In order to enable in vivo analysis of our gene therapy approach using AAV tropism as well as miRNA binding sites as trigger for expression the following constructs have been subcloned into the AAV context: (1) positive control, (2) off-targeting construct, (3) synthetic tuning construct and (4) on-targeting construct. All but of one virus were packaged in the adeno-associated virus (AAV) rep and cap gene with Adenovirus 5 (Ad5) as a helper plasmid. Accordingly, one virus construct was packaged into a shuffled cap gene from our homology based capsid shuffling attempt.
(1) The positive control consisted of the SV40 promoter driving a firefly luciferase (luc2) gene, thereby leading to an unspecific expression of the luciferase protein in all mice tissues.
In addition to packaging this construct into a wild type AAV virus, the positive control was also packaged as a transgene into our shuffled capsid which after selection pressure was already able to positively transduce Huh7 and HepG2 cells in cell culture.
(2) The off-targeting construct was composed of an SV40 promoter driving a firefly luciferase (luc2) gene with binding sites against miR-122 behind it. In order to achieve the highest expression in all mice cells but the liver cells, a perfect binding site of miR-122 was used for in vivo study.
(3) The synthetic tuning construct consisted of two viruses injected at the same time in the mice. The one virus packaged the expression construct of shRNA haat driven by the H1 promoter. The second virus packaged the following transgene: SV40 promoter driving luc2 with binding sites for shRNA haat behind it. In order to ensure a synthetic tuning effect a perfect binding site and one with a bulge that was introduced at position 9-12 were used for in vivo experiments, respectively. Those two binding sites should lead to a knockdown in the first case and a repression of luciferase expression in the latter in comparison to the positive control.
(4) The on-targeting construct consisted of two independent viruses which were co-infected into mice, as well. One of these viruses packaged the Tet Repressor (TetR) driven by an SV40 promoter. The expression of TetR is under the control of miR-122 as four binding sites of this miRNA were cloned into the 3’UTR of the gene. The second virus was composed of an sv40 promoter driving the Tet operator (TetO2) which monitors the expression of luc2. With this setup, luc2 expression should be inhibited by the TetR in all mice tissues except for liver cells, where TetR is downregulated by miRNA 122.
Virus Production
The viruses were produced on HEK 293-T cells and purified on an iodixanol gradient according to protocol.
In order to assess tissue tropism of the The TVroute was chosen so as to assess AAV serotype tissue tropism;
the luciferase transgene was used for visualizing the relative vector
distribution in all the animals in a real-time manner
bioluminescence imaging
Discussion
Methods
contructs
production of recombinant virus
procedure involving animals
The mouse experiments were conducted in accordance with the animal facility of the german cancer research institute of Heidelberg. Female NMRI mice were purchased from....??. At 8-10 weeks of age the animals were injected in the tail vein (TV), with ~1x10^11 particles of AAV-SV40-luciferase in 200µl of 1x phosphate-buffered saline. The mice are transferred to a holding device which restrains the mouse while allowing access to the tail vein. The tails were warmed before the injections and injections were carried out usind 27 gauge needles. All the mice recoverd from the injection quickly without loss of mobility or interruption of grooming activity.
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