On July 26, the California Institute of Regenerative Medicine announced $151 million worth of grants for research that would take stem cell therapies from the laboratory to the clinic. Among the recipients was Cedars-Sinai Medical Center in Los Angeles, which was awarded $17.8 million for work on amyotrophic lateral sclerosis (ALS), also called Lou Gehrig’s disease.
That team, led by Clive Svendsen, director of the Cedars-Sinai Regenerative Medicine Institute, proposed genetically modifying neural stem cells to secrete a growth factor called glial cell line-derived neurotrophic factor (GDNF), which has been shown in animal models to counter the massive motor neuron die-off typically associated with the disease. Following an initial round of small and large animal studies, Svendsen’s team hopes to implant those cells into the spinal cords of ALS patients, where they are expected to nurture the remaining motor neurons and possibly halt the disease’s inexorable progress.
“The idea is to protect the cells that are still present in the spinal cord, rather than replace the motor neurons that are dying,” explains Geneviève Gowing, a project scientist in the Svendsen laboratory who is actively contributing to this project.
Protecting existing cells, rather than replacing cells is a different strategy from the typical cell therapy often envisioned for stem cells, in which patient-specific cells are corrected and transplanted back into patients, and initial tests using human cells in a rat model have been promising, Gowing says. Perhaps more promising still, at least for those at the intersection of stem cells and neurodegenerative diseases, is the flurry of peer-reviewed papers and clinical trial data that have appeared over the past six months or so.
Researchers, armed mostly with patient-derived inducible pluripotent stem (iPS) cells, have turned these new tools on Parkinson’s disease (PD) and Huntington’s disease (HD), ALS and ataxia-telangiectasia (AT), trying to understand both how mutation leads to disease, and how those insights can lead to therapies.
It’s a significant technologic advance in the study of neurodegeneration, all agree. After all, one cannot easily biopsy a living brain, and animal models of adult-onset neurodegenerative diseases are often poor substitutes. Says Christopher Ross, Director of the Baltimore Huntington’s Disease Center at Johns Hopkins University School of Medicine, “This is the first time we’ve been able to model these adult-onset neurodegenerative diseases in cell culture using neurons from our actual patients.”
Ross participated in one of recent studies applying iPS cells to a neurodegenerative disease: Huntington’s. HD is caused by a mutation in the Huntingtin gene. In exon 1 of that gene lies a stretch of glutamine residues whose length varies between individuals. Those with 35 or fewer glutamine codons (CAG) are unaffected; those with 40 or more develop HD. Most people develop the disease in adulthood, but the longer the expansion, the earlier the age of onset and the greater the severity.
In one study, an international confederation of HD labs calling itself the “HD iPSC Consortium” created 14 iPS lines from HD patients with different length CAG expansions and differentiated them into the brain cells most severely affected in that disease, called medium spiny neurons. The team then monitored those cells’ behavior and gene expression patterns under a variety of growth conditions and cellular stresses, such as removal of growth factors or exposure to glutamate (which in high concentrations acts as an excitotoxin), and observed clear CAG-repeat expansion-length-associated toxic phenotypes similar to the disease state, explains Virginia Mattis, a postdoc in Svendsen’s lab and a lead scientist on the Cedars-Sinai consortium team.
For instance, HD lines with 60 or 180 CAGs were more likely to die from glutamate pulses or withdrawal of BDNF (brain-derived neurotrophic factor) than non-HD lines containing only 33 repeats. “That was really exciting to us, that we saw these definite repeat-associated phenotypes,” says Mattis.
Ross, who headed up the consortium’s Johns Hopkins team, says these cells fill a key gap in the tools available to HD researchers, because animal models of the disease share some qualities with the human disease but not the most crucial feature, massive neuronal cell death. “We’ve been able now for the first time using human neurons, to recapitulate the key biology of the disorder, the selective degeneration of these medium spiny neurons,” he says. And Ross and his team are now using those cells to study the disease’s biology and therapeutic strategies. For instance, the consortium found that adding BDNF to the growth medium could rescue, to some extent, CAG repeat expansion-dependent cell death. Now Ross’ team is looking for small molecule agonists that can replicate that activity more efficiently, which could potentially serve as human therapeutics.
The HD iPSC Consortium findings were reported in the August 3 issue of Cell Stem Cell. In the same issue was a second study, led by Lisa Ellerby of the Buck Institute for Research on Aging, that addressed one of the key goals of stem cell researchers: to repair and reimplant patient-derived cells. 
Starting with an HD iPS cell line previously generated by George Daley’s lab at Harvard, Ellerby’s team used homologous recombination to correct the HD mutation in those cells and showed that that fix restored the cells’ physiology to a more normal state.
“[In mutant cells] we see alterations in beta-cadherin, TGF-beta, BDNF, caspase activation,” Ellerby explains. “All those things were reversed in the corrected [cells].”
Her team then took the next logical step: differentiating those corrected cells to neural stem cells and implanting them into the brains of HD mice. Though the cells survived and differentiated in vivo, morphing into cells with the properties of medium spiny neurons, Ellerby does not yet know if they can actually repair neural damage in vivo, as that was not the goal of the study. Instead, she wants to delve into the biology of these cells, to understand what makes them tick. “We want to understand some of the basic properties of these cells in vivo,” she says.
Writing in the journal Cell Research, Juan Carlos Izpisua Belmonte and colleagues say the two HD iPS cell papers, “present very significant advances for iPSC-based disease modeling of HD and provide a potential donor source for cell replacement therapy.”  But, they note, significant hurdles remain, including that the cells do not completely recapitulate disease phenotypes, and cannot account for epigenetic influences such as environmental factors.
Nonetheless, the iPS cell approach is proving popular among neurodegenerative disease researchers. At the University of Queensland, Australia, Ernst Wolvetang and Martin Lavin became among the first researchers to create iPS cells from samples with a so-called “chromosomal instability syndrome” when they successfully reprogrammed fibroblasts from patients with ataxia-telangiectasia.  AT stems from a defect in the ATM DNA damage response and repair enzyme, which is involved in the reprogramming process underlying iPS cell development. That, explains Lavin, means iPS generation “wasn’t a trivial exercise.”
The trick in this case, he says, was to use “special culture conditions” and slowly acclimatize the cells to them — “easing them in,” as Lavin puts it. Now he and Wolvetang are using those cells as a platform for drug development and cell therapeutic development following genome editing.
At about the same time, another consortium reported increased chemical sensitivity and mitochondrial dysfunction (relative to normal cells) in iPS cells derived from both PD patients and asymptomatic individuals bearing mutations associated with familial PD.  The team was even able to correct the physiological abnormalities in PD iPS cells with agents like rapamycin and coenzyme-Q10, which counter the reactive oxygen species observed in these cells. That, says Ted Dawson, a Johns Hopkins University researcher who led one of the consortium groups, suggests it might be possible to fend off the disease pharmacologically — assuming a blood test for PD could be found.
At the Memorial Sloan-Kettering Cancer Center in New York, Lorenz Studer, Director of the Center for Stem Cell Biology, reported in December the ability to convert human embryonic stem cells into dopaminergic neurons, and their successful engraftment in various animal models of Parkinson’s disease, including mice, rats, and monkeys. 
According to Studer, researchers have known for years how to coax human ESCs into dopaminergic cells, but they could never get them to survive in animals. Complicating matters, less differentiated cells in the injected material often did survive and proliferate, leading to tumor-like neural structures. For nearly a decade, Studer says, he banged his head against that wall.
“I cannot tell you how many frustrated researchers I had in my lab that tried to solve this problem,” he says.
Recently, though, Studer realized he might have been following the wrong developmental cues. Normal dopaminergic neurons express a gene called FOXA2, a “classic marker” of a neurological structure called the floor plate, Studer says. That led him to suspect that he might get more effective dopamine cells if he made them from floor plate intermediates, rather than neuroepithelial precursors. When Studer’s team did that, they found the cells were considerably more potent, expressed FOXA2, and most importantly, could survive in vivo.
He put these new cells through several animal tests. One involves destroying the endogenous dopamine neurons on one side of the brain, producing a kind of asymmetrical behavior, Studer explains. A stimulated mouse in this test “actually spins around its own axis,” he explains. But injection of human ESC-derived dopamine cells completely reversed that behavior within three to four months, restoring the animals’ balance.
“I was nearly shocked when I saw how good it really worked,” Studer says.
Of course, it will be years before Studer’s approach, or any iPS cell strategy for that matter, makes it to the clinic. But other stem cell therapies are already there.
In July, Israel-based BrainStorm Cell Therapeutics released an interim safety report on its Phase I/II trial of NurOwn, an ALS therapy that uses patient bone marrow-derived mesenchymal stem cells and induces them to secrete neurotrophic growth factors prior to reinjection. According to a press release announcing the report, the treatment was generally safe, and “in some patients this pilot study demonstrated a tendency toward stabilization in some parameters in the ALS Functional Rating Scale.”
A few months earlier, Neuralstem reported in Stem Cells data from its own Phase I ALS trial.  According to President and CEO Richard Garr, the company’s formulation, comprising fetal tissue-derived neural stem cells, is not intended to replace the lost motor neurons found in ALS patients, but rather to support the cells that remain by synaptically “hooking up” with those cells and feeding them growth factors.
“We’re not replacing motor neurons, we’re trying to support them and nurture them back to health,” he says — a strategy that sounds not all that different from what Gowing and Svendsen are doing.
Neuralstem’s March publication detailed results from the trial’s first 12 participants, but to date, the company has performed a total of 18 surgeries, three of them in patients who had already received one round of injections. Each received between 5 and 15 injections of 100,000 cells apiece in the lumbar and/or cervical spine, Garr says.
As a Phase I safety study, the trial was not powered to look for efficacy, Garr stresses. Yet in five of six ambulatory patients studied, he notes, disease progression leveled off or improved, including one widely reported participant, Ted Harada, who stands out as a sharply rising black dotted line on charts of leg strength and overall clinical progress. In contrast, four other ambulatory patients on the graph are essentially static, and one continues to decline.
“If you look before the line, you can see that [Harada] was going downhill very fast, and he had not only a slowdown but a complete reversal of the symptoms,” Garr says. “And that goes out to 300 days. So this isn’t a transient effect.”
For the researchers trying to move the ball forward against such horrific neurodegenerative diseases, results like that can be gratifying. Oliver Cooper, a Harvard Medical School researcher and member of the NINDS PD iPS Consortium, recalls working late one night, going over some of the consortium’s preliminary data, and realizing they “had actually done something.”
“For something to show a phenotype, when it certainly wasn’t a given that that would happen, is something I’ll always remember,” he says.
 HD iPSC Consortium, “Induced pluripotent stem cells from patients with Huntington’s disease show CAG-repeat-expansion-associated phenotypes,” Cell Stem Cell, 11:264−78, 2012.
 M.C. An et al., “Genetic correction of Huntington’s disease phenotypes in induced pluripotent stem cells,” Cell Stem Cell, 11:253−63, 2012.
 S. Nayler et al., “Induced pluripotent stem cells from ataxia-telangiectasia recapitulate the cellular phenotype,” Stem Cells Transl Med, 1:523−35, 2012.
 O. Cooper et al., “Pharmacological rescue of mitochondrial deficits in iPSC-derived neural cells from patients with familial Parkinson’s disease,” Sci Transl Med, 4:141ra90, 2012.
 S. Kriks et al., “Dopamine neurons derived from human ES cells efficiently engraft in animal models of Parkinson’s disease,” Nature, 480:547−51, 2011.
 J.D. Glass et al., “Lumbar intraspinal injection of neural stem cells in patients with amyotrophic lateral sclerosis: Results of a Phase I trial in 12 patients,” Stem Cells, 30:1144−51, 2012.
 K. Zhang et al., “Huntington’s disease: Dancing in a dish,” Cell Res, 1−4. 2012.