Blood stem cells are also found in blood circulating through the body. Transplants replace patients , diseased blood stem cells with healthy cells from a donor. Within a week or two, the transplanted cells begin to reproduce normally, replacing the patient's blood and immune system. These transplants require a precise genetic match between patients and donors. Finding compatible donors for hearts and livers is easier than finding two people similar enough genetically to successfully exchange blood stem cells.
Many patients can receive transplants from their brothers or sisters or other close relatives.
But 70 percent of patients do not find compatible donors within their families, and must search for an unrelated donor. Finding unrelated donors would be nearly impossible without an international net work of marrow donor registries that make potential donors available to patients anywhere in the world. Michael needs a donor.