What Are Stem Cells?
As you probably remember from biology class, every living thing is made up of cells — including the human body. Cells are microscopic, but they power our bodies in amazing ways. For example, white blood cells help fight germs. Beta cells produce insulin to control sugars in our bodies. Melanocytes give skin its color.
Most of the time, each cell has a specific job to do. One cell can't do what another cell can, just as a doctor isn't trained to design a bridge and an engineer can't do surgery. So cells work as a team, grouping together to make up our tissues and organs.
But one type of cell is different. Stem cells that are produced in the bone marrow can develop into cells with different skills. In that way, stem cells are like students who have the choice of studying to be either doctors or engineers. None of the body's other cells can become new cells like this.
Blood Stem Cells
When you hear about stem cell transplants, they probably involve hematopoietic (pronounced: he-muh-toe-poy-EH-tik) stem cells. These stem cells form blood and immune system cells. Hematopoietic stem cells can become any of three different types of blood cells:
- red blood cells that carry oxygen
- white blood cells that fight infection
- platelets that help blood to clot
As well as being able to turn into different types of cells, stem cells can also replicate — meaning they can create new stem cells to keep the body healthy.
What Is a Stem Cell Transplant?
Stem cell transplants help people with severe blood or immune system illnesses. Stem cell transplants can help some people with certain kinds of cancer. They may also help people with non-cancerous diseases, such as serious immune deficiency problems, autoimmune diseases (like lupus), or blood disorders (thalassemia or sickle cell disease, for example).
With cancer, the body's cells grow in a way that's not normal. These abnormal cells then spread quickly throughout the body. With diseases like lupus, the immune system goes haywire and may damage healthy cells in the body. To fix these problems, doctors destroy damaged or abnormal cells and replace them with transplanted stem cells. The stem cells then duplicate and turn into healthy cells.
A stem cell transplant involves taking healthy stem cells and putting them into the bloodstream of someone who is sick. This is done through an intravenous (IV) line. It's similar to having a blood transfusion. Once the stem cells get inside the person's body, they go to work creating healthy new blood, bone marrow, and immune system cells.
Where Do the Stem Cells Come From?
Doctors get hematopoietic stem cells from one of three different places:
- bone marrow
- the bloodstream
- umbilical cord blood after the cord has been detached from a newborn baby
A person who provides the stem cells is called a donor. Donors don't have to be other people — sometimes a patient can act as his or her own donor.
Here's what happens when people donate their own stem cells: Before getting treatments like chemotherapy or radiation, doctors remove the person's stem cells from either the blood or bone marrow. This is called "harvesting" the stem cells. The stem cells are then frozen.
After the person has had chemotherapy or radiation, the cells are thawed and put back inside the body. Doctors may transplant new stem cells more than once — it all depends on what a patient needs. When a person donates his or her own cells, it's called an autologous (pronounced: ah-TOL-uh-gus) transplant.
Here's what happens when stem cells come from a separate donor: Separate donors are often siblings. Sometimes, parents will keep a newborn's umbilical cord blood for this purpose. But donors can also be other family members or even volunteers who aren't related to a patient.
Before collecting stem cells, doctors do tests to be sure the cells are a good match. If the patient and donor blood and tissue types don't match, the patient's body may reject the donor's stem cells. When someone other than the patient donates stem cells, it's called an allogeneic (pronounced: al-uh-juh-NEE-ik) transplant.
A lot can happen when introducing new cells to the body. Even if a donor is a good match, the body may still occasionally reject the transplant. This means that the body's own immune cells destroy the transplanted stem cells because they sense they are foreign.
Other times, the newly transplanted donor cells start attacking the patient's body. This condition is called graft-versus-host disease. It can be serious, but doctors are usually able to treat it with steroids and other medicines. If you are getting a stem cell transplant, your doctor will explain the different things that can happen.
Transplanting stem cells is a very complicated process. It might take several months to decide if a patient is a good candidate and find the best donor.
How Do Doctors Get Stem Cells From Donor to Patient?
After finding a good donor, doctors collect the stem cells. This may involve collecting stem cells from the donor's hip bone or taking blood from the donor, separating out the stem cells, and returning the blood to the donor's body. Sometimes doctors get the stem cells from a special blood bank where umbilical cord blood is stored (called a cord blood bank).
The next step in the transplantation process is conditioning therapy. The medical team gives the patient high doses of chemotherapy and/or radiation to kill unhealthy cells (like cancer cells) that are causing a person's illness. Sometimes the patient gets other types of medications that don't kill the cells, but that weaken the immune system instead.
Wiping out unhealthy cells or weakening the immune system might sound scary, but it can actually be helpful. Destroying bone marrow makes room for new stem cells to take hold. And a weak immune system isn't as likely to jump into high gear and attack the new cells. So there's less chance that the new cells will be rejected.
Now it's time for the actual transplant. This is done through an infusion where the stem cells are put in the patient's body through an IV line. After a stem cell infusion, the medical team watches the patient closely to make sure the new stem cells are settling into the bone marrow and beginning to make new blood cells (called engrafting). If another person donated the stem cells, doctors will watch for signs of rejection or graft-versus-host disease.
Engrafting takes an average of 2 weeks, but can be as quick as 1 week or as long as 6 weeks. The medical team gives the patient medicines to promote engrafting and prevent problems like rejection.
How Long Does it Take to Recover?
People who get stem cell transplants have a high risk of infection because the process affects the immune system. That makes it harder to fight bacteria and other germs that enter the body. People whose stem cell transplants come from donors have an even higher risk of infection because they need to take medicines to reduce the chance of rejection. These medicines can weaken the immune system.
Because of these risks, doctors won't release someone from the hospital until they are sure the transplant has been successful and the person is well enough to go home.
Getting out of hospital doesn't mean going back to normal life right away. Because of the risk of infection, it might be 3 months or more before someone who's had a stem cell transplant can go back to school, visit the mall, or go to a sporting event. That's because even a simple infection like a common cold can be life threatening for people whose immune systems need time to recover. Anywhere someone might come into contact with germs will be off limits.
Because stem cell transplants involve long isolation periods, they can be stressful. Luckily, medical teams know how tough that can be, and they know how important it is to get emotional support. Your doctor, a hospital social worker, or child life specialist can give you advice on getting through this difficult time. Don't hesitate to ask for help.
Reviewed by: Elana Pearl Ben Joseph, MD
Date reviewed: October 2012