text: It doesn't yet.  Most current stem cell therapies use adult stem cells from the patients own body.  They are simply extracted from one area and put into another.  They are not genetically altered in any way.  A method currently being developed is to use SCNT to created a 'cloned' stem cell that would match the patient exactly.  Actual gene therapy for humans is a long way off, owing to the difficulty in actually getting any vector to deliver the gene to enough cells in an effective manner.