Initially, patients will be evaluated to determine if they are good candidates for providing their own bone marrow cells or blood stem cells for transplant. If the bone marrow is extensively affected by cancer, transplant probably will not be an option. If the patient does not have an identical twin, an allogeneic transplant (cells from someone other than the patient or an identical twin) will be the only option. 

Those who are receiving stem cells from an allogeneic donor will have to be matched to an individual whose stem cells closely resemble their own. In looking for such a match, a set of proteins called human leukocyte-associated (HLA) antigens will be examined. These proteins are found on the surface of the cell and are identified through a blood test.

In general, the more HLA antigens that match between donor and patient, the greater the likelihood that the patient’s body will accept the new stem cells. A higher degree of match makes it less likely that the patient will develop graft-versus-host disease (GVHD) This is a complication that occurs when a donor’s white blood cells perceive the patient’s normal cells as foreign and attack them.  

When matching a patient to a donor other than an identical twin, a family member is the first choice, with brothers and sisters usually providing the best match. However, only 25 percent to 35 percent of patients have siblings who are an HLA match, according to the National Cancer Institute (NCI). A parent may not be considered an acceptable match because the patient will have HLA material from each parent.

If a suitable match is not found inside the family, the patient may need to contact a nationwide donor registry list maintained by the National Marrow Donor Program. According to the NCI, the likelihood of obtaining HLA-matched stem cells from an unrelated donor is approximately 50 percent. These odds improve significantly between individuals who share the same ethnic and racial background. However, many racial groups are underrepresented in the nationwide donor registry, making it even more difficult to find matches for patients who are African American or Asian.

In addition, because of the complexity and diversity of HLA antigens, it is extremely difficult to match patients to donors who are unrelated if the patient has uncommon or rare HLA antigens.

In some cases, stem cells will be obtained from umbilical cord blood. This can only take place when a pregnant woman makes arrangements with a cord blood bank before her baby’s birth. Public cord blood banks accept donations of umbilical cord blood that may be used in patients waiting for a match. Private cord blood banks store umbilical cord blood for a fee. These stem cells can be used in the child or another family member should the need arise in the future.

Families will most often consider storing umbilical cord blood privately when they have a child or close relative with a medical condition for which bone marrow transplants may be performed.  A family history of these conditions often is enough for parents to consider this option. Conditions treated with bone marrow transplants include:

• Leukemia
  
  
• Lymphoma
  
  
• Aplastic anemia (condition that prevents blood cell formation)
  
  
• Sickle cell anemia (genetic chronic anemia marked by sickle-shaped red blood cells)
  
  
• Severe combined immune deficiency (group of inherited disorders characterized by a lack of immune response)

Finally, stem cells also can be obtained from the bloodstream itself. This is often the source for autologous transplants (stem cells obtained from the patient), and it is also being used in an increasing number of allogeneic transplants.

Stem cells obtained from the patient must be largely free of cancer. After the cells have been harvested, they can be treated in a procedure known as “purging,” which removes any cancer cells from the harvested cells. This process helps minimize the chances of cancer returning after the transplant. The purging process also damages some healthy stem cells, so more cells are harvested before an autologous transplant than in other transplants to ensure an adequate supply of healthy cells.