The stem cell is the origin of life. It is a single cell that can give rise to progeny that differentiate into any of the specialized cells of embryonic or adult tissues; that is, it is totipotent. The ultimate stem cell, the fertilized egg, divides five or six times to give rise to branches (lines) of cells that form various differentiated organs. During these early divisions, each daughter cell retains totipotency. Then, through a series of divisions and differentiations, the embryonic stem cells (ESCs) lose potential and gain differentiated function (a process known as determination). During normal tissue renewal in adult organs, tissue stem cells give rise to progeny that differentiate into mature functioning cells of that tissue. Stem cells with less than totipotentiality are called "progenitor cells." Most stem cells are found in the bone marrow, but some are found in the boodstream. There are also stem cells in the umbilical cord blood.
Bone Marrow Transplants in Patients After Radiation and Chemotherapy
Bone marrow is the soft, spongelike material that is found in the cavities of your bones. It contains stem cells that produce blood cells. the chief function of bone marrow is to produce the three types of cells found in the blood: red blood cells, white blood cells, and platelets. Chemotherapy and radiation therapy, when given at very high doses, destroy the bone marrow and the body's ability to produce new blood cells.
Bone marrow transplants date back to the mid 1950s. They were developed as a potential therapy for fatal blood diseases such as leukemia and aplastic anemia. Healthy bone marrow from a donor, usually a family mamber (called an allogenic transplant), is transplanted into a patient whose diseased cells have been wiped out by radiation and chemotherapy.
Autologous transplants, using the patient's own bone marrow, became possible in the 1970s. In the 1990s, it became possible to replace blood cells by using a special type of cell that circulates in the blood vessels, called a peripheral stem cell. Peripheral stem cells, taken from the patient's own blood, began to be used to support patients undergoing high dose chemotherapy, making the process simpler and less expensive. Unlike bone marrow, which requires the patient to undergo general anesthesia to remove it, peripheral stem cells are easier to get. The process is similar to donating blood.
Today, bone marrow and peripheral stem cells support are used to regenerate the bone marrow so that it can begin dividing and producing blood cells after high-dose treatments are given for such cancer as leukemia, lymphoma, childhood brain tumors, and neuroblastoma. It is being evaluated in clinical trials for various types of cancer including breast, ovary, multiple myeloma and Wilm's tumor.
Different Kinds Of Transplants
There are three main types of transplants:
- Autologous, in which patients receive their own stem cells.
- Syngenic transplants, in which patients receive stem cells from an identical twin.
- Allogenic transplants, in which patients receive stem cells from somebody else, either from a family member or an unrelated person.
Peripheral stem cell or bone marrow support are not considered treatments themselves; both are being done to allow a patient to receive very high doses of radiation or chemotherapy. The treatment doses that are given are so high that they severely damage the bone marrow or might even destroy it. The damaged marrow needs to be replaced with healthy marrow to allow a person to produce new cells to allow that person to have the ability to fight off infections, clot blood and transport oxygen.
- Stem Cells Handbook (Hardcover)by Stewart Sell
- Marion Morra and Eve Potts. Choices