Before talking about the differences among sources of stem cells, it's important to first understand the transplant process itself, and the benefit of finding the best possible genetic matches for patients. During the 4-10 days before a conventional transplant, patients typically are given high doses of chemotherapy and radiation therapy causing cell counts to drop dramatically. On the day of the actual transplant, stem cells are injected intravenously, and find their way to the bone marrow. If successful, over the next several weeks, the hematopoietic stem cells will rebuild a new blood and immune system.80
One of the most important factors that affect the success of a transplant is HLA matching or immunological compatibility; the closer the relationship of the donor to the recipient, the greater the likelihood of finding an HLA match. The closer the genetic match, the less chance there is of the graft being rejected and the immune cells of the graft attacking the recipient - known as graft versus host disease. But a good match is hard to find.51
Stem cell transplants fall into two major categories:
Allogeneic Transplants: involve taking cells from one person and transplanting them into another person
Autologous Transplants: the patient is the source of his or her own stem cells for transplant
For allogeneic transplants, family members offer the best likelihood of success, but even among family members there are challenges. In fact, only one third of patients requiring a hematopoietic stem cell transplants have a compatible family donor.16 The other two thirds of patients must search the National Marrow Donor registry for an unrelated bone marrow or cord blood donor. Of those seeking a match through the hematopoietic stem cell registries, many will fail, leaving a major unmet medical need for transplant sources.51,52 About 9,000 patients a year die in the United States waiting for a bone marrow match, about one third of them are children.
Cord blood, which has typically been discarded as medical waste, provides an alternative source of hematopoietic stem cells. With cord blood, the degree of HLA mismatching that can be tolerated is greater than with bone marrow or peripheral blood.81 Stored cord blood is readily available to family members should the need arise - without having to wait for registries to find a match. The process is painless and there's a reduced risk of graft versus host disease.41 It's important to note, however, that the time to engraftment and the ability to treat adults are both cell dose dependent.