Internal Medicine Department
Hematology Division

Stem Cell Collection

A bone marrow transplant is done by transferring stem cells from one person to another. Stem cells can either be collected from the circulating cells in the blood (the peripheral system) or from the bone marrow.

What are stem cells?

Hematopoietic stem cells, or progenitor cells, are the very young or immature cells from which all blood cells are produced.  The stem cells are formed in the bone marrow (the spongy cavity in the center of large bones).  Each stem cell receives chemical signals that direct it to become a red cell, one of several kinds of white cell, or a small cluster of platelets.  This growth process occurs in the bone marrow space, and normally only mature cells are released into the peripheral blood stream.

What sources of stem cells are used for transplants?

Hematopoietic stem cells may be harvested directly from the bone marrow, or collected from peripheral blood after the stem cells are mobilized from the bone marrow.  The choice is determined by a number of factors such as the patient’s stage and type of disease, the treatment plan, or the donor’s age.    

Peripheral blood stem cells

Peripheral blood stem cells are collected by apheresis, a process in which the donor is connected to a special cell separation machine via a needle inserted in the vein. Blood is taken from one vein and is circulated though the machine which removes the stem cells and returns the remaining blood and plasma back to the donor through another needle inserted into the opposite arm. Several sessions may be required to collect enough stem cells to ensure a chance of successful engraftment in the recipient.

Bone Marrow Harvest

Bone marrow harvesting involves collecting stem cells with a needle placed into the soft center of the bone, the marrow. Most sites used for bone marrow harvesting are located in the hip bones and the sternum. The procedure takes place in the operating room. The donor will be anesthetized during the harvest and will not feel the needle. In recovery, the donor may experience some pain in the areas where the needle was inserted.

What occurs prior to stem cell collection?

Autologous donors are treated with appropriate therapy by their oncology doctor, and then referred to the bone marrow transplant program for evaluation and collection.  Allogeneic donors, when needed, are identified by tissue typing and matching with the recipient’s tissue type.

A workup is done on all donors to assess their health status.  The routine workup includes a physical examination, health history questions, blood tests, chest x-ray, and electrocardiogram (EKG).  Regulations require that stem cell donors be tested for the same infections diseases as any other blood donor.  These tests are for hepatitis, HIV (AIDS), Human T-cell leukemia (HTLV), syphilis, and other viral diseases such as cytomegalovirus, herpes, and West Nile. A sample from the donor must be tested within 30 days of each collection.  The results are reviewed by the transplant physician, and the donor is given the opportunity to discuss the workup and ask questions prior to giving consent for the stem cell collection. The donor is then scheduled for mobilization and collection.

What is mobilization?

Mobilization, or priming, is the process used to stimulate the donor’s marrow to produce extra stem cells and release them into the peripheral blood.  This is done by giving injections or shots of a growth factor called Neupogen® or G-CSF.  Autologous donors may receive a combination of chemotherapy plus growth factor, or growth factor alone.  Allogeneic donors receive growth factor only.  Priming is required for peripheral stem cell collections and generally not used for bone marrow harvest collections. 

How long does mobilization take?

Autologous donors may have a widely variable response to priming.  When chemotherapy plus growth factor is used, the last day of chemotherapy is called day 1, Neupogen® shots start on day 6, and the average time to begin collection is day 10–12. However, a longer time or additional growth factors may be required for adequate mobilization. Priming with growth factor alone is usually done for 4 days and collections begin on day 5.

The priming for allogeneic donors is usually scheduled to coincide with the recipient’s treatment so that the collections occur when the patient is ready to receive the stem cells.  The donor receives G-CSF for 3 or 4 days, depending upon the patient’s treatment plan, prior to start of collection on day 4 or 5.

The growth factor shots are given daily from the day they are started until the last day of collection.

How is the success of mobilization determined?

Before starting to collect stem cells, a small blood sample may be tested to determine if enough stem cells have moved into the peripheral blood.  For autologous donors, testing begins after the white blood cell count begins to recover following the chemotherapy dose used for priming, or on day 4 of priming with growth factor alone.   When the desired number of stem cells is detected in the blood, collections begin the following day.  If the stem cell count in the blood sample is not adequate, the donor continues to receive the shots and be monitored until there are enough stem cells available.

Allogeneic donors are assumed to have an adequate response to priming so pre-testing is not done and the donor is given a collection schedule.

How is the peripheral blood accessed?

There are several options for access to a donor’s peripheral blood.  If the donor has adequate size veins in the elbow area, needles similar to those used for whole blood donations, or short flexible catheters may be inserted on the day of collection.  Autologous donors usually have a semi-permanent tunneled double or triple lumen (two or three tubes inside a single tube) catheter placed that can be used for collection of peripheral stem cells as well as to return the stem cells for the transplant.  Allogeneic donors who do not have adequate veins may need a temporary double lumen catheter.  This type of catheter is inserted by a doctor into a large vein usually in the side of the neck. These options will be discussed with the donor before the stem cell collection.     

How and where are peripheral stem cells collected?

Stem cells are collected by a process called apheresis, which uses an instrument called a blood cell separator. The collection is done in a room associated with the transplant unit or the clinic.  The instrument can be moved to where ever it is to be used. The apheresis procedure is painless, but does require several hours. The donor may eat and drink during the collection, and family members may be present. A nurse will be assigned to monitor the donor.  A stem cell staff member stays with the donor throughout the collection. The donor is usually able to watch television, read, or sleep during the collection.

How does the apheresis process work?

Apheresis is a method used to collect only a specific part of the donor’s blood.  It works on the basis of centrifugation or rapid spinning of the donor’s blood.  A sterile tubing kit is installed in the instrument, as seen in the picture, each time a collection is done. The tubing kit provides a pathway for the donor’s blood and allows for connection to the access device.  The instrument uses small pumps to move blood and fluids through the system. One pump draws blood out of one arm or side of the catheter and directs it to the centrifuge where the blood is separated into red cell, white cell, and plasma layers.  A portion of the white cell layer, which includes the stem cells, and a small amount of plasma and red cells are diverted to a collection bag. The rest of the blood is returned to the donor in the other arm or the second side of the catheter. The volume of the collected stem cell product may range from 50 to 300 cc (1/4 to 1 cup). Blood is drawn out, separated, and returned in a continual process.  Only a small amount of blood is in the kit at any time, and is not a problem for adults and large children.  This small volume is still too much for children who weigh less than 19 kilograms (42 pounds).  If a child less than 19 kilograms is the donor, a unit of compatible red blood cells is used to fill the kit before starting the collection.

What fluids are used during apheresis?

Before collection starts, the kit is filled or primed with a sterile salt solution (normal saline). If donor blood is needed for a small child, a second prime is then done to fill the kit with red blood cells. At the end of collection, saline is again used to rinse the kit in order to return most of the donor’s red blood cells.

During the collection, an anticoagulant citrate solution is added to the donor’s blood at a measured rate to prevent it from clumping while in the machine.  The anticoagulated blood is returned from the machine, re-enters the donor’s circulation and eventually passes through the donor’s liver, where the solution is quickly metabolized (broken down).  All of the citrate is removed within a few hours.

How long does a collection take?

A system cell collection usually takes 3–4 hours.  Sometimes it may take 5–6 hours depending on the volume of blood processed through the machine.  The minimum volume processed for adults is 10–13 liters, and for children it is twice the calculated total blood volume of the child.  In some cases, large volume procedures may be performed on adults (15–22 liters) and children (up to six times the blood volume).  Factors which influence the amount of blood processed include the donor’s blood cell counts, the stem cell count, the cell dose needed, or the size of the donor.

How many stem cells are needed?

The number of stem cells needed varies with the treatment choice or the number of doses requested.  The ideal number is 5–10 million per kilogram of the recipient’s weight per transplant dose.  The minimum number is 1–2 million stem cells per kilogram per transplant dose.  Either amount will provide white cell engraftment, but red blood cells and platelets may recover faster with the larger amount.  The number of stem cells collected each day is totaled to determine the final collection dose.

How many days are needed to collect stem cells?

When stem cells are collected from healthy allogeneic donors who receive G-CSF, 1 to 2 days are usually enough to obtain the ideal number or dose of cells needed.  For patient’s receiving an attenuated transplant, two collections are routinely done.  Additional collections may be done if the cell dose is low or if other types of cells are needed.

The number of days required for autologous donors may vary from 1 to 5, with five generally the maximum.  Another priming cycle with additional growth factors and collections may be done if the first collection total is inadequate.

Each day of collection is processed separately, with only the number of stem cells being added together.

What are the side effects during stem cell collection?

The most common side effect is a buzzing or tingling feeling around the lips and mouth.  This is minor muscle contraction caused by the anticoagulant, which acts by binding the ionized calcium in the blood and is not harmful.  Rarely the tingling may extend to cramping of the hands, feet, legs, or stomach.  Some donors may also feel chilled.  These effects will stop shortly after the collection ends.

Other possible but rare effects may include fainting, vomiting, air embolus, (air in a vein) or unusual bleeding.

How are side effects controlled?

The buzzing can usually be controlled by eating extra calcium in the form of food, calcium rich Viactive® chews, or TUMS® tablets before and during the collection.  Extra blankets will help keep the donor warm.  The donor’s blood pressure, heart rate, and temperature are also watched during the collection.  Other measures may be implemented as needed.

When and how are stem cells stored?

The stem cells may be held 1–2 days in the refrigerator or infused the day they are collected if all of the recipient’s conditioning treatment has been completed.  If necessary, the stem cells can be frozen and stored for a long time. If the collected stem cells are to be frozen, some fluids and a chemical called DMSO must be added to protect the white blood cells during the freezing process.  The cells are then transferred to special bags to be frozen, and are stored in liquid nitrogen freezers until needed.  Each collection is generally stored in 2 or 4 bags, depending on how many cells are collected each day.

When are the stem cells given to the patient?

The stem cells are given back to the patient after the appropriate treatment is completed, and the drugs have been cleared from the patient’s body.

How are the stem cells infused?

If the stem cells are given the day of collection, they are infused much like a regular blood transfusion.  If the stem cells have been frozen and stored, the bags are brought to the patient’s room in a special transport container.  The bags are thawed one at a time in a pan of warm sterile saline. The stem cells are given back through the patient’s central catheter like a transfusion.  Each bag takes 15–20 minutes to infuse, and 8–10 bags may be given in 1 day.  If a patient has more than 10 bags stored for a single transplant, the infusion may take place on subsequent days.  Once the stem cells enter the patient’s blood stream, the circulation delivers them back to the bone marrow.  Chemical homing signals direct the stem cells to stay in the bone marrow and start to replenish the patient’s blood cells.  No special instruments are needed, and the stem cells are NOT injected back into the patient’s bone marrow.

What are the effects during the infusion?

When stem cells are infused fresh the day of collection, there is usually no side effect.  Frozen stem cells contain DMSO which may cause a strange taste and smell during infusion. The patient may eat something like hard candy or popsicles to cover the taste.  The DMSO may possibly cause a rise in blood pressure, nausea, and vomiting.  Very rarely it may cause the blood pressure to drop, changes in heart beat, or an allergic reaction.  The urine may have a red tinge for a few hours.  This is from the lysed (broken) red blood cells that are not protected during the freeze and thaw process. These effects usually last only a short time. These side effects can be treated as necessary.

How long does engraftment take?

After the stem cells are infused, they are carried in the blood stream until they pass through the bone marrow.  Chemical signals direct them to stay there, where they start to produce new stem cells and blood cells.  An average of 10–14 days are needed for enough white blood cells to be made that a count of 500 or more neutrophils (new-tro-fils) (one type of white blood cell) is seen for 3 days.  At that point the patient is said to be engrafted.  Red blood cells and platelets may take another 1–2 weeks to stabilize, and their engraftment is determined by diminished transfusion requirements.

Any other questions?

The apheresis staff can be reached at (801) 585-3370 Mon–Fri from 8:00 am to 5:30 pm to answer any questions. An apheresis staff member will be able to review any of this information with the donor or answer questions before starting the first collection.