Listeria monocytogenes mediated CFTR transgene transfer to mammalian cells

Genetically engineered E. coli invade epithelial cells and transfer their genetic cargo into the cells: an approach to a gene delivery system

PURPOSE

Despite advances in gene therapy, the lack of safe and efficient gene delivery systems limited the clinical effectiveness of gene therapy. Due to the inherent potential of bacteria, they can be considered as a good option for the gene transfer system. This study aimed to create a genetically engineered bacterium capable of entering epithelial cells and transferring its genetic cargo to the cell's cytoplasm, eventually expressing the gene of interest in the cell.

METHODS

The invasin (inv) gene from Yersinia pseudotuberculosis and the listeriolysin (hlyA) gene from Listeria monocytogenes were isolated by PCR assay and inserted into a pACYCDuet-1 vector. The recombinant plasmid was then transformed into E. coli strain BL21. Subsequently, pEGFP-C1 plasmids containing a CMV promoter were transformed into the engineered bacteria. Finally, the engineered bacteria containing the reporter genes were incubated with the HeLa and LNCaP cell lines. Fluorescence microscopy, flow cytometry, and TEM were used to monitor bacterial entry into the cells and gene expression. We used native E. coli strain BL21 as a control.

RESULTS

A fluorescence microscope showed that, in contrast to the control group, the manipulated E. coli were able to penetrate the cells and transport the plasmid pEGFP-C1 to the target cells. Flow cytometry also showed fluorescence intensity of 54.7% in HeLa cells and 71% in LNCaP cells, respectively. In addition, electron micrographs revealed the presence of bacteria in the cell endosomes and in the cytoplasm of the cells.

CONCLUSION

This study shows that genetically engineered E. coli can enter cells, transport cargo into cells, and induce gene expression in the target cell. In addition, flow cytometry shows that the gene transfer efficiency was sufficient for protein expression.

Bacteria and bacterial derivatives as delivery carriers for immunotherapy

There is growing interest in the role of microorganisms in human health and disease, with evidence showing that new types of biotherapy using engineered bacterial therapeutics, including bacterial derivatives, can address specific mechanisms of disease. The complex interactions between microorganisms and metabolic/immunologic pathways underlie many diseases with unmet medical needs, suggesting that targeting these interactions may improve patient treatment. Using tools from synthetic biology and chemical engineering, non-pathogenic bacteria or bacterial products can be programmed and designed to sense and respond to environmental signals to deliver therapeutic effectors. This review describes current progress in biotherapy using live bacteria and their derivatives to achieve therapeutic benefits against various diseases.

Clinical Experience and Recent Advances in the Development of Listeria-Based Tumor Immunotherapies

The promise of tumor immunotherapy to significantly improve survival in patients who are refractory to long-standing therapies, such as chemotherapy and radiation, is now being realized. While immune checkpoint inhibitors that target PD-1 and CTLA-4 are leading the charge in clinical efficacy, there are a number of other promising tumor immunotherapies in advanced development such as Listeria-based vaccines. Due to its unique life cycle and ability to induce robust CTL responses, attenuated strains of Listeria monocytogenes (Lm) have been utilized as vaccine vectors targeting both infectious disease and cancer. In fact, preclinical studies in a multitude of cancer types have found Listeria-based vaccines to be highly effective at activating anti-tumor immunity and eradicating tumors. Several clinical trials have now recently reported their results, demonstrating promising efficacy against some cancers, and unique challenges. Development of the Lm-based immunotherapies continues with discovery of improved methods of attenuation, novel uses, and more effective combinatorial regimens. In this review, we provide a brief background of Listeria monocytogenes as a vaccine vector, discuss recent clinical experience with Listeria-based immunotherapies, and detail the advancements in development of improved Listeria-based vaccine platforms and in their utilization.

Improved DNA delivery using invasive E. coli DH10B in human cells by modified bactofection method

E. coli mediated gene delivery faces a major drawback of low efficiency despite of being a safer alternative to viral vectors. This study showed a novel, simple and effective strategy to enhance invasive E. coli DH10B vector's efficiency in human epithelial cells. The bactofection efficiency of invasive E .coli vector was analyzed in nine cell lines. It demonstrated highest (16%) reporter gene (GFP) expression in cervical cells. Methods were employed to further enhance its efficiency by adding transfection reagents (trans-bactofection method) to promote entry into host cells, lysosomotropic reagents for escape from lysosomal degradation or antibiotics to lyse internalized bacteria. Increased bacterial entry, as elucidated from nil to 3% expression in liver cells, was obtained upon complexing bacteria with PULSin. Chloroquine mediated endosomal escape resulted in 7.2 folds increase whereas tetracycline addition to lyse internalized bacteria caused ≈90% of GFP in HeLa. Eventually, the combined effect of these three methods exhibited close to 100% GFP in cervical and remarkable increase of 138 folds in breast cells. This is the first study showing comparative study of vector's gene delivery ability in various epithelial cells of the human body with improving its delivery efficiency. These data demonstrated the potential of developed bactofection method to boost up the efficiency of other bacterial vectors also, which could further be used for effectual therapeutic gene delivery in human cells.

Increasing the bactofection capacity of a mammalian expression vector by removal of the f1 ori

Bacterial-mediated cancer therapy has shown great promise in in vivo tumour models with increased survival rates post-bacterial treatment. Improving efficiency of bacterial-mediated tumour regression has focused on controlling and exacerbating bacterial cytotoxicity towards tumours. One mechanism that has been used to carry this out is the process of bactofection where post-invasion, bacteria deliver plasmid-borne mammalian genes into target cells for expression. Here we utilised the cancer-targeting Salmonella Typhimurium strain, SL7207, to carry out bactofection into triple negative breast cancer MDA-MB-231 cells. However, we noted that post-transformation with the commonly used mammalian expression vector pEGFP, S. Typhimurium became filamentous, attenuated and unable to invade target cells efficiently. Filamentation did not occur in Escherichia coli-transformed with the same plasmid. Further investigation identified the region inducing S. Typhimurium filamentation as being the f1 origin of replication (f1 ori), an artefact of historic use of mammalian plasmids for single stranded DNA production. Other f1 ori-containing plasmids also induced the attenuated phenotype, while removal of the f1 ori from pEGFP restored S. Typhimurium virulence and increased the bactofection capacity. This work has implications for interpretation of prior bactofection studies employing f1 ori-containing plasmids in S. Typhimurium, while also indicating that future use of S. Typhimurium in targeting tumours should avoid the use of these plasmids.

A suicidal strain of Listeria monocytogenes is effective as a DNA vaccine delivery system for oral administration

In this study we determined the in vivo activity of model ovalbumin vaccines delivered by direct intramuscular delivery of plasmid DNA or oral delivery using a recombinant suicidal Listeria monocytogenes strain (rsΔ2). In a previous report we described how rsΔ2 is capable of delivering luciferase, as protein or DNA, in vitro, into non-dividing intestinal epithelial cells (Kuo et al., 2009). This is achieved by engineering a dual expression shuttle vector, pDuLX-Luc, that replicates in E. coli and rsΔ2 and drives gene expression from the Listeria promoter (Phly) as well as the eukaryotic cytomegalovirus promoter (CMV), thereby delivering both protein and plasmid DNA to the cell cytoplasm. For the current in vivo study rsΔ2 containing pDuLX-OVA was used to deliver both ovalbumin protein and the mammalian expression plasmid by the oral route. Controls were used to investigate the activity of this system versus positive and negative controls, as well as quantifying activity against direct intramuscular injection of expression plasmids. Oral administration of rsΔ2(pDuLX-OVA) produced significant titres of antibody and was effective at inducing targeted T-cell lysis (approximately 30% lysis relative to an experimental positive control, intravenous OVA-coated splenocytes+lipopolysaccharide). Intramuscular injection of plasmids pDuLX-OVA or p3L-OVA (which lacks the prokaryotic promoter) also produced significant CTL-mediated cell lysis. The delivery of the negative control rsΔ2 (pDuLX-Luc) confirmed that the observed activity was induced specifically by the ovalbumin vaccination. The data suggest that the oral activity of rsΔ2(pDuLX-OVA) is explained by delivery of OVA protein, expressed in rsΔ2 from the prokaryotic promoter present in pDuLX-OVA, but transfection of mammalian cells in vivo may also play a role. Antibody titres were also produced by oral delivery (in rsΔ2) of the p3L-OVA plasmid in which does not include a prokaryotic promoter.

Involvement of absent in melanoma 2 in inflammasome activation in macrophages infected with Listeria monocytogenes

Listeria monocytogenes invades the cytoplasm of macrophages and induces the activation of caspase-1 and the subsequent maturation of IL-1beta and IL-18. Although apoptosis-associated speck-like protein containing a caspase-activating and recruitment domain (ASC), an adaptor protein of nucleotide-binding oligomerization domain (Nod)-like receptors, has been shown to play an essential role in inducing this cellular response to L. monocytogenes, the mechanism has not been fully elucidated. In this study, we demonstrate the role of absent in melanoma 2 (AIM2), a recently described receptor of cytosolic DNA, in the activation of caspase-1 upon infection with L. monocytogenes. Secretion of IL-1beta and IL-18 from Nod-like receptor family, pyrin domain containing 3 (NLRP3) and Nod-like receptor family, caspase-activating and recruitment domain containing 4 (NLRC4) knockout macrophages in response to L. monocytogenes was only slightly decreased compared with the levels secreted from wild-type macrophages, whereas secretion from ASC knockout macrophages was completely impaired, suggesting that receptors other than NLRP3 and NLRC4 also take part in inflammasome activation in an ASC-dependent manner. To identify such receptors, the abilities of several receptor candidates (NLRP2, NLRP6, NLRP12, and AIM2) to induce the secretion of IL-1beta in response to L. monocytogenes were compared using the inflammasome system reconstructed in HEK293 cells. Among these receptor candidates, AIM2 conferred the highest responsiveness to the bacterium on HEK293 cells. Knockdown of AIM2 significantly decreased the secretion of IL-1beta and IL-18 from L. monocytogenes-infected macrophages. These results suggest that AIM2, in cooperation with NLRP3 and NLRC4, plays an important role in the activation of caspase-1 during L. monocytogenes infection.

Plasmid DNA Delivery by d-Alanine-Deficient Listeria monocytogenes

Optimal DNA vaccine efficacy requires circumventing several obstacles, including low immunogenicity, a need for adjuvant, and the costs of purifying injection grade plasmid DNA. Bacterial delivery of plasmid DNA may provide an efficient and low-cost alternative to plasmid purification and injection. Also, the bacterial vector may exhibit potential as an immune adjuvant in vivo. Thus, we elected to examine the use of cell-wall-deficient Listeria monocytogenes as a DNA delivery vehicle in vitro. First, the D-alanine-deficient (Deltadal-dat) L. monocytogenes strain DP-L3506, which undergoes autolysis inside eukaryotic host cells in the absence of D-alanine, was transformed with a plasmid encoding green fluorescent protein (GFP) under control of the CMV promoter (pAM-EGFP). Then COS-7 and MC57G cell lines were infected with the transformed DP-L3506 at various multiplicities of infection (MOI) in the presence or absence of D-alanine. Subsequent GFP expression was observed in both cell lines by 24 h post-infection with DP-L3506(pAM-EGFP). Notably, no GFP positive cells were observed when D-alanine was omitted. Although transfection efficiency initially increased as a result of D-alanine supplementation, high concentration or long-term supplementation led to sustained bacterial growth that killed the infected host cells, resulting in fewer GFP-expressing cells. Thus, efficient DNA delivery by transformed bacteria must balance bacterial invasion and survival with target cell health and survival.

Biotechnological applications of Listeria's sophisticated infection strategies

Listeria monocytogenes is a Gram‐positive bacterium that is able to survive both in the environment and to invade and multiply within eukaryotic cells. Currently L. monocytogenes represents one of the most well‐studied and characterized microorganisms in bacterial pathogenesis. A hallmark of L. monocytogenes virulence is its ability to breach bodily barriers such as the intestinal epithelium, the blood–brain barrier as well as the placental barrier to cause severe systemic disease. Curiously, this theme is repeated at the level of the interaction between the individual cell and the bacterium where its virulence factors contribute to the ability of the bacteria to breach cellular barriers. L. monocytogenes is a model to study metabolic requirements of bacteria growing in an intracellular environment, modulation of signalling pathways in the infected cell and interactions with cellular defences involving innate and adaptive immunity. Technical advances such as the creation of LISTERIA‐susceptible mouse strains, had added interest in the study of the natural pathogenesis of the disease via oral infection. The use of attenuated strains of L. monocytogenes as vaccines has gained considerable interest because they can be used to express heterologous antigens as well as to somatically deliver recombinant DNA to eukaryotic cells. A novel vaccine concept, the use of non‐viable but metabolically active bacteria to induced immunoprotective responses, has been developed with L. monocytogenes. In this mini‐review, we review the strategies used by L. monocytogenes to subvert the cellular functions at different stages of the infection cycle in the host and examine how these properties are being exploited in biotechnological and clinical applications.

Bactofection of lung epithelial cells in vitro and in vivo using a genetically modified Escherichia coli

Bacteria-mediated gene transfer ('bactofection') has emerged as an alternative approach for genetic vaccination and gene therapy. Here, we assessed bactofection of airway epithelial cells in vitro and in vivo using an attenuated Escherichia coli genetically engineered to invade non-phagocytic cells. Invasive E. coli expressing green fluorescent protein (GFP) under the control of a prokaryotic promoter was efficiently taken up into the cytoplasm of cystic fibrosis tracheal epithelial (CFTE29o-) cells and led to dose-related reporter gene expression. In vivo experiments showed that following nasal instillation the vast majority of GFP-positive bacteria pooled in the alveoli. Further, bactofection was assessed in vivo. Mice receiving 5 x 10(8) E. coli carrying pCIKLux, in which luciferase (lux) expression is under control of the eukaryotic cytomegalovirus (CMV) promoter, showed a significant increase (P<0.01) in lux activity in lung homogenates compared to untransfected mice. Surprisingly, similar level of lux activity was observed for the non-invasive control strain indicating that the eukaryotic CMV promoter might be active in E. coli. Insertion of prokaryotic transcription termination sequences into pCIKLux significantly reduced prokaryotic expression from the CMV promoter allowing bactofection to be detected in vitro and in vivo. However, bacteria-mediated gene transfer leads to a significantly lower lux expression than cationic lipid GL67-mediated gene transfer. In conclusion, although proof-of-principle for lung bactofection has been demonstrated, levels were low and further modification to the bacterial vector, vector administration and the plasmids will be required.

Improving live attenuated bacterial carriers for vaccination and therapy

Live attenuated bacteria are well established as vaccines. Thus, their use as carriers for prophylactic and therapeutic macromolecules is a logical consequence. Here we describe several experimental applications of bacteria to carry heterologous macromolecules into the murine host. First, Listeria monocytogenes are described that are able to transfer eukaryotic expression plasmids into host cells for gene therapy. High multiplicities of infection are still required for efficient gene transfer and we point out some of the bottlenecks that counteract a more efficient transfer and application in vivo. Then, we describe Salmonella enterica serovar Typhimurium (S. typhimurium) as an expression plasmid transfer vehicle for oral DNA vaccination of mice. We demonstrate that the stabilization of the plasmid transformants results in an improved immune response. Stabilization was achieved by replacing the origin of replication of the original high-copy-number plasmid by a low-copy-number origin. Finally, we describe Salmonella carriers for the improved expression of heterologous proteins. We introduce a system in which the plasmid is carried as a single copy during cultivation but is amplified several fold upon infection of the host. Using the same in vivo inducible promoter for both protein expression and plasmid amplification, a substantial increase in antigen expression in vivo can be achieved. A modification of this approach is the introduction of inducible gene expression in vivo with a low-molecular-weight compound. Using P(BAD) promoter and L-arabinose as inducer we were able to deliberately activate genes in the bacterial carrier. No background activity could be observed with P(BAD) such that an inducible suicide gene could be introduced. This is adding an important safety feature to such live attenuated carrier bacteria.

Functional transfer of eukaryotic expression plasmids to mammalian cells by Listeria monocytogenes: a mechanistic approach

BACKGROUND

Cystic fibrosis (CF) is one of the most common monogenic disorders in the caucasian population. Gene therapy for CF is principally feasible and bacterial transfer systems might provide novel possibilities for therapy. However, transfection efficiencies are low and need to be improved. Thus, more detailed understanding of the DNA transfer mechanism is necessary to systematically eliminate these restrictions.

METHODS

Functional transfer of GFP-CFTR (cystic fibrosis transmembrane conductance regulator) to eukaryotic cells using attenuated Listeria monocytogenes mediated gene transfer (bacteriofection) was shown by fluorescent microscopy, flow cytometry, immunoblotting and whole cell patch clamping. The characteristics of plasmid transfer were studied by use of electron and fluorescence microscopy, flow cytometry and Southern blotting. Polymerase chain reaction (PCR) was used to screen the genome of bacteriofected cells for cotransfer of chromosomal bacterial DNA.

RESULTS

Correct intracellular localization and functionality of the GFP-CFTR fusion protein after bacteriofection was shown. Efficient bacterial lysis and release of bacterial content was demonstrated using antibiotics to kill intracellular bacteria. Although only low transfection rates were observed, high numbers of transferred plasmids were detected in host cells under these conditions. However, they were associated with high molecular weight entities and not available to cytosolic transcription. Cotransfer of bacterial genomic DNA was observed in transfectants but occurred at low frequencies.

CONCLUSIONS

In this work we demonstrate that low rates of bacteria-mediated transfection are not due to poor invasion of bacteria, insufficient bacterial lysis, or plasmid DNA degradation. Our data suggest that the transferred plasmid DNA is associated with higher macromolecular structures inhibiting nuclear transport and transgene transcription.

Bacteria in gene therapy: bactofection versus alternative gene therapy

Recent advances in gene therapy can be attributed to improvements of gene delivery vectors. New viral and nonviral transport vehicles that considerably increase the efficiency of transfection have been prepared. However, these vectors still have many disadvantages that are difficult to overcome, thus, a new approach is needed. The approach of bacterial delivery could in the future be important for gene therapy applications. In this article we try to summarize the most important modifications that are used for the preparation of applied strains, difficulties that are related with bacterial gene delivery and the current use of bactofection in animal experiments and clinical trials. Important differences to the alternative gene therapy (AGT) are discussed. AGT resembles bacteria-mediated protein delivery, as the therapeutical proteins are produced not by host cells but by the bacteria in situ and the expression can be regulated exogenously. Although the procedure of bacterial gene delivery is far from being definitely solved, bactofection remains a promising technique for transfection in human gene therapy.

The use of transformed Escherichia coli for experimental angiogenesis induced by regulated in situ production of vascular endothelial growth factor--an alternative gene therapy

BACKGROUND

Defects in angiogenesis (blood vessel formation) are responsible for two most important causes of death in developed countries (ischemic heart disease and cancer). Vascular endothelial growth factor (VEGF) plays a pivotal role in physiological and pathological regulation of angiogenesis. In the last years several studies have indicated the possibilities of VEGF in the therapy of ischemic heart disease. However, especially VEGF gene therapy (naked DNA, plasmids and adenovirus mediated) is associated with adverse side effects regarding the expression regulation.

AIM

To prepare bacterial strains producing VEGF using plasmids containing the VEGF cDNA for the use in experimental angiogenesis.

METHODS AND RESULTS

Escherichia coli strain BL21(DE3) was transformed with Bluescript vector containing the inserts with cDNA sequences coding VEGF-A isoforms (VEGF121, VEGF164, VEGF189). Selection of recombinants was achieved by cultivating E. coli cells on ampicillin-added medium. The expression of target genes in the T7 expression system was induced by isopropyl-beta-D-thiogalactoside (IPTG). Polyacrylamide gel electrophoresis of the cell lysates showed the presence of polypeptides of molecular weight corresponding with known values of VEGF isoforms. Blood vessel formation induced by bacterial VEGF production was proved in vivo in mice seven days after intraperitoneal injection of transformed bacteria by light microscopy. CONCLUSION AND HYPOTHESIS: In summary, E. coli strain expressing VEGF was prepared and its biological effect confirmed. Bacteria, which produce angiogenic factors, provide a new modality for experimental angiogenesis and may be also suitable for clinical use. The in situ production of therapeutic proteins using optimalized prokaryotic expression systems can represent a useful tool for treatment based on molecular biomedicine. The main advantage of the described approach lies in the enhanced regulation control--bacterial expression can be regulated positively (induction by exogenous low molecular weight agents) and negatively (application of antibiotics). The hypothesis of alternative gene therapy should be proved in further studies.

Endostatin gene therapy delivered by Salmonella choleraesuis in murine tumor models

BACKGROUND

Some anaerobic and facultatively anaerobic bacteria have been used experimentally as anticancer agents because of their selective growth in tumors. In this study, we exploited attenuated Salmonella choleraesuis as a tumoricidal agent and a vector to deliver the endostatin gene for tumor-targeted gene therapy.

METHODS

Attenuated S. choleraesuis carrying a eukaryotic expression plasmid encoding reporter gene was used to evaluate its abilities of tumor targeting and gene delivery in three syngeneic murine tumor models. Furthermore, S. choleraesuis carrying the endostatin expression vector was administered intraperitoneally into tumor-bearing mice, and its antitumor effect was evaluated.

RESULTS

Systemically administered S. choleraesuis preferentially accumulated within tumors for at least 10 days, forming tumor-to-normal tissue ratios exceeding 1000-10,000 : 1. Transgene expression via S. choleraesuis-mediated gene transfer also persisted for at least 10 days. Host immune responses and tumor hypoxia may influence tumor-targeting potential of S. choleraesuis. When systemically administered into mice bearing melanomas or bladder tumors, S. choleraesuis carrying the endostatin expression vector significantly inhibited tumor growth by 40-70% and prolonged survival of the mice. Furthermore, immunohistochemical studies in the tumors revealed decreased intratumoral microvessel density, reduced expression of vascular endothelial growth factor (VEGF), and increased infiltration of CD8(+) T cells.

CONCLUSIONS

These results suggest that tumor-targeted gene therapy using S. choleraesuis carrying the endostatin expression vector, which exerts tumoricidal and antiangiogenic activities, represents a promising strategy for the treatment of solid tumors.

Murine pulmonary infection with Listeria monocytogenes: differential susceptibility of BALB/c, C57BL/6 and DBA/2 mice

Murine listeriosis is a paradigm to understand host pathogen interactions. Airway infections with Listeria monocytogenes, although representing a serious problem in early onset neonatal listeriosis, has not been investigated in detail in animal models so far. Here, the susceptibility of BALB/c, DBA/2 and C57BL/6 mice towards an intratracheal (i.t.) infection with virulent L. monocytogenes EGDe and the attenuated variant L. monocytogenes EGD hlyW491A(pERL3-CMVGFP) is reported. The course of infection was characterized by determination of bacterial numbers in the organs and assessment of the health condition of the mice. The distribution and cellular localization of Listeria in the airways was assessed by immunocytochemistry and confocal and electron microscopy. The differential susceptibility of inbred mouse strains to airway infections with L. monocytogenes could be assigned to the major virulence factor listeriolysin O. Resistant C57BL/6 mice were not affected by the two listerial strains. In contrast, BALB/c and DBA/2 mice showed differential susceptibility towards L. monocytogenes EGDe and attenuated bacteria, with all the mice being killed by the wild-type bacteria but rarely by the variant that secretes a listeriolysin of only 10% activity of that of the wild-type toxin. Thus, listeriolysin is a decisive factor for differential susceptibility against Listeria. After i.t. application, bacteria were predominantly localized in the peribronchiolar space and invaded alveolar macrophages but rarely lung epithelial cells. Dissemination from the lung into the deep organs started almost immediately after application, although a pulmonary bacterial reservoir remained during the first 4 days.

Bacteria-mediated DNA transfer in gene therapy and vaccination

The use of live attenuated bacterial vaccine strains allows the targeted delivery of macromolecules to mammalian cells and tissues via the mucosal route. Depending on their specific virulence mechanisms and inherent metabolic preferences, bacteria invade certain cell types and body niches where they consequently deliver their cargo. Recently, the ability of attenuated strains of Salmonella, Shigella and Yersinia spp., as well as Listeria monocytogenes and invasive Escherichia coli, to deliver eukaryotic expression plasmids into mammalian cells in vitro and in vivo has been discovered. The great potential of bacteria-mediated transfer of plasmid DNA encoding vaccine antigens and/or therapeutic molecules was demonstrated in experimental animal models of infectious diseases, tumours and gene deficiencies. The exact mechanism of DNA transfer from the bacterial vector into the mammalian host is not yet completely known. The understanding of molecular events during bacterial DNA transfer, however, will further the development of bacterial vector systems with great promise for various clinical applications.

Use of bacteria in anti-cancer therapies

While a number of valid molecular targets have been discovered for tumours over the past decade, finding an effective way of delivering therapeutic genes specifically to tumours has proved more problematic. A variety of viral and non-viral delivery vehicles have been developed and applied in anti-cancer gene therapies. However, these suffer from either inefficient and/or short-lived gene transfer to target cells, instability in the bloodstream and inadequate tumour targeting. Recently, various types of non-pathogenic obligate anaerobic and facultative anaerobic bacteria have been shown to infiltrate and selectively replicate within solid tumours when delivered systemically. This has prompted the development of cancer gene therapy protocols that use such bacteria as gene delivery vehicles. Here, we review the evidence for the success of these in pre-clinical models and clinical trials, as single modality treatments and in combination with conventional cancer therapies.

Bacteria as DNA vaccine carriers for genetic immunization

Genetic immunization with plasmid DNA vaccines has proven to be a promising tool in conferring protective immunity in various experimental animal models of infectious diseases or tumors. Recent research focuses on the use of bacteria, in particular enteroinvasive species, as effective carriers for DNA vaccines. Attenuated strains of Shigella flexneri, Salmonella spp., Yersinia enterocolitica or Listeria monocytogenes have shown to be attractive candidates to target DNA vaccines to immunological inductive sites at mucosal surfaces. This review summarizes recent progress in bacteria-mediated delivery of plasmid DNA vaccines in the field of infectious diseases and cancer.

Bactofection of mammalian cells by Listeria monocytogenes: improvement and mechanism of DNA delivery

Bacteria-mediated transfer of plasmid DNA into mammalian cells (bactofection) is a potent approach to express plasmid-encoded heterologous proteins (protein antigens, toxins or enzymes) in a large set of different cell types including phagocytic and nonphagocytic mammalian cells. Previously, we have described a Listeria monocytogenes-mediated DNA delivery system, which releases plasmid DNA directly into the cytosol of mammalian cells by partial self-destruction of the carrier bacteria. Here we report on a second generation of this phage lysin supported bactofection system, which is greatly improved with respect to plasmid stability, transfer efficacy and biosafety. In this case, DNA release is initiated by spontaneous bacterial lysis in the infected cells cytosol which is subsequently enhanced by the simultaneously released phage lysin produced by the intracellular carrier bacteria. Bacteria that are capable of cell-to-cell spread are found to be much more efficient in bactofection than their non spreading counterparts.

Genomics, transcriptomics, proteomics, and numbers

OBJECTIVE

To review the advances in clinically useful molecular biologic techniques and to identify their applications in clinical practice, as presented at the 11th Annual William Beaumont Hospital DNA Symposium.

DATA SOURCES

The 8 manuscripts submitted were reviewed, and their major findings were compared with literature on the same or related topics.

STUDY SELECTION

Manuscripts address the use of molecular techniques in microbiology to evaluate infectious disease and epidemiology; molecular microbiology methods, including rapid-cycle real-time polymerase chain reaction; peroxisome proliferator-activated receptor gamma as a potential therapeutic target in inflammatory bowel disease or colon cancer; the effect of nonapoptotic doses of the bisbenizamide dye Hoechst 33342 on luciferase expression in plasmid-transfected BC3H-1 myocytes; the routine use of cystic fibrosis screening and its challenges; and the use of flow cytometry and/or chromosomal translocation in the diagnostic evaluation of hematopoietic malignancies.

DATA SYNTHESIS

Three current issues related to the use of molecular tests in clinical laboratories are (1) the restriction on introducing new tests secondary to existing patents or licenses; (2) the preanalytic variables for the different specimen types currently in use, including whole blood, plasma, serum, fresh or frozen tissues, and free-circulating DNA; and (3) the interpretation of studies evaluating the association of complex diseases with a single mutation or single-nucleotide polymorphism. Molecular methods have had a major impact on infectious disease through the rapid identification of organisms, the evaluation of outbreaks, and the characterization of drug resistance when compared with standard culture techniques. The activation of peroxisome proliferator-activated receptor gamma stimulated by thiazolidinedione is useful in the treatment of type II diabetes mellitus and may have value in preventing inflammatory bowel disease or colon cancer. Hoechst 33342 binding to adenine-thymine-rich regions in the minor groove of DNA is a fluorescent stain for DNA and initiates apoptosis at >10 microg/mL. Lower doses of Hoechst 33342 promote luciferase expression by a mechanism that may involve binding to cryptic promoters facilitated by dye-associated misalignment of the tertiary structure of DNA. The routine use of cystic fibrosis screening is complicated by the more than 1000 mutations associated with the disease. The use of 4-color flow cytometry and the detection of chromosomal translocation are both invaluable aids in establishing the diagnosis of lymphoid or myeloid hematopoietic malignancies.

CONCLUSIONS

The current postgenomic era will continue to emphasize the use of microarrays and database software for genomic, transcriptomic, and proteomic screening in the search for useful clinical assays. The number of molecular pathologic techniques will expand as additional disease-associated mutations are defined.

DNA modification and functional delivery into human cells using Escherichia coli DH10B

The availability of almost the complete human genome as cloned BAC libraries represents a valuable resource for functional genomic analysis, which, however, has been somewhat limited by the ability to modify and transfer this DNA into mammalian cells intact. Here we report a novel comprehensive Escherichia coli-based vector system for the modification, propagation and delivery of large human genomic BAC clones into mammalian cells. The GET recombination inducible homologous recombination system was used in the BAC host strain E.coli DH10B to precisely insert an EGFPneo cassette into the vector portion of a approximately 200 kb human BAC clone, providing a relatively simple method to directly convert available BAC clones into suitable vectors for mammalian cells. GET recombination was also used for the targeted deletion of the asd gene from the E.coli chromosome, resulting in defective cell wall synthesis and diaminopimelic acid auxotrophy. Transfer of the Yersinia pseudotuberculosis invasin gene into E.coli DH10B asd(-) rendered it competent to invade HeLa cells and deliver DNA, as judged by transient expression of green fluorescent protein and stable neomycin-resistant colonies. The efficiency of DNA transfer and survival of HeLa cells has been optimized for incubation time and multiplicity of infection of invasive E.coli with HeLa cells. This combination of E.coli-based homologous recombination and invasion technologies using BAC host strain E.coli DH10B will greatly improve the utility of the available BAC libraries from the human and other genomes for gene expression and functional genomic studies.