Towards effective non-viral gene delivery vector

Abstract

Despite very good safety records, clinical trials using plasmid DNA failed due to low transfection efficiency and brief transgene expression. Although this failure is both due to poor plasmid design and to inefficient delivery methods, here we will focus on the former. The DNA elements like CpG motifs, selection markers, origins of replication, cryptic eukaryotic signals or nuclease-susceptible regions and inverted repeats showed detrimental effects on plasmids' performance as biopharmaceuticals. On the other hand, careful selection of promoter, polyadenylation signal, codon optimization and/or insertion of introns or nuclear-targeting sequences for therapeutic protein expression can enhance the clinical efficacy. Minimal vectors, which are devoid of the bacterial backbone and consist exclusively of the eukaryotic expression cassette, demonstrate better performance in terms of expression levels, bioavailability, transfection rates and increased therapeutic effects. Although the results are promising, minimal vectors have not taken over the conventional plasmids in clinical trials due to challenging manufacturing issues.

State of play and clinical prospects of antibody gene transfer

“…In addition to the choice of delivery method, transgene expression can be improved by modifying the make-up of pDNA constructs [115, 124]. Conventional pDNA consists of a transcription unit and bacterial backbone.…”

“…For therapeutic gene therapy, including antibody gene transfer, the presence of a bacterial backbone is clearly counterproductive. Of the different types of available minimal vectors [124], so far only minicircle DNA (mcDNA) has been reported for antibody gene transfer. Minicircles are plasmid molecules devoid of bacterial sequences, generated via a process of recombination, restriction and/or purification [124].…”

“…Of the different types of available minimal vectors [124], so far only minicircle DNA (mcDNA) has been reported for antibody gene transfer. Minicircles are plasmid molecules devoid of bacterial sequences, generated via a process of recombination, restriction and/or purification [124]. Elimination of the bacterial backbone has shown higher transfection efficiency and prolonged transgene expression in a variety of tissues [124, 128–130].…”

“…Minicircles are plasmid molecules devoid of bacterial sequences, generated via a process of recombination, restriction and/or purification [124]. Elimination of the bacterial backbone has shown higher transfection efficiency and prolonged transgene expression in a variety of tissues [124, 128–130]. Despite the benefits of these minimal vectors, clinical introduction is lagging behind because of the challenging manufacturing.…”

“…Despite the benefits of these minimal vectors, clinical introduction is lagging behind because of the challenging manufacturing. Ongoing advances in production and purification are expected to overcome these technical hurdles and promote clinical introduction [124]. …”