An allogeneic stem cell transplant is one that is obtained from another person, whose blood and immune make-up matches closely with your blood and immune components. The donor may be a parent, sibling, relative or a complete stranger.
Stem cells are the building blocks for all other types of cells that can convert into red blood cells, white blood cells and platelets. These cells are required to keep your body in a healthy state. In certain disease conditions such as cancers and other blood and bone disorders, your bone marrow loses its ability to produce stem cells that can differentiate into various other types of cells. In such conditions, stem cells transplants are recommended.
Uses of Allogeneic Stem Cell Transplantation
There are several disease conditions where allogeneic stem cell transplants are very useful. These include
• Hodgkin’s lymphoma
• Non-Hodgkin’s lymphoma
• Leukemia or blood cancer
• Multiple myeloma or skin cancer
• Aplastic anemia
• Sickle cell disease
• In conditions where the bone marrow has been destroyed by radiation or chemotherapy
How are stem cells matched with the donor?
The main requirement of any stem cells transplant is that the cells must match the patient’s own stem cells as closely as possible. This is determined by comparing a set of proteins called human leukocyte-associated (HLA) antigens, which are present on the cell surface. These proteins are matched with the donor’s proteins before deciding if the stem cells are a match or not. The higher the number of matching HLA antigens, the greater the chance that the procedure will be successful and that the patient’s body will not reject the new stem cells.
The National Cancer Institute says that the chances of a sibling having a closely matched HLA antigen profile are just about 25-35%, while that of an unrelated donor is 50%. Furthermore, HLA-matching is very successful when the donor and recipient have the same ethnic and racial background.
Harvesting Stem Cells from Donor
The stem cells are obtained from the donor either by bone marrow transplantation (BMT) or peripheral blood stem cell transplantation (PBSCT).
BMT is usually done under general anesthesia by inserting needles through the skin over the hip bone or the breastbone. The marrow is harvested through the liquid center and is processed to separate blood and bone tissue. The harvested stem cells are then frozen until the recipient is ready for transplantation. This procedure usually lasts for about 1 hour.PBSCT is performed by using a method called apheresis, wherein the donor’s blood is put through a machine that separates blood and stem cells. The separated stem cells are frozen, while the blood is returned to the donor via a central venous catheter. The whole process takes about 4-6 hours.
Risks associated with allogeneic transplants
The major risk associated with allogeneic transplants is Graft-versus-host disease (GVHD). In this condition, the transplanted cells attack the recipient’s cells mainly from the skin, gastrointestinal tract and liver leading to kin rashes, jaundice, liver disease, and diarrhea. This is a dangerous condition where the recipient is at an increased risk of infections and other immune related complications. The standard treatment for GVHD is removal of T-lymphocytes from the stem cell collection. Additionally, immunosuppressive drugs such as methotrexate, cyclosporine and prednisone are prescribed to halt the disease.
Other complications of allogeneic transplantation include
• Graft failure
• Fatal infections
• Veno-occlusive disease (VOD), which is a serious liver condition that manifests as liver, weight gain, increased fluid in the stomach and jaundice
• Nausea and vomiting
• Mouth sores
• Unexplained bleeding
The promise of allogeneic stem cell transplants is immense. Scientists are also exploring the use of these transplants in kidney cancer, juvenile arthritis and lupus. The main challenge is to match the donor and recipient cells as closely as possible.