Developing extrachromosomal gene expression vector technologies: an overview

Current Landscape and Emerging Opportunities of Gene Therapy with Non-viral Episomal Vectors

Gene therapy has proven to be extremely beneficial in the management of a wide range of genetic disorders for which there are currently no or few effective treatments. Gene transfer vectors are very significant in the field of gene therapy. It is possible to attach a non-viral attachment vector to the donor cell chromosome instead of integrating it, eliminating the negative consequences of both viral and integrated vectors. It is a safe and optimal express vector for gene therapy because it does not cause any adverse effects. However, the modest cloning rate, low expression, and low clone number make it unsuitable for use in gene therapy. Since the first generation of non-viral attachment episomal vectors was constructed, various steps have been taken to regulate their expression and stability, such as truncating the MAR element, lowering the amount of CpG motifs, choosing appropriate promoters and utilizing regulatory elements. This increases the transfection effectiveness of the non-viral attachment vector while also causing it to express at a high level and maintain a high level of stability. A vector is a genetic construct commonly employed in gene therapy to treat various systemic disorders. This article examines the progress made in the development of various optimization tactics for nonviral attachment vectors and the future applications of these vectors in gene therapy.

The infectious BAC genomic DNA expression library: a high capacity vector system for functional genomics

Gene dosage plays a critical role in a range of cellular phenotypes, yet most cellular expression systems use heterologous cDNA-based vectors which express proteins well above physiological levels. In contrast, genomic DNA expression vectors generate physiologically-relevant levels of gene expression by carrying the whole genomic DNA locus of a gene including its regulatory elements. Here we describe the first genomic DNA expression library generated using the high-capacity herpes simplex virus-1 amplicon technology to deliver bacterial artificial chromosomes (BACs) into cells by viral transduction. The infectious BAC (iBAC) library contains 184,320 clones with an average insert size of 134.5 kb. We show in a Chinese hamster ovary (CHO) disease model cell line and mouse embryonic stem (ES) cells that this library can be used for genetic rescue studies in a range of contexts including the physiological restoration of Ldlr deficiency, and viral receptor expression. The iBAC library represents an important new genetic analysis tool openly available to the research community.

Fast and efficient multitransgenic modification of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) represent a prime cell source for pharmacological research and regenerative therapies because of their extensive expansion potential and their ability to differentiate into essentially all somatic lineages in vitro. Improved methods to stably introduce multiple transgenes into hPSCs will promote, for example, their preclinical testing by facilitating lineage differentiation and purification in vitro and the subsequent in vivo monitoring of respective progenies after their transplantation into relevant animal models. To date, the establishment of stable transgenic hPSC lines is still laborious and time-consuming. Current limitations include the low transfection efficiency of hPSCs via nonviral methods, the inefficient recovery of genetically engineered clones, and the silencing of transgene expression. Here we describe a fast, electroporation-based method for the generation of multitransgenic hPSC lines by overcoming the need for any preadaptation of conventional hPSC cultures to feeder-free conditions before genetic manipulation. We further show that the selection for a single antibiotic resistance marker encoded on one plasmid allowed for the stable genomic (co-)integration of up to two additional, independent expression plasmids. The method thereby enables the straightforward, nonviral generation of valuable multitransgenic hPSC lines in a single step. Practical applicability of the method is demonstrated for antibiotic-based lineage enrichment in vitro and for sodium iodide symporter transgene-based in situ cell imaging after intramyocardial cell infusion into explanted pig hearts.

HLA-restricted presentation of WT1 tumor antigen in B-lymphoblastoid cell lines established using a maxi-EBV system

Lymphoblastoid cell lines (LCLs), which are established by in vitro infection of peripheral B-lymphocytes with Epstein-Barr virus (EBV), are effective antigen-presenting cells. However, the ability of LCLs to present transduced tumor antigens has not yet been evaluated in detail. We report a single-step strategy utilizing a recombinant EBV (maxi-EBV) to convert B-lymphocytes from any individuals into indefinitely growing LCLs expressing a transgene of interest. The strategy was successfully used to establish LCLs expressing Wilms' tumor gene 1 (WT1) tumor antigen (WT1-LCLs), which is an attractive target for cancer immunotherapy. The established WT1-LCLs expressed more abundant WT1 protein than K562 leukemic cells, which are known to overexpress WT1. A WT1-specific cytotoxic T lymphocyte line efficiently lysed the WT1-LCL in a human leukocyte antigen-restricted manner, but poorly lysed control LCL not expressing WT1. These results indicate that the transduced WT1 antigen is processed and presented on the WT1-LCL. This experimental strategy can be applied to establish LCLs expressing other tumor antigens and will find a broad range of applications in the field of cancer immunotherapy.

[T-DNA integration patterns in transgenic plants mediated by Agrobacterium tumefaciens]

The genetic transformation mediated by Agrobacterium tumefaciens has been widely applied to research of transgenic plants. As the vector of the exotic genes, the integration patterns of T-DNA fragments affects not only transformation efficiency and stability, but also expression properties of the transgenes. This review summaries the two major patterns and the rules of T-DNA integration in Agrobacterim-mediated transformation, rules of T-DNA mediated by Agrobacterium tumefaciens, as well as research tools for flanking sequence amplification. It is attempted to provide references for researches on transformation and T-DNA integration mutation mediated by Agrobacterium tumefaciens.