- What we’ll cover here
- What are stem cells and why are they transplanted?
- When do people need stem cell transplants?
- Types of stem cell transplants for treating cancer
- Sources of stem cells for transplant
- Allogeneic transplant: The importance of a matched donor
- What’s it like to donate stem cells?
- Getting rid of cancer cells in autologous transplants
- The transplant process
- Problems that may come up shortly after transplant
- After-transplant problems that may show up later
- Other issues related to transplants
- What questions should I ask my doctor before transplant?
- To learn more
Sources of stem cells for transplant
There are 3 possible sources of stem cells to use for transplants: bone marrow, the bloodstream (peripheral blood), and umbilical cord blood from newborns. Although bone marrow was the first source used in stem cell transplant, peripheral blood is used most often today.
Bone marrow is the spongy tissue in the center of bones. Its main job is to make blood cells that circulate in your body and immune cells that fight infection.
Bone marrow was the first source used for stem cell transplants because it has a rich supply of stem cells. The bones of the pelvis (hip) contain the most marrow and have large numbers of stem cells in them. For this reason, cells from the pelvic bone are used most often for a bone marrow transplant. Enough marrow must be removed to collect a large number of healthy stem cells.
For a bone marrow transplant, the donor gets general anesthesia (drugs are used to put the patient into a deep sleep so they don’t feel pain). A large needle is put through the skin and into the back of the hip bone. The thick, liquid marrow is pulled out through the needle. This is repeated several times until enough marrow has been taken out (harvested). (For more on this, see the section called “What’s it like to donate stem cells?”)
The harvested marrow is filtered, stored in a special solution in bags, and then frozen. When the marrow is to be used, it’s thawed and then given just like a blood transfusion. The stem cells travel to the recipient’s bone marrow. There over time, they engraft or “take” and begin to make blood cells. Signs of the new blood cells usually can be measured in the patient’s blood tests in about 2 to 4 weeks.
Normally, few stem cells are found in the blood. But giving hormone-like substances called growth factors to stem cell donors a few days before the harvest causes their stem cells to grow faster and move from the bone marrow into the blood.
For a peripheral blood stem cell transplant, the stem cells are taken from blood. A very thin flexible tube (called a catheter) is put into one of the donor’s veins and attached to tubing that carries the blood to a special machine. The machine separates the blood, and keeps only the stem cells. The rest of the blood goes back to the donor. This takes several hours, and may need to be repeated for a few days to get enough stem cells. The stem cells are filtered, stored in bags, and frozen until the patient is ready for them. (For more on this, see the section called “What’s it like to donate stem cells?”)
After the patient is treated with chemo and/or radiation, the stem cells are given in an infusion much like a blood transfusion. The stem cells travel to the bone marrow, engraft, and then grow and make new, normal blood cells. The new cells are usually found in the patient’s blood a few days sooner than when bone marrow stem cells are used, usually in about 10 to 20 days.
Umbilical cord blood
Not everyone who needs an allogeneic stem cell transplant can find a well-matched donor among family members or among the people who have signed up to donate. For these patients, umbilical cord blood may be a source of stem cells. Around 30% of unrelated hematopoietic stem cell transplants are done with cord blood.
A large number of stem cells are normally found in the blood of newborn babies. After birth, the blood that is left behind in the placenta and umbilical cord (known as cord blood) can be taken and stored for later use in a stem cell transplant. The cord blood is frozen until needed.
A cord blood transplant uses blood that normally is thrown out. The first cord blood transplant was done in 1988, and its use has been growing ever since. For more information on donating cord blood, see the section called “What’s it like to donate stem cells?”
A possible drawback of cord blood is the smaller number of stem cells present. But this is partly balanced by the fact that each cord blood stem cell can form more blood cells than a stem cell from adult bone marrow. Still, cord blood transplants can take longer to engraft and start working.
To be safe, most cord blood transplants done so far have been in children and smaller adults. Researchers are now looking for ways to use cord blood for transplants in larger adults. One approach that is being taken is to find ways to increase the numbers of these cells in the lab before the transplant. Another approach is the use of the cord blood from 2 infants at the same time for one adult transplant, called a dual-cord-blood transplant. A third way cord blood is being used is in a mini-transplant. In this case, the bone marrow is not completely destroyed so there are some host stem cells left before and during the time that the cord blood stem cells engraft. Other strategies to better use cord blood transplants are being actively studied.
Which stem cell source is best?
All 3 sources of stem cells can be used for the same goal: to give the patient healthy stem cells that will mature into healthy blood cells. There may be some pros and cons to each source, but all are usually able to provide the needed number of stem cells (with the exception noted above in umbilical cord blood).
At first, all stem cell transplants were bone marrow transplants. But today peripheral blood stem cell transplants are much more common. Often, doctors are able to harvest more stem cells from peripheral blood than from bone marrow. It’s also easier for donors to give peripheral blood stem cells than bone marrow. Another plus for peripheral blood stem cell transplants is that the recipient’s blood count often recovers faster than with a bone marrow transplant. But the risk of chronic graft-versus-host disease is somewhat higher with peripheral blood stem cell transplants than with bone marrow transplants.
Cord blood transplant may be an option if a good match can’t be found among volunteer stem cell donors. Even though well-matched cord blood is generally best, studies suggest that cord blood doesn’t have to be as closely matched as bone marrow or peripheral blood. This may be an advantage for patients with rare tissue types. This type of transplant also does not require a separate donation procedure and may reduce the severity of graft-versus-host disease (described in the section called “Problems that may come up shortly after transplant”). There’s also less risk of acute and chronic graft-versus-host disease linked to cord blood, and when these things do happen, they tend to be less severe. But cord blood cells usually take longer to engraft. This leaves the patient at high risk for infection and bleeding longer than is seen with transplanted marrow or peripheral blood stem cells. Another drawback is that, unlike bone marrow transplant or peripheral blood stem cell transplant, the donor cannot be called back for more after the cord blood stem cells are used.
Last Medical Review: 08/23/2012
Last Revised: 10/24/2012