And if some of that mRNA happens to land in cells that don't readily get replaced, like heart muscle, what happens next? >There is no known pathway of persiste

And if some of that mRNA happens to land in cells that don't readily get replaced, like heart muscle, what happens next? >There is no known pathway of persistence in this mechanism No known, and published in a paper, pathway. Engineering is about using things in practice we don't yet understand. They didn't know why suspension bridges kept falling down, so they just used a "safety factor" to decide how much to over-build a structure vs its theoretical capacity. We have no idea what the long term consequences are of this gene treatment. It's not possible to have 10 year or more data on something just cooked up in the past 3 years.