The Role of Stem Cells in Transplantation

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Stem cells are able to repair and replace damaged tissues and organs, and can be transplanted into patients to treat many diseases. In this lesson, we will learn how stem cells are used in transplantation.

What are Stem Cells?

Did you know that every cell in your body came from one single cell? Muscle cells, blood cells, nerve cells, and so many other cell types all came from a single fertilized egg cell. When a stem cell divides to form a specialized cell, this is called differentiation. All stem cells are able to differentiate; but some can differentiate into any of the types of cells in your body, while others can only differentiate into a few cell types. Because a fertilized egg cell is totally capable of producing all the types of cells in your body, it is called a totipotent stem cell.

At first, in a very early embryo, all the cells are totipotent, but soon they begin to differentiate into different types of tissues. The cells are now called pluripotent stem cells because they can form many types of cells, but not all. As stem cells continue to divide and differentiate, they become multipotent, meaning that they can form several types of related cells, but not other types of cells. Once the cells are fully differentiated into specialized cells, they are called unipotent.

Totipotent stem cells in an embryo are able to develop into all the cell types in your whole body.
image of stem cell differentiation

Although totipotent and pluripotent stem cells are only found in very early embryos, this is not true for multipotent stem cells. Even after you are born and grow up, you still have some of these stem cells in your body. They help you to grow, repair damage, and replace cells as they age and wear out.

Bone Marrow Stem Cells

Only multipotent stem cells are present in adults. Even though these cells have lost the ability to differentiate into any type of specialized cell, they can still form many cell types and as a result, have some really important medical uses. Most adult stem cells are found in bone marrow; the majority of these are called hematopoietic stem cells. This means that they can form any of the blood cells in your body. That includes red blood cells, white blood cells, and platelets. There are also other stem cells in your bone marrow that can differentiate into connective tissues like muscle, bone, and fat.

A hematopoietic stem cell in the bone marrow can differentiate into all of the blood cells (red, white, and platelets) in the body. Other types of stem cells in the bone marrow can differentiate into connective tissue like muscle and bone.
bone marrow stem cells

Transplantation of Bone Marrow Stem Cells

The most common use of stem cells in medicine is in bone marrow transplantation. If you have a type of cancer that affects the bone marrow or immune system, such as leukemia or lymphoma, you might need a bone marrow transplant. To understand how bone marrow transplants are performed, let's look at the case of a patient named Phillip. Phillip has leukemia and to cure it, he needs a bone marrow transplant. Before the new bone marrow can be transplanted, Phillip's own stem cells must first be destroyed by radiation or high doses of chemotherapy. Then, new bone marrow will be infused to repopulate his bone marrow with healthy, cancer-free stem cells. There are two types of bone marrow transplants that a patient like Phillip might have: autologous and allogeneic.

If his doctors choose to perform an autologous transplant, some bone marrow stem cells will be removed from Phillip and stored in a freezer before his remaining stem cells are destroyed. Then, the stored stem cells will be infused back into his blood. Autologous bone marrow transplants are good because you don't have to find a compatible donor and deal with the risk of rejection following the transplant. But there is always a risk that you will transplant back some cancer cells with the healthy cells.

The other type of bone marrow transplant that Phillip might have is an allogeneic transplant. In this procedure, bone marrow cells are taken from a closely matched donor and then given to a patient whose bone marrow has been destroyed. The advantage of allogeneic transplant is that you know the bone marrow is healthy. The disadvantage is the risk that the patient's body may reject the bone marrow; drugs to suppress the immune system will be necessary to reduce that risk.

Adult stem cells are usually extracted from bone marrow using a long needle. Then they can be transplanted to a patient who needs new bone marrow.
bone marrow biopsy

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