Production of antibodies against Bacillus thuringiensis delta-endotoxin by injecting its plasmids

Performance of high quality minicircle DNA for in vitro and in vivo gene transfer

Plasmid DNA is frequently used particularly for nonviral gene therapy. Conventional plasmid DNA contains bacterial backbone and resistance gene sequences, as well as immunogenic CpG motifs. These components are not required for transgene expression. They represent a potential risk for safe clinical application and reduce gene transfer rates as well as transgene expression. To overcome these drawbacks, the minicircle technology is removing such sequences, to improve performance and also to reduce DNA size. Here, we show the effective production of luciferase, GFP, or lacZ-carrying minicircle DNA with high yield and reproducible high quality. They are used for lipofection or electroporation gene transfer into human melanoma and colon carcinoma cell lines. Comparison of respective parental plasmid and minicircle-mediated luciferase gene transfer shows improved luciferase expression by minicircle in all cell lines. This is not associated with increase in intracellular minicircle copy numbers after lipofection or electroporation. The minicircles rather mediate enhanced transgene mRNA transcription compared to their parental plasmids. In addition, FACS analysis revealed increase in counts of GFP positive cells after minicircle gene transfer, indicating higher gene transfer rates. Furthermore, minicircle showed also improved performance in vivo after jet-injection gene transfer. Therefore, availability of minicircles with reproducible high quality and sufficient amount makes them an applicable and effective alternative to conventional plasmid gene vectors.

Peripheral non-viral MIDGE vector-driven delivery of beta-endorphin in inflammatory pain

Background

Leukocytes infiltrating inflamed tissue produce and release opioid peptides such as β-endorphin, which activate opioid receptors on peripheral terminals of sensory nerves resulting in analgesia. Gene therapy is an attractive strategy to enhance continuous production of endogenous opioids. However, classical viral and plasmid vectors for gene delivery are hampered by immunogenicity, recombination, oncogene activation, anti-bacterial antibody production or changes in physiological gene expression. Non-viral, non-plasmid minimalistic, immunologically defined gene expression (MIDGE) vectors may overcome these problems as they carry only elements needed for gene transfer. Here, we investigated the effects of a nuclear localization sequence (NLS)-coupled MIDGE encoding the β-endorphin precursor proopiomelanocortin (POMC) on complete Freund's adjuvant-induced inflammatory pain in rats.

Results

POMC-MIDGE-NLS injected into inflamed paws appeared to be taken up by leukocytes resulting in higher concentrations of β-endorphin in these cells. POMC-MIDGE-NLS treatment reversed enhanced mechanical sensitivity compared with control MIDGE-NLS. However, both effects were moderate, not always statistically significant or directly correlated with each other. Also, the anti-hyperalgesic actions could not be increased by enhancing β-endorphin secretion or by modifying POMC-MIDGE-NLS to code for multiple copies of β-endorphin.

Conclusion

Although MIDGE vectors circumvent side-effects associated with classical viral and plasmid vectors, the current POMC-MIDGE-NLS did not result in reliable analgesic effectiveness in our pain model. This was possibly associated with insufficient and variable efficacy in transfection and/or β-endorphin production. Our data point at the importance of the reproducibility of gene therapy strategies for the control of chronic pain.

Use of minicircle plasmids for gene therapy

A large number of cancer gene therapy clinical trials are currently being performed that are attempting to evaluate novel approaches to eliminate tumor cells by the introduction of genetic material into patients. One of the most important objectives in gene therapy is the development of highly safe and efficient vector systems for gene transfer in eukaryotic cells. Currently, viral and nonviral vector systems are used, both having their advantages and limitations. Minicircles are novel supercoiled minimal expression cassettes, derived from conventional plasmid DNA by site-specific recombination in vivo in Escherichia coli for the use in nonviral gene therapy and vaccination. Minicircle DNA lacks the bacterial backbone sequence consisting of an antibiotic resistance gene, an origin of replication, and inflammatory sequences intrinsic to bacterial DNA. In addition to their improved safety profile, minicircles have been shown to greatly increase the efficiency oftransgene expression in various in vitro and in vivo studies. In this chapter, we describe the production, purification, and application of minicircle DNA and discuss the rationale of the improved gene transfer efficiencies compared to conventional plasmid DNA.

Occurrence of the transgenic corn cry1Ab gene in freshwater mussels (Elliptio complanata) near corn fields: evidence of exposure by bacterial ingestion

The purpose of this study was to examine the contamination of cry1 and cry1Ab genes from Bacillus thuringiensis and transgenic corn in feral freshwater mussels collected from sites located in proximity of corn fields. In addition, mussels were transplanted for 2 months to a site in the Huron River, upstream to the Richelieu River, which is subject to intensive corn farming. Mussels were significantly contaminated by both genes in their gills, digestive glands, and gonads, as determined by qPCR methodology. Gene sequence analysis confirmed the presence of transgenic corn cry1Ab gene in mussel tissues. In an attempt to explain the presence of the transgene in mussel tissues, heterotrophic bacteria were grown from surface water and sediment samples on agar plates in the Richelieu River in May and August. The transgene was found at two out of six surface water samples and in one sediment sample. The study revealed that exposure to transgenic corn cry1Ab gene in mussels seems to proceed by ingestion of microorganisms during feeding.

Minicircle-DNA production by site specific recombination and protein-DNA interaction chromatography

BACKGROUND

Conventional plasmid-DNA (pDNA) used in gene therapy and vaccination can be subdivided into a bacterial backbone and a transcription unit. Bacterial backbone sequences are needed for pDNA production in bacteria. However, for gene transfer application, these sequences are dispensable, reduce the overall efficiency of the DNA agent and, most importantly, represent a biological safety risk. For example, the dissemination of antibiotic resistance genes, as well as the uncontrolled expression of backbone sequences, may have profound detrimental effects and unmethylated CpG motifs have been shown to contribute to silencing of episomal transgene expression. Therefore, an important goal in nonviral vector development is to produce supercoiled pDNA lacking bacterial backbone sequences.

METHODS

A method is described to provide circular, supercoiled minimal expression cassettes (minicircle-DNA) based on two processes: (i) an inducible, sequence specific, in vivo recombination process that is almost 100% efficient and (2) a novel affinity-based chromatographic purification approach for the isolation of the minicircle-DNA.

RESULTS

Quantitative real-time polymerase chain reaction analysis, capillary gel electrophoresis and restriction analysis of the recombination products, and the minicircle-DNA revealed a recombination efficiency greater than 99.5% and a purity of the isolated minicircle-DNA of more than 98.5%.

CONCLUSIONS

The results obtained in the present study demonstrate that the described technology facilitates the production of highly pure minicircle-DNA for direct application in gene therapy and vaccination. The process described is efficient, stable and suitable for further scale-up in industrial large-scale manufacturing.

Occurrence and persistence of Bacillus thuringiensis (Bt) and transgenic Bt corn cry1Ab gene from an aquatic environment

Genetically modified corn crops and suspensions of Bacillus thuringiensis (Bt) are currently used to control pest infestations of insects of the Lepidoptera family. For this purpose, the cry1Ab gene coding for protein delta-endotoxin derived from B. thuringiensis kurstaki (Btk), which is highly toxic to these insects, was inserted and expressed in corn. The aims of this study were to examine the occurrence and persistence of the cry1Ab gene from Btk and Bt corn in aquatic environments near fields where Bt corn was cultivated. First, an optimal DNA preparation and extraction methodology was developed to allow for quantitative gene analysis by real-time polymerase chain reaction (qPCR) in various environmental matrices. Second, surface water and sediment were spiked in vitro with genomic DNA from Bt or Bt corn to evaluate the persistence of cry1Ab genes. Third, soil, sediment, and water samples were collected before seeding, 2 weeks after pollen release, and after corn harvesting and mechanical root remixing in soils to assess cry1Ab gene content. DNA was extracted with sufficient purity (i.e., low absorbance at 230 nm and absence of PCR-inhibiting substances) from soil, sediment, and surface water. The cry1Ab gene persisted for more than 21 and 40 days in surface water and sediment, respectively. The removal of bacteria by filtration of surface water samples did not significantly increase the half-life of the transgene, but the levels were fivefold more abundant than those in unfiltered water at the end of the exposure period. In sediments, the cry1Ab gene from Bt corn was still detected after 40 days in clay- and sand-rich sediments. Field surveys revealed that the cry1Ab gene from transgenic corn and from naturally occurring Bt was more abundant in the sediment than in the surface water. The cry1Ab transgene was detected as far away as the Richelieu and St. Lawrence rivers (82 km downstream from the corn cultivation plot), suggesting that there were multiple sources of this gene and/or that it undergoes transport by the water column. Sediment-associated cry1Ab gene from Bt corn tended to decrease with distance from the Bt cornfield. Sediment concentrations of the cry1Ab gene were significantly correlated with those of the cry1Ab gene in surface water (R=0.83;P=0.04). The data indicate that DNA from Bt corn and Bt were persistent in aquatic environments and were detected in rivers draining farming areas.

A novel minimal-size vector (MIDGE) improves transgene expression in colon carcinoma cells and avoids transfection of undesired DNA

Viral and plasmid vectors may cause unwanted immunological side effects resulting from the expression of nontherapeutic genes contained in their sequence. Furthermore, replication-defective viral vectors carry the potential risk of recombination with wild-type viruses or activation of oncogenes. A new vector type for minimalistic, immunologically defined gene expression (MIDGE) may overcome these problems. MIDGE is a minimal-size gene transfer unit containing the expression cassette, including promoter, gene, and RNA-stabilizing sequence, flanked by two short hairpin oligonucleotide sequences. The resulting vector is a small, linear, covalently closed, dumbbell-shaped molecule. DNA not encoding the desired gene is reduced to a minimum. Here, we transfected colon carcinoma cell lines using cationic lipid, cationic polymer, and electroporation with several MIDGE vectors and corresponding plasmids containing transgenes encoding enhanced green fluorescent protein (eGFP) and human interleukin-2 (hIL-2). Transfection efficiency as measured qualitatively and quantitatively with eGFP was found to be comparable for both vector types. However, hIL-2 secretion and eGFP expression were approximately two- to fourfold higher in most cells transfected with these transgenes using MIDGE vectors compared to the plasmid control. This report demonstrates the advantages of this new vector type and its prospects for ex vivo gene therapy studies.

Resistance to Coccidioides immitis in mice after immunization with recombinant protein or a DNA vaccine of a proline-rich antigen

Two inbred strains of mice (BALB/c and C57BL/6) were vaccinated with either recombinant expression protein of a Coccidioides immitis spherule-derived proline-rich antigen (rPRA) in monophosphoryl lipid A-oil emulsion adjuvant or a DNA vaccine based on the same antigen. Four weeks after vaccination, mice were infected intraperitoneally with arthroconidia. By 2 weeks, groups of mice receiving saline or plasmids with no PRA insert exhibited significant weight loss, and quantitative CFUs in the lungs ranged from 5.9 to 6.4 log10. In contrast, groups of mice immunized with either rPRA or DNA vaccine had significantly smaller pulmonary fungal burdens, ranging from 3.0 to 4.5 log10 fewer CFUs. In vitro immunologic markers of lymphocyte proliferation and gamma interferon (IFN-gamma) release after splenocytes were stimulated with rPRA correlated with protection. Also, plasma concentrations of rPRA-specific total immunoglobulin G (IgG), IgG1, and IgG2a showed increases in vaccinated mice. These studies expand earlier work by demonstrating protection in mice which differ in H-2 background, by using an adjuvant that is potentially applicable to human use, and by achieving comparable protections with a DNA-based vaccine. Our in vitro results substantiate a Th1 response as evidenced by IFN-gamma release and increased IgG2a. However, IgG1 was also stimulated, suggesting some Th2 response as well. PRA is a promising vaccine candidate for prevention of coccidioidomycosis and warrants further investigation.

DNA-antiviral vaccines: new developments and approaches--a review

Current vaccines can be divided into "live," "recombinant" and "killed" vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a "cold chain." Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed "DNA-, genetic- or nucleic acid-immunization," is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

Minicircle: an improved DNA molecule for in vitro and in vivo gene transfer

Minicircles are a new form of supercoiled DNA molecule for nonviral gene transfer which have neither bacterial origin of replication nor antibiotic resistance marker. They are thus smaller and potentially safer than the standard plasmids currently used in gene therapy. They were obtained in E. coli by att site-specific recombination mediated by the phage lambda integrase, which was used to excise the expression cassette from the unwanted plasmid sequences. We produced two minicircles containing the luciferase or beta-galactosidase gene under the control of the strong human cytomegalovirus immediate-early enhancer/promoter. Comparing maximal differences, these minicircles gave 2.5 to 5.5 times more reporter gene activity than the unrecombined plasmid in the NIH3T3 cell line and rabbit smooth muscle cells. Moreover, injection in vivo into mouse cranial tibial muscle, or human head and neck carcinoma grafted in nude mice resulted in 13 to 50 times more reporter gene expression with minicircles than with the unrecombined plasmid or larger plasmids. Histological analysis in muscle showed there were more transfected myofibers with minicircles than with unrecombined plasmid.

Repressor titration: a novel system for selection and stable maintenance of recombinant plasmids

The propagation of recombinant plasmids in bacterial hosts, particularly in Escherichia coli, is essential for the amplification and manipulation of cloned DNA and the production of recombinant proteins. The isolation of bacterial transformants and subsequent stable plasmid maintenance have traditionally been accomplished using plasmid-borne selectable marker genes. Here we describe a novel system that employs plasmid-mediated repressor titration to activate a chromosomal selectable marker, removing the requirement for a plasmid-borne marker gene. A modified E.coli host strain containing a conditionally essential chromosomal gene (kan) under the control of the lac operator/promoter, lac O/P, has been constructed. In the absence of an inducer (allolactose or IPTG) this strain, DH1 lackan , cannot grow on kanamycin-containing media due to the repression of kan expression by LacI protein binding to lac O/P. Transformation with a high copy-number plasmid containing the lac operator, lac O, effectively induces kan expression by titrating LacI from the operator. This strain thus allows the selection of plasmids without antibiotic resistance genes (they need only contain lac O and an origin of replication) which have clear advantages for use as gene therapy vectors. Regulation in the same way of an essential, endogenous bacterial gene will allow the production of recombinant therapeutics devoid of residual antibiotic contamination.

DNA vaccines

Observations in the early 1990s that plasmid DNA could directly transfect animal cells in vivo sparked exploration of the use of DNA plasmids to induce immune responses by direct injection into animals of DNA encoding antigenic proteins. This method, termed DNA immunization, now has been used to elicit protective antibody and cell-mediated immune responses in a wide variety of preclinical animal models for viral, bacterial, and parasitic diseases. DNA vaccination is particularly useful for the induction of cytotoxic T cells. This review summarizes current knowledge on the vectors, immune responses, immunological mechanisms, safety considerations, and potential for further application of this novel method of immunization.