Gregory Hale, assistant professor of pediatrics at the University of Kentucky College of Medicine, is a bone marrow transplant expert. He also has an appointment with the Division of Blood and Marrow Transplantation at the Markey Cancer Center. He provides the following answer.
Blood that remains in the human umbilical cord and placenta after birth supplies doctors with a rich source of hematopoietic progenitor cells (stem cells), the precursors of all other blood cells. Bone marrow from donors has traditionally been used as a source of stem cells for restoration of diseased bone marrow, but researchers have demonstrated that cord blood provides an excellent alternative source. Thus, cord blood is utilized for the treatment of many diseases--such as leukemia, sickle cell anemia and Hodgkin's disease--that are typically remedied by bone marrow transplants (see table).
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All of these diseases have been treated with allogeneic cord blood transplants--cases where blood has been collected from a familial or unrelated donor, as opposed to autologous transplants, in which the patient's own blood is utilized. Transplantation is nonsurgical; the infusion of stem cells is similar to receiving a blood transfusion.
In many bone marrow transplant cases, the search for an appropriate donor can prove difficult at best. There appear to be several advantages to using stem cells from umbilical cord blood, including rapid availability, potential to expand the ethnic diversity of the donor pool (minorities are vastly underrepresented in bone marrow donor pools), no donor risk, less likelihood of viral contamination and less risk of graft-versus-host disorder (GVHD).
GVHD is a significant consideration because stem cells from a donor's bone marrow often recognize the host as foreign, resulting in complications after transplantation. Cord blood stem cells are potentially less immunologically active and may pose less risk of GVHD than stem cells from bone marrow.
One consideration to physicians, however, is the direct relationship between the number of stem cells needed and the weight of the patient. The volume of umbilical blood collected at birth averages 80 to 100 milliliters; thus, the majority of transplants have been pediatric cases. By using bone marrow, the doctor has a large supply of stem cells. Researchers are diligently seeking methods to increase the number of cord blood stem cells for use in larger adult patients. Other areas under investigation include the degree to which human leukocyte antigen (HLA)-mismatched grafts can be utilized and the use of gene therapy in cord blood stem cells.
The future holds great promise for the use of umbilical cord blood stem cells. In the transplantation discipline, collection of data from clinical trials will continue to improve knowledge, thereby helping to increase survival rates.