Identification of the murine firefly luciferase-specific CD8 T-cell epitopes

A mini-intronic plasmid (MIP): a novel robust transgene expression vector in vivo and in vitro

The bacterial backbone (BB) sequences contained within a canonical plasmid DNA dampen exogenous transgene expression by tenfold to 1,000-fold over a period of a few weeks following transfection into quiescent tissues such as the liver. Minicircle DNA vectors devoid of bacterial plasmid backbone sequences overcome transgene silencing providing persistent transgene expression. Because, we recently established that the length rather than sequence of the DNA flanking the transgene expression cassette is the major parameter affecting transgene silencing, we developed an alternative plasmid propagation process in which the essential bacterial elements for plasmid replication and selection are placed within an engineered intron contained within the eukaryotic expression cassette. As with the minicircle vector, the mini-intronic plasmid (MIP) vector system overcomes transgene silencing observed with plasmids but in addition provides between 2 and often 10 times or higher levels of transgene expression compared with minicircle vectors containing the same expression cassette in vivo and in vitro. These improved plasmids will benefit all studies involving gene transfer/therapy approaches.

A combination of intradermal jet-injection and electroporation overcomes in vivo dose restriction of DNA vaccines

Background

The use of optimized delivery devices has been shown to enhance the potency of DNA vaccines. However, further optimization of DNA vaccine delivery is needed for this vaccine modality to ultimately be efficacious in humans.

Methods

Herein we evaluated antigen expression and immunogenicity after intradermal delivery of different doses of DNA vaccines by needle or by the Biojector jet-injection device, with or without the addition of electroporation (EP).

Results

Neither needle injection augmented by EP nor Biojector alone could induce higher magnitudes of immune responses after immunizations with a high dose of DNA. After division of a defined DNA dose into multiple skin sites, the humoral response was particularly enhanced by Biojector while cellular responses were particularly enhanced by EP. Furthermore, a close correlation between in vivo antigen expression and cell-mediated as well as humoral immune responses was observed.

Conclusions

These results show that two optimized DNA vaccine delivery devices can act together to overcome dose restrictions of plasmid DNA vaccines.

Adeno-associated virus serotype 9-mediated pulmonary transgene expression: effect of mouse strain, animal gender and lung inflammation

Gene therapy holds great potential for the treatment of various acquired and inherited pulmonary diseases. Among various viral vectors, adeno-associated viral (AAV) vectors have been most frequently used in different clinical trials of pulmonary gene therapy. In the present study, we examined the kinetics and duration of transgene expression, vector biodistribution and development of neutralizing antibodies (NAB) in mice after pulmonary application of AAV2/9 vector. The pulmonary route of application did not affect any of the measured parameters. Transgene expression and biodistribution analysis at day 450 post-application confirmed the systemic spread of the vector after pulmonary delivery. Using SPB(-/-) mice, the study shows that AAV2/9-mediated gene expression is influenced by animal gender but not mouse genotype and is insensitive to the presence of lung inflammation. Lower expression levels were observed in male compared with female mice, and transient immunosuppression with dexamethasone significantly reduced the development of NAB in both genders of mice. The study thus advances this serotype for further development and use as a therapeutic vector.

Development of S/MAR minicircles for enhanced and persistent transgene expression in the mouse liver

We have previously described the development of a scaffold/matrix attachment region (S/MAR) episomal vector system for in vivo application and demonstrated its utility to sustain transgene expression in the mouse liver for at least 6 months following a single administration. Subsequently, we observed that transgene expression is sustained for the lifetime of the animal. The level of expression, however, does drop appreciably over time. We hypothesised that by eliminating the bacterial components in our vectors, we could improve their performance since bacterial sequences have been shown to be responsible for the immunotoxicity of the vector and the silencing of its expression when applied in vivo. We describe here the development of a minimally sized S/MAR vector, which is devoid of extraneous bacterial sequences. This minicircle vector comprises an expression cassette and an S/MAR moiety, providing higher and more sustained transgene expression for several months in the absence of selection, both in vitro and in vivo. In contrast to the expression of our original S/MAR plasmid vector, the novel S/MAR minicircle vectors mediate increased transgene expression, which becomes sustained at about twice the levels observed immediately after administration. These promising results demonstrate the utility of minimally sized S/MAR vectors for persistent, atoxic gene expression.

Systematic evaluation of AAV vectors for liver directed gene transfer in murine models

Vectors based on adeno-associated viruses (AAVs) are being evaluated for use in liver-directed gene therapy. Candidates have been preselected on the basis of capsid structure that plays an important role in determining performance profiles. We describe a comprehensive and statistically powered set of mouse studies designed to compare the performance of vectors based on seven novel AAV capsids. The key criteria used to select candidates for successful gene therapy are high level and stable transgene expression in the absence of toxicity. Based on these criteria, the best performing vectors, AAV8, AAVhu.37, and AAVrh.8, will be further evaluated in nonhuman primates (NHPs).

PiggyBac transposon-based inducible gene expression in vivo after somatic cell gene transfer

Somatic cell gene transfer has permitted inducible gene expression in vivo through coinfection of multiple viruses. We hypothesized that the highly efficient plasmid-based piggyBac transposon system would enable long-term inducible gene expression in mice in vivo. We used a multiple-transposon delivery strategy to create a tetracycline-inducible expression system in vitro in human cells by delivering the two genes on separate transposons for inducible reporter gene expression along with a separate selectable transposon marker. Evaluation of stable cell lines revealed 100% of selected clones exhibited inducible expression via stable expression from three separate transposons simultaneously. We next tested and found that piggyBac-mediated gene transfer to liver or lung could achieve stable reporter gene expression in mice in vivo in either immunocompetent or immune deficient animals. A single injection of piggyBac transposons could achieve long-term inducible gene expression in the livers of mice in vivo, confirming our multiple-transposon strategy used in cultured cells. The plasmid-based piggyBac transposon system enables constitutive or inducible gene expression in vivo for potential therapeutic and biological applications without using viral vectors.

Activation of transgene-specific T cells following lentivirus-mediated gene delivery to mouse lung

Integrating lentiviral vectors based on the human immunodeficiency virus type-1 (HIV-1) can transduce quiescent cells, which in lung account for almost 95% of the epithelial cell population. Pseudotyping lentiviral vectors with the envelope glycoprotein from the Ebola Zaire virus, the lymphocytic choriomeningitis virus (LCMV), the Mokola virus, and the vesicular stomatitis virus (VSV-G) resulted in transduction of mouse alveolar epithelium, but gene expression in the lung of C57BL/6 and BALB/c mice waned within 90 days of vector injection. Intratracheal delivery of the four pseudotyped lentiviral vectors resulted in transgene-specific T-cell activation in both mouse strains, albeit lower than that achieved by intramuscular injection of the vectors. We performed an adoptive transfer of luciferase-specific T cells, isolated from spleen or lung of donor mice injected with VSV-G-pseudotyped lentivirus vector expressing luciferase into the muscle or lung, respectively, into recipient recombination-activating gene (RAG)–deficient mice transduced in lung with adenovirus expressing firefly luciferase (ffluc2). Gene expression declined within 7 days of adoptive transfer approaching background levels by day 36. Taken together, our results suggest that the loss of transduced cells in lung is due to VSV-G.HIV vector–mediated activation of transgene-specific T cells rather than as result of normal turnover of airway cells.