As far as I'm aware of, Aubrey de Grey has presented two options for introducing xenohydrolases into cells: enzyme replacement therapy (ERT) and gene therapy. The problem with ERT is that one would have to cross the blood-brain barrier, which provides some difficulties. But one cannot transfer genes into all brain cells either. That would be needed in order to get rid of tau (the protein that forms tangles inside neurons). The option that some genetically modified cells would secrete the enzymes into the blood stream to be picked up by others wouldn't help here, as this would require crossing the blood-brain barrier, even if the modified cells were in the brain. This is something I see as problematic and worth some attention. If it has been thought out, then fine.
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Advocacy & Research for Unlimited Lifespans