Question: If genes can be transplanted from animals to humans, why can’t the gene that produces insulin be transplanted from an animal to a patient with diabetes for a cure?

Simone Sturniolo answered on 21 Jun 2013:

Excellent insight there. The problem is that there is a difficulty. See, there’s not even a need to use animals: the best thing would be to copy the gene from another human (it doesn’t take much to do so, a drop of his blood would be enough!) and put it into the patient’s DNA. Problem is, the easiest point to change an organism’s DNA is when he’s an embryo – a single cell waiting to develop into a full organism. When you’re grown up, you have billions and billions of cells, and each of them has a copy of DNA inside of its nucleus – and you should modify ALL of them for the change to be effective (ok, for diabetes, probably only the pancreatic ones, since they’re the ones who produce insulin, but that’s still a lot). It’s not completely impossible – it’s called genetic therapy and they’re working on it. The idea is to use a genetically modified virus to take the new gene inside a developed organism’s DNA. Viruses usually “hijack” a cell’s DNA in order to reproduce themselves: this instead would use them to hijack it into what we want it to be. A quick Google search reveals they’re already testing this method on animals:

http://www.diabetes.org/for-media/2013/gene-therapy-used-in-dogs-to-treat-type1-diabetes.html

Science surely is awesome! And judging from this and other questions you seem to have nice ideas and a lot of specific knowledge – you should probably become a genetic engineer or a medical researcher (well, you would probably do so even without my advice)!