Olfactory mucosa for transplant-mediated repair: a complex tissue for a complex injury?

Damage to the brain and spinal cord leads to permanent functional disability because of the very limited capacity of the central nervous system (CNS) for repair. Transplantation of cells into regions of CNS damage represents one approach to enhancing this repair. At present, the ideal cell type for transplant-mediated repair has not been identified but autologous transplantation would be advantageous. Olfactory tissue, in part because of its capacity for regeneration, has emerged as a promising source of cells and several clinical centers are using olfactory cells or tissues in the treatment of CNS damage. Until now, the olfactory ensheathing cell, a specialized glial cell of the olfactory system has been the main focus of attention. Transplants of this cell have been shown to have a neuroprotective function, support axonal regeneration, and remyelinate demyelinated axons. However, the olfactory mucosa is a heterogeneous tissue, composed of a variety of cells supporting both its normal function and its regenerative capacity. It is therefore possible that it contains several cell types that could participate in CNS repair including putative stem cells as well as glia. Here we review the cellular composition of the olfactory tissue and the evidence that equivalent cell types exist in both rodent and human olfactory mucosa suggesting that it is potentially a rich source of autologous cells for transplant-mediated repair of the CNS.