AAV integrates at a relatively low efficiency compared to other viral vectors, and the majority of your gene expression comes from episomal non-integrated DNA. This is generally considered to be an advantage (lower chance of integration in oncogenes) but does mean that the delivered gene will not be replicated and expressed in daughter cells if your target cell is dividing.
-- You're right, in the majority of cases, AAV cannot be administered twice but it's actually an issue of immune response and not integration. After the first administration, the body generates AAV capsid-specific antibodies which will neutralize the second administration before the gene is effectively delivered. But, there are different serotypes (capsids) of AAV, so you could administer AAV8 and then still be able to administer AAV9 the next time.
AAV naturally have a packing capacity of 4.7kb, which is potentially enough for a small promoter, TALE, and some nucleases. George church had a paper this summer involving AAV delivery of TALE fusions. AAV may not be so good for CRISPR though, but I guess we'll see what Editas Medicine comes up with.
Also you should definitely check out the work from Carl June delivering zinc finger nucleases to T-cells (ex vivo) to remove the CCR5 receptor, to create an immune system invisible to HIV. They're looking at using RNA electroporation instead of viral vectors because the short term transient expression of the nuclease is completely sufficient for genome engineering, whereas AAV is great when you need stable expression.
Lots of fun stuff to think about when choosing a vector!
And since it's my first post I'll add - I am a huuuge fan of this listserv.
On Wednesday, December 18, 2013 3:28:19 AM UTC-5, Mega [Andreas Stuermer] wrote:
On Wednesday, December 18, 2013 3:28:19 AM UTC-5, Mega [Andreas Stuermer] wrote:
While thinking about thene therapy once again, one question arised:
Usually, the Adeno-Associated visus integrates into a specific locus in chromosome 19. But the integration site does not seem to be very sequence specific.
Now, what I wonder: Once you had a AAV-gene therapy, you cannot have a second one? Or will the second therapy using the same vector integrate randomly? Or some other place in chromosome 19?
I know that's not diy bio, but a lot of smart people here :D
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