My dad researched doing exactly this for 30 years. They had several treatments go to clinical trial, though I believe none of theirs have gone forward.

It's known as gene therapy: https://en.m.wikipedia.org/wiki/Gene_therapy

The same lab used a genetically modified virus to develop an oral rabies vaccine that is in wide use today.

This was dad's boss: https://nrc.canada.ca/en/stories/foundations-discovery-honouring-work-canadian-researcher-dr-frank-graham