- How much blood and stem cells does a typical umbilical cord hold?
The median size of cord blood collections in family banks is 60mL or 2 ounces. That small volume of liquid corresponds to 470 million Total Nucleated Cells (TNC) or 1.8 million cells that test positive for the stem cell marker CD34. Thus, most healthy full-term babies have over a million blood-forming stem cells in their umbilical cord blood. By comparison, most public cord blood banks will only keep collections that are much bigger than average, and throw out the donations that are below a threshold of a billion TNC, corresponding to a blood volume of about 90-100 mL or 3 ounces.
Sun, JJ et al., Transfusion Sept. 2010; 50(9):1980-1987
- Processing: Must cord blood be processed before storage?
The earliest cord blood transplants were performed with whole cord blood. Thus, it is not absolutely necessary to process cord blood in order to save patient lives. There has never been a prospective randomized trial to compare transplant patient outcomes with cord blood that had been stored whole versus processed.
Most cord blood banks, both public and private, now process cord blood to remove both the plasma and the red cells, and cryo-preserve the remaining buffy coat holding stem cells. Some banks also save the removed red cells and plasma in companion storage. Some banks save a sample of maternal blood.
The removal of plasma is also called volume reduction. The volume reduction enables more collection units to fit in a freezer and requires less cryogenic nitrogen per unit.
Also, the majority of banks remove red blood cells prior to freezing, primarily because these cells often burst during freezing and release iron from hemoglobin that can be toxic. The alternate to removing the red cells before freezing is to wash any broken cells out of the collection upon thaw. Removing the red cells also removes the donor's blood type (the ABO and Rh types). When cord blood goes from a donor to a patient for a transplant, the donor and patient can be compatible on all the HLA types used for transplant matching and still have incompatible red blood types.
- Are related donors better for transplants?
The overall answer is yes, but this is a complex topic.
The two important measures of patient outcome are: long-term survival, and the impact on quality of life from graft-versus-host disease (GvHD). Sibling donors tend to trigger less GvHD. Also, sibling donors are available faster than searching for an unrelated donor, and patients have better survival when they go to transplant faster after diagnosis.
The exact comparison of outcome between sibling or unrelated donor varies with the patient diagnosis. The NMDP website has a page on this, with numerous references. For many cancers the outcomes are comparable, although sibling donors have a slight edge. The largest study was by Weisdorf et al. 2002, for over 2900 patients with CML leukemia. When correcting for all other factors, the survival with sibling donor vs unrelated donor was 68% vs. 61%. Sibling donors show a significant improvement for pediatric cord blood transplants of hereditary disorders. The European Blood and Marrow Transplantation Group (EBMT) reported 3 year survival rates of 95% from a sibling donor vs. 61% from an unrelated donor.
Weisdorf, D.J. et al. Blood 2002; 99:1971-1977.
Bizzetto, R. et al. (EBMT) Haematologica 2011; 96(01):134-141