Sources of stem cell transplants
Strictly speaking, a peripheral blood stem cell transplant (PBSCT) refers to the use of blood stem cells which have been collected from the blood stream (i.e. peripheral) while a bone marrow transplant (BMT) refers to the use of blood stem cells collected directly from the bone marrow. Stem cells can also be collected from the umbilical cord blood of newborn babies (cord blood transplant).
You will find that many people just stick to using the terms bone marrow or stem cell transplant regardless of the source of the stem cells.
On the day of the transplant, stem cells are simply given intravenously (through a vein) almost like a blood transfusion. From there they travel to the bone marrow, set up home and begin to rebuild the body’s blood and immune systems.
Peripheral blood stem cell harvest
In most cases stem cells are collected directly from the bloodstream. An autologous transplant uses the patient’s own stem cells. These are collected in advance and frozen until the scheduled date of the transplant. While stem cells normally live in your marrow, a combination of chemotherapy and a growth factor (a drug that stimulates stem cells) called granulocyte colony stimulating factor (G-CSF) is used to expand the number of stem cells in your marrow and cause them to spill out into the circulating blood.
In an allogeneic transplant where the stem cells are donated from another person, the donor has to undergo a series of G-CSF injections (usually four doses given over four days) to stimulate the stem cells to enter the bloodstream. Some people experience flu-like symptoms including mild to severe bone pain, fevers, chills and headaches while using G-CSF. The doctor may recommend paracetamol to relieve any discomfort.
Once the peripheral blood stem cells (PBSC) are at a certain level in the bloodstream the donor or patient is attached to a blood cell separator (apheresis machine) where the cells are withdrawn from the blood in a process similar to dialysis. The apheresis machine draws blood from the body, spins the blood very quickly, collects the part that contains the blood stem cells, and returns the rest of the blood back to the body. This is a continuous process. This procedure is usually carried out in the outpatient department of a hospital.
A peripheral blood stem cell collection usually takes three to four hours. A certain number of stem cells are needed for a blood stem cell transplant and they may not all be collected on the first day. It is sometimes necessary to come back on the following day to repeat the procedure. The stem cells may be used immediately or frozen (cryopreserved) and stored until they are infused on the day of the transplant. Blood stem cells can remain frozen for many months or years before they are used.
Bone marrow harvest
Collecting stem cells directly from the bone marrow is a surgical procedure usually carried out in an operating theatre under a general anaesthetic. Stem cells are collected from the back of the donor’s hip (iliac crest). A special needle is passed through the skin and into the centre of the bone. The bone marrow fluid is then drawn into a syringe attached to the end of the needle. This is done repeatedly until enough bone marrow fluid has been collected. The whole procedure takes about one or two hours to complete.
The bone marrow is processed to remove fragments of bone, red cells, fat and other unwanted tissue. After this it may be used immediately, or it may be frozen (cryopreserved) to be used at a later date.
Umbilical (and placental) cord blood collection
In newborn babies, the umbilical cord and placenta contain a rich supply of blood stem cells. These stem cells are capable of repopulating the bone marrow and producing blood cells. Cord blood can be collected by the midwife, doctor or another designated collector immediately after delivery and the cutting of the umbilical cord without causing any harm to the newborn baby. Cord blood banks are located in most of Australia’s capital cities.