Stem cells: potential therapy for age-related diseases.

Aging is associated with a progressive failing of tissues and organs of the human body leading to a large number of age-related diseases. Regenerative medicine is an emerging clinical discipline that aims to employ cellular medicines (normal cells, ex vivo expanded cells, or tissue-engineered organs) to restore the functions of damaged or defective tissues and organs and thus to "rejuvenate" the failing aging body. One of the most important sources for cellular medicine is embryonic and adult (somatic) stem cells (SSCs). One example of SCCs with enormous clinical potential is the mesenchymal stem cells (MSCs) that are present in the bone marrow and are able to differentiate into cell types such as osteoblasts, chondrocytes, endothelial cells, and probably also neuron-like cells. Because of the ease of their isolation and their extensive differentiation potential, MSCs are among the first stem cell types to be introduced in the clinic. Some recent studies have demonstrated the possible use of MSCs in systemic transplantation for systemic diseases, local implantation for local tissue defects, as a vehicle for genes in gene therapy protocols, or to generate transplantable tissues and organs in tissue-engineering protocols. However, several challenges confront the use of these cells in the clinic, ranging from biological challenges (e.g., how to isolate a homogenous populations of the cells with specific criteria from the bone marrow and how to expand them ex vivo without affecting their differentiation potential) to biotechnological challenges (e.g., how to develop easy methods for quality control of the cellular-based products). While it is expected that cellular medicines will decrease the burden of several age-related diseases, it is not clear whether they can change the course of the aging process itself and thus prolong human life.