Using 3D printer to develop treatment for spinal cord injury


3D printed device

Spinal cord injuries (SCIs) affect approximately 300,000 Americans, with about 18,000 new cases occurring per year. One of these patients, Jake Javier, who we have written about many times over the past several years, received ten million stem cells as part of a CIRM-funded clinical trial and a video about his first year at Cal Poly depicts how these injuries can impact someone’s life.

Currently, there is nothing that completely reverses SCI damage and most treatment is aimed at rehabilitation and empowering patients to lead as normal a life as possible under the circumstances. Improved treatment options are necessary both to improve patients’ overall quality of life, and to reduce associated healthcare costs.

Scientists at UC San Diego’s School of Medicine and Institute of Engineering in Medicine have made critical progress in providing SCI patients with hope towards a more comprehensive and longer lasting treatment option.

shaochen chen

Prof. Shaochen Chen and his 3D printer

In a study partially funded by CIRM and published in Nature Medicine, Dr. Mark Tuszynski’s and Dr. Shaochen Chen’s groups used a novel 3D printing method to grow a spinal cord in the lab.

Previous studies have seen some success in lab grown neurons or nerve cells, improving SCI in animal models. This new study, however, is innovative both for the speed at which the neurons are printed, and the extent of the neuronal network that is produced.

To achieve this goal, the scientists used a biological scaffold that directs the growth of the neurons so they grow to the correct length and generate a complete neuronal network. Excitingly, their 3D printing technology was so efficient that they were able to grow implants for an animal model in 1.6 seconds, and a human-sized implant in just ten minutes, showing that their technology is scalable for injuries of different sizes.

When they tested the spinal cord implants in rats, they found that not only did the implant repair the damaged spinal cord tissue, but it also provided sustained improvement in motor function up to six months after implantation.

Just as importantly, they also observed that blood vessels had infiltrated the implanted tissue. The absence of vascularized tissue is one of the main reasons engineered implants do not last long in the host, because blood vessels are necessary to provide nutrients and support tissue growth. In this case, the animal’s body solved the problem on its own.

In a press release, one of the co-first authors of the paper, Dr. Kobi Koffler, states the importance and novelty of this work:

“This marks another key step toward conducting clinical trials to repair spinal cord injuries in people. The scaffolding provides a stable, physical structure that supports consistent engraftment and survival of neural stem cells. It seems to shield grafted stem cells from the often toxic, inflammatory environment of a spinal cord injury and helps guide axons through the lesion site completely.”

In order to make this technology viable for human clinical trials, the scientists are testing their technology in larger animal models before moving into humans, as well as investigating how to improve the longevity of the neuronal network by introducing proteins into the scaffolds.



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.”

Related Links:

Extra dose of patience needed for spinal cord injury stem cell therapies, rat study suggests

2017 has been an exciting year for Asterias Biotherapeutics’ clinical trial which is testing a stem cell-based therapy for spinal cord injury. We’ve written several stories about patients who have made remarkable recoveries after participating in the trial (here and here).

But that doesn’t mean researchers at other companies or institutes who are also investigating spinal cord injury will be closing up shop. There’s still a long way to go with the Asterias trial and there’s still a lot to be learned about the cellular and molecular mechanisms of spinal cord injury repair, which could lead to alternative options for victims. Continued studies will also provide insights on optimizing the methods and data collection used in future clinical trials.

Human neuronal stem cells extend axons (green) three months after transplantation in rat model of spinal cord injury. Image: UCSD

In fact, this week a team of UC San Diego scientists report in the Journal of Clinical Investigation that, based on brain stem cell transplant studies in a rat model of spinal cord injury, recovery continues long after the cell therapy is injected. These findings suggest that collecting clinical trial data too soon may give researchers the false impression that their therapy is not working as well as they had hoped.

In this study, funded in part by CIRM, the researchers examined brain stem cells – or neural stem cells, in lab lingo – that were derived from human embryonic stem cells. These neural stem cells (NSCs) aren’t fully matured and give rise to nerve cells as well as support cells called glia. Previous studies have shown that when NSCs are transplanted into rodent models of spinal cord injury, the cells mature into nerve cells, make connections with nerves within the animal and can help restore some limb movement.

But the timeline for the maturation of the NSCs after transplantation into the injury site wasn’t clear because most studies only measured recovery for a few weeks or months. To get a clearer picture, the UCSD team analyzed the fate and impact of human NSCs in adult rats with spinal cord injury from 1 month to 1.5 years – the longest time such an experiment has been carried out so far. The results confirmed that the transplanted NSCs did indeed survive through the 18-month time point and led to recovery of movement in the animals’ limbs.

To their surprise, the researchers found that the NSCs continued to mature and some cell types didn’t fully specialize until 6 months or even 12 months after the transplantation. This timeline suggests that although the human cells are placed into the hostile environment of an injury site in an animal model, they still follow a maturation process seen during human development.

The researchers also focused on the fate of the nerve cells’ axons, the long, thin projections that relay nerve signals and make connections with other nerve cells. Just as is seen with normal human development, these axons were very abundant early in the experiment but over several months they went through a pruning process that’s critical for healthy nerve function.

Altogether, these studies provide evidence that waiting for the clinical trial results of stem cell-based spinal cord injury therapies will require an extra dose of patience. Team lead, Dr. Mark Tuszynski, director of the UC San Diego Translational Neuroscience Institute, summed it up this way in a press release:

Mark Tuszynski, UCSD

“The bottom line is that clinical outcome measures for future trials need to be focused on long time points after grafting. Reliance on short time points for primary outcome measures may produce misleadingly negative interpretation of results. We need to take into account the prolonged developmental biology of neural stem cells. Success, it would seem, will take time.”