Stem Cell Collection Methods
Stem cells from donors are obtained by collecting bone marrow, peripheral blood, or umbilical cord blood. The easiest method is cord blood collection. Normally discarded after a baby’s birth, cord blood is especially rich in stem cells. Many parents donate their babies’ cord blood to cord blood banks.
The other two collection methods—bone marrow and peripheral blood—are more complex. The collection method used depends on the patient’s disease and other factors.
Harvesting Bone Marrow Stem Cells
Bone marrow is full of stem cells available for harvest. Marrow harvest is done in an operating room under general anesthesia or, sometimes, spinal anesthesia, so the donor won’t feel anything during the procedure. Small incisions (1/8 inch long) are made on both sides of the lower back. A needle is inserted through these incisions into the pelvic bones, and bone marrow is removed using a syringe to aspirate (suck) it out.
When enough bone marrow has been removed, typically a quart or quart and a half for an adult, the incisions are bandaged. No stitches are required. Some donors need to stay in the hospital overnight; most go home the same day. This depends on how the person feels after having anesthesia.
Sometimes a donor needs blood transfusions during the harvest to replace the blood being collected. Donors most often give one to two units of their own blood two to four weeks prior to harvest (an autologous donation) and then have their blood transfused back to them during the harvest procedure.
Donors should arrange for someone else to drive them home from the hospital. The bandage on the lower back must stay in place for at least twenty-four hours after the surgery. After that it’s okay to remove the bandage and take a shower. Small strips of adhesive may be on the incision sites; they will fall off over the next week.
After the surgery, the area around the hips may be sore for several days. Mild pain relievers such as acetaminophen (Tylenol) or ibuprofen are usually enough to relieve the discomfort. A fever of up to 101°F for twenty-four hours after having anesthesia is common. If fever persists beyond a day and is accompanied by other symptoms, the donor should call a doctor. Symptoms of infection include extreme tenderness, redness, swelling, and drainage. Infections or other complications are very rare.
Donors should take it easy for a day or two after the harvest surgery. It is normal to feel very tired after bone marrow donation. Most donors feel back to normal after one to two weeks.
Collecting Peripheral Blood Stem Cells
Stem cells may be harvested from the bloodstream rather than the bone marrow. Donating stem cells in this way is similar to donating blood.
Before the stem cells are collected, they are first "mobilized," or pushed out of the bone marrow and into the circulating (peripheral) blood. One of two methods will be used to collect the stem cells: growth factor medication or growth factor medication with chemotherapy (used only in autologous transplant, when the BMT patient is also the stem cell donor). The collection process is sometimes called leukapheresis, which means "taking away white blood cells."
Growth factor mobilization. To mobilize the stem cells, a medication called a growth factor or colony-stimulating factor is given. Growth factors are human proteins that are normally produced by our bodies to stimulate blood cell production and growth.They can increase the number of stem cells in the bloodstream. The growth factor drug is given as an injection under the skin with a very small needle each day for six to seven days. Some donors feel a little pain at the injection site. Side effects are usually mild and may include general aches and bone pain, flulike symptoms, and low-grade fever. The bony aches may increase after each day’s injection.
Growth factor medication with chemotherapy. For some patients receiving autologous transplants, growth factor medication is combined with "priming" chemotherapy. The chemotherapy is usually given for two to three days. The growth factors are then given to accelerate white blood cell recovery from chemotherapy and to mobilize stem cells into the blood for collection. Ten to fourteen days after chemotherapy, the white blood cell count recovers and the number of stem cells in the blood is much higher than normal.
The stem cells are collected in an outpatient procedure called leukapheresis, or, more generally, apheresis. A blood cell separation machine is used to remove some of the stem cells from the bloodstream.
The machine is hooked up to the donor’s central venous catheter. The catheter has two separate lumens (tubes) within it. If no central venous catheter is available, two separate IVs may be inserted into large peripheral veins, or a temporary catheter with two lumens may be placed in a neck vein.
Blood is drawn from one lumen or IV and circulated through the blood cell separation machine. As blood goes through the machine, the white cell portion, which is now enriched with stem cells, is removed for freezing and storage. The blood continues through the machine, and red cells are returned to the donor through the other catheter lumen or IV.
This procedure may temporarily lower the donor’s blood calcium level, which may cause a tingling sensation around the mouth or in the hands and feet. To relieve these symptoms, the donor may take antacid tablets that are high in calcium, or calcium may be infused. The collection process can also lower the donor’s platelet count. If this happens, he or she will be watched closely for signs of bleeding.
Each collection will last four to five hours, and several collections may be required depending on the number of cells needed. The hospital will provide snacks during each collection, or donors can bring their own food. Reading, watching television or movies, resting, and talking with visitors can help pass the time.
After the stem cells are collected, the collection bag is sent to a processing laboratory, where the cells are counted and processed. A preservative is added to them and, if the transplant is scheduled at a later date, the cells are frozen.
Some patients are reevaluated after stem cell collection to see how they responded to the priming therapy. This reevaluation (restaging) can include CT scans, X-rays, blood tests, and a bone marrow biopsy.
