Today, a team of Polish researchers is reporting that it has re-established sensation and limited movements in a previously paralyzed patient. The technique involved both the transplantation of nerve fibers from the leg and a suspension of support cells obtained from the olfactory area of the brain. The results, while striking, only apply to a single patient; more work will need to be done to determine if the approach can work generally.
Spinal cord injuries are notoriously difficult to heal. Although there are nerve cells throughout the spinal cord, the majority of its function is performed by the long axons that extend up and down the length of the body. The axons transmit sensory signals to the brain and receive muscle commands back.
Injuries to the spinal cord sever these connections. The injured region generally forms a thick scar that inhibits the regrowth of axons, leaving regions below that point permanently severed from the brain. The result is paralysis and a lack of sensation. Attempts at therapies have focused on overcoming the effect of this scar. While we've learned a lot about the inhibition of nerve growth, what we've learned has not resulted in any significant successes.
The new work follows up on one idea that's been under consideration for a number of years: using cells from the olfactory system, which handles our sense of smell. Unlike many other areas of the nervous system, the cells in our nose that register the presence of scent molecules turn over regularly. The region of the brain that receives the signal from the nose, the olfactory bulb, must constantly send out new axons to communicate with the replacement cells. Thus, the olfactory system must be doing something to encourage axon growth, and that something could be the key to restoring it to a damaged spinal cord.
The technique used in Poland is built upon the foundations of all this previous knowledge. During the procedure, the scar tissue that had built up on the severed ends of the spinal cord was removed. To bridge the 8mm gap that developed in the patient, nerve fibers were obtained from the legs of the patient.
But it's the use of olfactory cells that is most striking. In order to obtain cells for transplant, the team performed brain surgery and removed an entire olfactory bulb. The cells were then dissociated and grown in culture. Rather than focusing on nerve cells, the authors obtained support cells called olfactory ensheathing cells, which normally cover and nurture the axons of nerve cells. These cells were then injected into the site where the nerve fibers were implanted.
For months afterward, nothing much happened. At five months, the patient began to regain sensation in areas that were affected by the paralysis. Around the same time, muscle mass began increasing in the left thigh, which was accompanied by the ability to perform limited voluntary movements. By 10 months, the increase in sensation began to accelerate, while voluntary muscle control returned to the right leg. Around this time, the patient was able to walk with the assistance of leg braces, support, and a healthcare worker. Later, the patient was able to walk on his own with leg braces and a walker.
The paper leaves off there, but the BBC has obtained exclusive access to the patient and his physicians. As a result, we know that the patient is Darek Fidyka, and he was paralyzed during a stabbing. We can also watch video of his restored ability to walk.
The authors argue that the restored motion is a product of the procedure, rather than a normal healing process. Healing typically happens within the first few months of injury, while Fidyka showed no improvements, even after a heavy therapy program, prior to the surgery.
But the bigger question is why the procedure worked in his case. As evidenced by the long research history, lots of other groups have tried similar approaches on other spinal injuries without reporting any successes. We'll have to wait for the group to try it on other patients to learn whether this success is a product of something distinct to the procedure or something distinct to Fidyka.