Obtaining olfactory ensheathing cells from extra-cranial sources a step closer to clinical transplant-mediated repair of the CNS?

extraordinary regenerative properties of the peripheral olfactory system, and the role played by olfactory ensheath-ing cells (OEC), have been known for many years (Doucette, 1990). However, until recently this niche of neurobiology remained relatively obscure, attracting the attention of an enthusiastic, but relatively small band of scienti®c devotees. The OEC's sudden rise to prominence has happened because of the recent con¯uence of the OEC biology tributary with the mainstream of clinically orientated neurobiology, aiming to overcome the regenerative shortcomings of the CNS by cell transplantation. The concept of removing cells from an area that regenerates ef®ciently and relocating them in one that does not is not a new one, and transplantation of Schwann cells from the periferal nervous system, where regeneration occurs with tolerable ef®ciency, into the CNS has a long track record. Given the pro-regenerative properties of OECs one can reasonably ask why the OEC transplantation ®eld has taken so long to get going? The answer lies in part in the inadequacies of transplanted Schwann cells; evident from the fact that Schwann cell transplantation is not in widespread clinical use despite occasional reports of success in rodent models. Hence the quest for alternative cells to transplant, and hence the current enthusiasm for OECs, which is based on several observations. Firstly, transplanted OECs support regeneration of long tract axons and functional recovery in models of spinal cord injury making them a strong candidate to help restore function following traumatic injury to the spinal cord (Li et al., 1997; Ramon-Cueto et al., 2000). Secondly, transplanted OECs will remyelinate persistently demyelinated axons and restore ef®cient conduction thereby making them a candidate transplant cell to repair foci of persistent demyelination in multiple sclerosis (Imaizumi et al., 1998). This repair repertoire is similar to that of Schwann cells, but whereas the latter's value is limited by their unfavourable interactions with reactive or scarring astrocytes, there is some evidence both in vitro and in vivo that transplanted OECs are not similarly affected (Ramo Ân-Cueto et al., 1998; Lakatos et al., 2000). A case can therefore be made that OECs are the preferable cell to transplant. Results such as these trigger efforts to convert promising experimental data into effective clinical practice. This conversion involves a broad range of problems, many of which are dif®cult to overcome, and make the initial proof-of-principle experiments seem relatively straightforward by comparison. Nevertheless, attempts are under way. Recently it has been …