You don't necessarily need to hit every cell in an organism to produce useful therapies. Most cells aren't going to be expressing the gene that's causing a dise

You don't necessarily need to hit every cell in an organism to produce useful therapies. Most cells aren't going to be expressing the gene that's causing a disease, only cells in the affected tissue or organ need to be treated. In some cases, you may not even need to get all of the affected cells, just repairing a subset could improve outcomes. (1/8 of a functioning pancreas is a lot better than 0/8)