Bone marrow transplant 2

This blog entry continues a discussion of the elements of the special type of stem cell transplant known as bone marrow transplant. Many of the procedures will be similar for other kinds of stem cell transplants. Most of the information here is adapted from http://cancer.healthcentersonline.com/bloodbonecancer/bonemarrowtransplants3.cfm

Before the bone marrow transplant procedure

A group of specialists, known as the transplant team, are usually involved with all aspects of the bone marrow transplantation. The team may include:

• Physicians who specialize in oncology, hematology, and bone marrow transplantation and infectious diseases
• Transplant nurses
• Dieticians
• Physical therapists
• Social workers

Initially, a patient is evaluated to see whether she is a good candidates for providing her own marrow cells or blood stem cells for transplantation (autologous transplant). Stem cells obtained from the patient (autologous transplant) must be largely free of any cancer. After the cells have been harvested, they can be treated in a procedure known as purging that removes any cancer cells from the harvested cells. This helps minimize the chances of the 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 that enough healthy cells will be available.

If the patient’s bone marrow is extensively affected  by cancer, an outside donor will be necessary. The choice of donor begins with a person most closely related genetically (an identical twin = syngeneic transplant) and progresses down the sequence as far as necessary (allogeneic transplants). The object is to find a donor with stem cells closely resembling the patient’s. The focus for matching is on a set of proteins called human leukocyte–associated (HLA) antigens, which are found on the surface of the cell and are identified through a blood test.

In general, the more HLA antigens match between donor and patient, the greater the likelihood that the donor’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), a complication that occurs when a donor’s white blood cells identify normal cells in the patient’s body as foreign and attack them. 

When matching a patient to an outside donor (other than an identical twin), a family member is the first choice, with brothers and sisters usually providing the best match. According to the National Cancer Institute (NCI), only 25 to 35 percent of patients have siblings who are an HLA match.

If a suitable match is not found inside the family, help will be needed from the nationwide donor registry list maintained by the National Marrow Donor Bank. The odds of finding HLA–matched stem cells in an unrelated donor are 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 in which bone marrow transplants are sometimes used. 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 red blood cell formation)
• Sickle cell anemia (chronic anemia marked by sickle–shaped red blood cells)
• Severe combined immune deficiency (group of inherited disorders characterized by a lack of immune response)

Marie Godfrey, PhD   <!--break-->