Stem Cell Program | Adult Stem Cells

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.

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.

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 Daley Lab 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.

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.