Although modern medicine has provided the ability to cure infections and malignancy, the ability to repair damaged organs is less advanced. Solid organ transplantation has been performed successfully, but is fraught with problems such as rejection, infection, and secondary malignancy from immunosuppression. Organ shortages create ethical issues with respect to the equitable distribution of donated tissues. Regenerative medicine, the field devoted to rebuilding damaged organs from stem cells, may provide alternatives to solid organ transplantation. However, the field of regenerative medicine is in its infancy. The potential sources of the tissues to regenerate organs include cloned cells, embryonic or fetal stem cells, or adult stem cells. Although each of these sources of stem cells has potential biological advantages and disadvantages, ethical and legal concerns have been raised by cloning (1-4) and the use of embryonic and fetal stem cells (5).

Adult stem cells might provide medical solutions that avoid the ethical and legal problems of cloning and fetal stem cell approaches. Until recently, stem cells from adult tissues were believed restricted in their capacity to produce tissues other than the tissue from which they arose. A number of studies have challenged this view. Specifically, these studies have suggested that adult stem cells from various organs are plastic, meaning that they can differentiate not only into their original source tissue, but also into cells of unrelated tissue.

Bone marrow transplant has been used to treat nonhematopoietic disorders such as osteogenesis imperfecta (6) and metachromatic leukodystrophy. However, in the case of osteogenesis imperfecta, transplanted mesenchymal stem cells are believed to be the source of reparative osteo-cytes. In metachromatic leukodystrophy, the mechanism of improvement is unknown, but is thought to be related to a bystander effect of cells, with normal aryl sulfatase circulating past diseased neurons (7,8). The role of the hematopoietic stem cell as a replacement for diseased osteocytes or neurons

From: Adult Stem Cells Edited by: K. Turksen © Humana Press Inc., Totowa, NJ

has not been advocated as a possible mechanism for transplant-induced improvement in these disorders.

Adult stem cell plasticity might allow, for instance, use of bone marrow stem cells to replace damaged myocardial cells following ischemic damage, pancreatic islet cells to cure insulin-dependent diabetes, or cells from the substantia nigra to cure Parkinson's disease. However, as exciting as the prospect is for adult stem cells to solve some of our most daunting medical challenges, newer studies have challenged the interpretation of some of the pioneer studies that generated this excitement. This chapter is an overview of the current controversies in adult stem cell biology.

0 0

Post a comment