Bone Marrow Transplants
Bone marrow transplants are complicated but can save a child with cancer
By Joanne Kurtzberg, MD and Dennis Clements , MD. PhD, MPH

When normal levels of treatment for a child with cancer aren’t enough, more extreme measures may be necessary. Higher levels of radiation, used to kill cancerous cells, can also threaten important bone marrow and necessitate a bone marrow transplant -- a complicated but lifesaving procedure.

In a bone marrow transplant, the sick child’s bone marrow is permanently replaced with new bone marrow.

The transplant itself is simple; the marrow is infused into the blood like a blood transfusion.

However, before the transplant, the child has typically been treated with up to two weeks of high doses of potentially lethal chemotherapy or radiation therapy (or both) that cause side effects for one to three months afterwards.

During this time, the child experiences many complications, is at high risk for developing a serious or fatal infection, and must be hospitalized in an isolation unit.

Cells from the transplant begin to grow after about one month, but full recovery takes one to two years. Children undergoing the procedure cannot go to school, church, malls, movies, or other group activities for approximately one year.

What Is Bone Marrow?
Bone marrow is the body’s blood factory, manufacturing millions of blood cells every day. It produces red blood cells that carry oxygen, white blood cells that fight infection, and platelets -- small particles that help with blood clotting.

Bone marrow is one of the only organs in the body that produces new cells on a continuous basis. This makes bone marrow susceptible to serious side effects from chemotherapy used to treat patients with cancer.

Chemotherapy kills dividing cells regardless of whether they are normal or cancer cells. The only dividing cells in our bodies are our hair cells, the cells that line the mouth, stomach and intestines, and the bone marrow cells. That’s why chemotherapy commonly causes side effects like hair loss, mouth sores, vomiting and diarrhea (called mucositis), and low blood counts.

Low blood counts can lead to serious infections or bleeding and can be life-threatening.

In some patients with cancer, the standard doses of chemotherapy or radiation therapy fail to cure their disease. If too much chemotherapy is given, the bone marrow will be permanently damaged and the patient won’t be able to make blood cells, a complication that would be fatal.

To treat the cancer but avoid permanent loss of bone marrow function, a transplant is given to rescue the bone marrow from the toxic effects of the therapy necessary to cure resistant cancer.

Bone Marrow Donors
Most of the time, another person’s blood stem cells must serve as the donor cells. Donors must be matched through a system called human leukocyte antigens (HLA).

This system identifies proteins on the surface of our cells which code for our unique identity. Each of us has six important proteins -- three inherited from our mother and three from our father.

In a typical family, each parent will match halfway and each sibling will have a 25 percent chance of matching the patient. Since a full match is best, many patients don’t have a close enough match in their family.

The National Marrow Donor Program (NMDP) was established 20 years ago to allow adults to donate their blood stem cells to a patient in need of a bone marrow donor. Currently there are over seven million adults who have volunteered to participate in the NMDP registry. The NMDP has facilitated over 20,000 transplants in the past 17 years.

Even with the NMDP, roughly half of the patients in need of a bone marrow transplant cannot find a fully matched donor. Umbilical cord blood, a relatively new source of blood stem cells, which doesn’t have to match completely, can be used for some patients’ transplants.

Umbilical cord blood is the baby’s blood left over in the afterbirth (placenta) after the baby is born. It can be collected without any risk to the mother or baby. In fact, it is frequently discarded as waste, but is now known to contain lifesaving stem cells similar to those found in bone marrow.

The blood can be collected from the afterbirth within minutes of the baby’s birth and then stored at ultra-cold temperatures until needed for a transplant. With support of the National Institutes of Health, the NMDP, and private philanthropy, approximately 15 public cord blood banks have been established in the U.S. to provide cord blood donors for patients in need of transplantation therapy.

Treating Genetic Diseases
While bone marrow transplantation has traditionally been used to treat patients with cancer, it also can be used to correct genetic diseases.

Diseases which cause defective blood formation like sickle cell anemia, thalassemia, or immune deficiency (bubble boy disease) can be cured with a bone marrow transplant.

We’ve learned that the bone marrow can also be a “factory” to produce an enzyme or protein that might be missing in a child with a metabolic disease. While these diseases are very rare, they cause severe damage to the brain, heart, liver, lungs, eyes, and other organs during childhood.

If a transplant is performed early in the course of the disease, before too much damage has occurred, the disease is corrected and organ damage is prevented.

Recently, exceptional successes have been seen in young children with Hurler syndrome, Krabbe disease, adrenoleukodystrophy (Lorenzo’s oil disease), and other diseases.

Success Rates
Today bone marrow transplantation is performed only in children with very serious and life-threatening conditions. The majority of children going through the procedure have a life expectancy of less than one year without treatment.

About half of the children who have a transplant are cured of their underlying disease. The others die from relapses of their disease or complications from the procedure.

Younger children and infants with genetic diseases and children who have only had one relapse of their cancer have the best prognosis. In these cases 70 to 90 percent of children do well.

Bone marrow transplantation is also teaching us about what cells can do to repair damaged tissues.

Five to 10 years from now, what we are learning from bone marrow transplantation today could lead to the development of less risky cellular therapies that will repair and regenerate tissues and organs damaged by disease, accidents, or treatment.

Joanne Kurtzberg, MD, is a pediatric hematologist oncologist who directs the Children’s Blood and Marrow Transplant Program at Duke. She is also the founder and director of the Carolinas Cord Blood Bank at Duke, a public cord blood banking facility. Dennis Clements , MD. PhD, MPH, is the chief medical officer of Duke Children's Hospital. For more information, visit www.dukehealth.org

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