Stem Cell Program

Stem Cell Program | Adult Stem Cells

What are adult stem cells?

Although commonly used and accepted, the term "adult stem cells" refers to cells that are actually found in infants and children as well as in adults. Adult stem cells produce the different kinds of cells that maintain the body’s tissues and organs, and, importantly, they have the ability to divide and reproduce indefinitely. These cells typically produce the type of tissue in which they are found. Adult stem cells are sometimes also called somatic stem cells.

Various types of adult stem cells have been identified in many organs and tissues. They range from cells that are able to form many different kinds of tissues to more specialized cells that form just some of the cells of a particular tissue or organ. Mesenchymal stem cells, for example, are adult stem cells that form fat cells, cartilage, bone, tendon, ligaments, muscle cells, skin cells and even nerve cells. In contrast, hematopoietic stem cells give rise to blood cells only (red cells, white cells and platelets), while neural stem cells form only cells in the nervous system. 

Often confused with adult stem cell, progenitor cells are early descendants of stem cells that can differentiate to form one or more kinds of cells, but cannot divide and reproduce indefinitely. 

Some tissues and organs have more adult stem cells than others. Those organs with fewer or no stem cells (the heart, for example) don’t readily regenerate when they are injured or diseased.

Scientists around the world are actively studying ways to isolate different kinds of adult stem cells, to control and expand the rate at which they make copies of themselves, and to learn how to direct them to form the specific cell types needed for treatment.

Why are adult stem cells important?

Adult stem cells are the body’s toolbox, called into action by normal wear and tear on the body, and when serious damage or disease attack. Researchers believe that adult stem cells also have the potential, as yet untapped, to be tools in medicine. Scientists and physicians are working toward being able to treat patients with their own stem cellsor with banked donor stem cells that match them genetically.

Grown in large enough numbers in the lab, then transplanted into the patient, these cells could repair an injury or counter a disease — providing more insulin-producing cells for people with type 1 diabetes, for example, or cardiac muscle cells to help people recover from a heart attack. This approach is called regenerative medicine.

A number of challenges must be overcome before the full therapeutic potential of adult stem cells can be realized. There are typically very few stem cells in any one single tissue and they are very hard to collect, so scientists are exploring more practical ways of harvesting, growing and maintaining them. More work is also needed to find ways to redirect the different kinds of cells to where they’re needed in the body, preferably without the need for surgery or other invasive methods.

Research in all aspects of adult stem cells and their potential is underway at Boston Children’s Hospital. Realizing that potential will require years of research, but promising strides are being made.

Where do we get adult stem cells?

There are several ways adult stem cells can be isolated, most of which are being actively explored by our researchers.

From the body itself

Scientists are discovering that many tissues and organs contain a small number of adult stem cells that help maintain them. Adult stem cells have been found in the brain, bone marrow, lung, blood vessels, skeletal muscle, skin, teeth, gut, liver, and other (although not all) organs and tissues. They are thought to live in a specific area of each tissue, where they may remain dormant (sometimes for years), dividing and creating new cells only when they are activated by tissue injury, disease or anything else that makes the body need more cells.

Adult stem cells can be isolated from the body in different ways, depending on the tissue. Blood stem cells, for example, can be taken from a donor’s bone marrow, from blood in the umbilical cord when a baby is born, or from a person’s circulating blood. Mesenchymal stem cells, which can make bone, cartilage, fat, fibrous connective tissue, and cells that support the formation of blood can also be isolated from bone marrow. Neural stem cells (which form the brain’s three major cell types) have been isolated from specific parts of the brain and spinal cord. Isolating adult stem cells, however, is just the first step. The cells then need to be grown to large enough numbers to be useful for treatment purposes. The laboratory of Leonard Zon, MD, director of the Stem Cell Program, has developed a technique for boosting numbers of blood stem cells that’s now in Phase I clinical testing.

From amniotic fluid

Amniotic fluid, which bathes the fetus in the womb, contains fetal cells including mesenchymal stem cells, which are able to make a variety of tissues. Many pregnant women elect to have amniotic fluid drawn to test for chromosome defects, the procedure known as amniocentesis. This fluid is normally discarded after testing, but surgeon Dario Fauza, MD, a principal investigator at Boston Children's and an affiliate member of the Stem Cell Program, has been investigating the idea of isolating mesenchymal stem cells and using them to grow new tissues for babies who have birth defects detected while they are still in the womb, such as congenital diaphragmatic hernia. These tissues would match the baby genetically, so would not be rejected by the immune system, and could be implanted either before or after the baby is born.

From pluripotent stem cells

Induced pluripotent stem cells (iPS cells) are stem cells created from a patient’s own cells (skin or blood) and can be expanded almost indefinitely while holding the capacity to create all types of cells and tissues. Scientists at Boston Children’s and elsewhere are using them to produce different kinds of adult stem cells, progenitors or even mini-organs that can be then transplanted back to restore function. Laboratories around the world, including the lab George Daley, MD, PhD, are testing different chemical and mechanical factors that might prod iPS cells into forming distinct kinds of tissues. Adult stem cells made in this fashion would match the patient genetically, eliminating both the problem of tissue rejection and the need for toxic therapies to suppress the immune system. In addition, any genetic mutations from the patient that may be present in a patient’s iPS cells can be repaired by gene-editing or gene therapy before returning the healthy transplanted product back into the patient.

From other unrelated cells

A number of research groups have reported that cells can be forced to differentiate into apparently unrelated cell types (i.e. skin cells into blood cells, or blood cells into cardiac muscle cells). This phenomenon, called transdifferentiation or direct reprogramming, has been reported in animals and more recently in human cells, and has the potential to induce regenerative capacity directly in the tissue without the need to isolate or expand pluripotent cells outside the body of the patient. The recipes for transdifferentiation are not very efficient yet, but research is underway to try to optimize them and assess their long-term safety and efficacy. Researchers like Fernando Camargo, PhD, are exploring direct reprogramming to turn liver cells into liver progenitors that can repair the tissue directly in the damaged organ. 

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