Stem Cells in Medicine
January 10, 2013
The most common and accepted use of stem cells in medicine is a bone marrow transplant in which physicians attempt to change a patient’s blood cells from one type to another. In the case of cancers like leukemia or diseases like sickle-cell anemia, the transplant aims to erase all the diseased cells and replace them with a new line of blood-type cells derived from donor stem cells. The process itself is painful and has variable success rates, but when it works patients can be cured.
The Fountain of Youth drove explorer Ponce de Leon to the discovery of new worlds, and this mythical fascination with renewal pre-dates the Ancient Greeks. Today, promise lies in small cells called stem cells that have the ability to self-renew and transform into cells of differing types. The International Society for Cellular Therapy has defined stem cells by the following criteria: (i) they are adherent to plastic material in the laboratory, (ii) they express specific proteins on their outer surface much like you have unique traits that identify your heritage, and (iii) these cells can be directed to transform into bone cells, fat cells, cartilage cells, etc. The potential to form new organs and to revitalize aged tissues are the reasons that stem cells are researched so intensely and need to be scrutinized carefully. Stem cells can be harvested from an embryo or an adult. Embryonic stem cells are removed “in utero” from a fertilized egg and these cells have the greatest potential; however, their acquisition is controversial and their use highly regulated. Adults have an abundant supply of stem cells originating from blood and tissues. Cord blood is a commonly harvested source of adult stem cells originating from the blood stream (hematopoietic stem cells).
In addition, stem cells are found in your fat, bones and cartilage to name a few sites. These cells are called mesenchymal stem cells and they differ from hematopoietic stem cells in the markers expressed on their surface. Differing stem cells appear primed to better renew differing tissues, and the key is determining the correct factors that drive these cells to become a certain tissue type. So far, there is much promise and a few successes utilizing stem cells to treat diseases. In addition to the bone marrow transplant, many clinical trials and experimental studies are underway attempting to harness the potential of stem cells. The few mentioned here are only the tip of a large and growing iceberg.
During a heart attack the muscle cells within the heart die and are replaced by scar tissue. Your heart then changes shape and size in an attempt to successfully pump blood again; however, it rarely recovers the same capacity it had before the attack. Current therapies aim to prevent a future attack; however, physicians in Europe are using stem cells retrieved from patient’s bone marrow to regenerate muscle in the scarred areas. The early results have shown a modest gain in muscle cells and function. Long-standing wounds from trauma, diabetes or venous insufficiency are a serious problem and can take up to years to heal, sometimes never closing at all. Recent studies using stem cells in fat taken from liposuction specimens have shown improved healing rates and new blood vessel formation in problem wounds. In our own lab at Emory University, we have shown a four-fold increase in blood vessel formation with the addition of these stem cells. The next step is to apply these techniques to improve the quality of damaged skin and organs.
The notions that paralyzed patients can walk again and that kidneys can be built in the lab are the reasons the U.S. government has invested heavily over the last decade in stem cell research. They are also the reasons that many companies and even physicians have licensed and marketed the promise of these cells without ensuring the efficacy. We have the basic building blocks, but directing these cells to become complete organs or prevent cancer is beyond our current knowledge. You should be excited at the future potential, but be cautious about current promises that appear too good to be true.