Allogenic Stem Cell Transplant

Allogeneic = Non Self Donor. In this procedure, a donor's HLA-matched stem cells are collected and transplanted into the patient. HLA matching is the process of determining if the donor and the patient share certain critical genes that educate the immune system. The safest allogeneic transplants occur when donors and patients share the same HLA genes. Because these genes are all on one of our chromosomes and because we each inherit a chromosome from each parent, there is a 1:4 chance that a brother or sister will have the same HLA genes. When there is not a brother or sister who is a match for the patient, we often are able to find a close match among the millions of volunteer donors in the international HLA registry. 

Recent advances in our understanding of immune recovery after an allogeneic transplant have allowed us to also use half matched or "haplo" donors in patients without other donor options. This is still an experimental procedure in our program, offered on a protocol basis.

"Mini" Transplants

Before an allogeneic transplant, the patient is admitted to the hospital to undergo intensive treatment with chemotherapy or radiation. Sometimes the goal is simply to replace the patient's bone marrow and immune system with new cells from the donor rather than kill huge numbers of cancer cells. In this case, less intensive therapy can be used in a "mini" allogeneic transplant. The appropriate use of this kind of transplant is complicated and will be discussed with you if it is an option. After the treatment, whether standard or "mini," the previously collected donor stem cells are transplanted back into the patient in a manner similar to a regular blood transfusion.

This allogeneic transplant procedure helps patients overcome dangerous side effects resulting from the intensive treatment's destruction of white and red blood cells and platelets and privodes a new immune system for the patient. Without new stem cells, patients would have too few white cells to ward off a life-threatening infection. They would also develop anemia because of low numbers of red cells and bleeding problems caused by too few platelets, which help the blood to clot. These new donor immune cells can serve as another potential treatment for the patient's cancer (see the next section).

The Engrafted Immune System

After an allogeneic (donor) stem cell transplant, the patient's bone marrow cells are replaced with new, healthy donor cells. These cells will produce the white blood cells, red blood cells and platelets that the patient needs for a healthy blood system. Moreover, all of the cells that comprise the patient's immune system are replaced, resulting in a completely new immune system. These new donor immune cells often can recognize any residual cancer cells in the patient as "foreign invaders" and directly attack and kill them. This is a very useful therapy for patients that do not respond well to other standard therapies. Every cancer has a different sensitivity to this immune attack, so this treatment does not work with all cancers. Fortunately, most cancers of the bone marrow do respond.

Graft versus Host Disease (GVHD)

Unfortunately, there is a potential downside to this form of therapy in that the new immune cells may recognize some normal parts of the patient as "foreign invaders" and attack these normal cells. This complication is called "graft versus host disease," where "graft" refers to the donor cells and "host" refers to the patient. The better the HLA match between the donor and patient, the lower the chances of severe GVHD. Certain new post-transplant procedures have allowed us to use only half-matched—or "haplo"— donors. Preliminary results suggest that the rate of GVHD is close to that of other allogeneic transplants.  This is still an experimental procedure. 

Graft versus host disease can be a life-threatening problem and is the major complication of an allogeneic transplant. If an allogeneic transplant is part of your therapy, we will discuss this issue with you extensively.

For more information, please call the Temple Bone Marrow Transplant Program at 215-214-3122.

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