The most difficult element to understand about adult stem cells is their purpose in the human body. While embryonic stem cells are, in effect, the blank slate upon which all of the tissue, organs and structure of the human body is drawn, the adult stem cell has a different, though related, overall function. It is a repair cell. Sitting quiescently in bone marrow, tooth enamel, adipose (fat) tissues and other places in the body, these cells “wake up” upon receiving signals related to injury – inflammation.
Their function is to begin the cascade of healing when the human body is injured. The number of stem cells in an adult human begins declining shortly after birth. It is, in fact, this decline in the number of stem cells that ultimately leads to wear, deterioration and finally, death.
So, when the human body is injured, the adult stem cells “wake up”, move through the body to the site of injury, express proteins to down and regulate inflammation, express other proteins to stimulate new cellular growth, recruit new growth factor proteins and then, themselves, begin to change into the very cellas that have been damaged. Through this process, these cells are giving and receiving signals with surrounding environment. This is an extremely important aspect and one of the central discoveries regarding stem cells and the point that differentiates them from any other cell.
The most common therapeutic use of stem cells by physicians in the United States is to harvest them from one part of the body where they exist in greater amounts and then re-implant them at the site of injury – where they are most needed but are in short supply. For adults with diminishing stores of stem cells, this is an effective way to stimulate healing at sites of injury.
Frankly, this process of harvesting cells (be they bone marrow, skin, fat or any other cells) from one part of the body and then re-implanting them in another part has been an important aspect of medicine for, literally, hundreds if not thousands of years.
What makes this discussion so relevant is that physicians are now specifically targeting stem cells (i.e., repair cells) for concentration, re-implanting and expansion before re-implanting.