Schwann cell transplantation: a repair strategy for spinal cord injury?

Schwann cells (SCs), when implanted in the injured spinal cord, support regeneration of axons, myelinate or ensheathe regenerated axons in a normal way, reduce cyst formation in the injured tissue, reduce secondary damage of tissue around the initial injury site, and modestly improve limb movements. If SC transplantation is combined with additional treatments such as methylprednisolone, neurotrophins, GDNF, olfactory ensheathing cells, chondroitinase, or elevation of cAMP levels, more axons (including those from neurons in the brainstem) regenerate into and out of the SC implant and further improve locomotion. Recent work to improve SC migration from the implant into the spinal cord by polysialylating NCAM on the SC surface has led to the novel finding that corticospinal axon growth is promoted by SCs. Recent studies are cited showing that when astrocytes extend slender processes into an implant instead of forming a sharp boundary they are permissive rather than inhibitory to axonal regrowth. The interfaces that comprise the "on-ramps" and the "off-ramps" are key to the success of a SC implant to span the injury site and to foster axon regeneration across the injury.