A bone marrow stem cell transplant uses stem cells derived from bone marrow to provide a fresh and healthy source of new blood cells which in turn, allows for a patient to receive higher doses of chemotherapy to treat certain types of cancer such as leukaemia. This ultimately means that a person has a better chance of surviving cancer. The bone marrow stem cells may be allogeneic and therefore donated by a family member of stranger, or they may be autologous, which utilizes a patient’s own stem cells.
Importance of Bone Marrow
Bone marrow is the soft tissue found in the centre of bones. It is here that new blood cells are formed; stem cells are considered the parent cells of these blood cells. Stem cells in the marrow have the vital task of creating a person’s three blood cell types. These are:
- Red blood cells: transport oxygen
- White blood cells: fight disease
- Platelets: aid in clotting after injury
Bone marrow stem cells are found in bone marrow and in a person’s blood. After stem cells multiply, they form immature blood cells, which are then subject to a collection of changes that allow them to develop into mature blood cells. Once mature, the blood cells migrate from the marrow and are introduced into the bloodstream, where they provide important functions in keeping the body alive and healthy.
Effects Of Chemotherapy On Bone Marrow
Because chemotherapy operates by destroying the fast growing cancer cells, higher levels are generally more effective for killing cancer cells. Similar to cancer cells, however, bone marrow cells grow quickly and are also very sensitive to chemotherapy treatment. The chemotherapy can eventually destroy the marrow completely, which then prevents new and healthy blood cells from developing.
Autologous Bone Marrow Stem Cell Harvest
In an autologous transplant, a patient’s own stem cells are used. The problem here is that the patient’s bone marrow and peripheral blood usually have a lot of cancer cells, so isolating stem cells can’t generally occur until the patient is in remission.
A patient will usually receive some chemotherapy to reduce cancer cells before stem cells are collected. The harvested stem cells are also treated to ensure that no cancer cells remain. Higher doses of chemotherapy are then given, sometimes alongside complete body radiation, to confirm that no cancer remains. Stem cells are then transplanted back into the body via a rapid injection. Stem cells will eventually migrate to the bone marrow, where they latch onto other cells there and develop into the different blood cells.
Allogeneic Bone Marrow Stem Cell Harvest
In the allogeneic transplant, a suitable donor is used; this may be a family member or a person unrelated to the patient. Similar to the autologous bone marrow stem cell harvest, a patient receives high doses of chemotherapy and possibly also radiation therapy. This therapy will destroy the patient’s marrow and immune system, so that the patient’s immune system can’t attack the transplanted cells that are received from the donor. Graft rejection is a very real concern for allogeneic transplants, where the recipient’s immune system recognizes the transplanted cells as ‘foreign’ and launches an immune attack. Prior to the transplant, red blood cells in the stem cell sample are usually identified and discarded and particularly so if the donor’s blood group is different from that of the patient.
Stem cells are then infused into the patient via an intravenous line over several hours. Stem cells travel to the patient’s bone marrow where they develop and produce the blood cells necessary for blood functioning. Patients may also still be given drug therapy for some time to reduce the chances of immune rejection.
Bone marrow stem cell harvests are clearly a life saving technique for those suffering from certain cancers such as leukaemia. They are one of the ‘older’ stem cell therapies and have been proven effective for decades now. There are, however, still issues of rejection that warrant further development and refinement of stem cell harvesting techniques. It is hoped that scientists will continue to focus on research to improve the odds of success for this important treatment.