CALLING THE STEM CELL RACE
We’ve been waiting 20 years for human embryonic stem cells to deliver spare parts. MEGAN MUNSIE takes a look at the winners coming down the track.
ON 6 NOVEMBER 1998, the world woke to news of an astonishing discovery. James Thomson and his colleagues at the University of Wisconsin-madison had generated stem cells from human embryos. Unlike other types of stem cells, these were ‘pluripotent’ – meaning they had the potential to generate any type of body tissue if given the right signals.
FOR MANY, THIS news and the accompanying claims that embryonic stem (ES) cells could revolutionise medicine, appeared to come out of the blue. However, for those of us already working in the stem cell space it was the vital next step in exploring the potential of stem cell science.
Back in 1998, I was a keen PHD student, part of the stem cell research effort at Monash University. I was trying to create pluripotent stem cells from the skin cells of a mouse. The idea was to first clone a mouse embryo from its skin cell and harvest the ES cells. In the lab next door, Ben Reubinoff had been working with Alan Trounson and Martin Pera for several years to see if they could make embryonic stem cells from donated human embryos – effectively in parallel to their colleagues in Wisconsin.
There was a lot of excitement about how we might one day be able to use these cells to make ‘replacement’ body tissues – effectively ‘on demand’– and alleviate suffering for many patients. Although we all recognised this was going to take an enormous amount of effort – and time – to deliver.
Outside the lab if I mentioned that I worked in stem cell research, I was met with overwhelming curiosity. But people also wondered why we couldn’t just use adult stem cells which are found in some of our organs. Many people I spoke to already knew somebody who had been helped by a stem cell transplant using bone marrow or cord blood. Why did we need to use human embryos and ES cells at all?
The reason was, and still is, that adult stem cells are not able to generate any type of tissue because they are not ‘pluripotent’. Bone marrow stem cells, for instance, can regenerate an immune system but they cannot regenerate the pancreas or brain tissue. The only source of pluripotent cells was surplus human embryos – originally created in an IVF clinic and then donated to research.
In 2007, Japanese scientists made a landmark discovery that side-stepped the need to use embryos. They were able to manipulate ordinary human skin cells to make them pluripotent (a much more elegant and effective approach than my attempts with mice skin cells during my PHD). Dubbed induced pluripotent
stem cells or IPSC, these cells share the same desirable features as ES cells. They can be grown in the lab and coaxed to form specific types of body cells.
But both sources of pluripotent stem cells also carry the risk that they could form a tumour if we don’t fully direct their developmental fate. Any clinical application must meticulously weed out the stem cells as part of the laboratory recipe used to make the replacement cells. For me, the crucial challenge is how to harness the potential of stem cells to develop safe and effective treatments.
These days, as the head of the outreach and policy program for Stem Cells Australia, a nationwide consortium of Australian stem cell scientists, I spend a lot of my time talking to the public. To some extent I’ve become a ‘race caller’ – frequently asked to predict what new treatments are likely to come galloping down the track. Sometimes I’m asked to offer an opinion on stem cell ‘treatments’ that are not on the track at all. Promoted as a sure thing and available now for a price, these interventions lack credible evidence that they work or are even safe. Providers are effectively peddling hope and should be viewed with caution.
Fortunately, we do have providers committed to responsibly advancing the field with lots of bona fide contenders in clinical trials. So with my binoculars firmly in place, here is my reading of what’s coming down the track.
Leading the charge towards the clinic is a possible treatment for the most common cause of age-related vision loss: macular degeneration. In Australia about one in seven people over the age of 50 have some evidence of this disease. In this condition, damage to the cells at the back of the eye – the macula – affects central vision and the ability to read, drive and recognise faces. The actual ‘seeing’ cells in the macula are intact but sight is lost because a tiny underlying patch of darkly pigmented cells are damaged. Known as retinal pigmented epithelial cells or RPE cells, they act like a pit stop team, feeding and clearing away waste for the highly active cells of the retina.
Because the number of RPE cells needed is very small and pluripotent stem cells readily develop into this exact tissue (you can easily spot a patch of darkly pigmented cells in the dish), macular degeneration has long been a favourite. Clinical trials are now underway in the United States, United Kingdom and Japan to determine whether replacing faulty RPE cells with those made in the lab from either human embryonic stem cells or induced pluripotent stem cells could help.
At this early stage, safety is a key concern. The surgical technique to deliver the cells carries the risk of detaching the retina and causing further vision loss. In May 2018, the London Project to Cure Blindness announced that two patients with macular degeneration – specifically what’s called the ‘wet’ form due to extensive blood vessel growth under the retina – had improved their vision with no significant sideeffects after participating in a clinical trial.
Another early entrant in the race to the clinic is type 1 diabetes. It’s a disease caused by friendly fire: the immune system seeks and destroys the beta cells of the pancreas. These remarkable cells can both sense rising blood sugar levels and release the exact amount of insulin needed to lower glucose levels to normal. When these cells are destroyed, which often occurs in childhood, the person is no longer able to control their blood sugar levels.
More than 120,000 Australians manage the disease with regular injections of insulin. But they can’t regulate their blood sugar levels as precisely as beta cells do. And there are consequences: high blood sugar levels can damage the blood vessels in the heart, eyes and kidneys, while low levels can be fatal. Some patients have been lucky enough to receive a whole pancreas transplant or tissues containing beta cells from cadavers. But there are two problems. First, transplant donors are in short supply. Second, the donated tissue will likely suffer the fate of the original: attack by the immune system. Enter pluripotent stem cells. Supply is no longer a problem. After two decades of trying, scientists are now able to make large quantities of fully functional beta cells in the lab. And
as far as keeping the immune system at bay, several start-up companies have come up with the ‘tea-bag’ approach. They encase the beta cells in a porous capsule. Like tea leaves, the beta cells are netted in but soluble factors easily move in and out across the net, including insulin and blood-borne glucose as well as other nutrients. Crucially, the net also stops marauding immune cells from getting to the beta cells.
The Californian company, Viacyte, is trialling a ‘teabag’ about the size and shape of a credit card. Made of surgical grade polymer, the capsule encases immature beta cells (they’re more robust if they mature inside the body), and is inserted just under the patient’s skin.
The key challenge, so far, is providing intimate contact with surrounding blood vessels so that the transplanted cells increase in number and survive. In June this year, the company reported its results at a meeting of the American Diabetes Association. Overall, they said there was a low rate of survival, but when cells did survive they produced insulin.
The company is now evaluating a second device that allows the patient’s blood vessels to grow through the walls of the capsule.
A strong stayer in the race to the clinic is Parkinson’s disease (PD). Predominantly a disease of ageing, around 1% of people over the age of 60 suffer from it.
The disease results from the death of brain neurons that release the neurotransmitter dopamine. Like a conductor, dopamine ensures different parts of the brain act in synchrony to execute routine movements. Without dopamine, patients have trouble controlling their walking and experience tremors in their hands and other parts of their bodies. Could replacing the faulty dopamine-producing neurons with healthy ones provide a way to combat PD?
More than 20 years ago, a few different research groups around the world gave it a try. Using human foetal tissue, they dissected out the dopamineproducing cells, and surgically implanted these into the brains of patients, specifically in a region called the ‘striatum’. Some patients improved, but others reported significant side effects, particularly uncontrollable jerky movements known as dyskinesia. Questions were asked about whether the correct types of cells were being transferred to the correct part of the brain and further experiments were put on hold. A key question was whether pluripotent stem cells could offer a more precise and reliable source of dopamineproducing cells.
Jump forward to 2018 and several groups are on the cusp of testing new types of replacement cells for PD in a series of clinical trials. Years of research has shown that ES cells and IPS cells can be directed to develop into the correct type of neurons and that sufficiently large numbers can be generated.
When tested in animals, the dopamine-producing cells corrected movement disorders and did not form tumours.
This time around, rather than working in silos, different groups of researchers in Japan, Sweden, UK and US have banded together in a coalition called G-force PD. Although each group is using a slightly different approach for their clinical trial, by sharing their results and expertise they hope to bring a cellbased therapy for PD closer to reality.
SKIN, STEM CELLS AND BUTTERFLY CHILDREN
Skin stem cells have long been solid performers for growing skin grafts to treat severe burns. But in November 2017, headlines ran hot with a report that a seven-year-old refugee Syrian boy, on the verge of death from a genetic skin condition, had been saved by a graft of skin stem cells corrected by gene therapy.
Hassan, now living with his family in Germany, suffered from a severe form of Epidermolysis Bullosa (EB). It’s been referred to as the “worst disease you’ve never heard of”. It affects about 500,000 people worldwide, and can be caused by mutations to 18 different genes. In each case, the mutation disrupts the anchoring of the skin’s upper layer, the epidermis, to the underlying dermis. The result is skin that tears as easily as a butterfly’s wing. The only treatment is painful bandaging and re-bandaging.
Hassan’s skin had started blistering from birth but by the time he was seven, a bacterial infection had robbed him of 80% of his skin cover. In a last ditch effort to save his life, his German doctors contacted veteran stem cell researcher Michele De Luca at the University of Modena and Reggio Emilia in Italy. In 2006, De Luca had used skin grafts corrected by gene therapy to treat a leg wound of a woman who suffered from the same form of EB that Hassan suffered from. It was caused by a mutation to a gene called LAMB3.
De Luca’s team took a tiny patch of skin containing stem cells from Hassan’s groin. They also spliced a copy of the LAMB3 gene into a benign virus. Then they infected the skin cells with the virus which ferried the LAMB3 gene into their DNA. The genetically
SPINAL CORD INJURY
corrected skin grew into a sheet which was grafted onto Hassan’s body. Five months after the first graft, Hassan was discharged. A month later he was back at school and playing soccer. Thanks to the genetically corrected stem cells, his grafted skin no longer blisters or shreds. The executive director of the Dystrophic Epidermolysis Bullosa Research Association of America dubbed Hassan’s treatment “a sea change to the world of EB”. Besides de Luca’s group, Peter Marinkovich and Jean Tang at Stanford University School of Medicine, United States, are also trialling genetically-corrected skin grafts for a different type of EB. One of the front runners at the start of the stem cell race was spinal cord injury. Perhaps you remember the actor Christopher Reeve, aka Superman? Following a horse riding accident that left him a quadriplegic, he campaigned tirelessly for researchers to be allowed to use human embryonic stem cells to treat spinal cord injury which claims about 180,000 new cases each year. Perhaps thanks to his efforts in 2010, the world saw the first clinical trial using cells made from human ES cells.
Conducted by the California based biotech company Geron, the researchers had directed ES cells to develop into precursors of ‘oligodendrocytes’. These octopus-like cells wind their arms around neurons in the spinal cord to provide electrical insulation as well as nurturing factors. With a spinal cord injury, these important support cells can be lost. Four patients were injected with stem cell-derived oligodendrocyte precursors soon after their injury. Controversially, Geron discontinued the study in 2011 to refocus their business. Asterias Biotherapeutics picked up the baton
and last July, in a company press release, reported the results of an early clinical trial on 25 additional patients who were all injected with oligodendrocyte precursors three to six weeks post-injury. They reported no serious adverse events and that four patients recovered a degree of motor function that may increase their ability to lead an independent life. However, we have to wait to see the peer reviewed published results before we can assess the state of progress.
Beyond replacing oligodendrocytes made from ES cells, other clinical trials are testing different types of cells ranging from neurons obtained from donated foetal tissue to using the patient’s own cells obtained from the back of the nose where they play an important role in supporting the regeneration of the olfactory neurons. Some types of transplanted cells may act as paramedics, helping damaged motor neurons to recover. Others are designed to directly replace spinal cord neurons.
It remains too early to tell which approach will result in long-term improvements. While many with spinal cord injury are eager for even small improvements such as bladder or bowel control, patients should be careful about trying marketed experimental procedures outside well-conducted clinical trials as they may cause further harm. In a chilling example, one young woman who sought treatment using olfactory cells developed a large, painful mucus-secreting tumour in her spine and no improvement of her paraplegia. Unfortunately, many stem cell ‘cures’ promoted online, especially for spinal cord injury, lack credibility. Seeking advice from your medical specialist is the best way to find out more. If they don’t know about a trial or claimed treatment, it is probably a mirage.
Marked as a long shot for many years, stem cell research is starting to pay dividends for kidney disease. Though it’s not ready to provide transplants, it is already helping to discover new treatments.
Kidneys are the body’s vital cleansing and balancing system. They filter waste products and toxins from our blood into urine, maintain the body’s water balance and also make hormones important for regulating blood pressure and the production of red blood cells.
Kidney disease, which affects one in 10 Australians, damages the filtration units called nephrons. The major causes are diabetes and high blood pressure. Once gone, the nephrons cannot regenerate. But waiting for a donated kidney can take years; close to 1,000 Australians are currently on the waiting list for a transplant. This health crisis has catapulted researchers into trying to recreate kidney tissue from pluripotent stem cells – an immense challenge as these are complex biological machines composed of many interacting parts.
Melissa Little’s group, based at the Murdoch Children’s Research Institute in Melbourne, have pioneered this research. In 2015, they successfully grew tiny kidney-like structures that were showcased on the cover of Nature with the headline: “Kidney in a dish”. While their mini-kidneys possess many of the working parts of a mature kidney, there’s a long way to go before they can be used as transplants. The plumbing for example – bringing blood in and taking waste out – is not yet functional. Also they are tiny, smaller than the tip of your finger.
Nevertheless these mini-kidneys are already making a difference to our understanding of how kidneys develop and what goes awry in kidney disease, especially the hereditary form. For example, researchers were recently able to make mini-kidneys from a child suffering from a rare genetic condition that can cause end-stage kidney disease. They did it by first generating IPS cells from the child’s skin. In the lab they were able to observe structural abnormalities in the child’s cells and also showed that when the genetic mutation was corrected, the structural defect was corrected. This provides a new insight into inherited kidney disease where previously we knew very little about how these conditions develop.