By Anne Bennett
Swingle and Marjorie Centofanti
A vibrant woman stricken with ALS and a young neurology researcher both rest their hopes in the curative powers of stem cells.
More than 350 times a year, Jeff Rothstein diagnoses a case of amyotrophic lateral sclerosis or ALS. Patients come from around the world to see this neurologist. Sometimes they arrive for a consultation; sometimes they come because they hope to get in on a clinical trial of a new drug. On the last day of July 2000, the patient sitting across from Rothstein was a 54-year-old woman from Baltimore, named Laurie Russell.
Six weeks earlier, Russell had undergone a battery of tests because she had been told it was necessary to rule out ALS in connection with certain symptoms she had been experiencing. Now she listened intently as Rothstein explained to her and her husband the defining characteristics of this deadly degenerative disease. ALS attacks motor neurons, the cells of the brain and spinal cord t
hat power the muscles. One by one, these nerve cells expire, and the muscles they control falter and then atrophy. This, Rothstein said, never once taking his eyes off Russell, causes a progressive paralysis, that spreads inexorably from one set of muscles to the next, ending in death.
Rothstein reviewed the classic signs of ALS: cramps and muscle weakness, symptoms Russell had come to know all too well. But the hallmark of ALS, he continued, is something called fasciculations, a sort of uncontrollable twitching that ripples along the muscles when they are at rest. "Look at the muscles in her arm," Rothstein said, turning to Russell's husband, Edgie. "I think you'll see what I'm talking about."
And it was true, sickeningly so, for under the skin on Laurie's arm, her husband could clearly see her muscles twittering away. "What's the prognosis?" Edgie asked.
"Statistics say two to five years," Rothstein replied.
"But nothing is certain, Jeff," Laurie broke in, looking Rothstein straight in the eye, for she is a very direct, confident woman. "Someone here is going to find a cure. And I'm going to help them do it."
Not so long ago, ALS was known as an "orphan disease," because it is rare, affecting about 25,000 people in the United States, and thus not well-funded by drug manufacturers looking to develop large-scale, lucrative remedies. But since November 1998 when researchers at the University of Wisconsin and in John Gearhart's laboratory at Johns Hopkins first reported the isolation of pluripotent stem cells, this degenerative disease has gained a higher profile.
Pluripotent human stem cells are basic building blocks of the human body. They're the blank slates of the cell world that give rise to all the specialized tissue types that compose a person: muscle cells, skin cells, nerve cells and every other kind. Over the last few years, Gearhart and others have learned to grow stem cells in the laboratory, a capability that offers enormous possibilities to those looking for a way to halt the death sentence that goes with ALS. Today, researchers around the world are investigating ways to replace stem cells dying in the nervous system through disease or injury. Should human trials of stem cell therapy begin, the first patients recruited likely will be those with ALS. It's probable, also, that Hopkins, with its Center for ALS Research and established international clinic for patients with this condition, will run these trials.
Russell has been a doer and mover in Baltimore ever since 1983 when she arrived here with her husband and two young sons. Raised in Wilmington, she graduated in 1967 from the University of Pennsylvania and practiced as a nurse before setting out on 25 years as a fund-raiser for the arts, hospitals and other organizations. She's been active in her sons' schools and in her church, and recently completed a term as president of the Baltimore Opera Guild. Tall and blonde, with a quick, high-wattage smile, Russell was always on the go. Those episodes with leg cramps nagged at her, but she chalked them up to over-exercise.
Then, starting in February 2000 something happened that Russell couldn't ignore. "My right foot kept getting tingly," she remembers. "I'd shake it out and it would get sort of floppy." That winter, she and her husband vacationed in the Caribbean. "One night, we walked down the beach and the strangest thing happened. My ankle kept caving in. I really couldn't walk. 'When we get back to Baltimore,' Edgie said, 'you're going to a doctor.'"
By June, Russell had been referred to Hopkins' Neuromuscular Clinic. There, what she had thought would be a brief appointment turned out to be an obstacle course, its most memorable feature the painful electroneuromyography. Unbeknown to Russell, the EMG, which measures the muscles' electrical activity, is the classic component of an ALS diagnosis. A trained technician inserts needles, like those used in acupuncture, into the biceps, triceps and leg muscles. Spontaneous activity when muscles are at rest is a bad sign, suggesting that the impulses along the nerve routes are interrupted, or denervated.
"I knew something was wrong because they came back to do the arm over again, and I'd had no symptoms in my arms," Russell recalls.
ALS takes time to diagnose, and it's largely done by ruling out lesser medical conditions. But neurologists familiar with the classic symptoms often have a sinking feeling from the start when they meet someone in the early stages of the disease. Often, and this was true in Russell's case, the patient is the last to know.
Around the same time that Laurie Russell was going through tests, across the street in the sunny lab of Douglas Kerr, a neurology researcher and a technician were observing two rats nosing around a lab bench. The first, bright-eyed, whiskers twitching, sought out bits of lab chow and started to eat. But something, it became clear, was odd about the rat's hindquarters. Its lower back arched like a trestle on a railway bridge from a phenomenon called kyphoscoliosis caused by weak thoracic muscles. And though the animal scurried quickly enough that the lab tech jumped to restrain it, the rat also dragged its useless hind legs behind, paw pads up.
The tech placed the second frisky rat on the bench. Like its companion, it limped, but this rodent had only a slight humpback. And, unlike the first, it stood on all fours. Its feet could move.
The difference between these two animals marks a sea change in the way doctors one day could treat people with ALS and other diseases that affect broad areas of the nervous system. Both rats had become paralyzed in the laboratory. The second rat, however, had received an infusion of stem cells and now could once more use its legs. This second rat is the living embodiment of the theory guiding the work of Kerr and his lab group. These researchers believe that stem cells hold the potential to be plunked down in the midst of injured tissue and respond to a welter of chemical messages with the directive: HEAL.
The first task Kerr set for himself in his Hopkins lab was to develop an animal model for ALS. One reason so few treatments exist to alter the course of this neurodegenerative motor condition and others like it is that researchers have never adequately replicated the diseases in laboratory animals. Without models for studying the nature of a disease and for testing potential drug treatments, there is little chance of finding a cure. Kerr's plan would be to replicate the symptoms of ALS and then to introduce neuron stem cells over a broad swath of the nervous system in the stricken animals. Because the stem cells available to him had been derived from mice, his first animal model would be in mice. This would lessen the chance that the stem cells might be rejected.
Kerr chose to use a germ called the Sindbis virus to mimic the effects of ALS. Sindbis seeks out and specifically destroys motor neurons. But unlike ALS, it attacks these neurons in a hit-or-miss fashion. To make the Sindbis strike thousands of cells in the way the large-system disease ALS does, Kerr selected an especially virulent strain. The model of paralysis he created wasn't a perfect mimic of ALS. By nature, Sindbis kills only one of two broad tracts of motor neurons, the lower ones that run from the spinal cord to muscles. ALS also destroys the upper motor neurons, those that extend from the brain's motor cortex to the spinal cord. Still, once Sindbis had stricken the mice, the researchers in Kerr's lab had a close laboratory replication of ALS.
Now, Kerr began to focus on solving the basic problem of getting the stem cells into the animals. His plan was to inject the cells into two groups of mice: those that had been paralyzed and a normal control group. By observing the difference in how the stem cells behaved in the injured and noninjured mice, he would begin to understand stem cells' ability to repair damaged neurons.
To introduce the cells into the mice, Kerr chose what seemed the least invasive route, the cerebrospinal fluid that bathes both brain and spinal cord. In the reverse of a spinal tap, he slowly suffused the fluid with liquid-suspended mouse pluripotent stem cells. Then he waited.
Within weeks, the microscope confirmed that in both groups of mice the stem cells had floated, as though on wind, along the entire spinal cord. The difference was that in the Sindbis-injured mice, stem cells had migrated straight into the spinal cord sites of the dying cells. "As though," Kerr says, "some sign directed them precisely to the damage." In the uninjured mice, the stem cells stayed put outside the cord.
Whatever was happening to help the mice wasn't obvious, though. Fewer than 10 percent of the stem cells showed characteristic nervous system molecules in their cell membranes, so it wasn't clear that the migrating stem cells had morphed into motor neurons. What was clear was that after eight weeks, roughly half of the paralyzed mice could plant their feet. They were using their legs.
People generally cope with fatal disease in one of three ways. Some sink into despair; some tackle the disability head on; and some decide to live out their days to the fullest extent. Laurie Russell chose the last course. After her diagnosis she circled herself with old friends. Even in her weakened state, she traveled to Europe, and sailed the Caribbean on a chartered sailboat.
In one important way, though, Russell tackled her disease head on. She became head of the development committee for the board of the Center for ALS Research, the Hopkins-based center that brings together more than 30 scientists worldwide. "For the rest of my life I'll probably be raising money to help solve the problem of ALS," she says.
Still, as the days went by, more and more Russell stayed home. She lives in Maryland horse country, a gloriously beautiful corner of the world known as the Worthington Valley. From her deck, the rolling countryside looks much as it might have 100 years ago. Not another house is in sight. Purple martin birdhouses, high on their poles, overlook a large pond. A flock of geese descend, a feather-filled commotion. This was Russell's setting as her ALS began to progress.
And human stem cells now were available. John Gearhartwho first isolated pluripotent stem cells at Hopkins and is one of the people in the world who knows most about growing these cultureshad learned how to tweak his cells to make them more robust. In the early months of 2001, these were the stem cells that Gearhart carried to Doug Kerr in a small plastic Petri dish. Kerr was ready to repeat his previous study. Only this time his paralyzed animals would be rats. And this time, they would be treated with human stem cells.
Using rats, Kerr reasoned, would take care of one of the drawbacks of the mouse experimentsthe animals' tiny nervous systems. The target space for the stem cells outside the spinal cords had been so minuscule, a twitch of the hand would send them flying. But with rats Kerr faced another problem.
These rodents are slow to catch Sindbis virus, even the specialized strain he had used before. He would need to develop an even more potent Sindbis. His virology background came in handy. Kerr infected one rat brain directly with the existing virus and after a time collected a small amount of a slightly more virulent strain that had prospered there. This he injected it into a second rat. Several days later, the virus he harvested from this rat brain proved even more powerful. It took him a full year, but through this "serial passage," Kerr produced a rapidly dividing Sindbis that could wreak havoc on rat motor neurons.
In the fall of 2000, Kerr inoculated 21 adult rats and 15 controls with this super-virulent Sindbis virus. A week later, the rats had cleared the virus, and the lab team injected roughly 300,000 new human stem cells into each paralyzed rat's spinal fluid. By spring, the animals with stem cells could move their hind legs. Many even could walk, if imperfectly. Treated with human stem cells, these rats had recovered movement every bit as well as the mice in the earlier study. The untreated rats in the control group remained paralyzed. Kerr and his team were elated.
But one crucial step still hadn't taken place. The lab group didn't understand the process that had restored the animals' movement. Either the stem cells had somehow reconstituted the weakened and dying nerve cells, protecting them from further harm, or the stem cells themselves had become neurons, taking over some of the function of the lost cells. Without this critical piece of information, no one would be able to move into developing a therapy for ALS.
And so, late in the evening of Friday, Dec. 12, 2000, instead of going home to his wife and toddler daughter, Kerr sat at the microscope in his lab scanning the first slides of tissues from his recovered rats, trying to pinpoint the phenomenon that had gone to work on their spinal cords. His 'scope centered on the ventral horn, a nerve tract in the spinal cord that motor diseases damage most.
The view through the eyepiece was kaleidoscopic. Nerve cells showed up red from a tag they'd received. Some cells glowed both red and green, meaning they were nerve cells with long extensions reaching out from the spinal cord-the rat's own motor neurons. Others were blue-the color of the still-healthy but undifferentiated stem cells. Then, Kerr spotted a scattering of far less common cells. He stared hard. These cells were red and green but with an unmistakable dark blue nucleus. And suddenly he knew what he was seeing. He had found the first visual proof that pluripotent stem cells were able to change into motor neurons.
"Ninety-plus percent of the time what you do in science fails," Kerr says, recalling the rush of that moment. "But that was the most amazing thing I've ever seen. It was addictive enough to keep me going for a lifetime."
A lot has happened to Laurie Russell since she was diagnosed with ALS a year and a half ago. Back then, she was playing tennis. Now, without the short brace she wears on her right leg, she cannot walk unassisted. Early on, she occasionally used her beribboned cane. Now a wheelchair's common. She's fallen, she's dropped things. Of necessity, she's had to school herself in matters of simple safety. She can no longer climb stairs and has started to lose control of her hands. "I'd like to write notes, but my hand gets tired. I got something that makes the pencil thicker, but it's hard to use. I can't grab onto it," she says, exasperated. "On the computer, I make so many mistakes."
Stem cell therapy, Kerr says, could still be five years away from being tested on humans. Two of those years will involve safety studies on higher animals to ensure that the cells don't introduce pathogens, differentiate endlessly or evena greater worryshift into cancer. Those studies have already begun. Recently, Kerr's team contacted the FDA asking for guidelines on making the transition to human trials.
But to give back to a paralyzed human the most basic limb movement, Kerr knows, will require thousands of replacement nerve cells, each having reached a unique destination. Yet he also believes that if stem cells can be made to create a new neural circuitry that bypasses damaged bits, the nervous system might be retrained to work effectively. "Effective"though not "perfect"he says, might be enough to help people with chronic spinal cord injury like Christopher Reeve, or those with ALS like Laurie Russell.
At this point, Russell is doing about all she can medically. She's taking Rilutek. The only drug now available for ALS, it's been shown to add several months to life. She's learning to live entirely in the present. "I don't look too far in advance. I look from today to tomorrow, because I know that tomorrow I won't be much worse than I am today," she says.
Russell has one hope: if stem cell therapy does move into clinical trials anytime soon, that she can be the first human subject. "This is the only thing that's going to save me," she says.