USE OF SCHWANN-CELLS TO INDUCE REPAIR OF ADULT CNS TRACTS

The ability of transplanted Schwann cells to modify the sprouts formed by cut central axons, and in particular to induce branching and exten sion of axon sprouts, is an encouraging sign for their possible future use in repair. The accessibility of the Schwann cells in the cultu re stage before transplantation offers a practical opportunity for genet ic engineering (e.g. to introduce genes directing the expression of sp ecific growth factors) which might be useful in designing a future met hod for the repair of human spinal injury. It must be borne in mind, h owever, that even the most successful cases of peripheral nerve grafts have shown only a limited proportion of axons growing back from the g rafts into the environment of the CNS (Carter et al., 1989). When we c onstructed Schwann cell columns in the thalamus (Brook et al., 1994), we did not observe axons leaving the artificial tracts. In our experim ents with Schwann cells transplanted into the spinal cord (Li & Raisma n, 1994), the axons have only been studied within the graft, and we ha ve as yet not been able to assess the extent to which they re-enter th e CNS. For effective regeneration to occur, regenerating axons must no t only be able re-enter their original pathways and elongate along the m, but also leave them in a correct manner - i.e. by making appropriat e choices from a wide range of destinations. Therefore the effectivene ss of a Schwann cell ''bridging'' repair must depend upon the self-reo rganising capacity of the adult CNS (e.g. Florence et al., 1996).