Scientists repair spinal cord injuries in monkeys using human stem cells

Human neuronal stem cells extend axons (green). (Image UCSD)

An exciting development for spinal cord injury research was published this week in the journal Nature Medicine. Scientists from the University of San Diego School of Medicine transplanted human neural progenitor cells (NPCs) into rhesus monkeys that had spinal cord injuries. These cells, which are capable of turning into other cells in the brain, survived and robustly developed into nerve cells that improved the monkeys’ use of their hands and arms.

The scientists grafted 20 million human NPCs derived from embryonic stem cells into two-week-old spinal cord lesions in the monkeys. These stem cells were delivered with growth factors to improve their survival and growth. The monkeys were also treated with immunosuppressive drugs to prevent their immune system from rejecting the human cells.

After nine months, they discovered that the NPCs had developed into nerve cells within the injury site that extended past the injury into healthy tissue. These nerve extensions are called axons, which allow nerves to transmit electrical signals and instructions to other brain cells. During spinal cord injury, nerve cells and their axon extensions are damaged. Scientists have found it difficult to regenerate these damaged cells because of the inhibitory growth environment created at the injury site. You can compare it to the build-up of scar tissue after a heart attack. The heart has difficulty regenerating healthy heart muscle, which is instead replaced by fibrous scar tissue.

Excitingly, the UCSD team was able to overcome this hurdle in their current study. When they transplanted human NPCs with growth factors into the monkeys, they found that the cells were not affected by the inhibitory environment of the injury and were able to robustly develop into nerve cells and send out axon extensions.

Large numbers of human axons (green) emerge from a lesion/graft sites. Many axons travel along the interface (indicated by arrows) between spinal cord white matter (nerve fibers covered with myelin) and spinal cord gray matter (nerves without the whitish myelin sheathing). Image courtesy of Mark Tuszynski, UC San Diego School of Medicine.

The senior scientist on the study, Dr. Mark Tuszynski, explained how their findings in a large animal model are a huge step forward for the field in a UCSD Health news release:

“While there was real progress in research using small animal models, there were also enormous uncertainties that we felt could only be addressed by progressing to models more like humans before we conduct trials with people. We discovered that the grafting methods used with rodents didn’t work in larger, non-human primates. There were critical issues of scale, immunosuppression, timing and other features of methodology that had to be altered or invented. Had we attempted human transplantation without prior large animal testing, there would have been substantial risk of clinical trial failure, not because neural stem cells failed to reach their biological potential but because of things we did not know in terms of grafting and supporting the grafted cells.”

Dr. Tuszynski is a CIRM-grantee whose earlier research involved optimizing stem cell treatments for rodent models of spinal cord injury. We’ve blogged about that research previously on the Stem Cellar here and here.

Tuszynski recently was awarded a CIRM discovery stage research grant to develop a candidate human neural stem cell line that is optimized to repair the injured spinal cord and can be used in human clinical trials. He expressed cautious optimism about the future of this treatment for spinal cord injury patients emphasizing the need for patience and more research before arriving at clinical trials:

“We seem to have overcome some major barriers, including the inhibitory nature of adult myelin against axon growth. Our work has taught us that stem cells will take a long time to mature after transplantation to an injury site, and that patience will be required when moving to humans. Still, the growth we observe from these cells is remarkable — and unlike anything I thought possible even ten years ago. There is clearly significant potential here that we hope will benefit humans with spinal cord injury.”


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Stem cell therapy for Parkinson’s disease shows promise in monkeys

Tremors, muscle stiffness, shuffling, slow movement, loss of balance. These are all symptoms of Parkinson’s disease (PD), a neurodegenerative disorder that progressively destroys the dopamine-producing neurons in the brain that control movement.

While there is no cure for Parkinson’s disease, there are drugs like Levodopa and procedures like deep brain stimulation that alleviate or improve some Parkinsonian symptoms. What they don’t do, however, is slow or reverse disease progression.

Scientists are still trying to figure out what causes Parkinson’s patients to lose dopaminergic neurons, and when they do, they hope to stop the disease in its early stages before it can cause the debilitating symptoms mentioned above. In the meantime, some researchers see hope for treating Parkinson’s in the form of stem cell therapies that can replace the brain cells that are damaged or lost due to the disease.

Dopaminergic neurons derived from induced pluripotent stem cells. (Xianmin Zeng, Buck Institute)

Promising results in monkeys

This week, a team of Japanese scientists reported in the journal Nature that they treated monkeys with Parkinson’s-like symptoms by transplanting dopaminergic neurons made from human stem cells into their brains. To prevent the monkeys from rejecting the human cells, they were treated with immunosuppressive drugs. These transplanted neurons survived for more than two years without causing negative side effects, like tumor growth, and also improved PD symptoms, making it easier for the monkeys to move around.

The neurons were made from induced pluripotent stem cells (iPSCs), which are stem cells that can become any cell type in the body and are made by transforming mature human cells, like skin, back to an embryonic-like state. The scientists transplanted neurons made from the iPSCs of healthy people and PD patients into the monkeys and saw that both types of neurons survived and functioned properly by producing dopamine in the monkey brains.

Experts in the field spoke to the importance of these findings in an interview with Nature News. Anders Bjorklund, a neuroscientist at Lund University in Sweden, said “it’s addressing a set of critical issues that need to be investigated before one can, with confidence, move to using the cells in humans,” while Lorenz Studer, a stem-cell scientist at the Memorial Sloan Kettering Cancer Center in New York City, said that “there are still issues to work out, such as the number of cells needed in each transplant procedure. But the latest study is ‘a sign that we are ready to move forward.’”

Next stop, human trials

Jun Takahashi

Looking ahead, Jun Takahashi, the senior author on the study, explained that his team hopes to launch a clinical trial testing this iPSC-based therapy by the end of 2018. Instead of developing personalized iPSC therapies for individual PD patients, which can be time consuming and costly, Takahashi plans to make special donor iPSC lines (called human leukocyte antigen or HLA-homozygous iPSCs) that are immunologically compatible with a larger population of patients.

In a separate study published at the same time in Nature Communications, Takahashi and colleagues showed that transplanting neurons derived from immune-matched monkey iPSCs improved their survival and dampened the immune response.

The Nature News article does a great job highlighting the findings and significance of both studies and also mentions other research projects using stem cells to treat PD in clinical trials.

“Earlier this year, Chinese researchers began a Parkinson’s trial that used a different approach: giving patients neural-precursor cells made from embryonic stem cells, which are intended to develop into mature dopamine-producing neurons. A year earlier, in a separate trial, patients in Australia received similar cells. But some researchers have expressed concerns that the immature transplanted cells could develop tumour-causing mutations.

Meanwhile, researchers who are part of a Parkinson’s stem-cell therapy consortium called GForce-PD, of which Takahashi’s team is a member, are set to bring still other approaches to the clinic. Teams in the United States, Sweden and the United Kingdom are all planning trials to transplant dopamine-producing neurons made from embryonic stem cells into humans. Previously established lines of embryonic stem cells have the benefit that they are well studied and can be grown in large quantities, and so all trial participants can receive a standardized treatment.”

You can read more coverage on these research studies in STATnews, The San Diego Union Tribune, and Scientific American.

For a list of projects CIRM is funding on Parkinson’s disease, visit our website.

Using skin cells to repair damaged hearts

heart-muscle

Heart muscle  cells derived from skin cells

When someone has a heart attack, getting treatment quickly can mean the difference between life and death. Every minute delay in getting help means more heart cells die, and that can have profound consequences. One study found that heart attack patients who underwent surgery to re-open blocked arteries within 60 minutes of arriving in the emergency room had a six times greater survival rate than people who had to wait more than 90 minutes for the same treatment.

Clearly a quick intervention can be life-saving, which means an approach that uses a patient’s own stem cells to treat a heart attack won’t work. It simply takes too long to harvest the healthy heart cells, grow them in the lab, and re-inject them into the patient. By then the damage is done.

Now a new study shows that an off-the-shelf approach, using donor stem cells, might be the most effective way to go. Scientists at Shinshu University in Japan, used heart muscle stem cells from one monkey, to repair the damaged hearts of five other monkeys.

In the study, published in the journal Nature, the researchers took skin cells from a macaque monkey, turned those cells into induced pluripotent stem cells (iPSCs), and then turned those cells into cardiomyocytes or heart muscle cells. They then transplanted those cardiomyocytes into five other monkeys who had experienced an induced heart attack.

After 3 months the transplanted monkeys showed no signs of rejection and their hearts showed improved ability to contract, meaning they were pumping blood around the body more powerfully and efficiently than before they got the cardiomyocytes.

It’s an encouraging sign but it comes with a few caveats. One is that the monkeys used were all chosen to be as close a genetic match to the donor monkey as possible. This reduced the risk that the animals would reject the transplanted cells. But when it comes to treating people, it may not be feasible to have a wide selection of heart stem cell therapies on hand at every emergency room to make sure they are a good genetic match to the patient.

The second caveat is that all the transplanted monkeys experienced an increase in arrhythmias or irregular heartbeats. However, Yuji Shiba, one of the researchers, told the website ResearchGate that he didn’t think this was a serious issue:

“Ventricular arrhythmia was induced by the transplantation, typically within the first four weeks. However, this post-transplant arrhythmia seems to be transient and non-lethal. All five recipients of [the stem cells] survived without any abnormal behaviour for 12 weeks, even during the arrhythmia. So I think we can manage this side effect in clinic.”

Even with the caveats, this study demonstrates the potential for a donor-based stem cell therapy to treat heart attacks. This supports an approach already being tested by Capricor in a CIRM-funded clinical trial. In this trial the company is using donor cells, derived from heart stem cells, to treat patients who developed heart failure after a heart attack. In early studies the cells appear to reduce scar tissue on the heart, promote blood vessel growth and improve heart function.

The study from Japan shows the possibilities of using a ready-made stem cell approach to helping repair damage caused by a heart attacks. We’re hoping Capricor will take it from a possibility, and turn it into a reality.

If you would like to read some recent blog posts about Capricor go here and here.