What Are Stem Cells?

Cells make up every living thing — including the human body. They're microscopic, but powerful. For example, white blood cells help fight germs. Beta cells make 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. So cells work as a team, grouping together to make up our tissues and organs.

But one type of cell is different. Stem cells can develop into cells with different skills.

What Are Blood Stem Cells?

The term stem cell transplants usually refers to hematopoietic (pronounced: heh-mat-uh-poy-ET-ik) stem cells. These are made in the bone marrow and 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

Besides being able to turn into different types of cells, stem cells can also replicate. This means they can create new stem cells to keep the body healthy.

What Is a Stem Cell Transplant?

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.

When the stem cells get inside the person's body, they start making healthy new blood, bone marrow, and immune system cells.

Why Are Stem Cell Transplants Done?

Stem cell transplants can help people with:

• severe blood or immune system illnesses
• some kinds of cancer
• 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 cells can spread throughout the body. With immune system 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 replicate and turn into healthy cells.

Where Do the Stem Cells Come From?

Doctors get hematopoietic stem cells from three different places:

• bone marrow
• the bloodstream
• umbilical cord blood after the cord is no longer attached to a newborn baby

A person who provides the stem cells is called a donor. Using donor cells is called an allogeneic (pronounced: al-low-juh-NEE-ik) transplant.

When stem cells come from a donor:

• 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 they collect 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.

Donors don't have to be other people — sometimes people can act as their own donor. This is called an autologous (pronounced: aw-TOL-uh-gus) transplant.

When people donate their own stem cells:

• Doctors remove stem cells from either the blood or bone marrow. They do this before the person gets treatments like chemotherapy or radiation. This is called harvesting the stem cells. The stem cells are then frozen.
• After the person has had chemo or radiation, the thawed cells are put back inside the body. Doctors may transplant new stem cells more than once — it depends on what a patient needs.

Transplanting stem cells is a complicated process. It might take several months to decide if a patient is a good candidate and find the best donor.

What Happens Before the Transplant?

After finding a good donor, doctors collect the stem cells. They do this by:

• collecting stem cells from the donor's hip bone
  or
• taking blood from the donor, collecting the stem cells, and returning the blood to the donor's body

Sometimes doctors get the stem cells from umbilical cord blood stored in a cord blood bank.

The next step is conditioning therapy. The medical team gives the patient high doses of chemotherapy and/or radiation to kill the unhealthy cells causing the illness. Sometimes the patient gets other types of medicines 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 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 body will reject the new cells.

What Happens During the Transplant?

The actual transplant is done through an infusion. This is when the stem cells are put in the patient's body through an IV line.

What Happens After the Transplant?

Patients are closely watched after a stem cell infusion. The medical team will make sure the new stem cells settle into the bone marrow and begin to make new blood cells (called engrafting).

Engrafting usually takes about 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.

What Problems Can Happen?

If another person donated the stem cells, doctors will watch for signs of:

• rejection: Even if a donor is a good match, the body may still reject the transplant. This means the body's immune cells destroy the transplanted stem cells because they sense they are foreign.
• graft-versus-host disease: This is when the transplanted donor cells attack the patient's body. It can be serious, but doctors usually can treat it with steroids and other medicines.

How Long Does it Take to Recover?

Before someone can go home from the hospital, doctors make sure that:

• the transplant succeeded
• the person is doing well

Going home doesn't mean going back to normal life right away. The risk of infection means that it might be 3 months or more before the person can go back to school, visit the mall, or go to a sporting event. That's because even a simple infection like a cold can be life-threatening for people whose immune systems need time to recover.

Looking Ahead

Being treated for cancer or another serious condition can be stressful for anyone. Stem cell transplants involve long isolation periods, which can add to the stress.

Your health care team knows how tough that can be, and how important it is to get emotional support. Your doctor, a hospital social worker, or child life specialist can help you get through this difficult time, so be sure to ask.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date Reviewed: 15-08-2018