CrateDane t1_jc35zy4 wrote on March 13, 2023 at 6:27 PM

Reply to comment by NOAEL_MABEL in CRISPR vs AAV - how do they differ? by HueX1

> > > > > Contrast that to AAV. AAV doesn’t really integrate into a genome (well isn’t supposed to in theory) - they work by creating what’s known as an episome (i.e a circular piece of dna that persists in cells and gets translated into the desired protein). AAVs can only shutoff a mutant gene if they carry a payload like siRNA/microRNA or something. AAVs never really fix the mutant gene, the episome just expresses the protein that’s not working. I suppose over the long run AAVs might not really ‘cure’ a genetic disease, because the episome will likely dilute out over time with cell divisions. You can only really administer an AAV once too because of immunogenicity issues.

That's often how they are used in practice, but unmodified AAVs are capable of insertion, in humans mostly at the AAVS1 locus.

NOAEL_MABEL t1_jc38vig wrote on March 13, 2023 at 6:46 PM

Yes, that’s why I wrote “in theory”. In reality, it isn’t that clean, even with modification.

Integration may not just be occurring at AAVS1, but all over the place. Studies have detected things like complex vector rearrangements and truncated vector genomes across multiple animals models inserted around transcriptional units. There seems to be no preference for gene coding regions and no clustering of integration sites.

In fact, The FDA had a CTGTAC meeting in 2021 to discuss these issues: https://www.fda.gov/advisory-committees/cellular-tissue-and-gene-therapies-advisory-committee/2021-meeting-materials-cellular-tissue-and-gene-therapies-advisory-committee