In an allogeneic transplant, a person’s stem cells are replaced with new, healthy stem cells. The new cells come from a donor or from donated umbilical cord blood. Chemotherapy or a combination of chemotherapy and radiation therapy is given before the transplant. This therapy kills the cancer cells, stops the patient’s immune system from working like it normally does, or both. The new stem cells are then added to the patient’s bloodstream through a tube. The procedure is like a blood transfusion.
Read our guide to allogeneic stem cell transplants. It helps you and your caregivers understand what to expect throughout your transplant journey.
Types of Allogeneic Transplantation
In an unmodified, or conventional, stem cell transplant, all of the stem cells are given to the patient without making any changes in a laboratory. The transplanted cells include a type of immune cell called T cells. Unmodified transplants are better for people who have a risk of relapse and who can take the medications that prevent the complication known as graft-versus-host disease.
In T cell-depleted transplants, the T cells are taken out of the stem cells in a laboratory. T cells from donated stem cells can cause graft-versus-host disease (GVHD) in the patient. After they are removed, the remaining donated cells, including blood-forming stem cells, are given to the patient. New T cells will form in the patient from the donor’s stem cells. These new T cells are less likely to cause GVHD than the donor’s T cells.
Because T cell-depleted transplants have a lower risk of GVHD, people are not required to take medications to prevent GVHD after the transplant.
In a cord blood transplant, the stem cells come from the umbilical cord and placenta of a healthy newborn. The chance of graft-versus-host-disease after a cord blood transplant is low, Because of that, a very close tissue type match between the patient and the newborn donor isn’t as important.
Cord blood transplants can be a good choice for people without a matched donor. This is particularly the case for people who need conventional transplants. Learn more about Memorial Sloan Kettering’s research on cord blood transplantation.
For people with certain types of cancer that has comes back after a stem cell transplant, doctors may slowly give them more T cells from the original donor. The low levels of T cells can stop the cancer without causing much graft-versus-host disease.
Finding a Donor
If your doctor tells you that you need an allogeneic transplant, finding a donor will be an important step.
The immune system can tell the difference between your body’s own cells and cells that are foreign. It works to destroy the foreign cells. Because of this, your donor’s tissue type should match yours as closely as possible. If the donor is not a close match, your immune system might react badly to the transplant and cause complications. These complications may be serious and difficult to treat.
Often the best donor is a patient’s brother or sister who has inherited the same human leukocyte antigen (HLA) genes. But only about one person in four who could be helped by allogeneic transplant has this ideal donor. For the remaining 75 percent of people, doctors check other family members, who may be only a partial HLA match (also known as a haplo match), or volunteer donor registries. In some cases, umbilical cord blood stored in public banks can be used for allogeneic transplantation.
The National Marrow Donor Program has a list of potential stem cell donors. It also is linked with other national and international registries. Together there are more than 10 million potential donors. If you need a stem cell transplant and do not have a matching donor in your family, you can use your HLA type to search for potential unrelated donors. You can also search for cord blood units from the National Cord Blood Program.
Online searches may find a number of potential matches, but only a transplant center can tell whether they are suitable and available. If you choose Memorial Sloan Kettering to be your transplant center, we will work with you to look through the matches. For more information, please call 212-639-7431.
Harvesting the Donor’s Stem Cells
If you get a transplant from a family member or from an unrelated donor, doctors will first collect, or harvest, the blood-forming stem cells from your donor’s bone marrow or blood.
Bone marrow collected in an operating room while the donor is under general anesthesia. A doctor puts a hollow needle into the rear and sometimes the front hipbone, both of which have a lot of bone marrow. The breastbone is another place with a lot of marrow, but it is very rarely collected there. The donor will not need stitches, but will have some pain and tenderness at the site of the harvest for about a week.
Until recently, stem cells were taken only from the bone marrow. Today, doctors can also collect stem cells from a donor’s circulating blood. These are known as peripheral blood stem cells. They are collected using a procedure called apheresis. Unlike a bone marrow harvest, apheresis does not have to be done in an operating room, and the donor does not have to be given general anesthesia.
A few days before the procedure, donors are usually given a medication called G-CSF (filgrastim, Granix®, Neupogen®, Zarxio®) or GM-CSF (sargramostim, Leukine®), or a combination of the two. These medications increase the number of stem cells being made. They can cause flu-like symptoms and bone pain for a few days.
Apheresis takes several hours over two to four days. The blood comes out through a tube that’s put in one of the donor’s veins. It then goes through a machine that separates the stem cells from the other blood cells. The other blood cells are then returned to the donor. The stem cells collected during the procedure are either used immediately or are frozen and stored.