Are there any unfavorable aspects of cord blood transplants from unrelated donors?

The main disadvantage of cord blood is that the volume collected is fixed and relatively small. Therefore, the number of stem cells available for transplantation is low compared to the number of cells that can be collected in customizable bone marrow or peripheral blood stem cell harvests. The average total nucleated cell dose (number of nucleated cells per kilogram of the patient's weight) in a cord blood graft, for example, is less than about 1/10th that of the average bone marrow graft. As a consequence, engraftment (the return of nucleated blood cells, red blood cells and platelets) to the patient's blood is slower with cord blood than with bone marrow transplants. Cord blood transplant patients, therefore, may be more vulnerable to infection in the first two to three months after their transplant. This problem is greatest for adolescents and adults because they require a relatively large number of cells. [See Ongoing Research for encouraging news about stem cell expansion].

A cord blood transplant also may give the patient one of the rare genetic diseases of the blood or immune system. Families who donate cord blood are asked about their ethnic background and family history of genetic diseases. Cord blood is tested for common genetic diseases such as sickle cell anemia. And we obtain information about diseases that may be found in the infant before he or she is sent home after birth. However, some genetic diseases may not be apparent in the child for months or years and will not be found or even suspected by current screening methods. At present, it is also not possible to test for all of these rare diseases. Thus, there is a chance that a cord blood transplant may transmit to a patient a rare serious genetic disease that was not recognized beforehand.

Another disadvantage of cord blood is that the donor cells come from a newborn infant that will not be available for an additional donation of cells or bone marrow. In bone marrow transplants, on the other hand, the donor may be asked to make a donation of white blood cells (T-lymphocytes or T-cells) to help fight a recurrence of leukemia or development of lymphoma. Or a second marrow donation might be needed if the first one fails to engraft. T-cell donations and second transplants from the same donor are not available with cord blood. Another cord blood unit from a different donor would have to be given if the first one fails.