Long-term Tumorgenicity of Induced Pluripotent Stem Cells

A paper from the Okano laboratory has shown that implantation of neural stem cells made from induced pluripotent stem cells can still form tumors ever after a long period of time.

This paper is an important contribution to the safety issues surrounding induced pluripotent stem cells (iPSCs). As noted in previous posts, iPSCs are made from adult cells by means of genetic engineering and cell culture techniques. In short, by introducing four different genes into adult cells and then culturing them in a special culture medium, a fraction of these cells will de-differentiate into cells that resemble embryonic stem cells in many ways, but are not exactly like them.

The Okano laboratory made iPSCs using viruses that integrate into the genome of the host cell, which is not the safest option. However, because in the four-gene cocktail that is normally used to reprogram these cells (Oct-4, Klf-4, Sox2, and c-Myc), the c-Myc gene is often thought to be the main cause of tumor formation. Okano and his collaborators made their iPSCs without the c-Myc gene, but only used the three-gene cocktail of Oct-4, Klf-4, and Sox2. Such a cocktail is much less efficient that the four-gene cocktail, but it supposed to make iPSCs that are altogether safer.

These iPSCs were differentiated into neural stem cells that grew as tiny spheres of cells, and these “neurospheres” were transplanted into the spinal cords of mice that had suffered a spinal cord injury. The implanted cells differentiated into neurons and glial cells and restored some neural function to these mice. However, the mice were observed for a long period of time after the implantations to assess the long-term safety of these implanted cells.

After 105 days, the implanted mice began to show deterioration of their neural function and their spinal cords showed tumors. It is clear that the Oct-4 gene that was used in the reprogramming procedure was the reason for the tumor transformation.

Graphical Abstract 20141213

This experiment, once again, calls into question the safety of any method for iPSC generation that leaves the transfected genes in the reprogrammed cells. I reported in a previous post that skin cells made from iPSCs that had their transgenes left in them were good at causing tumors and not as good as forming skin cells, but iPSCs without their reprogramming transgenes were safer and more effective tools for regenerative medicine.  This experiment also shows that c-Myc is not the only concern with iPSCs.  Any of the transgenes used for reprogramming can cause problems, and they must be removed if iPSCs are going to produce safe, differentiated cells.  Finally, this experiment pretty much shows that the use of retrovirus tools to introduce genes into cells for the sake of reprogramming is a bad idea if those cells are going to be used for regenerative medicine.  Non-integrating tools are much safer and preferable in these cases.

The Okano paper appeared in Stem Cell Reports.

Compact Spinal Implants to Help Spinal Cord Injured Patients Walk

An interdisciplinary research team at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland led by Dr. Grégoire Courtine and Dr. Stéphanie P. Lacour has recently lifted the curtain on their flexible spinal implant called the electronic dura (or e-Dura). According to Courtine and Lacour, this implant greatly improves spinal injury rehabilitation in spinal cord injured rats.

In a paper published by this team earlier in the journal Science this month, the EPFL team showed that, because of its flexibility, this next-generation e-Dura implant lasts longer (up to two months) and causes much less damage than traditional implants.

These latest results are an extension of earlier research in 2012 in which Courtine and Lacour published breath-taking results that showed spinal cord-injured rats that should have been paralyzed had regained the ability to walk, run, and even climb stairs.

Spinal cord injury results in loss of control over the part of the body below the point of injury. Courtine and his coworkers were able to reactivate the spinal cord in rats with a specific combination of drugs plus electrical stimulation to simulate the excitatory input from the brain. The drugs they used, monoamine agonists, bind to receptors and activate them in the same way that such neurotransmitters would in healthy subjects. When the spinal cord was exposed to these drugs plus mild electrical stimulation, the activated nerve cells in the spinal column produced movement in the paralyzed animals.

Spinal Cord Implant to help the Cripples walk

This movement, however, was largely involuntary, since the brain was not able to communicate with the area below the injured spinal cord. However, over time, as the animals trained and repeatedly walked in their harnesses (which kept them safe from falling); they became more confident in their ability to walk again. In fact, the EPFL team noticed a fourfold growth of new nerves in the spinal cord. This new nerve growth eventually restored communication between the brain and the injured area of the spine.

Courtine, whose eyes sparkle as he passionately talks about his research, is eager to take these findings to the clinic to see if they can help human beings who have suffered a catastrophic spinal cord injury. In preparation for clinical trials, however, they came up against another problem and that was the need for a long-term spinal implant that could deliver the chemical and electrical stimulation needed to initiate spinal cord healing. Courtine hopes that his e-Dura can satisfy this need.


The e-Dura meets two important criteria for spinal implants: durability and biocompatibility. In order to reduce the number of surgical procedures an injured patient must undergo, an implantable device needs to last a long time. It also has to be biocompatible and flexible. Early generation implants caused inflammation and the formation of scar tissue, which usually offset any positive results the implant provided.

When tested on laboratory animals, Courtine’s laboratory applied the e-Dura implant beneath the protective dura mater, directly on the spinal cord. Thankfully, the implant did not cause any adverse effects and lasted long enough for the paralyzed animals to complete their rehabilitation. Functionally, the implant also performed very well.

The e-Dura unit contains very small microfluidic channels that are embedded on a flexible silicon substrate. The device delivers precise amounts of drugs directly to the nerve cells in the spinal cord. Cracked gold conducting wires and electrodes that are made of a composite material that consists of silicon and platinum send electrical signals to the injured spinal cord. Electronic circuitry in the implant also provides the opportunity for the EPFL team to monitor the electrical messages sent back and forth to the brain as the new nerves are activated.

Indeed, this research is wonderfully exciting, but it is unclear how well it will work in humans. First of all, humans will probably need a different cocktail of drugs or a distinct electrical stimulation pattern to stimulate the spinal cord to heal itself. As with much clinical research at the beginning stages, there many unanswered questions to date. Advanced clinical trials will hopefully uncover some of these idiosyncrasies that characterize the injured human spinal cord and such answers are an integral part of providing a protocol that applies uses technology to human patients.

While exoskeleton technology also continues to approach consumer markets, it would be better to return to people their natural ability to walk. However you slice it, spinal cord injury patients may have more options in the coming years.

Grafted Stem Cells Display Robust Growth in Spinal Cord Injury Model

University of San Diego neuroscientists have used an animal model of spinal cord injury to test the ability of engrafted stem cells to regenerate damaged nerves. Mark Tuszynski and his team built on earlier work with implanted neural stem cells and embryonic stem cell-derived neural stem cells in rodents that had suffered spinal cord injuries.

In this study, Tuszynski and others used induced pluripotent stem cells that were made from a 86-year-old male. This shows that skin cells, even from human patients who are rather elderly, have the ability to be reprogrammed into embryonic stem cell-like cells. These cells were differentiated into neural stem cells and then implanted into the spinal cords of spinal cord-injured rodents.

The injured spinal cord is a very hostile place for implanted cells. Inflammation in the spinal cord summons white blood cells to devour cell debris. White blood cells are rather messy eaters and they release enzymes and toxic molecules that can kill off nearby cells. Also, regenerating cells run into a barrier made by support cells called glial cells that inhibit regenerating neurons from regenerating. Thus, the injured spinal cord is quite the toxic waste dump.

To get over this, Tuszynski and his coworkers treated their induced pluripotent stem cell-derived neural stem cells with growth factors. In fact, when the cells were implanted into the animal spinal cords, they were embedded in a matrix that contained growth factors. After three months, Tuszynski and his colleagues observed extensive axonal growth projecting from grafted neurons that reached long distances in both directions along the spinal cord from the brain to the tail end of the spinal cord. These sprouted axons appeared to make connections with the existing rat neurons. Importantly, these axons extended from the site of the injury, which is astounding given that the injured area of the spinal cord has characteristics that are inimical to neuronal and axon growth.

Even though Tuszynski and others showed that neural stem cells made from embryonic stem cells can populate the damaged spinal cord, using induced pluripotent stem cell-derived neural stem cells has an inherent advantage since these cells are less likely to be rejected by the patient’s immune system. Furthermore, the induced pluripotent stem cell-derived neural stem cells showed dramatic growth in the damaged spinal cord, but the implanted animals did not regain the use of their forelimbs. The implanted human cells were fairly young when the implanted animals were tested. Therefore, they might need to mature before they could restore function to the implanted animals.

“There are several important considerations that future studies will address,” Tuszynski said. “These include whether the extensive number of human axons make correct or incorrect connections; whether the new connections contain the appropriate chemical neurotransmitters to form functional connections; whether connections once formed are permanent or transient; and exactly how long it takes human cells to become mature. These considerations will determine how viable a candidate these cells might before use in humans.”

Tuszynski and his group hope to identify the most promising neural stem cell type for repairing spinal cord injuries. Tuszynski emphasized their commitment to a careful, methodical approach:

“Ultimately, we can only translate our animal studies into reliable human treatments by testing different neural stem cell types, carefully analyzing the results, and improving the procedure. We are encouraged, but we continue to work hard to rationally to identify the optimal cell type and procedural methods that can be safely and effectively used for human clinical trials.”

Nose Stem Cells Help Bulgarian Man Walk With Braces

Darek Fidyka, a 38-year-old Bulgarian man, was severely injured by a stab wound in 2010 and consequently lost the ability to walk.

Now, a new procedure using stem cells from his nose has given him the ability to walk with the help of braces.

Olfactory ensheathing cells or OECs (also known as olfactory ensheathing glial or OEGs) are found in the olfactory system, inside the skull and in the covering of cells that lines the roof of the nose. OECs share similarities to other glial cells like Schwann cells, astrocytes, and oligodendrocytes. OECs can aid the extension of neural projections known as axons from the nasal tissue to the olfactory glomeruli. OECs can do this because they secrete several interesting neurotrophic factors and cell adhesion molecules and migrate along with the regenerating axons. Because of these properties, OECs can escort axonal extension through glial scars that are made in a spinal cord after a spinal cord injury. These scars inhibit the outgrowth of new axons but OECs can allow regenerating axons to bridge these glial scars.

An advantage of OECs is that they can coexist with astrocytes, the cells that contribute to the formation of the glial scar, and even seem to prevent the out-of-hand response astrocytes have in response to injury in which they synthesize a host of molecules that inhibit axon regeneration called “inhibitory proteoglycans.”

The pioneering technique used in this procedure, according to Geoffrey Raisman, a professor at University College London’s (UCL) institute of neurology, used OECs to construct a kind of bridge between two stumps of the damaged spinal column.

“We believe… this procedure is the breakthrough which, as it is further developed, will result in a historic change in the currently hopeless outlook for people disabled by spinal cord injury,” said Riesman, who led this research project.

Raisman, who is a spinal injury specialist at UCL, collaborated with neurosurgeons at Wroclaw University Hospital in Poland to remove one of Fidyka’s olfactory bulbs, which give people their sense of smell, and transplant his olfactory ensheathing cells (OECs) in combination with. olfactory nerve fibroblasts (ONFs) into the damaged spinal cord areas. Following 19 months of treatment, Fidyka recovered some voluntary movement and some sensation in his legs.

The Nicholls Spinal Injury Foundation, a British-based charity which part-funded the research, said in statement that Fidyka was continuing to improve more than predicted, and was now able to drive and live more independently.

OECs have been used before to treat spinal cord injury patients. I refer you to chapter 27 in my book, The Stem Cell Epistles, to learn more about these. The novel technique in this paper is the additional use of nasal fibroblasts and the construction of a bridge between the two damaged remnants of the spinal cord.

The reason OECs were recruited to treat spinal cord injuries is that when axons that carry information about smells are damaged, the neuron simply regenerates its atonal extension, which grows into the olfactory bulbs. OECs facilitate this process by re-opening the surface of the olfactory bulbs in order for the new axons to enter them. Thus Raisman and others have the notion that transplanted OECs in the damaged spinal cord could equally facilitate the regeneration of severed nerve fibers.

Raisman also added that the technique used in this case, that is bridging the spinal cord with nerve grafts from the patient, had been used in animal studies for years, but was never used in a human patient in combination with OECs.

“The OECs and the ONFs appeared to work together, but the mechanism between their interaction is still unclear,” he said in a statement about the work.

Several spinal cord injury experts who were not directly involved in this work said its results offered some new hope. However, they were also quick to add that more work needed to be done to precisely determine what had led to this success. More patients must be successfully treated with this procedure before its potential can be properly assessed.

“While this study is only in one patient, it provides hope of a possible treatment for restoration of some function in individuals with complete spinal cord injury,” said John Sladek, a professor of neurology and pediatrics at the University of Colorado School of Medicine in the United States.

Raisman and his team now plan to repeat the treatment technique in between three and five spinal cord injury patients over the next three to five years. “This Nose will enable a gradual optimization of the procedures,” he told Reuters.

Transplanted Mesenchymal Stem Cells Prevent Bladder Scarring After Spinal Cord Injury

A collaborative research effort between laboratories from Canada and South Korea have shown that a cultured mesenchymal stem cell line called B10 can differentiate into smooth muscle cells and improve bladder function after a spinal cord injury.

Spinal cord injury can affect the lower portion of the urinary tract. Overactive bladder, urinary retention, and increased bladder thickness and fibrosis (bladder scarring) can result from spinal cord injuries. Human mesenchymal stem cells (MSCs) can differentiate under certain conditions into smooth muscle. For this reason, MSCs have therapeutic potential for patients who have suffered from spinal cord injuries.

Seung U. Kim and his colleagues from Gachon University Gil Hospital in Inchon, South Korea have made an immortalized human mesenchymal stem cell line by transfecting primary cell cultures of fetal human bone marrow mesenchymal stem cells with a retroviral vector that contains the v-myc oncogene. This particular cells line, which they called HM3.B10 (or B10 for short), grows well in culture and can also differentiates into several different cell types.

In this present study, which was published in the journal Cell Transplantation, Kim and his colleagues and collaborators injected B10 hMSCs directly into the bladder wall of mice that had suffered a spinal cord injury but were not treated showed no such improvement.

“Human MSCs can secrete growth factors,” said study co-author Seung U. Kim of the Division of Neurology at the University of British Columbia Hospital, Vancouver, Canada. “In a previous study, we showed that B 10 cells secrete various growth factors including hepatocyte growth factor (HGF) and that HGF inhibits collagen deposits in bladder outlet obstructions in rats more than hMSCs alone. In this study, the SCI control group that did not receive B10 cells showed degenerated spinal neurons and did not recover. The B10-injected group appeared to have regenerated bladder smooth muscle cells.”

Four weeks after the initial spinal cord injury, the mice in the B10-treated group received injections of B10 cells transplanted directly into the bladder wall. Kim and his team used magnetic resonance imaging (MRI) to track the transplanted B10 cells. The injected B10 cells had been previously labeled with fluorescent magnetic particles, which made them visible in an MRI.

“HGF plays an essential role in tissue regeneration and angiogenesis and acts as a potent antifibrotic agent,” explained Kim.

These experiments also indicated that local stem cell injections rather than systemic, intravenous infusion was the preferred method of administration, since systemic injection caused the hMSCs get stuck largely in the blood vessels of the lungs instead of the bladder.

The ability of the mice to void their bladders was assessed four weeks after the B10 transplantations. MRI analyses clearly showed strong signals in the bladder as a result of the labeled cells that had been previously transplanted. Post-mortem analyses of the bladders of the transplanted group showed even more pronounced differences, since the B10-injected animals had improved smooth muscle cells and reduced scarring.

These results suggest that MSC-based cell transplantation may be a novel therapeutic strategy for bladder dysfunction in patients with SCI.

“This study provides potential evidence that an human [sic] stable immortalized MSC line could be useful in the treatment of spinal cord injury-related problems such as bladder dysfunction.” said Dr. David Eve, associate editor of Cell Transplantation and Instructor at the Center of Excellence for Aging & Brain Repair at the University of South Florida. “Further studies to elucidate the mechanisms of action and the long-term effects of the cells, as well as confirm the optimal route of administration, will help to illuminate what the true benefit of these cells could be.”

Human Stem Cell-Derived Neurons Grow New Axons In Spinal Cord Injured Rats

A stem cell-based treatment for spinal cord injury took one more baby step forward when scientists from the laboratory of Mark Tuszynski at the at the University of California, San Diego used cells derived from an elderly man’s skin to regrow neural connections in rats with damaged spinal cords.

Tuszynski and others published their results in the Aug. 7 online issue of the journal Neuron. In that paper, Tuszynski and his co-worker report that human stem cells triggered the growth of numerous axons in the damaged spinal cord. Axons are those fibers that extend from the main part or body a neuron (nerve cell) that serve to send electrical impulses away from the body to other cells. Some of these new axons even grew into the animals’ brains.

Axon picture

Dr. Mark Tuszynski is a professor of neurosciences at the University of California, San Diego. “This degree of growth in axons has not been appreciated before,” he said. However, Tuszynski also cautioned that there is still much to be learned about how these newly established nerve fibers behave in laboratory animals. He likened the potential for stem-cell-induced axon growth to nuclear fusion. If it’s contained, you get energy; if it’s not contained, you get an explosion. “Too much axon growth into the wrong places would be a bad thing,” Tuszynski added.

Stem cell researchers have examined the potential for stem cells to restore functioning nerve connections in people with spinal cord injuries. Embryonic stem cells have been used to make new neurons and to also make “oligodendrocyte progenitor cells” or OPCs, which make the insulating myelin sheath that enwraps the axons of spinal nerves. However, several other types of stem cells can make OPCs and new neurons and these stem cells do not come from embryos (for more, see chapter 27 of my book, The Stem Cell Epistles).

In this study, Tuszynski and his team used induced pluripotent stem cells or iPSCs, which are derived from mature adult cells by means of genetic engineering and cell culture techniques. They used cells from a healthy 86-year-old man and genetically reprogrammed so that they were reprogrammed into iPSCs. These iPSCs were then differentiated into neurons that were implanted into a special scaffold embedded with proteins called growth factors, and then grafted into the spinal cords of laboratory rats with spinal cord injuries.

Over the course of several months, these animals showed new, mature neurons and extensive growth in the cells’ axons. These fibers grew through the injury-related scar tissue in the animals’ spinal cords and connected with resident rat neurons.

This is an enormous advance, because the wounded spinal cord creates a “Glial scar” that contains a host of molecules that repel growing axons. Even though this glial scar prevents the immune system from leaking into the spinal cord and destroying it, this same scar prevents the regeneration of damaged neurons and their severed axons.

Glial scar axon repulsion

Dr. David Langer, director of neurosurgery at Lenox Hill Hospital in New York City said: “One of the big obstacles [in this type of research] is this area of scarring in the spinal cord. Getting neurons to traverse it is a real challenge,” said Langer, who was not involved in the research. “The beauty of this study,” he said, “is that they got the neurons to survive and traverse the scar.”

Langer also cautioned, much like Tuszynski, that this experimental success is just a preliminary step. There are, in his words, “huge questions” as to whether or not these axons can make appropriate connections and actually restore function to spine-damaged lab animals. “It’s not just a matter of having the cables,” Langer said. “The wiring has to work.”

And even if this stem cell approach does pan out in animals, Langer added, it would all have to be translated to humans. “We have a long way to go until we’re there,” he said. “It’s not that people shouldn’t have hope. But it should be a realistic hope.”

A few biotech companies have already launched early-stage clinical trials using embryonic (Geron) or fetal stem cells (StemCells Inc) to treat patients with spinal cord injuries. But Tuszynski said his team’s findings offer a cautionary note about moving to human trials too quickly. “We still have a lot to learn,” he said. “We want to be very sure these axons don’t make inappropriate connections. And we need to see if the new connections formed by these axons are stable.”

Ideally, Tuszynski added, if stem cells were to be used in treating spinal cord injuries, they’d be generated as they were in this study — by creating them from a patient’s own cells. That way, he explained, patients would not need immune-suppressing drugs afterward.

Gene Inhibitor Plus Fish Fibrin Restore Nerve Function Lost After a Spinal Cord Injury

Scientists at UC Irvine’s Reeve-Irvine Research Center have discovered that injections of salmon fibrin injections into the injured spinal cord plus injections of a gene inhibitor into the brain restored voluntary motor function impaired by spinal cord injury.

Gail Lewandowski and Oswald Steward, director of the Reeve-Irvine Research Center at UCI, examined rodents that had received spinal cord injuries.  They were able to heal the damage by developmentally turning back the clock in a molecular pathway that is critical to the formation of the corticospinal nerve tract, and by providing a scaffold for the growing neurons so that the axons of these growing neurons could grow and make the necessary connections with other cells.  Their research was published in the July 23 issue of The Journal of Neuroscience.

The work of Steward and Lewandowski is an extension of previous research at UC Irvine from 2010.  Steward and his colleagues discovered that the axon of neurons grow quite well once an enzyme called PTEN is removed from the cells.  PTEN is short for “phosphatase and tensin homolog,” and it removes phosphate groups from specific proteins and lipids.  In doing so, PTEN signals to cells to stop dividing and it can also direct cells to undergo programmed cell death (a kind of self-destruct program).  PTEN also prevents damaged tissues from regenerating sometimes, because it is a protein that puts the brakes of cell division.  Mutations in PTEN are common in certain cancers, but the down-regulation of PTEN is required for severed axons to re-form, extend, migrate to their original site, and form new connections with their target cells.

PTEN function


After two years, team from U.C. Irvine discovered that injections of salmon fibrin into the damaged spinal cord or rats filled cavities at the injury site and provided the axons with a scaffolding upon which they could grow, reconnect and facilitate recovery. Fibrin produced by the blood system when the blood vessels are breached and it is a fibrous, insoluble protein produced by the blood clotting process.  Surgeons even use it as a kind of surgical glue.

“This is a major next step in our effort to identify treatments that restore functional losses suffered by those with spinal cord injury,” said Steward, professor of anatomy & neurobiology and director of the Reeve-Irvine Research Center. “Paralysis and loss of function from spinal cord injury has been considered irreversible, but our discovery points the way toward a potential therapy to induce regeneration of nerve connections.”

In their study, Steward and Lewandowski subjected rats to spinal cord injuries, and then assessed their defects.  Because these were upper back injuries, the rats all showed impaired forelimb (hand) movement.  Steward and Lewandowski then treated these animals with a combination of salmon fibrin at the site of injury and a modified virus that made a molecule that inhibited PTEN.  These viruses were genetically engineered adenovirus-associated viruses encoded a small RNA that inhibited translation of the PTEN gene (AAVshPTEN).  This greatly decreased the levels of PTEN protein in the neurons.  Other rodents received control treatments of only AAVshPTEN and no salmon fibrin.

The results were remarkable.  Those rats that received the PTEN inhibitor alone showed no improvement in their forelimb function, but those animals who were given AAVshPTEN plus the salmon fibrin recovered forelimb use (at least reaching and grasping).

“The data suggest that the combination of PTEN deletion and salmon fibrin injection into the lesion can significantly enhance motor skills by enabling regenerative growth of corticospinal tract axons,” Steward said.

Corticospinal Nerve tract

Statistics compiled by the Christopher & Dana Reeve Foundation suggests that approximately 2 percent of Americans have some form of paralysis that is the result of a spinal cord injury.  Spinal cord injuries break connections between nerves and muscles or nerves and other nerves.  Even injuries the size of a grape can cause complete loss of function below the level of the injury.  Injuries to the neck can cause paralysis of the arms and legs, an absence of sensation below the shoulders, bladder and bowel incontinence, sexual dysfunction, and secondary health risks such as susceptibility to urinary tract infections, pressure sores and blood clots due to an inability to move one’s legs.

Steward said the next objective is to learn how long after injury this combination treatment can be effectively administered. “It would be a huge step if it could be delivered in the chronic period weeks and months after an injury, but we need to determine this before we can engage in clinical trials,” he said.