Note: This column is for information purposes only and is not intended as a substitute for professional medical advice.

Q: A post-polio newsletter said that there may be a cure for PPS utilizing the poliovirus that did us in. The poliovirus will revitalize polio survivors' motor neurons and we will hopefully be brought back to the condition we were in before PPS set in. Is this possible?

A: Possible, yes. And much more likely to help polio survivors than stem cell research [see January 2001 Post-Polio Forum]. But still an extremely difficult proposition.

Researcher Casey Morrow created what he calls poliovirus "replicons," neutralized and hollowed out polioviruses into which he placed a gene that causes neurons to make a non-poliovirus protein. He injected replicons into the spinal cords of mice where the "Trojan horse" poliovirus was taken inside the motor neuron and the gene went to work, making the non-polio protein. There is hope that Morrow's replicons will be able to get inside polio survivors' damaged brain and spinal cord neurons and insert genes for human proteins that will restore failing neurons. But there are big hurdles to be overcome.

First, you can't inject anything into polio survivors' spinal cords or brain stems without causing more damage to the remaining, functioning neurons. Morrow thinks that replicons could instead be injected into the spinal fluid, where they would then get into the neurons just as did the original poliovirus. However, 21 percent of polio survivors with PPS have active antibodies to poliovirus in their spinal fluid. "Most immunized people would not have sufficient antibodies to neutralize the replicons," says Morrow. "We were still able to get gene delivery using animals previously immunized against poliovirus. This is most probably due to the replicons entering the cell before interaction with anti-polio antibodies." But Morrow injected the replicons directly into the mouse spinal cord, not into the spinal fluid where poliovirus antibodies might have the time to interact with and disable the replicons.

Second, if replicons do enter poliovirus-damaged neurons, what protein would they tell the neurons to produce? "The 'holy grail' is to devise a way to repair damaged neurons," says Morrow. "Our goal would be to use replicons that would produce nerve growth factors. Extensive pre-clinical testing will be needed to determine which factor, or combination, will be effective."

Recent experiments in mice suggest that nerve growth factor itself may help polio survivors. Neuroscientist Jonathan Cooper found that he could boost the size of neurons by injecting NGF directly into the brains of mice. Increasing neuron size might be helpful since polio survivors' remaining motor neurons are smaller than normal size. However, motor neurons' protein-making "factories" have been shown to be breaking apart in polio survivors with new muscle weakness. So increasing the size of neurons with broken protein-making machinery would make them bigger, but they wouldn't necessarily function better.

Whatever protein is inserted would not only have to fix disintegrating protein factories but also unplug the "tubules" within the neuron that were stopped up during the poliovirus attack. The tubules are the microscopic pipes that carry proteins and neurochemicals from where they are made inside the neuron to where they are released and cause muscles to contract. New proteins won't help much if they can't get to where they need to go.

How soon might poliovirus replicons be available to test on polio survivors with PPS? "I can't really say," says Morrow. "I do not envision the replicons initially going into polio survivors. More than likely, the replicons would be used to treat spinal cord injury-causing paralysis or ALS (Lou Gehrig's disease). The pre-clinical testing on mice--and later on monkeys--would be needed to address safety issues. I would hope that within the next five or so years new, safe therapies will be available."

Will the poliovirus itself turn out to be the cure for PPS? We'll have to wait and see. But even if the scientific hurdles can be overcome and replicons and protein-manufacturing genes can restore poliovirus-damaged neurons, there must be remaining neurons to be rebuilt. Even if the replicon cavalry arrives as soon as five years from now, polio survivors must save the neurons they have left by continuing to follow "the golden rule": If anything causes fatigue, weakness or pain, DON'T DO IT--or do much less of it.