Toward defining the regenerative potential of olfactory mucosa: establishment of Schwann cell-free adult canine olfactory ensheathing cell preparations suitable for transplantation.

Olfactory mucosa (OM)-derived olfactory ensheathing cells (OECs) are attractive candidates for autologous cell transplantation-based therapy of nervous system injury. However, defining the regenerative capacity of OM-derived OECs is impeded by the fact that cell cultures used for transplantation may contain significant amounts of contaminating trigeminal nerve Schwann cells that escape identification by sharing in vitro expression of OEC markers. The aim of the present study, therefore, was to quantify contaminating Schwann cells in OEC preparations and to develop a protocol for their specific depletion. Based on the observation that freshly dissociated, but not cultured, OECs and Schwann cells display differential expression of HNK-1 and p75(NTR), magnet-activated cell sorting (MACS) was used to deplete myelinating (HNK-1-positive) and nonmyelinating (p75(NTR)-positive) Schwann cells from primary cell suspensions containing HNK-1-/p75(NTR)-negative OECs. Upregulation of p75(NTR) expression in OECs during culturing allowed their subsequent MACS-based separation from fibroblasts. Immunofluorescence analysis of freshly dissociated OM prior to MACS depletion revealed that 21% of the total and 56% of all CNPase-positive cells, representing both OECs and Schwann cells, expressed the Schwann cell antigens HNK-1 or p75(NTR), indicating that freshly dissociated OM prior to culturing contained as many Schwann cells as OECs, while olfactory bulb (OB) primary cell suspensions revealed lower levels of Schwann cell contamination. Interestingly, neurite growth of neonatal rat dorsal root ganglion (DRG) neurons cocultured with OM-OECs, OB-OECs, and fibular nerve (FN) Schwann cells used as control was significantly higher in the presence of OECs than of Schwann cells. The first report on identification and specific depletion of Schwann cells from OEC preparations provides a solid basis for future efforts to fully define the regenerative potential of nasal mucosa OECs.