Neural Crest Stem Cells from Adult Bone Marrow: A New Source for Cell Replacement Therapy?

Neurodegenerative disease is a generic term used for a wide range of acute and chronic conditions whose etiology is unknown such as Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis (ALS), Alzheimer's disease, but also now for other neurological diseases whose etiology is better known but which are also concerned by a chronic lost of neurons and glial cells such as multiple sclerosis (MS), stroke, and spinal cord injury. Although the adult brain contains small numbers of stem cells in restricted areas, the central nervous system exhibits limited capacity of regenerating lost tissue. Therefore, cell replacement therapies of lesioned brain have provided the basis for the development of potentially powerful new therapeutic strategies for a broad spectrum of human neurological diseases. However, the paucity of suitable cell types for cell replacement therapy in patients suffering from neurological disorders has hampered the development of this promising therapeutic approach. Stem cells are classically defined as cells that have the ability to renew themselves continuously and possess pluripotent or multipotent ability to differentiate into many cell types. Besides the germ stem cells devoted to give rise to ovocytes or spermatozoides, those cells can be classified in three subgroups: embryonic stem cells (ES), induced pluripotent stem cells (iPS) and somatic stem cells (Figure 1). ES cells are derived from the inner mass of blastocyst and are considered as pluripotent stem cells as these cells can give rise to various mature cells from the three germ layers. iPS cells are also pluripotent stem cells, however, those cells derived from adult somatic cells such as skin fibroblasts are genetically modified by introduction of four embryogenesis-related genes (Takahashi et al., 2007; Park et al., 2008). Finally, tissue-specific stem cells known as somatic or adult stem cells are more restricted stem cells (multipotent stem cells) and are isolated from various fetal or adult tissues (i.e. hematopoietic stem cells, bone marrow mesenchymal stem cells, adipose tissuederived stem cells, amniotic fluid stem cells, neural stem cells, etc.; Reviewed by Kim and de Vellis, 2009).