A tractable method for simultaneous modifications to the head and tail of bacteriophage lambda and its application to enhancing phage-mediated gene delivery

There is considerable interest in the use of bacteriophage vectors for mammalian cell gene transfer applications, due to their stability, excellent safety profile and inexpensive mass production. However, to date, phage vectors have been plagued by mediocre performance as gene transfer agents. This may reflect the complexity of the viral infection process in mammalian cells and the need to refine each step of this process in order to arrive at an optimal, phage-based gene transfer system. Therefore, a flexible system was designed that alowed for the introduction of multiple modifications on the surface of bacteriophage lambda. Using this novel method, multiple peptides were displayed simultaneously from both the phage head and tail. Surface head display of an ubiquitinylation motif greatly increased the efficiency of phage-mediated gene transfer in a murine macrophage cell line. Gene transfer was further increased when this peptide was displayed in combination with a tail-displayed CD40-binding motif. Overall, this work provides a novel system that can be used to rationally improve bacteriophage gene transfer vectors and shows it may be possible to enhance the efficiency of phage-mediated gene transfer by targeting and optimizing multiple steps within the viral infection pathway.     

Recombinant λ-phage nanobioparticles for tumor therapy in mice models

Lambda phages have considerable potential as gene delivery vehicles due to their genetic tractability, low cost, safety and physical characteristics in comparison to other nanocarriers and gene porters. Little is known concerning lambda phage-mediated gene transfer and expression in mammalian hosts. We therefore performed experiments to evaluate lambda-ZAP bacteriophage-mediated gene transfer and expression in vitro. For this purpose, we constructed recombinant λ-phage nanobioparticles containing a mammalian expression cassette encoding enhanced green fluorescent protein (EGFP) and E7 gene of human papillomavirus type 16 (λ-HPV-16 E7) using Lambda ZAP- CMV XR vector. Four cell lines (COS-7, CHO, TC-1 and HEK-239) were transduced with the nanobioparticles. We also characterized the therapeutic anti-tumor effects of the recombinant λ-HPV-16 E7 phage in C57BL/6 tumor mice model as a cancer vaccine. Obtained results showed that delivery and expression of these genes in fibroblastic cells (COS-7 and CHO) are more efficient than epithelial cells (TC-1 and HEK-239) using these nanobioparticles. Despite the same phage M.O.I entry, the internalizing titers of COS-7 and CHO cells were more than TC-1 and HEK-293 cells, respectively. Mice vaccinated with λ-HPV-16 E7 are able to generate potent therapeutic antitumor effects against challenge with E7- expressing tumor cell line, TC-1 compared to group treated with the wild phage. The results demonstrated that the recombinant λ-phages, due to their capabilities in transducing mammalian cells, can also be considered in design and construction of novel and safe phage-based nanomedicines.     

Genetic selection of phage engineered for receptor-mediated gene transfer to mammalian cells.

Although phage display is a powerful way of selecting ligands against purified target proteins, it is less effective for selecting functional ligands for complex targets like living cells. Accordingly, phage display has had limited utility in the development of targeting agents for gene therapy vectors. By adapting a filamentous bacteriophage for gene delivery to mammalian cells, however, we show here that it is possible to screen phage libraries for functional ligands capable of delivering DNA to cells. For example, when targeted with epidermal growth factor (EGF), M13 bacteriophage were capable of delivering a green fluorescent protein (GFP) gene to EGF receptor bearing cells in a ligand-, time-, and phage concentration-dependent manner. The EGF-targeted phage transduced COS-1 cells in a highly specific manner as demonstrated by competition with excess free EGF or alternatively with anti-EGF receptor antibodies. We further demonstrate that EGF-phage can be selected, by their ability to transduce EGF receptor bearing cells from libraries of peptide display phage. When phage were incubated with COS-1 cells, EGF ligand-encoding sequences were recovered by PCR from FACsorted, GFP-positive cells and the EGF-displaying phage were enriched 1 million-fold by four rounds of selection. These data suggest the feasibility of applying molecular evolution to phage gene delivery to select novel cell-specific DNA-targeting ligands. The same approach could be used to select genetically altered phage that are specifically designed and evolved as gene therapy vectors.     

In vivo gene delivery and expression by bacteriophage lambda vectors

AIMS: Bacteriophage vectors have potential as gene transfer and vaccine delivery vectors because of their low cost, safety and physical stability. However, little is known concerning phage-mediated gene transfer in mammalian hosts. We therefore performed experiments to examine phage-mediated gene transfer in vivo. METHODS AND RESULTS: Mice were inoculated with recombinant lambda phage containing a mammalian expression cassette encoding firefly luciferase (luc). Efficient, dose-dependent in vivo luc expression was detected, which peaked within 24 h of delivery and declined to undetectable levels within a week. Display of an integrin-binding peptide increased cellular internalization of phage in vitro and enhanced phage-mediated gene transfer in vivo. Finally, in vivo depletion of phagocytic cells using clodronate liposomes had only a minor effect on the efficiency of phage-mediated gene transfer. CONCLUSIONS: Unmodified lambda phage particles are capable of transducing mammalian cells in vivo, and may be taken up -- at least in part -- by nonphagocytic mechanisms. Surface modifications that enhance phage uptake result in more efficient in vivo gene transfer. SIGNIFICANCE AND IMPACT OF THE STUDY: These experiments shed light on the mechanisms involved in phage-mediated gene transfer in vivo, and suggest new approaches that may enhance the efficiency of this process.     

A simple method for displaying recalcitrant proteins on the surface of bacteriophage lambda

Bacteriophage lambda (λ) permits the display of many foreign peptides and proteins on the gpD major coat protein. However, some recombinant derivatives of gpD are incompatible with the assembly of stable phage particles. This presents a limitation to current λ display systems. Here we describe a novel, plasmid-based expression system in which gpD deficient λ lysogens can be co-complemented with both wild-type and recombinant forms of gpD. This dual expression system permits the generation of mosaic phage particles that contain otherwise recalcitrant recombinant gpD fusion proteins. Overall, this improved gpD display system is expected to permit the expression of a wide variety of peptides and proteins on the surface of bacteriophage λ and to facilitate the use of modified λ phage vectors in mammalian gene transfer applications.     

Design, construction and function of a multicopy display vector using fusions to the major coat protein of bacteriophage M13.

Incorporation of numerous copies of a heterologous protein (bovine pancreatic trypsin inhibitor; BPTI) fused to the mature major coat protein (gene VIII product; VIII) of bacteriophage M13 has been demonstrated. Optimization of the promoter, signal peptide and host bacterial strain allowed for the construction of a working vector consisting of the M13 genome, into which was cloned a synthetic gene composed of a lac (or tac) promoter, and sequences encoding the bacterial alkaline phosphatase signal peptide, mature BPTI and the mature coat protein. Processing of the BPTI-VIII fusion protein and its incorporation into the bacteriophage were found to be maximal in a host bacterial strain containing a prlA/secY mutation. Functional protein is displayed on the surface of M13 phage, as judged by specific interactions with antiserum, anhydrotrypsin, and trypsin. Such display vectors can be used for epitope mapping, production of artificial vaccines and the screening of diverse libraries of proteins or peptides having affinity for a chosen ligand. The VIII display phage system has practical advantages over the III display phage system in that many more copies of the fusion protein can be displayed per phage particle and the presence of the VII fusion protein has little or no effect on the infectivity of the resulting bacteriophage.     

A vehicle for DNA transfer and for recovery of transferred genes: lambda Charon phage-pBR322 hybrid

Recombinant Charon 4A phages accommodating the Herpes simplex virus (HSV-1) thymidine kinase (tk) gene, the ampicillin-resistance (ApR) gene, and the replication origin of pBR322 were constructed. The phage DNA was introduced into mouse Ltk- cells by a free DNA transfer method or phage-mediated DNA transfer method [Ishiura et al., Mol. Cell. Biol. 2 (1982) 607]. Analyses of the physical state of the transferred DNA in the recipient cell genome showed that a DNA fragment as long as 12.7 kb was integrated intact into 67% and less than 40% of the Ltk- transformant cells by phage-mediated DNA transfer and by free DNA transfer, respectively. We also developed a new rapid method for recovery of the transferred gene from the Ltk+ cell into Escherichia coli; the method depends on the fact that the recombinant lambda phage carrying the ApR gene and replication origin of pBR322 transduces lambda-lysogenic bacteria to ApR and is maintained as a plasmid. Using this method the HSV-1 tk gene from one Ltk+ transformant was rapidly and successfully recovered without any rearrangement of the target sequence.     

Ligand-mediated protection against phage lysis as a positive selection strategy for the enrichment of epitopes displayed on the surface of E. coli cells

We present a novel strategy, termed CISTEM, which allows direct in vivo screening of polypeptides displayed on the surface of E. coli cells by a combination of ligand-mediated protection and phage-mediated selection. The effectiveness of this new approach was demonstrated by displaying the T7.tag on the surface of E. coli as a fusion with the outer membrane protein A, the receptor for bacteriophage K3. A monoclonal T7.tag antibody was used as protective ligand for T7.tag-displaying cells and phage K3 for the elimination of unprotected cells. When populations of bacteria, containing between 6 to 10,000 cells displaying the T7.tag and approximately 10(8) cells displaying an unrelated OmpA fusion protein, were infected with phage K3, specific and antibody-dependent survival of T7.tag displaying cells was observed, yielding an enrichment factor of up to 10(7)-fold. The CISTEM technology was used to select sequences from a T7.tag-based, randomised library and the results were compared to those obtained from selection by MACS with the same library. Together, these results reveal a novel in vivo screening strategy in which an E. coli phage receptor is used as display plafform and selection is performed in suspension upon addition of a protective ligand and a bacteriophage. Extentions and modifications of the basic strategy should lead to novel applications for the identification of protein-ligand interactions.     

Recombinant polymer-protein fusion: a promising approach towards efficient and targeted gene delivery

BACKGROUND: Synthetic vectors such as polymers have the potential to reduce the safety problems associated with viral vectors; however, their low transfection efficiency limits their clinical utility. To study the critical steps involved in an efficient transgene expression, there is a need for creative approaches that allow a systematic correlation between gene carrier structure and properties necessary for successful gene transfer. Using recombinant techniques a prototype vector comprised of tandem repeating units fused to a targeting moiety was biosynthesized to mediate gene transfer in mammalian cell lines. The carrier was designed to have the structure of (KHKHKHKHKK)6-FGF2 where lysine (K) residues would allow complexation with plasmid DNA, basic fibroblast growth factor (FGF2) to target cells over-expressing FGF2 receptors (FGFR), and histidine (H) residues to facilitate escape from the endosomal compartments. METHODS: The gene carrier was biosynthesized in E. coli, purified using a Ni-NTA column, characterized, complexed with pDNA, and the complexes were used to transfect NIH 3T3, T-47D and COS-1 mammalian cell types known to express FGFR. RESULTS: Results demonstrate the successful cloning and expression of the gene carrier with over 95% purity. The molecular weight of the gene carrier was determined by MALDI-TOF to be 27 402. Amino acid content analysis and Western blot confirmed the expression of the gene carrier in E. coli. The vector was able to condense pDNA, induce cell proliferation in NIH 3T3 fibroblasts, and mediate transgene expression in NIH 3T3, T-47D and COS-1 mammalian cell types. CONCLUSION: Genetic engineering techniques show promise for systematic investigation of structure-activity relationships of non-viral gene delivery vectors.     

High-frequency phage-mediated gene transfer among Escherichia coli cells, determined at the single-cell level

Recent whole-genome analysis suggests that lateral gene transfer by bacteriophages has contributed significantly to the genetic diversity of bacteria. To accurately determine the frequency of phage-mediated gene transfer, we employed cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) and investigated the movement of the ampicillin resistance gene among Escherichia coli cells mediated by phage at the single-cell level. Phages P1 and T4 and the newly isolated E. coli phage EC10 were used as vectors. The transduction frequencies determined by conventional plating were 3x10(-8) to 2x10(-6), 1x10(-8) to 4x10(-8), and <4x10(-9) to 4x10(-8) per PFU for phages P1, T4, and EC10, respectively. The frequencies of DNA transfer determined by CPRINS-FISH were 7x10(-4) to 1x10(-3), 9x10(-4) to 3x10(-3), and 5x10(-4) to 4x10(-3) for phages P1, T4, and EC10, respectively. Direct viable counting combined with CPRINS-FISH revealed that more than 20% of the cells carrying the transferred gene retained their viabilities. These results revealed that the difference in the number of viable cells carrying the transferred gene and the number of cells capable of growth on the selective medium was 3 to 4 orders of magnitude, indicating that phage-mediated exchange of DNA sequences among bacteria occurs with unexpectedly high frequency.     

Targeted gene delivery to mammalian cells by filamentous bacteriophage.

We report that prokaryotic viruses can be re-engineered to infect eukaryotic cells resulting in expression of a reporter gene inserted into the bacteriophage genome. Phage capable of binding mammalian cells expressing the growth factor receptor ErbB2 and undergoing receptor-mediated endocytosis were isolated by selection of a phage antibody library on breast tumor cells and recovery of infectious phage from within the cell. As determined by immunofluorescence, F5 phage were efficiently endocytosed into 100 % of ErbB2 expressing SKBR3 cells. To achieve reporter gene expression, F5 phage were engineered to package the green fluorescent protein (GFP) reporter gene driven by the CMV promoter. These phage when applied to cells underwent ErbB2-mediated endocytosis leading to GFP expression. GFP expression occurred only in cells overexpressing ErbB2, was dose-dependent reaching, 4 % of cells after 60 hours and was detected with phage titers as low as 2.0 x 10(7) cfu/ml (500 phage/cell). The results demonstrate that bacterial viruses displaying the appropriate antibody can bind to mammalian receptors and utilize the endocytic pathway to infect eukaryotic cells, resulting in expression of a reporter gene inserted into the viral genome. This represents a novel method to discover targeting molecules capable of delivering a gene intracellularly into the correct trafficking pathway for gene expression by directly screening phage antibodies. This should significantly facilitate the identification of appropriate targets and targeting molecules for gene therapy or other applications where delivery into the cytosol is required. This approach can be adapted to directly select, rather than screen, phage antibodies for targeted gene expression. The results also demonstrate the potential of phage antibodies as an in vitro or in vivo targeted gene delivery vehicle.     

Phage-mediated conjugative transfer of plasmids in Staphylococcus aureus]

It was shown possible to transfer nonconjugative plasmids during joint cultivation of the donor and recipient cells by transduction and phage-mediated conjugation. In the latter case it was necessary that the phage in the medium was free and the prophage was present in the recipient cells. Differences in the regularities of the transfer of the nonconjugative plasmids mobilized by the conjugative plasmid or phage were observed.     

Design and evolution of artificial M13 coat proteins

Using simple design and selective pressure, we have evolved an artificial M13 bacteriophage coat protein. M13 coat proteins first reside in the bacterial inner membrane and subsequently surround the DNA core of the assembled virus. The artificial coat protein (ACP) was designed and evolved to mimic both functions of the natural M13 coat proteins, but with an inverted orientation. ACP is a non-functional coat protein because it is not required for the production of phage particles. Instead, it incorporates into a phage coat which still requires all the natural coat proteins for structural integrity. In contrast with other M13 coat proteins, which can display polypeptides as amino-terminal fusions, ACP permits the carboxy-terminal display of large polypeptides. The results suggest that viruses can co-opt host membrane proteins to acquire new coat proteins and thus new functions. In particular, M13 bacteriophage can be engineered for new functions, such as carboxy-terminal phage display.     

Adapter-Directed Display: A Modular Design for Shuttling Display on Phage Surfaces

A novel adapter-directed phage display system was developed with modular features. In this system, the target protein is expressed as a fusion protein consisting of adapter GR1 from the phagemid vector, while the recombinant phage coat protein is expressed as a fusion protein consisting of adapter GR2 in the helper phage vector. Surface display of the target protein is accomplished through specific heterodimerization of GR1 and GR2 adapters, followed by incorporation of the heterodimers into phage particles. A series of engineered helper phages were constructed to facilitate both display valency and formats, based on various phage coat proteins. As the target protein is independent of a specific phage coat protein, this modular system allows the target protein to be displayed on any given phage coat protein and allows various display formats from the same vector without the need for reengineering. Here, we demonstrate the shuttling display of a single-chain Fv antibody on phage surfaces between multivalent and monovalent formats, as well as the shuttling display of an antigen-binding fragment molecule on phage coat proteins pIII, pVII, and pVIII using the same phagemid vectors combined with different helper phage vectors. This adapter-directed display concept has been applied to eukaryotic yeast surface display and to a novel cross-species display that can shuttle between prokaryotic phage and eukaryotic yeast systems.     

Engineering M13 for phage display

Phage display is achieved by fusing polypeptide libraries to phage coat proteins. The resulting phage particles display the polypeptides on their surfaces and they also contain the encoding DNA. Library members with particular functions can be isolated with simple selections and polypeptide sequences can be decoded from the encapsulated DNA. The technology's success depends on the efficiency with which polypeptides can be displayed on the phage surface, and significant progress has been made in engineering M13 bacteriophage coat proteins as improved phage display platforms. Functional display has been achieved with all five M13 coat proteins, with both N- and C-terminal fusions. Also, coat protein mutants have been designed and selected to improve the efficiency of heterologous protein display, and in the extreme case, completely artificial coat proteins have been evolved specifically as display platforms. These studies demonstrate that the M13 phage coat is extremely malleable, and this property can be used to engineer the phage particle specifically for phage display. These improvements expand the utility of phage display as a powerful tool in modern biotechnology.     

Plasmid transfer via transduction from Streptococcus thermophilus to Lactococcus lactis

Using Streptococcus thermophilus phages, plasmid transduction in Lactococcus lactis was demonstrated. The transduction frequencies were 4 orders of magnitude lower in L. lactis than in S. thermophilus. These results are the first evidence that there is phage-mediated direct transfer of DNA from S. thermophilus to L. lactis. The implications of these results for phage evolution are discussed.     

Dual genetically encoded phage-displayed ligands

M13 bacteriophage display presents polypeptides as fusions to phage coat proteins. Such phage-displayed ligands offer useful reagents for biosensors. Here, we report a modified phage propagation protocol for the consistent and robust display of two different genetically encoded ligands on the major coat protein, P8. The results demonstrate that the phage surface reaches a saturation point for maximum peptide display.     

Wild-type intracellular bacteria deliver DNA into mammalian cells

Gene transfer in vitro from intracellular bacteria to mammalian phagocytic and non-phagocytic cells and in vivo in mice has been reported. The bacteria used as DNA delivery vectors were engineered to lyze upon entry in the cell due to impaired cell wall synthesis for Shigella flexneri and invasive Escherichia coli , or production of a phage lysin for Listeria mono- cytogenes . In vivo gene transfer was obtained with attenuated Salmonella typhimurium and resulted in stimulation of mucosal immunity. We report that wild-type intracellular human pathogens, such as L. monocytogenes EGD or LO28 and S. flexneri M90T, mediate efficient in vitro transfer of functional genes into epithelial and macrophage cell lines. A low- efficiency transfer was obtained from strain EGD to mouse peritoneal macrophages. DNA transfer with S. typhimurium was observed only from atten-uated aroA strain SL7207 into COS-1 cell line. As demonstrated by the study of listeriolysin-defective L. monocytogenes or of S. typhimurium SL7207 aroA engineered to secrete listeriolysin, escape of bacteria or of plasmid DNA from the intracytoplasmic vacuole is required for transfer of genetic information to occur.