell cycle arrest.

Functional consequences of amyloidosis mutation for gelsolin polypeptide -- analysis of gelsolin-actin interaction and gelsolin processing in gelsolin knock-out fibroblasts

Gelsolin, an actin-modulating protein, derived from a single gene exists in intracellular and secreted forms. A point mutation at position 187 of both forms of gelsolin causes familial amyloidosis of the Finnish type (FAF). Here, we expressed both isoforms of the wild-type and FAF mutant gelsolin in mouse embryonic gelsolin-null fibroblasts. We demonstrate that the FAF mutation does not interfere with the normal actin-modulating function of intracellular gelsolin, and that aberrant processing of secreted FAF gelsolin to FAF amyloid precursor takes place in the gelsolin-negative background. These results suggest that, in patients with FAF, symptoms are caused by the accumulation in their tissues of amyloid derived from plasma gelsolin and are not due to functional differences in cytoplasmic gelsolin.

Inhibition of NF2-negative and NF2-positive primary human meningioma cell proliferation by overexpression of merlin due to vector-mediated gene transfer

OBJECT

The absence of in vitro models of neurofibromatosis Type 2 (NF2)-defective meningiomas has limited investigative efforts to study the biological effects of this gene in the pathogenesis of these tumors. The goals of this report are to show that gene transfer vectors can efficiently express the wild-type NF2 transgene into primary meningioma cells and to determine effects on cellular proliferation.

METHODS

In this study, the authors have compared the transducing capacities of a retrovirus, an adenovirus, and a herpes simplex virus amplicon vector for use in primary human meningioma cells harvested from human tumors excised from patients with and without NF2. Transduction efficiencies with the latter vector approached 100% and it was selected to transfer the wild-type NF2 transgene into these cells. Western blot analysis confirmed that vector-mediated gene transfer mediated the expression of the NF2-encoded polypeptide merlin. Overexpression of merlin significantly inhibited the proliferation of both NF2-negative and NF2-positive human meningioma cells when compared to the proliferation of cells transduced with a control vector.

CONCLUSIONS

This study demonstrates the feasibility of using vector-mediated gene transfer to study wild-type NF2 gene function in short-term cultures of primary human meningioma cells.

Gene transfer approaches to the lysosomal storage disorders

The work summarized in this paper used animal and cell culture models systems to develop gene therapy approaches for the lysosomal storage disorders. The results have provided the scientific basis for a clinical trial of gene transfer to hematopoietic stem cells (HSC) in Gaucher disease which is now in progress. The clinical experiment is providing evidence of HSC transduction, competitive engraftment of genetically corrected HSC, expression of the GC transgene, and the suggestion of a clinical response. In this paper we will review the progress made in Gaucher disease and include how gene transfer might be studied in other lysosomal storage disorders.

Cytotoxic T lymphocytes define multiple peptide isoforms derived from the melanoma-associated antigen MART-1/Melan-A

Peptides derived from the melanoma-associated MART-1/Melan-A antigen are currently implemented in immunotherapy for inducing or augmenting T-cell responses directed against peptides expressed by autologous tumor cells in HLA-A2+ patients with melanoma. Here, we describe the specificity of the T-cell clone SK29-FFM1.1, which secretes GM-CSF in response to a panel of synthetic MART-1/Melan-A-derived peptides, including the naturally presented ILTVILGVL(32-40), but exhibits cytotoxicity and IFN-gamma secretion exclusively to the MART-1/Melan-A derived peptide AAGIGILTV(27-35). In addition, cytotoxic T-lymphocyte (CTL) clone SK29-FFM1.1 recognizes 3 different naturally processed and presented peptides on HLA-A2+ MART-1/Melan-A+ melanoma cells, as defined by cytotoxicity and IFN-gamma and GM-CSF secretion. Processing and presentation of MART-1/Melan-A peptides appears to be different in cells of non-melanocytic origin, as shown by the characterization of naturally presented peptides displayed by HLA-A2+ colorectal cancer cells transduced with a MART-1/Melan-A gene-containing retrovirus. Our data suggest that multiple epitopes, including ILTVILGVL and different isoforms of AAGIGILTV derived from MART-1/Melan-A may be naturally presented by melanoma cells to the immune system.

Gene therapy for canine alpha-L-iduronidase deficiency: in utero adoptive transfer of genetically corrected hematopoietic progenitors results in engraftment but not amelioration of disease

Canine alpha-L-iduronidase (iduronidase) deficiency is a model of the human lysosomal storage disorder mucopolysaccharidosis type I (MPS I). We used this canine model to evaluate the therapeutic potential of hematopoietic stem cell (HSC) gene therapy for enzyme deficiencies. In previous studies, iduronidase-deficient dogs infused with autologous marrow cells genetically modified to express iduronidase had long-term engraftment with provirally marked cells, but there was no evidence of proviral iduronidase expression or clinical improvement. The presence of humoral and cellular immune responses against iduronidase apparently abrogated the therapeutic potential of HSC gene therapy in these experiments. To evaluate HSC gene therapy for canine MPS I in the absence of a confounding immune response, we have now performed in utero adoptive transfer of iduronidase-transduced MPS I marrow cells into preimmune fetal pups. In three separate experiments, 17 midgestation fetal pups were injected with 0.5-1.5 x 10(7) normal or MPS I allogeneic long-term marrow culture (LTMC) cells transduced with neo(r)- or iduronidase-containing retroviral vectors. Nine normal and three MPS I pups survived the neonatal period and demonstrated engraftment of provirally marked progenitors at levels of up to 12% for up to 12 months. However, the proportion of provirally marked circulating leukocytes was approximately 1%. Neither iduronidase enzyme nor proviral-specific transcripts were detected in blood or marrow leukocytes of any MPS I dog. Humoral immune responses to iduronidase were not detected in neonates, even after "boosting" with autologous iduronidase-transduced LTMC cells. All MPS I dogs died at 8-11 months of age from complications of MPS I disease with no evidence of amelioration of MPS I disease. Our results suggest that iduronidase-transduced primitive hematopoietic progenitors can engraft in fetal recipients, contribute to hematopoiesis, and induce immunologic nonresponsiveness to iduronidase in MPS I dogs. However, the therapeutic potential of HSC gene transfer in this model of iduronidase deficiency appears to be limited by poor maintenance of proviral iduronidase gene expression and relatively low levels of genetically corrected circulating leukocytes.

Metalloprotease-mediated ligand release regulates autocrine signaling through the epidermal growth factor receptor

Ligands that activate the epidermal growth factor receptor (EGFR) are synthesized as membrane-anchored precursors that appear to be proteolytically released by members of the ADAM family of metalloproteases. Because membrane-anchored EGFR ligands are thought to be biologically active, the role of ligand release in the regulation of EGFR signaling is unclear. To investigate this question, we used metalloprotease inhibitors to block EGFR ligand release from human mammary epithelial cells. These cells express both transforming growth factor alpha and amphiregulin and require autocrine signaling through the EGFR for proliferation and migration. We found that metalloprotease inhibitors reduced cell proliferation in direct proportion to their effect on transforming growth factor alpha release. Metalloprotease inhibitors also reduced growth of EGF-responsive tumorigenic cell lines and were synergistic with the inhibitory effects of antagonistic EGFR antibodies. Blocking release of EGFR ligands also strongly inhibited autocrine activation of the EGFR and reduced both the rate and persistence of cell migration. The effects of metalloprotease inhibitors could be reversed by either adding exogenous EGF or by expressing an artificial gene for EGF that lacked a membrane-anchoring domain. Our results indicate that soluble rather than membrane-anchored forms of the ligands mediate most of the biological effects of EGFR ligands. Metalloprotease inhibitors have shown promise in preventing spread of metastatic disease. Many of their antimetastatic effects could be the result of their ability to inhibit autocrine signaling through the EGFR.

Gene therapy with autologous, interleukin 2-secreting tumor cells in patients with malignant melanoma

We vaccinated metastatic melanoma patients with irradiated, autologous melanoma cells genetically engineered to secrete interleukin 2 (IL-2) to investigate whether an anti-tumor immune response would be induced. Melanoma cell cultures were established from surgical specimens and were engineered to secrete IL-2 by infection with recombinant retrovirus. Twelve patients were vaccinated subcutaneously one, two, or three times with approximately 10(7) irradiated, autologous, IL-2-secreting tumor cells. Treatment was well tolerated, with local reactions at 11 of 24 injection sites and minor systemic symptoms of fever and headache after 6 injections. One patient developed anti-tumor DTH after the first vaccination and showed an increased response after the second vaccination. Anti-autologous tumor CTLs could be detected prevaccination in the peripheral blood of seven patients and their activity increased after vaccination in four patients. No UICC-defined clinical responses were seen, but three patients had stable disease for 7-15 months, one of whom has not yet progressed (15+ months). Thus, patient vaccination with autologous, genetically engineered tumor cells is feasible and safe. Anti-tumor DTH and CTLs can be induced in some patients with such a vaccine.

Expression of major histocompatibility complex antigens in squamous cell carcinomas of the head and neck: effects of interferon gene transfer

The effect of retroviral-mediated interferon-gamma (IFN-gamma) gene transfer on major histocompatibility complex (MHC) class I and II antigen expression was investigated in 13 head and neck squamous carcinoma cell lines. Six cell lines exhibited increased MHC class I expression, and 10 exhibited increased MHC class II expression after IFN-gamma gene transfer. Differences in MHC antigen expression between parental and transduced cell lines were significant (P = 0. 002) only for cell lines that upregulated MHC class II expression. After incubation in medium containing 100 U/mL recombinant IFN-gamma, or in medium from IFN-gamma retrovirus-transduced NIH 3T3 cells, 12 cell lines significantly upregulated MHC class I expression, and 9 significantly upregulated MHC class II expression. Only cell lines that exhibited increased MHC class II expression after retroviral transduction also upregulated class II expression with exogenous IFN-gamma treatment. Thus some head and neck squamous carcinoma cell lines can upregulate MHC class I and II expression after exogenous application of either IFN-gamma or IFN-gamma retroviral transduction. These are promising findings for head and neck cancer immunotherapy and gene therapy.

Expression of interferon-gamma by stromal cells inhibits murine long-term repopulating hematopoietic stem cell activity

Several lines of evidence suggest that overexpression of interferon gamma (IFN-gamma) in the marrow microenvironment may play a role in the pathogenesis of marrow suppression in aplastic anemia. We previously showed that overexpression of IFN-gamma by marrow stromal cells inhibits human long-term culture initiating cell activity assayed in vitro to a much greater degree than the addition of soluble IFN-gamma. The effect of IFN-gamma on true repopulating stem cells assayed in vivo has not been studied previously. We compared the effect of co-culture of murine marrow cells in the presence of stromal cells transduced with a retroviral vector expressing murine IFN-gamma vs stromal cells transduced with a control neo vector. Using a murine congenic competitive repopulation assay, there was significantly less long-term repopulating stem cell activity remaining after culture on mIFN-gamma-expressing stroma as compared to control stroma. We also investigated the effect of directly transducing murine bone marrow cells with the mIFN-gamma or control vector. Marrow cells transduced with either vector were transplanted into W/Wv recipient mice. The percentage of vector-containing cells in the mIFN-gamma mice was significantly lower than in the control mice, suggesting that mIFN-gamma-transduced primitive cells may not have survived culture, or that mIFN-gamma directly decreases gene transfer into repopulating cells. Despite no significant differences in white or red blood cells in the mice transplanted with the mIFN-gamma-transduced cells, the number of bone marrow colony-forming unit-C 16 weeks after transplantation was significantly lower in the IFN-gamma group. These data indicate that ectopic or overexpression of mIFN-gamma, especially by marrow microenvironmental elements, may have a marked effect on primitive hematopoiesis as assayed in vivo.

Large-scale manufacturing of safe and efficient retrovirus packaging lines for use in immunotherapy protocols

BACKGROUND

The use of gene modified T lymphocytes for immunotherapy in a cancer or AIDS clinical trial requires an efficient, safe ex vivo method for modification of these cells at manufacturing scale. Since retroviruses have been shown to be a moderately effective means of stably integrating therapeutic genes into T lymphocytes, we wanted to create packaging and producer cell lines that would produce replication competent retrovirus (RCR)-free supernatants, at large scale (> 200 l), and transduce with high efficiency.

METHODS

cDNA expression plasmids containing only coding sequences for gagpol or env were built and sequentially transfected into human 293 cells. Packaging and producer clones were characterized for stability, titer and RCR. A producer clone delivering chimeric immune receptors was scaled-up and supernatants used to transduce patient T lymphocytes for clinical studies. PCR and RT-PCR assays were utilized to evaluate the transmission of HERV-H sequences. Relative infectivity of producer clones pseudotyped with different envelopes was determined by transduction and RT assays.

RESULTS

RCR-free, human 293 split-genome packaging lines, pseudotyped with amphotropic, xenotropic, or 10A1 envelopes, were created. A CC49 zeta producer clone was scaled-up to 5 x 54 l lots and supernatants used to safely and efficiently transduce patient T lymphocytes with minimal ex vivo manipulation. While 293 cells express HERV-H mRNA, the transmission frequency in our packaging clones was less than 1 HERV-H sequence per 5 x 10(5) proviral integrations. Additionally, 10A1 and xenotropic packaging lines had higher infectivities than the amphotropic clone.

CONCLUSION

These packaging lines represent the safest configuration for the large-scale production of retroviral vectors, and are capable of producing high titer, RCR-free retroviral vector for large scale clinical use. While all three clones efficiently transduce human T lymphocytes, the 10A1 clone has the highest infectivity. These packaging cell lines will be valuable for use in human gene therapy protocols.

Stable alphavirus packaging cell lines for Sindbis virus and Semliki Forest virus-derived vectors

Alphavirus vectors are being developed for possible human vaccine and gene therapy applications. We have sought to advance this field by devising DNA-based vectors and approaches for the production of recombinant vector particles. In this work, we generated a panel of alphavirus vector packaging cell lines (PCLs). These cell lines were stably transformed with expression cassettes that constitutively produced RNA transcripts encoding the Sindbis virus structural proteins under the regulation of their native subgenomic RNA promoter. As such, translation of the structural proteins was highly inducible and was detected only after synthesis of an authentic subgenomic mRNA by the vector-encoded replicase proteins. Efficient production of biologically active vector particles occurred after introduction of Sindbis virus vectors into the PCLs. In one configuration, the capsid and envelope glycoproteins were separated into distinct cassettes, resulting in vector packaging levels of 10(7) infectious units/ml, but reducing the generation of contaminating replication-competent virus below the limit of detection. Vector particle seed stocks could be amplified after low multiplicity of infection of PCLs, again without generating replication-competent virus, suggesting utility for production of large-scale vector preparations. Furthermore, both Sindbis virus-based and Semliki Forest virus-based vectors could be packaged with similar efficiency, indicating the possibility of developing a single PCL for use with multiple alphavirus-derived vectors.

Expression of the human hepatocyte growth factor cDNA in primary cultures of rat hepatocytes

Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are primary mitogens for hepatocytes in culture. hepatocytes express the HGF-receptor MET but not HGF itself. To investigate the influence of autocrine HGF expression on the proliferative potential of hepatocytes, primary cultures were submitted to retrovirus-mediated transduction of the human hgf (huHGF) cDNA. Expression of the transduced cDNA revealed a minimum 2-fold increase in HGF-mRNA, whereas expression of the Escherichia coli beta-galactosidase gene remained even. Estimation of huHGF copy numbers showed there was a minimum 4-fold increase, suggesting an increase in the population of transduced cells. Immunoprecipitation of excreted huHGF and growth bioassays proofed that HGF was present and functional. HGF is excreted into the medium and therefore, by diffusion, available to transduced and non-transduced cells. The increase in huHGF-transduced cells suggests that the autocrine pathway as opposed to the paracrine pathway, which are both present at the same time, confers a growth advantage to these cells.