Currently, blood stem cells are the only type of adult stem cell used regularly for treatment; they have been used since the late 1960s in the procedure now commonly known as bone marrow transplant. Transplants of neural stem cells have been tried in small numbers of patients with brain disorders such as Parkinson disease, and the FDA recently approved a clinical trial of neural stem cells for spinal cord injury.
Preliminary research in animals has found that bone marrow stromal cells, injected into a damaged heart, can have beneficial effects. And researchers at Children’s Hospital Boston have shown in a mouse model that the same cells, injected into the blood, help protect against chronic lung disease in premature newborns.
In some cases, it may be possible to infuse the stem cells into the blood, as in a bone marrow transplant. The cells find their own way to the proper location and begin forming the cells and tissues needed. In other cases, the cells may need to be injected directly into the organ or tissue that needs them.
The ultimate goal is for the cells to take up residence in their proper places in the body, divide repeatedly and form functioning tissues—or repair diseased tissue. It’s not always clear how this happens. In some cases, the transplanted cells may become part of the tissue or organ; in others, they may secrete growth factors that stimulate cells already residing there.
For adult stem cells to be successful treatments, they must:
1) Reproduce in large enough quantities to provide the amounts needed for treatment. Some adult stem cells have a very limited ability to divide, making it difficult to multiply them in large numbers. Scientists around the world are trying to find ways of encouraging them to multiply. The Stem Cell Program at Boston Children’s Hospital, for example, recently discovered that a drug called PGE2 can multiply numbers of blood stem cells. PGE2 is now being tested in patients with leukemia and lymphoma to see if it will help them rebuild their blood systems.
2) Create the needed cell types, either in the laboratory or after they’ve been transplanted into the body.
3) Be safe. A host of clinics around the world offer supposed stem-cell therapies with claims of complete success, but these treatments must still be considered experimental and potentially risky until much more work is done to ensure their safety. For example, when adult stem cells are provided from a donor, precautions must be taken to avoid rejection by the patient’s immune system. Unless the patient is his or her own donor, or unless a donor is found with an identical tissue type, the patient will need to take powerful drugs to suppress the immune system so the transplanted cells or tissues won’t be rejected. In addition, if adult stem cells are manipulated incorrectly, there is a risk of cancer.