[iamleppert]

I had hemophilia gene therapy. It worked for a period of time but the results were not permanent. The problem with many of the gene therapies is that they do not change the nuclear DNA, they just insert copies of working genes into the cell. If a cell dies, it’s gone. The results aren’t carried through to new cells during division.

The other problem is with viral vector based gene therapy is you can’t have it again. You develop antibodies which prevent it from working again, and it could cause a dangerous immune response.

Then there’s the cost. My single treatment cost $3 million as part of a clinical trial, and lasted about 3 years. Normally, it costs about $1 million a year for my normal factor product, which I had to go back on. So I guess it was a wash and it was nice to be free of the medication for a few years. But it’s definitely not perfect and has its own limitations.

[JPLeRouzic]

I am sorry you experience this disease. I have a question: You said "they do not change the nuclear DNA, they just insert copies of working genes into the cell ... The results aren’t carried through to new cells during division."

Isn't this a bit contradictory? I mean, if they insert copies of working genes into the cell, it is in nuclear DNA, so when the cells divide, the daughter cells carry the new gene?

I can imagine other cases, for example, progenitor cells were not infected, cells that do not divide, etc...

Thanks for any answer

[iamleppert]

The working genes they insert are just into the cell envelope itself, not into the cell nucleus. There are actually a lot of DNA that is free floating around in the cell, and are used during protein synthesis, called episome or non-integrated DNA. This is distinct from the DNA inside the nucleus, which gets copied from generation to generation.

There are techniques that work on modifying nuclear DNA but from my understanding it's much harder (like using CRISPR) and has a lot more risks for things like causing cancer due to off-site editing.

The scales that this technology works is mind-boggling. 10^12 to 10^14 per kg of body weight of individual viral particles that all must do the same thing, and work correctly at scale. Even a few errors could cause serious problems.

[JPLeRouzic]

Thanks, I learned something today!

[puzzlingcaptcha]

AAV-based vectors are specifically non-integrating. Wild-type AAVs can integrate, but in the absence of rep protein they will instead persist in the cell nucleus in the form of episomal concatemers - long, circular DNA structures containing multiple copies of the virus DNA. These will not replicate when a cell proliferates - they will instead dilute with each division. This makes them desirable for treating diseases affecting post-mitotic tissue like muscle, less so for, say, bone marrow. Unless transient expression (but not as transient as with NLPs) is what you want.

[JPLeRouzic]

Thanks, I thought AAV-based vectors were integrating. Then it's not surprising that some clinical trials using AAV vectors were unsuccessful while the pre-clinical studies were successful, it's looks more a way of cheating than a creating an effective new therapy.