Methods of Transfection with Messenger RNA Gene Vectors

Non-viral gene delivery vectors with messenger RNA (mRNA) as a carrier of genetic information are among the staple gene transfer vectors for research in gene therapy, gene vaccination and cell fate reprogramming. As no passage of genetic cargo in and out of the nucleus is required, mRNA-based vectors typically offer the following five advantages: 1) fast start of transgene expression; 2) ability to express genes in non-dividing cells with an intact nuclear envelope; 3) insensitivity to the major gene silencing mechanisms, which operate in the nucleus; 4) absence of potentially mutagenic genomic insertions; 5) high cell survival rate after transfection procedures, which do not need to disturb nuclear envelope. In addition, mRNA-based vectors offer a simple combination of various transgenes through mixing of several mRNAs in a single multi-gene cocktail or expression of a number of proteins from a single mRNA molecule using internal ribosome entry sites (IRESes), ribosome skipping sequences and proteolytic signals. However, on the downside, uncontrolled extracellular and intracellular decay of mRNA can be a substantial hurdle for mRNA-mediated gene transfer. Procedures for mRNA delivery are analogous to DNA transfer methods, which are well-established. In general, there are three actors in the gene delivery play, namely, the vector, the cell and the transfer environment. The desired outcome, that is, the efficient delivery of a gene to a target cell population, depends on the efficient interaction of all three parties. Thus, the vector should be customised for the target cell population and presented in a form that is resistant to the aggressive factors in the delivery milieu. At the same time, the delivery environment should be adjusted to be more vector-friendly and more cell-friendly. The recipient cells should be subjected to a specific regimen or artificially modified to become receptive to gene transfer with a particular vector and resistant to the environment. As a rule, barriers outside tissues (e.g. mucus) and an aggressive intercellular environment complicate gene delivery in vivo, which, therefore, requires more complex gene transfer procedures than transfection of tissue culture cells. This review is focused on transfection methods for mRNA vectors, which rely either on the forceful propulsion of mRNA inside the target cells (e.g. by electroporation or gene gun) or on the complexing of mRNA with other substances (e.g. polycationic transfection reagents) for delivery via endocytic pathways

Silencing of Transgene Expression: A Gene Therapy Perspective

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RecET driven chromosomal gene targeting to generate a RecA deficient Escherichia coli strain for Cre mediated production of minicircle DNA

BACKGROUND: Minicircle DNA is the non-replicating product of intramolecular site-specific recombination within a bacterial minicircle producer plasmid. Minicircle DNA can be engineered to contain predominantly human sequences which have a low content of CpG dinucleotides and thus reduced immunotoxicity for humans, whilst the immunogenic bacterial origin and antibiotic resistance marker gene sequences are entirely removed by site-specific recombination. This property makes minicircle DNA an excellent vector for non-viral gene therapy. Large-scale production of minicircle DNA requires a bacterial strain expressing tightly controlled site-specific recombinase, such as Cre recombinase. As recombinant plasmids tend to be more stable in RecA-deficient strains, we aimed to construct a recA(- )bacterial strain for generation of minicircle vector DNA with less chance of unwanted deletions. RESULTS: We describe here the construction of the RecA-deficient minicircle DNA producer Escherichia coli HB101Cre with a chromosomally located Cre recombinase gene under the tight control of the araC regulon. The Cre gene expression cassette was inserted into the chromosomal lacZ gene by creating transient homologous recombination proficiency in the recA(- )strain HB101 using plasmid-born recET genes and homology-mediated chromosomal "pop-in, pop-out" of the plasmid pBAD75Cre containing the Cre gene and a temperature sensitive replication origin. Favourably for the Cre gene placement, at the "pop-out" step, the observed frequency of RecET-led recombination between the proximal regions of homology was 10 times higher than between the distal regions. Using the minicircle producing plasmid pFIXluc containing mutant loxP66 and loxP71 sites, we isolated pure minicircle DNA from the obtained recA(- )producer strain HB101Cre. The minicircle DNA preparation consisted of monomeric and, unexpectedly, also multimeric minicircle DNA forms, all containing the hybrid loxP66/71 site 5'-TACCGTTCGT ATAATGTATG CTATACGAAC GGTA-3', which was previously shown to be an inefficient partner in Cre-mediated recombination. CONCLUSION: Using transient RecET-driven recombination we inserted a single copy of the araC controlled Cre gene into the lacZ gene on the chromosome of E. coli recA(- )strain HB101. The resultant recA(- )minicircle DNA producer strain HB101Cre was used to obtain pure minicircle DNA, consisting of monomeric and multimeric minicircle forms. The obtained recA(- )minicircle DNA producer strain is expected to decrease the risk of undesired deletions within minicircle producer plasmids and, therefore, to improve production of the therapeutic minicircle vectors

Functional expression of Rab escort protein 1 following AAV2-mediated gene delivery in the retina of choroideremia mice and human cells ex vivo

Choroideremia (CHM) is an X-linked retinal degeneration of photoreceptors, the retinal pigment epithelium (RPE) and choroid caused by loss of function mutations in the CHM/REP1 gene that encodes Rab escort protein 1. As a slowly progressing monogenic retinal degeneration with a clearly identifiable phenotype and a reliable diagnosis, CHM is an ideal candidate for gene therapy. We developed a serotype 2 adeno-associated viral vector AAV2/2-CBA-REP1, which expresses REP1 under control of CMV-enhanced chicken β-actin promoter (CBA) augmented by a Woodchuck hepatitis virus post-transcriptional regulatory element. We show that the AAV2/2-CBA-REP1 vector provides strong and functional transgene expression in the D17 dog osteosarcoma cell line, CHM patient fibroblasts and CHM mouse RPE cells in vitro and in vivo. The ability to transduce human photoreceptors highly effectively with this expression cassette was confirmed in AAV2/2-CBA-GFP transduced human retinal explants ex vivo. Electroretinogram (ERG) analysis of AAV2/2-CBA-REP1 and AAV2/2-CBA-GFP-injected wild-type mouse eyes did not show toxic effects resulting from REP1 overexpression. Subretinal injections of AAV2/2-CBA-REP1 into CHM mouse retinas led to a significant increase in a- and b-wave of ERG responses in comparison to sham-injected eyes confirming that AAV2/2-CBA-REP1 is a promising vector suitable for choroideremia gene therapy in human clinical trials. © 2013 The Author(s)

Methods of Transfection with Messenger RNA Gene Vectors

Abstract Non-viral gene delivery vectors with messenger RNA (mRNA) as a carrier of genetic information are among the staple gene transfer vectors for research in gene therapy, gene vaccination and cell fate reprogramming. As no passage of genetic cargo in and out of the nucleus is required, mRNA-based vectors typically offer the following five advantages: 1) fast start of transgene expression; 2) ability to express genes in nondividing cells with an intact nuclear envelope; 3) insensitivity to the major gene silencing mechanisms, which operate in the nucleus; 4) absence of potentially mutagenic genomic insertions; 5) high cell survival rate after transfection procedures, which do not need to disturb nuclear envelope. In addition, mRNA-based vectors offer a simple combination of various transgenes through mixing of several mRNAs in a single multi-gene cocktail or expression of a number of proteins from a single mRNA molecule using internal ribosome entry sites (IRESes), ribosome skipping sequences and proteolytic signals. However, on the downside, uncontrolled extracellular and intracellular decay of mRNA can be a substantial hurdle for mRNAmediated gene transfer. Procedures for mRNA delivery are analogous to DNA transfer methods, which are well-established. In general, there are three actors in the gene delivery play, namely, the vector, the cell and the transfer environment. The desired outcome, that is, the efficient delivery of a gene to a target cell population, depends on the efficient interaction of all three parties. Thus, the vector should be customised for the target cell population and presented in a form that is resistant to the aggressive factors in the delivery milieu. At the same time, the delivery environment should be adjusted to be more vector-friendly and more cell-friendly. The recipient cells should be subjected to a specific regimen or artificially modified to become receptive to gene transfer with a particular vector and resistant to the environment. As a rule, barriers outside tissues (e.g. mucus) and an aggressive © 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. intercellular environment complicate gene delivery in vivo, which, therefore, requires more complex gene transfer procedures than transfection of tissue culture cells. This review is focused on transfection methods for mRNA vectors, which rely either on the forceful propulsion of mRNA inside the target cells (e.g. by electroporation or gene gun) or on the complexing of mRNA with other substances (e.g. polycationic transfection reagents) for delivery via endocytic pathways