Stem cells are unique cells located in bone marrow or peripheral blood that can develop into red blood cells, white blood cells, and platelets. The goal of cancer treatments such as radiation therapy and chemotherapy is to destroy cancer cells. Unfortunately bone marrow and other healthy cells are damaged in the process.
An allogeneic stem cell transplant provides the cancer patient with healthy stem cells from another person, a donor, following cancer treatment. The best stem cell donor is a sibling, whose tissue type matches the patient's as closely as possible.
Tissue type is defined by pairs of genetic markers on white blood cells called human leukocyte antigens. One of each pair is inherited from the mother and father. The more closely the donor and patient's markers match, the more successful an allogeneic stem cell transplant is likely to be.
For patients who do not have a family member with matching tissue, it is possible to find a donor through a bone marrow registry. Once an appropriate donor is identified, stem cells from the donor's blood can be harvested through a simple, non-surgical procedure known as apheresis.
For this procedure, medication is given a few days prior to collection to encourage stem cells to leave the bone marrow and enter the blood. Blood is then withdrawn from one arm and circulated through an apheresis machine, or a "cell separator," where the stem cells are removed. The remaining blood components are returned through the catheter in the other arm.
Stem cells are returned or "transplanted" back into the body through a central line. It takes 2-3 weeks before the transplant "takes," or engrafts, and begins to produce healthy new blood cells.
Graft-versus-host disease can occur when the donor's cells are recognized by the patient's (host's) body as foreign. To prevent graft-versus-host disease and graft rejection, medications are usually given to the patient for the first 3-6 months following transplantation.
