different sources of
stem cells
Continued from previous issue
Embryonic stem cells are obtained from the embryo and possess the potential for differentiation into a wide range of cell lineages. Although they hold immense promise to differentiate into the cell type of choice, ethical issues are associated with the use of these cells, and these issues need to be resolved before the promise of therapeutic treatment using embryonic stem cells can be brought into general patient therapeutic treatment plans. Currently, bone marrow (BM) is the most common source of adult stem cells for hematopoietic stem cell transplants and cellular therapies. The stem cells obtained from BM are mesenchymal stem cells (MSCs), which are pluripotent adult stem cells that can differentiate into many different cell types, including osteoblasts, chondrocytes, adipocytes, neurons, cardiac myocytes, and vascular endothelial cells. BM harvest is a surgical procedure that usually requires general anesthesia or sedation, and the proliferative potential and differentiation capacity of the BM MSCs from older donors seems to be reduced. Thus, interest has been increasing in using other sources of stem cells from adult and fetal tissue (1).
Another source of regenerative cells has been the relatively recent practice of preserving umbilical cord tissue and cells. With AF cells, it takes 20 to 24 hours to double the number of cells collected, faster than for umbilical cord stem cells (28 to 30 hours) and BM stem cells (more than 30 hours) (19). The progenitor cells that are derived have shown a high self-renewal capacity with more than 300 population doublings. In addition, although scientists have been able to isolate and differentiate, on average, only 30% of MSCs extracted from a child’s umbilical cord shortly after birth, the success rate for AF-derived MSCs has been close to 100% (20). Furthermore, extracting cells from the AF bypasses the problems associated with a technique termed donor–recipient human leukocyte antigen (HLA) matching, which involves transplanting cells (19).
Thus, the amnion has been used as a physiologic wound dressing and as a graft for skin wound coverage (7–10). Heil et al (21) demonstrated that patients with occlusive vascular disease developed a prominent collateral vascular network below the occlusive site through spontaneous arteriogenesis (the remodeling of existing arterio-arteriolar anastomoses to developed functional arteries) and angiogenesis (new capillary growth induced by hypoxic conditions) after being injected. Human AM has proved to be a versatile temporary biologic dressing in studies involving hundreds of patients during the past century. The first reported use of fetal membranes was in skin transplantation in the early 1900s (22,23). AM was also used on burned and ulcerated skin surfaces, and clinicians reported a lack of infection, a marked decrease in pain, and an increased rate of re-epithelialization of the traumatized skin surfaces. Others have demonstrated the use of AM as a biologic dressing for open wounds, including burns and chronic ulceration of the legs (24).
In traditional medicine, the first reported use was by Davis (22) in 1910 at John Hopkins Hospital for burns and ocular wounds in 550 cases. Sabella (23), in 1914, reported similar positive findings. Numerous reports were published during the 1940s and 1950s, until the 1970s when the human immunodeficiency virus/acquired immunodeficiency syndrome became epidemic, and its