Various news outlets are often found reporting on people with spinal cord injuries going to Lisbon, Portugal for what the outlets usually (mistakenly) refer to as an "adult stem cell" treatment. As of early May, 52 people have traveled to Portugal to have this surgery, with anecdotal reports of mixed amounts of recovery. (Primarily sensory, with modest one-to-two functional levels of return at best; not average or minimal levels of return, but maximum.)
What do we really know about the treatment?
We know that Dr. Lima extracts the nasal mucosa which (when unpurified) contains olfactory ensheathing cells, mucosal glands, cilia, fibroblasts, and a number of other cell types. Dr. Lima then cuts out a part of the spinal cord to remove scar tissue (which may also contain surviving axons) and transplants the extracted nasal mucosa across the site of injury.
Why is he transplanting the nasal mucosa?
The nasal mucosa is a component of the olfactory system, which is a part of the central nervous system known to perpetually regenerate itself throughout our lifetimes. The belief is that cells of the nasal mucosa produce growth factors that will allow nerves in the spinal cord to overcome native inhibitory signals and regenerate.
Are there really stem cells in there?
A recent study from Brisbane, Australia reports that there are.
Are the stem cells responsible for the reported recovery?
This is the tricky question, which requires a small amount of background knowledge before answering.
Nerve cells transmit information through the spinal cord by electrical impulses called action potentials. Nerve cells are insulated by a fatty substance known as myelin that allows action potentials to travel long distances.
Spinal cord injuries that do not sever the spinal cord usually cause cells around the site of injury (that survive the injury) to lose their myelin insulation. As unmyelinated cells cannot pass on action potentials, simply restoring the myelin in a sufficient number of cells can result in functional recovery.
With that as background, the primary function of olfactory ensheathing cells in the nasal mucosa (and elsewhere) is to myelinate cells. Therefore, the recovery noted in those who received such transplants may be due to the olfactory ensheathing cells, and not any stem cells that may survive the transplant.
So, are the stem cells responsible for the recovery? Yes or No?
Without further information, it is impossible to know. The recovery may be the result of the stem cells, the olfactory ensheathing cells, a combination of the two, or something else entirely such as the removal of the scar tissue or the intensive rehabilitation after the surgery.
Is anyone currently working to find out what causes this recovery?
The Australian team mentioned earlier began a human clinical trial earlier this year to determine whether the recovery is due to the olfactory ensheathing cells.
Would embryonic stem cells work better?
A direct embryonic stem cell transplantation would likely show a lower, or a comparable, degree of recovery. Such a transplantation would have a risk of forming a tumor in the spinal cord, which wouldn't be pretty.
Any future therapy involving embryonic stem cells will require that they be grown into specific cell types prior to transplantation. Geron is working on a treatment based on these principles and are hoping to initiate a clinical trial in 2006.
Is the "Adult stem cells cure paralysis" claim an Urban Legend?
While the reported benefits are helpful, they are by no means a cure for all the issues involved with paralysis. As mentioned above, the stem cells may not even be responsible for the limited recoveries that have occurred.