Stem Cells: Are They the Solution?

Cell transplantation for a claimed "cure" of spinal cord injuries (SCI) have become a reality in numerous treatment centers/clinics around the world despite the lack of validation in clinical trials.  Hundreds of “stem cell tourists” travel outside North America every year to seek treatment with these unproven cell therapies.  Only recently, two clinical trials have been approved by the FDA and Swissmed, respectively, and begun to enrol patients for the primary purpose to study safety and possibly efficacy of cell transplantation into the injured human spinal cord.  These trials will be briefly reviewed. At the time of writing this abstract in September of 2011, Geron Corporation had treated 4 patients with a human embryonic stem cell derived oligodendrocyte precursor cell and Stell Cell Inc. initiated the first neural stem cell transplant.  In this presentation the audience will be introduced to the most prominent candidate cell types for transplantation, as well as the rationales for their applications to the spinal cord. SCI variably interrupt the nerve fibres connecting the brain with the spinal cord and are quite heterogeneous regarding level of the spine and degrees of severity.   Thus, SCI cause losses of motor and sensory functions in addition to impaired sexual function, bowl and bladder control and blood pressure regulation.   Usually some nerve fibres are spared at the site of lesion, yet lose their insulation material (myelin) which also leads to impulse conduction blocks. Hence, the objectives of cell transplantations are to replace myelin and to promote regeneration of the interrupted nerve fibres across the site of injury.  Moreover, transplanted cells can modulate the inflammatory response after an injury (typically when given within days) and they provide factors that enhance endogenous repair responses in the injured spinal cord.  In our own laboratories we favour a stem (progenitor) cell from the skin that combines many of these desired effects.  These so-called Skin Progenitor-derived Schwann cells, when injected up to 2 months after spinal cord injury of rats, integrate and bridge the lesion sites, promote the growth of thousands of nerve fibres and stimulate the participation of their endogenous counterpart cells. Importantly, with delayed transplantation at 8 weeks after SCI, the treated rats show continued improvements in locomotion which were not seen in control animals. The challenges of translating cell transplantation strategies to the human clinic will be discussed and alternative candidate treatments for the injured spinal cord as they emerged in animal studies will be pointed out.