Gene therapy is a promising approach for treating a large spectrum of human diseases and particularly monogenic diseases that can be corrected
through gene replacement therapy based on introducing a functional copy of the defective gene.
Basically what was happening when you use a hematopoietic stem cell to correct an inherited metabolic disease is that
through engraftment of that cell you are allowing that cell to become the
replacement source for the missing enzyme or other factor - almost like a cellular form of
gene therapy or, as I call it, «poor man's
gene therapy».