Multipotent adult progenitor cells: an update.

The quintessential stem cell is the embryonal stem (ES) cell which has unlimited self-renewal and multipotent differentiation potential. Stem cells have also been identified in most tissues. Compared with ES cells, tissue-specific stem cells have less self-renewal ability and, although they differentiate into multiple lineages, they are not multipotent. A large number of recent published studies have suggested that tissue-specific stem cells may have the ability to generate cells of tissues from unrelated organs. We have identified a population of primitive cells in normal human, rodent, and possibly other mammalian postnatal tissues that have, at the single cell level, multipotent differentiation and extensive proliferation potential, which we named multipotent adult progenitor cell (MAPC). We will discuss studies aimed at determining whether MAPCs also exist in bone marrow of other species, whether MAPCs exist in vivo or are a culture phenomenon, to further characterize MAPCs using gene expression profiling, and effects of in vivo transplantation of MAPCs.