Few of us know what they are or exactly how they work. But many of us have heard about the healing powers of stem cells, as well as the controversy surrounding them. Stem cells are well-debated and highly complex — with promises ranging from fixing damaged knees to regenerating receding hairlines.

But what are stem cells? And, what’s all the fuss all about?

Director of the Cleveland Clinic’s Center for Regenerative Medicine and Surgery, Amy Lightner, MD, shares the differences between stem cell types, how stem cells can be used and when to be cautious of claims that might be too good to be true.

What are stem cells?

When most of us think of stem cells, we probably recall images of Dolly the cloned sheep. While it’s true that Dolly was born of stem cells, her place in science history is just one of many advancements in the field.

In fact, there are many different types of stem cells, each of which has different responsibilities and abilities. What unifies them is their ability to regenerate into new cells.

“Regenerative medicine is an emerging field that uses innovative treatments to help regenerate or heal cell function that’s lost due to aging, disease or injury,” Dr. Lightner explains. “The way we achieve this is by using stem cells in large quantities, targeted to a certain area, that the body uses to promote healing.”

Adult stem cells

Adult stem cells are the only type of stem cells that are currently approved for medical use in the United States by the U.S. Food and Drug Administration (FDA). The term “adult stem cells” is a little confusing because they’re actually found in infants, children and adults. These cells live in a variety of tissue in our bodies — including bone marrow, muscles, your brain, your intestines and more.

Think of adult stem cells as a little army of cells that can regenerate themselves into new cells to maintain and repair the tissue or muscle where they’re found. The catch with adult stem cells is that they can’t become different types of cells (for example, blood stem cells can only become new blood cells, not skin or brain cells).

Embryonic stem cells

Unlike adult stem cells, embryonic stem cells have many more possibilities. Harvested during an embryo’s blastocyst stage (about five or six days after an embryo has been fertilized in a lab), embryonic stem cells have the potential to become any type of cell (called pluripotent cells). For these reasons, embryonic stem cells are the type of stem cells that generate the controversy most people associate with the topic.

Perinatal stem cells

Researchers have discovered stem cells in amniotic fluid as well as umbilical cord blood. These stem cells have the ability to change into specialized cells. Amniotic fluid fills the sac that surrounds and protects a developing fetus in the uterus. Researchers have identified stem cells in samples of amniotic fluid drawn from pregnant women for testing or treatment — a procedure called amniocentesis.

What is stem cell therapy and what does it help treat?

Stem cell therapy has been around since the 1970s, when the first adult bone marrow cells were used to treat blood disease. A bone marrow transplant allows a recipient whose bone marrow cells have been damaged by chemotherapy or disease to receive healthy bone marrow stem cells from a donor.

“Those stem cells have the potential to mature within the blood system into different immune cells that recognize and fight off different types of blood cancer. And they also have the ability to heal,” says Betty Hamilton, MD, Cleveland Clinic’s Department of Hematology and Medical Oncology.

Bone marrow transplants are currently used to treat diseases including:

• Lymphoma;

• Leukemia;

• Multiple myeloma;

• Neuroblastoma.

Stem cell therapies of tomorrow

Dr. Hamilton and Dr. Lightner agree that we’re only just beginning to scratch the surface of stem cell therapy. In recent years, during the height of the COVID-19 pandemic, many clinical trials were underway to explore whether stem cells could be used to help treat the damaged lungs in people severely affected by the disease.

“I think ‘potential’ is the perfect word to describe stem cells,” says Dr. Hamilton. “We know they have these anti-inflammatory and regenerative properties where they can provide a significant improvement to someone suffering from a certain disease. There are so many diseases where inflammation happens, and something needs to be repaired, and so any help the immune system can get provides a lot of potential.”

Scientists are also researching whether adult stem cells can turn into pluripotent stem cells, which would allow the cells to change into any cell type without involving the use of embryonic stem cells.