In my eyes (peripheral blood) hematopoietic stem cell (or bone marrow) transplantation is the best way to cure sickle cell disease.
Transplants are usually done in children under age 16 who have had sickle cell complications like pain and strokes.
The child first gets strong chemotherapy drugs to destroy its bone marrow and damaged red blood cells. Then, the child gets healthy hematopoietic stem cells or bone marrow from another person (allogeneic transplantation). These stem cells then will start to make healthy red blood cells.
Older people do not get transplants as often because they are more likely to have complications.