Bone-Marrow vs Stem-Cell Transplantation

In section 2 of the Transplant Basics page I listed the two parts of the transplant procedure.  The first part is the same for both-bone marrow and stem-cell transplant recipients; the patient is exposed to a very high dose of radiation and/or chemotherapy in an attempt to kill their disease entirely.  This first step, unfortunately, destroys the bone-marrow in your body, and your immune system along with it.

The way that these two procedures differ is in the second step.  Bone-marrow transplant patients need a donor.  This donor must a) be a tissue match for the patient, and b) have an uncontaminated immune system.  Bone-marrow tissue is removed from the donor, and after the patient’s own contaminated immune system is killed off, the donated and refined bone-marrow is placed in the patient, where a new, hopefully uncontaminated immune system begins to grow.

Stem-Cell transplant patients may use a donor or they may donate their own stem cells.  Because there is no question about tissue matches and therefore no possibility of rejection when a patient uses his own cells generally a stem cell transplant patient is his or her own donor unless this procedure proves unsuccessful.  If you are your own donor, the transplant procedure is an autologous one.  If you have a donor, it’s called an allegeneic transplant.

The reason an autologous, donor-less transplant is possible with stem-cells and not bone-marrow, has to do with the nature of stem-cells themselves.  Adult Stem-cells are born in the bone-marrow and normally that is where they stay.  They exist there for a short period of time until they become matured elements of our blood.  Once that happens they are released into the blood stream where they fulfill their destiny of transporting oxygen, fighting infection, and clotting injured tissue, etc.  In the past that meant that if you wanted the stem-cells, you had to take them along with the bone-marrow itself.

Stem-cell transplants became possible only with two recent scientific developments:

1. Medically-accelerated growth of stem-cells.
2. Loosening of the stem-cells from their bone-marrow mooring so that they can be released into the blood stream while still in their undifferentiated state.

Once the stem-cells are released from their bone-marrow, a simple blood harvesting follows.  Blood is drawn out of your body for collection via an Aphaeresis line (more on that later).  It is filtered through a centrifuge to isolate and collect the heavier stem-cells, and then the rest of the blood is immediately returned.

In about four hours the Red Cross (who normally does the harvesting) may be able to collect enough stem-cells to be used for the transplant itself.  Because the process is painless and very low risk, this procedure is done under out-patient status.  The collected cells are processed and then frozen immediately after harvesting.  After the high-dosage radiation and/or chemotherapy is administered, the stem-cell fluid is thawed at your bedside and reintroduced to the patient’s blood supply via a simple IV line.  The process is exactly the same as a blood transfusion.

Harvesting bone-marrow doesn’t take any longer than harvesting blood cells, but the process involves more discomfort.  For this reason the donor undergoes the procedure in an operating room while under a general anesthesia.  During this process, anywhere from a liter to a liter and a half of bone-marrow liquid is removed – generally from the large hip bones.  This fluid is then processed and volume reduced before it is frozen for use later during the transplant.

The other reason for in-patient status during bone-marrow harvesting is due to the risk involved.  Sometimes the donor requires a blood transfusion during or following this process due to loss of marrow.  Generally a bone-marrow donor will not be in the hospital for more than 24 hours, and in some cases they will be released from the hospital a few hours after the harvesting, after observation to ensure that no transfusions or follow-up pain treatments are required.

During the actual transplant, the processed bone-marrow fluid is thawed and infused directly into the patient’s blood stream just like a normal blood transfusion.  This is essentially the same step as for a stem-cell transplant infusion.  This fluid will find its way into the recipient’s bone-marrow where it will anchor itself and begin the blood-production process again.  Returning blood counts to safe levels will generally take days to weeks, while the successful growth of a new immune system may take up to a year in total.  At the end of that year the patient receives the same inoculations and booster shots as a one-year old infant.

As you can see, harvesting stem-cells is simpler, less painful, and less risky than harvesting bone-marrow.  Both procedures involve periodic bone-marrow biopsies, though, so there’s no escaping that altogether.  The details of this test will be covered in the Pre-Transplant Tests and Prep page, as will more detailed specifics of the two harvesting processes.