Well some people have been benefiting from stem cell therapy for a long time, at least in a crude way with bone marrow transplants.
22 years ago they also tried the first gene therapy for a condition called severe combined immunodeficiency (SCID). It worked. They tried something similar on 10 kids with SCID in 2000. Turns out by 2007 4 of the 10 had developed leukaemia so yes we can have gene therapies but let's not rush them. There's very dangerous complications if we're not careful.