Mesenchymal Stem Cells for Cell Therapy and Tissue Regeneration in Urology

Abstract

Adult stem cells are defined as clonogenic, self-renewing progenitor cells that reside in adult tissues and can generate one or more specialized types of cells required for the function of that tissue. The majority of adult tissues contain their own stem/ progenitor cells that are capable of maintaining, generating, and replacing terminally differentiated cells within the tissue in response to physiologic cell turnover or tissue damage resulting from injury. Stem cell populations in the bone marrow were the first adult stem cell populations to be described, but in recent years adult stem populations have been demonstrated in the brain,1, 2 skin, 3 and muscle 4, hair follicle and the gastrointestinal tract. Adult stem cells, especially hematopoietic stem cells, are the best understood cell type in stem cell biology 5, yet they remain an area of intense study, as their potential for therapy may be applicable to a myriad of degenerative disorders. These cells are a particularly attractive option for cell therapy and tissue engineering applications because they can be used in autologous therapies, thus avoiding any complications associated with immune rejection. Research into adult stem cells has progressed slowly in the past, mainly because true stem cells are present in extremely low numbers in adult tissue6-8, and because adult nonmesenchymal stem cells have been challenging to isolate, expand and maintain in culture. Some cells, such as those of the liver, pancreas and nerve, have very low proliferative capacity in vitro, and the functionality of some cell types is reduced after the cells are cultivated. These issues have limited the use of adult stem cells in tissue engineering and cell therapy research. However, the discovery of native targeted progenitor cells has allowed some of these limitations to be overcome. Native targeted progenitor cells are tissue specific unipotent cells derived from most organs. These cells are already programmed to become a specific cell type, and as with adult stem cells, native progenitor cells can be obtained from the specific organ to be regenerated, expanded, and used in the same patient without rejection, in an autologous manner 9-26. By studying the niche in which the progenitor cells reside, as well as by exploring conditions that promote the differentiation of these cells, it has been possible to overcome some of the problems facing cell expansion in vitro. Major advances in cell culture techniques have been made within the past decade, and these techniques make the use of autologous cells possible for clinical application. In this