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PubMed1995

Enhanced transduction efficiency of retroviral vectors coprecipitated with calcium phosphate.

Retroviral vectors are being used increasingly in clinical gene therapy protocols but low transduction frequencies are presenting a significant obstacle to progress. In this paper we report a simple method to enhance the efficiency of ex vivo retroviral gene transfer. Calcium chloride is added to the vector stock and calcium phosphate precipitates out of solution in complex with the retroviral vectors. When such coprecipitated vectors were used for gene transfer, the vector titres were increased at least five-fold and as much as 50-fold compared with the titres obtained in standard polybrene-enhanced infection protocols. Titre enhancement was not dependent on the starting concentration of vector, was equally effective for ecotropic and amphotropic vectors on a variety of mouse and human cells, and was not associated with any alteration in vector host range properties. The method may be of value to concentrate retroviral vectors and to enhance the efficiency of gene transfer in selected human gene therapy protocols.

Animals↗

PubMed1994

Retroviral vector design for long-term expression in murine hematopoietic cells in vivo.

A series of retroviral vectors containing the human glucocerebrosidase (GC) cDNA driven by various promoters have been constructed in an attempt to discover which vector design can most efficiently transduce murine hematopoietic stem cells (HSCs) and drive expression of the transferred gene in hematopoietic cells of mice reconstituted with the transduced stem cells. The simplest vector, LG, in which the GC gene is driven by the viral LTR, was the most efficient vector at infecting HSCs, with an average viral copy number in hematopoietic tissues of 3 copies/cell in recipient mice. In general, the viral vectors that contained any additional promoters or enhancers to drive expression of either the GC gene or a selectable marker gene (Neo) had lower titers and/or transduced HSCs at a lower efficiency. This was seen most markedly when the human phosphoglycerate (PGK) promoter was used to drive the human GC cDNA. Despite repeated attempts to obtain a high titer producer clone, this virus consistently produced low titers and subsequently resulted in the lowest proviral copy numbers in long-term reconstituted mice. Only the viral LTR and PGK promoter were capable of driving significant levels of human GC RNA in hematopoietic cells of long-term reconstituted mice, with a much lower level of RNA generated by an internal herpes TK or SV40 immediate early promoter. Insertion of the internal transcription unit in the opposite orientation relative to the viral LTRs had a detrimental effect on gene expression. The levels of RNA generated by a hybrid LTR containing the myeloproliferative sarcoma virus enhancer were higher in bone marrow-derived macrophages than in nonadherent cells of the bone marrow when compared with the LG vector. The presence of an internal promoter to drive expression of the human GC cDNA did not seem to have a detrimental effect on expression levels from the viral LTR. In fact, in the presence of an internal TK or PGK promoter expression from the LTR was increased despite the presence of lower proviral copy numbers. Insertion of a second gene (Neo) into the vector had a negative impact on long-term expression in hematopoietic cells in vivo; however, this seems to be due solely to the lower transduction efficiency of this vector. Overall, the highest levels of GC activity in macrophages of long-term reconstituted mice were generated by the LG vector; however, these levels were variable.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Effects of the gag region on genome stability: avian retroviral vectors that contain sequences from the Bryan strain of Rous sarcoma virus.

We have previously described replication-competent Schmidt Ruppin-A Rous sarcoma virus (RSV)-based retroviral vectors that can be used to deliver and express genes in avian cells. We have continued to modify the prototype vectors to develop a more versatile and efficient system. Substitution of the polymerase (pol) region from the Bryan high-titer RSV (BH-RSV) for the SR-A RSV pol region of these retroviral vectors causes these viruses to replicate more efficiently. We cloned the gag regions from two independent BH-RSV-transformed cell lines and tested whether substituting either of these gag regions would improve the replication and/or gene expression of the vectors. Chimeric vectors were constructed in which the gag region of the prototype vector (SR-A RSV) was replaced with the corresponding segment of BH-RSV gag in vectors that had either the original SR-A RSV pol or the BH-RSV pol region. All vectors contained the bacterial chloramphenicol acetyltransferase gene (CAT). The results indicate that different SR-A RSV and BH-RSV gag-pol chimeras can significantly affect the level of viral and CAT gene expression. The insertion of one of the BH-RSV gag regions, but not the other, gave rise to viruses with unstable genomes.

Amino Acid Sequence↗

PubMed1995

Foreign gene expression by human adenovirus type 5-based vectors studied using firefly luciferase and bacterial beta-galactosidase genes as reporters.

Adenovirus (Ad) vectors have been used extensively to obtain high-level expression of foreign genes in mammalian cells and are currently being studied for use as live viral-vectored vaccines and as gene transfer vectors for gene therapy. Many Ad recombinants have been generated that express foreign genes inserted in early region 3 (E3); however, little has been done to study the importance for gene expression of regulatory sequences flanking the gene. We have generated a series of Ad5 helper-independent vectors that contain the firefly luciferase gene or the bacterial beta-galactosidase gene (LacZ) with or without simian virus 40 (SV40) regulatory sequences, combined with E3 deletions of 1.88 or 2.69 kb. The greatest levels of luciferase expression were obtained with a vector containing the luciferase gene under the control of the SV40 promoter and polyadenylation signal inserted in a 1.88-kb E3 deletion. In contrast, LacZ expression was highest with a vector containing the LacZ gene with just the SV40 polyadenylation sequence combined with a 1.88-kb E3 deletion. It was also observed that regardless of the SV40 sequences flanking the reporter gene or the E3 deletion used, expression from the luciferase recombinants was dependent on viral DNA replication, whereas expression from the LacZ recombinants was only partially reduced when DNA replication was blocked. Analyses of RNA by dot blot hybridizations revealed that the levels of reporter gene-specific mRNA for various vectors in each series did not vary significantly. These results indicate that the kinetics and efficiency of expression of genes inserted into the E3 region, in nonconditional helper-independent vectors, may be more strongly dependent on the sequences in the foreign gene insert itself than on flanking regulatory sequences such as those used here, derived from SV40.

Adenoviruses, Human↗

PubMed1991

Effects of vector cutting on its recombination with the chromosomal immunoglobulin gene in hybridoma cells.

We have analyzed the effects of linearizing vector DNA on the frequency and pathway of its recombination with the homologous chromosomal gene. The pSV2neo vector bearing a 4.3-kb fragment encoding the mouse immunoglobulin mu heavy chain constant (C mu) region was cut either at sites within the C mu segment or outside C mu and then transferred to hybridoma cells bearing a mutant mu gene. The frequency of recombinant cells producing normal mu was then measured. For most cut sites, whether in regions of homology or of nonhomology, linearization of the transferred DNA enhanced the recombination frequency between the vector and chromosomal mu genes. When the vector was either uncut or cut at SacI in the region of homology, G418-resistant mu m+ recombinants were found to have integrated the vector by a single reciprocal homologous crossover; the enzyme site (SacI) used for cutting was present in the recombinants. By contrast, when the vector had been linearized at PvuI or SfiI in the region of nonhomology, vector integration involved nonhomologous crossovers, either between transferred DNA molecules or between transferred and chromosomal DNA, and the vector cut sites were absent in these recombinants. Some recombinants were found to have an unaltered as well as recombinant mu gene, suggesting that the nonhomologous recombination process might have involved sister chromatids.

Animals↗

PubMed1992

Improved gene expression by a U3-based retroviral vector.

To improve the expression of the genes transduced by retroviral vectors, we have constructed a U3-based retroviral vector and evaluated its effect on the expression of an insert from the internal promoter. The unique feature of the vector is that the transduced gene is inserted at the U3 region of the 3' long terminal repeats (LTR). Consequently, in the infected cells the gene is duplicated and transferred to the 5'-LTR. When compared with the conventional retroviral vectors which insert the gene within the retroviral transcriptional unit, the U3-based vectors greatly enhanced the expression of the transduced gene under all three promoters tested, viz. the cytomegalovirus immediately early gene promoter (CMV), the SV40 early gene promoter (SV), and the herpes simplex virus thymidine kinase gene promoter (TK). The SV and TK promoters which were previously shown suppressed by the retroviral promoter in the conventional construction restored their potencies in the U3-based vectors. Our results therefore suggested that the U3-based vectors are more advantageous than the conventional vectors for gene expression.

Animals↗

PubMedDate not supplied

Approaches to vector control: new and trusted. 2. Molecular targets in the insect midgut.

The midgut of blood-feeding insects is an important site for the activity of antibodies and drugs ingested with the blood meal. These agents can be directed at molecular targets in the midgut, and may affect the insect directly by reducing its fitness, or indirectly by blocking transmission of a disease organism to the vector. Both of these result in eventual disease control. Immunization with crude vector or parasite preparations can result in isolation of vaccine candidates which are very effective but often of unknown function. Conversely, by examining carefully the vector's biology and its interactions with the parasite, it is possible to identify various physiological or cellular systems and vector-parasite interactions that can be interfered with. Examples of both approaches are presented in this paper. Anti-vector vaccines offer tremendous potential for disease control, as they can affect the parasite reproductive rate in a number of ways--reducing vector longevity, fecundity or competence. This is most striking if life expectancy of the vector is reduced to a period less than the extrinsic life cycle of the parasite. The rationale often presented for examining molecular systems in vectors is their control potential; it is clearly appropriate to re-examine many of these systems and realistically assess their applicability.

Animals↗

PubMedDate not supplied

Studies on direct and indirect effects of DNA damage on mutagenesis in monkey cells using an SV40-based shuttle vector.

We are using an SV40-based shuttle vector, pZ189, to study mechanisms of mutagenesis in mammalian cells. The vector can be treated with mutagens in vitro and replicated in animal cells; resulting mutants can be selected and amplified in bacteria for DNA sequencing. This versatile vector system has allowed us to explore several different questions relating to the mutagenic process. We have studied the direct effects of template damage caused by UV or benzo[a]pyrene diolepoxide by treating vector DNA with these agents and then replicating the damaged DNA in monkey cells. Mutational mechanisms were deduced from the spectrum of mutations induced in the supF target gene of the vector DNA. To study the role of indirect effects of DNA damage on mutagenesis in mammalian cells, we have treated the cells and the vector DNA separately with DNA-damaging agents. We find that pretreatment of cells with DNA-damaging agents, or with conditioned medium from damaged cells, causes an enhancement of mutagenesis of a UV-damaged vector. Thus, DNA damage can act indirectly to enhance the mutagenic process. We also have preliminary evidence that pZ189 can be used in an in vitro DNA replication system to study the process of mutation fixation on the biochemical level. We believe that the pZ189 vector will prove to be as useful for in vitro studies of mutational mechanisms as it has been for in vivo studies.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1991

Amplification of Epstein-Barr virus-based shuttle vectors by ultraviolet light in human cells.

In order to approach the mechanism of gene amplification, we have developed a model system in human cells based on the use of episomally-replicating shuttle vectors. Shuttle vectors carrying the replication origin of the Epstein-Barr virus can be stably maintained in human cells. These vectors replicate as an episome with a low copy number. We also constructed hybrid plasmids containing both the EBV and the SV40 replication origins. These molecules are able to replicate episomally either like an EBV vector or like SV40 if the SV40 large T antigen is provided at the same time. UV irradiation of both human adenovirus transformed 293 or SV40-transformed MRC5 host cells leads to vector amplification whatever the type of replication origin used for the episomal maintenance. Our result clearly shows that the EBV latent replication origin (OriP), in the presence of the Epstein-Barr nuclear antigen-1 (EBNA-1) and the SV40 large T antigen, is sensitive to over-replication in UV-irradiated human cells. Since the UV doses were small enough to induce very little damage, if any, on the plasmid sequences, this amplification should be mediated through a cellular factor acting in trans. The interest in using shuttle vectors for this kind of study lays in the easy analysis of the amplified vectors in rescued bacterial colonies. The accuracy of the amplification process can be monitored by studying restriction maps of individual plasmid molecules or more precisely the integrity of a target gene, such as the lacZ' sequence, carried by our vectors.

Cells, Cultured↗

PubMed1988

High-level transient expression of influenza virus proteins from a series of SV40 late and early replacement vectors.

We have constructed a collection of simian virus 40 (SV40) plasmid vectors useful for transient or constitutive expression of cDNA or genomic DNA in animal cells. Most vectors contain several unique restriction sites downstream from the SV40 late or early promoter, and are available with or without the virus-specific splicing signals. The use of these vectors for transient expression in monkey cells of X47 (H3N2) influenza hemagglutinin (HA) and matrix protein (M1) was demonstrated. Membrane-bound (HAm) as well as secreted forms of the HA glycoprotein lacking the sequence of the C-terminal anchor (HA-) have been obtained. Depending on the insert, the type of vector and the amount of transfected DNA, HA levels in COS cells [Gething and Sambrook, Nature 293 (1981) 620-625] transfected with late replacement SV40 vectors vary from 10(9) (HAm) to 10(8) (HA-) molecules per transfected cell. The maximum expression levels with early replacement vectors in COS cells are at least 50 times lower. In addition to the optimalization and the characterization of the expression of each vector-coded influenza protein, cotransfections, including vectors expressing HAm, neuraminidase (NA) and M1, were undertaken. The latter experiments did not result in a measureable amount of HAm or NA in the cell culture medium, suggesting that expression of these three structural viral proteins does not result in budding of (empty) influenza particles from the cell surface.

Antibodies, Viral↗

PubMed1988

Entrapment of recombinant plasmids in SeaPlaque agarose plugs and their rapid purification from recircularised vectors.

A simple method is described which permits both the separation and concentration of circular recombinant plasmids from smaller plasmid vectors that are an undesirable by-product of a ligation reaction. SeaPlaque agarose plugs are used to entrap open-circular forms of recombinant plasmids during electrophoresis. In the example described over 98% of supercoiled, open-circular and linear forms of the 2.9-kb Bluescript plasmid vector, as well as the equivalent dimer forms, pass through the 1.4% SeaPlaque plug. Circular recombinant plasmids greater in length than the vector dimer are entrapped within the plug. By increasing the concentration of SeaPlaque, recombinants smaller than the vector dimer are retained in the trap, but with a concomitant increase in contamination by open-circular vector dimers. For most library constructions the high ratio of insert to vector used during the ligation reaction reduces the formation of vector dimers and makes this level of contamination inconsequential. The recombinant plasmids can be extracted readily from the SeaPlaque plug by excising it, melting the agarose and extracting with phenol. Alternatively, the excised plug can be melted and the recombinant plasmids used to transform bacteria, or mammalian cells, directly in the agarose. The procedure should be valuable for cloning large inserts for 'jumping' and 'linking' libraries, for large inserts in general where recircularisation is a low-frequency event, e.g., minichromosomes, for pulsed-field gel electrophoresis applications, and for hosts and vectors where genetic selection of the recombinant is not possible.

Cloning, Molecular↗

PubMed1991

Plasmid cloning vectors that integrate site-specifically in Streptomyces spp.

Cloning vectors based on the Streptomyces ambofaciens plasmid pSAM2 and the streptomycete phage phi C31 were developed for use in Streptomyces spp. These vectors replicate in Escherichia coli but integrate by site-specific recombination in Streptomyces spp. Both pSAM2-based and phi C31-based vectors transformed a number of different Streptomyces spp; however, the phi C31-based vectors consistently transformed at higher frequencies than pSAM2-based vectors. Southern analysis indicated that the phi C31-based vectors integrated at a unique site in the S. ambofaciens chromosome, while the pSAM2-based vectors gave complex patterns which could indicate structural instability or use of multiple loci. Both types of vectors utilize the apramycin (Am)-resistance gene which can be selected in E. coli and Streptomyces spp. with either Am or the commercially available antibiotic Geneticin (G418).

Blotting, Southern↗

PubMed1992

Characterization and properties of a novel plasmid vector for Bacillus thuringiensis displaying compatibility with host plasmids.

A novel plasmid vector, composed of a 1.7-kb Bacillus thuringiensis (B.t.) replicon, a multiple cloning site, and an erythromycin-resistance marker gene from Bacillus subtilis, was constructed for use in B.t. Unlike other vectors which have been reported to be acceptable for B.t., this new B.t. vector was stably maintained in the absence of Er and did not displace host plasmids, some of which carry crystal protein-encoding genes (cry genes). The compatibility of this B.t. vector with native plasmids is highly desirable when introducing new cry genes into a wild-type B.t. strain. When a cryIIIA gene of B.t. tenebrionis was cloned in this vector and introduced into B.t. kurstaki (kur) HD119, cryIIIA was highly expressed without affecting the level of expression of native cry genes. The stability of this vector and its compatibility with native B.t. plasmids were achieved by subcloning only nucleotide sequences required for the vector to replicate in B.t. The origin of replication was first cloned on a 9.6-kb Bg/II fragment from a 75-kb plasmid of B.t. kur HD73 and then localized to a 2.4-kb region within the 9.6-kb fragment. Sequencing of the 2.4-kb region revealed the presence of an open reading frame (ORF), encoding a putative 312-amino acid (aa) protein. The deduced aa sequence of the ORF showed no homology to any published aa sequences. Deletion analysis indicated that the B.t. vector required at least the ORF and up to 300 bp surrounding the ORF, in order to replicate.

Amino Acid Sequence↗

PubMed1995

New vectors for manipulation and selection of functional yeast artificial chromosomes (YACs) containing human DNA inserts.

A set of fragmentation vectors is described which produce a deletion series of smaller yeast artificial chromosomes (YACs) from a larger parent YAC with the insertion of a eukaryotic selectable marker. In addition, new vectors were designed to permit integration of the genes encoding neomycin (neo) or hygromycin B (hyg) resistance into YACs containing inserts of human DNA. All these vectors are compatible with the yeast host strain AB1380, in which most human genomic YAC libraries are maintained. Linearized vector DNA is used to transform yeast cells in which homologous recombination between human DNA in the YAC and the Alu sequence in the fragmentation or integrating vector produces terminal deletions from the acentromeric (URA3) end of the YAC or insertion of the vector into the YAC, respectively. A set of directional deletions of a YAC is useful for genomic mapping, restriction analysis and functional measurements of large chromosomal regions. The neo and hyg eukaryotic markers permit the study of gene function after introduction of deleted YACs into mammalian cells. Transformation of YACs with the fragmentation vectors resulted in fragmentation in 21-46% of the clones examined; transformation with the integrating vector resulted in integration in 46% of the clones examined.

Base Sequence↗

PubMed1994

Generation of high-titer pseudotyped retroviral vectors with very broad host range.

Encapsidation of the VSV G protein into the virions of MoMLV-derived retroviral vectors in the absence of other VSV-encoded proteins is shown to be an efficient process, although the exact mechanism for this process is currently unclear. Unlike the conventional retroviral vectors bearing the amphotropic envelope protein, the pseudotyped virus has the ability to withstand the shearing forces encountered during ultracentrifugation. This property of the pseudotyped virus enables the generation of high-titer retroviral vector stocks and has potential application for in vivo gene therapy studies. We have found as many as four copies of a pseudotyped vector to integrate into the genome of a single cell when a high multiplicity of infection was used to infect the cells. Multiple integration events were not observed with amphotropic retroviral vectors, probably because of their low virus titers. In addition, when retroviral vectors are pseudotyped with the VSV G protein, they acquire the host range of VSV and are able to infect nonmammalian cells derived from fish, Xenopus, mosquito, and Lepidoptera. Since techniques for efficient gene transfer in some of these nonmammalian systems are not currently available, retrovirus-mediated gene transfer described here should be useful for transgenic and other genetic studies in lower vertebrate species. The inability to establish a stable cell line expressing the VSV G protein, however, limits large-scale production of the pseudotyped retroviral vectors. Generation of stable packaging cell lines for the pseudotyped retroviral vectors is a major challenge for the future.

3T3 Cells↗

PubMed1995

A controlled study of adenoviral-vector-mediated gene transfer in the nasal epithelium of patients with cystic fibrosis.

BACKGROUND: Cystic fibrosis is a monogenic disease that deranges multiple systems of ion transport in the airways, culminating in chronic infection and destruction of the lung. The introduction of a normal copy of the cystic fibrosis transmembrane conductance regulator (CFTR) gene into the airway epithelium through gene transfer is an attractive approach to correcting the underlying defects in patients with cystic fibrosis. We tested the feasibility of gene therapy using adenoviral vectors in the nasal epithelium of such patients. METHODS: An adenoviral vector containing the normal CFTR complementary DNA in four logarithmically increasing doses (estimated multiplicity of infection, 1, 10, 100, and 1000), or vehicle alone, was administered in a randomized, blinded fashion to the nasal epithelium of 12 patients with cystic fibrosis. Gene transfer was quantitated by molecular techniques that detected the expression of CFTR messenger RNA and by functional measurements of transepithelial potential differences (PDs) to assess abnormalities of ion transport specific to cystic fibrosis. The safety of this treatment was monitored by nasal lavage and biopsy to assess inflammation and vector replication. RESULTS: The adenoviral vector was detected in nasal-lavage fluid by culture, the polymerase chain reaction (PCR), or both in a dose-dependent fashion for up to eight days after vector administration. There was molecular evidence of gene transfer by reverse-transcriptase PCR assays or in situ hybridization in five of six patients treated at the two highest doses. However, the percentage of epithelial cells transfected by the vector was very low (< 1 percent), and measurement of PD across the epithelium revealed no significant restoration of chloride transport or normalization of sodium transport. At the lower doses of vector, there were no toxic effects. However, at the highest dose there was mucosal inflammation in two of three patients. CONCLUSIONS: In patients with cystic fibrosis, adenoviral-vector-mediated transfer of the CFTR gene did not correct functional defects in nasal epithelium, and local inflammatory responses limited the dose of adenovirus that could be administered to overcome the inefficiency of gene transfer.

Adenoviruses, Human↗

PubMed1988

A poxvirus-derived vector that directs high levels of expression of cloned genes in mammalian cells.

High levels of expression of cloned genes have been obtained in mammalian cells by using poxvirus-derived insertion/expression vectors. These vectors employ the cis-acting element (CAE I) that directs the transcription of one of the most strongly expressed genes of cowpox virus. This gene (the 160K gene) encodes the 160-kDa protein that is the major component of the A-type cytoplasmic inclusions. Its counterpart in vaccinia virus (VV) is the 94K gene contained in the HindIII A fragment of the viral DNA. Two insertion vectors have been constructed; each is designed to allow cloned genes to be placed immediately downstream of a modified version of CAE I within a poxvirus genome. One vector, p1200, enables the CAE I-cloned-gene constructs to be inserted into the thymidine kinase gene of VV. This vector was used to create a VV recombinant that directed expression of the chloramphenicol acetyltransferase (CAT) gene. The other vector, p2101, enables the CAE I-cloned-gene constructs to be inserted into the VV 94K gene. The prototype of this vector was used to create a VV recombinant that directed expression of a hybrid CAT-lacZ gene. Infection of cultured human cells with these recombinants led to high levels of synthesis of either the CAT gene product or the CAT-lacZ gene product. Each of these proteins was produced in quantities that were easily detected by Coomassie blue staining of total cell proteins resolved by polyacrylamide gel electrophoresis. We estimate that these vectors are capable of directing the synthesis of milligram amounts of gene product per 10(9) mammalian cells.

Animals↗

PubMed1993

Stable in vivo expression of the cystic fibrosis transmembrane conductance regulator with an adeno-associated virus vector.

Adeno-associated virus (AAV) vectors expressing the normal cystic fibrosis transmembrane conductance regulator (CFTR) cDNA complement the cystic fibrosis (CF) defect in vitro. Unlike other DNA virus vectors, AAV is a stably integrating virus, which could make possible long-term in vivo complementation of the CF defect in the airway epithelium. We report AAV-CFTR gene transfer and expression after infection of primary CF nasal polyp cells and after in vivo delivery of AAV-CFTR vector to one lobe of the rabbit lung through a fiberoptic bronchoscope. In the rabbit, vector DNA could be detected in the infected lobe up to 6 months after administration. A 26-amino acid polypeptide sequence unique to the recombinant AAV-CFTR protein was used to generate both oligonucleotide probes and a polyclonal antibody which allowed the unambiguous identification of vector RNA and CFTR protein expression. With these reagents, CFTR RNA and protein were detected in the airway epithelium of the infected lobe for up to 6 months after vector administration. AAV vectors do, therefore, efficiently promote in vivo gene transfer to the airway epithelium which is stable over several months. These findings indicate that AAV-CFTR vectors could potentially be very useful for gene therapy.

Amino Acid Sequence↗