Toward the Realization of the World's First Spinal Cord Regenerative Medicine Using iPS Cells

Professor Hideyuki Okano and Professor Masaya Nakamura, School of Medicine

2022/04/22

Last December, Keio University Hospital transplanted neural progenitor cells derived from human iPS cells into a patient with a spinal cord injury for the first time in the world. This first clinical study for spinal cord injury, for which there is still no fundamental treatment, is gathering great expectations and attention. We spoke with Professor Hideyuki Okano of the Department of Physiology and Professor Masaya Nakamura of the Department of Orthopedic Surgery, who have co-led this team and have been researching regenerative medicine for spinal cord injury for over 20 years.

Professor Masaya Nakamura (at a press conference on January 14, 2022, after performing the cell transplant for the first case)

-First, could you tell us what led you to become involved in the research and treatment of spinal cord injury?

Nakamura: When I was in the School of Medicine, I was on the Basketball Team. In the winter of my second year, I went skiing with my teammates in Happo, Nagano, and a junior student one year below me injured his neck on the slopes. At the time, however, I didn't understand what a spinal cord injury was. When we arrived at Keio University Hospital after a three-and-a-half-hour journey with the ambulance crew from Happo, I genuinely thought, "He'll be saved now, he'll be cured once the surgery is over."

A while after the accident, I visited his family home. He came out operating an electric wheelchair with his chin. I don't know how to describe how I felt at that moment... My teammate, who I had been playing with just a short while ago, could only move his shoulders; his elbows, hands, and feet wouldn't move. "What? Why? Why can't this be fixed?" I was struck by anger, and it felt like I had been struck by lightning.

After that, he transferred from the School of Medicine to the Faculty of Letters and began working as a librarian. I felt frustrated that spinal cord injuries couldn't be cured, and at the same time, I was incredibly influenced by his determination to accept his situation and live life to the fullest. At the time, I didn't often say out loud that I wanted to cure spinal cord injuries, but even after 40 years, my feelings haven't changed. His existence is without a doubt the origin of who I am today.

Okano: I originally entered the School of Medicine because I wanted to do research. As a student, I was absorbed in the molecular study of oncogenes, but research was already advanced at places like the Massachusetts Institute of Technology (MIT), so I was unsure about my career path. So, I boldly visited the National Cancer Center and went to see Dr. Takashi Sugimura, who was the director of the research institute at the time. Of course, since I didn't have an appointment, his secretary was about to turn me away, but Dr. Sugimura happened to come out and ask, "What's this?" and we ended up talking for about 30 minutes.

I thought Dr. Sugimura would encourage me to continue cancer research, but he didn't. He said, "You know, it's probably best to do something that no one else is doing. That's how I've lived my life." He then told me how he, a leader in cancer research, had carved out his own original path. I was so impressed; it was a real eye-opener.

Thinking about "a field no one else was working in," I came up with the idea of elucidating neural structures using molecular biology research methods. In the early 80s, there were hardly any methods used in neuroscience research other than morphology and electrophysiology. With the recommendation of the respected neuroscientist Dr. Katsuhiko Mikoshiba, I joined the Department of Physiology and began researching the development of the nervous system. In fact, before entering university, an acquaintance of my father who had a spinal cord injury had told me, "I hope you'll cure diseases like this in the future." As it turned out, I ended up on a path that would fulfill that wish.

-Professor Okano, you then continued your basic research on neural development for 15 years.

Okano: I graduated from university in 1983, and in 1989, I went to Johns Hopkins University in the U.S. to study neural development in Drosophila. In 1991, I discovered Musashi, a molecule expressed in neural stem cells. After returning to Japan, I continued my research, and in 1998, I was the first in the world to discover and publish a paper showing that Musashi is also expressed in the adult human brain—meaning that neural stem cells exist there.

These neural stem cells are the source cells that create various other cells, such as neurons, astrocytes, and oligodendrocytes. The existence of neural stem cells in the adult human brain meant that the nervous system, previously thought to be non-regenerative, might be able to regenerate. The public response after the paper's publication was huge, and I began to receive letters from patients with spinal cord injuries and intractable neurological diseases, asking me to find a cure.

I also moved to Osaka University in 1997, where I was greatly influenced by Dr. Tadamitsu Kishimoto, who was the dean of the medical school at the time and an immunology researcher. Dr. Kishimoto discovered the cytokine IL-6, and antibodies against its receptor have been used as treatments for chronic rheumatoid arthritis and Castleman's disease, and more recently for COVID-19 pneumonia. Seeing Dr. Kishimoto, who embodied the principles that "basic research is only meaningful when it is useful in the clinic" and "breakthrough basic research can cure intractable diseases," I wanted to be like him and began to seriously pursue basic research in regenerative medicine with a clinical focus.

-I hear that the two of you teamed up after reuniting while Professor Nakamura was studying in the U.S.

Nakamura: Although I joined the orthopedic surgery department to research spinal cord regeneration, at that time, it was an era when "spinal cord regeneration is just a pipe dream" was the common belief. I felt the limits of research in Japan. So, against the opposition of those around me, I went to America by myself. However, even at the institution where I started collaborative research, I couldn't conduct the research I wanted due to various circumstances.

In the spring of 1999, under those circumstances, Professor Okano, who was at Osaka University at the time, was invited to NASA for a peer review and came to Washington, D.C. I went to pick him up at Dulles Airport, and we talked about our recent situations by the Potomac River, where the cherry blossoms were in bloom. Professor Okano then said, "In that case, why don't you come to Osaka University and study the technical aspects?" After that, I temporarily returned to Japan for about a month and received intensive training at Osaka University on how to culture neural stem cells. Thanks to that, I was able to return to Georgetown University with a wealth of know-how and continue my research. Without that, I might have given up and cut my studies abroad short.

Okano: At that time, I was also struggling to figure out how to cure spinal cord injury with neural stem cells. While I taught Professor Nakamura the technical aspects, such as cell culture methods, at Osaka University, I also received various ideas from him regarding spinal cord injury.

Nakamura: I still haven't forgotten what Professor Okano said to me in the car on the way back from the lab at Osaka University back then. He said, "Masaya-sensei, regenerative medicine is still in a state of chaos. No one has emerged yet. We have no choice but to break through here. Let's take on the world together." At the time, I had dreams but had not yet accomplished anything, and I was very inspired by his words. I thought that if I worked with him, I might be able to achieve something.

Okano: After that, by coincidence, we both returned to Keio around the same time. In April 2001, the new Center for Integrated Medical Research was established at Keio, and we began research on spinal cord regeneration using human neural stem cells with Professor Nakamura and other excellent researchers. Meeting Professor Nakamura in D.C. in '99 was, in many ways, the starting point of our research.

-Could you explain the mechanism of spinal cord regeneration using neural stem cells?

Okano: "Regeneration" is the process of redoing "development." By transplanting neural stem cells into the spinal cord, the developmental phenomena that produce neurons, astrocytes, and oligodendrocytes are repeated. This allows severed neural circuits to be reconstructed, and glial cells to supplement axons to reform myelin sheaths. In other words, tissue that has been damaged is histologically repaired and functionally regenerated.

In fact, by the early 2000s, we already knew that "transplanting neural stem cells can cure spinal cord injury." We had transplanted fetal-derived neural stem cells into mouse and monkey models of spinal cord injury and confirmed a dramatic recovery of motor function.

-So you had already succeeded in spinal cord regeneration in animal experiments even before the discovery of iPS cells.

Okano: Yes. Just when we thought we could finally proceed with transplantation into humans, it didn't happen. This was because in 2006, it was judged that "the clinical application of fetal-derived neural stem cells is premature." Due to ethical regulations, we were unable to reach the clinical trial stage in Japan, and we were frustrated.

It was then, in 2007, that Dr. Shinya Yamanaka of Kyoto University discovered iPS cells. I had heard about iPS cells even before the paper was published and was convinced that "this will work." Subsequently, we succeeded in creating neural stem cells from iPS cells provided by Dr. Yamanaka. Furthermore, in 2012, we successfully transplanted human-derived iPS cells into mice and monkeys with spinal cord injuries.

-So there were many more difficulties to overcome before transplantation into humans could actually be realized.

Okano: It took about 10 years to determine the conditions for creating cells that could be administered to humans. This is because while neural stem cells divide and proliferate to create nerve cells and glial cells, they can become tumors if they don't stop dividing at the appropriate point. It took a long time to determine the number of cells to transplant and the culture conditions needed to create cells that would engraft properly, repair tissue, and not form tumors.

Nakamura: Establishing iPS cells was, of course, a world-first technology, so it was still developing, and it would be upgraded every few years. It's a great thing to have better iPS cells, but when the iPS cells change, the method of differentiation induction also changes, and differentiation takes several months. Furthermore, we have to transplant the created cells into animals and confirm that no tumors form after several months. We were often held up for years at a time, and those days were really tough.

Okano: There were many times when I held my head in my hands, thinking, "What was this past year for? It's been no progress..." (laughs). Furthermore, before the clinical study, we had to clear strict release criteria—for example, whether there was any viral contamination or mutations in cancer-related genes. We checked these one by one, and the final evaluation was completed on August 31, 2020. After that, there were many twists and turns, such as the suspension of patient recruitment due to the spread of COVID-19, but on December 8 of last year, 2021, we were finally able to perform the cell transplant for the first case.

Nakamura: There were various things, both scientific and non-scientific, but I don't think any of it was a waste. Since we are delivering this to patients, our policy is to do our best with the science. So, even if we fall, we don't just get up; we learn something and stand up again. That's how we've come this far.

Okano: That's right. It took a very long time and a lot of effort, but the various knowledge and experiences accumulated throughout the process have become our confidence. Also, to get to the world's first surgery, we were supported by teams both inside and outside of Keio, including the entire Keio University Hospital, as well as collaborating medical institutions like the Murayama Medical Center and the Center for iPS Cell Research and Application (CiRA) at Kyoto University. I am very grateful for that.

-Please give us an overview of this clinical study and tell us your honest feelings right now.

Nakamura: This clinical trial targets patients in the subacute phase, two to four weeks after spinal cord injury, specifically those with the most severe degree of injury—complete paralysis. We transplanted approximately two million neural progenitor cells derived from human iPS cells into the center of the injured spinal cord. Over the next year, we will confirm safety, including the absence of tumorigenicity. We will also provide the same rehabilitation as regular patients and verify whether there is any functional improvement compared to patients who have not received the cell transplant. We plan to conduct this clinical trial on three more patients, for a total of four. Having finished the first surgery, I feel like we've finally made it this far, but at the same time, I feel like we're standing at a new starting point.

Okano: Being able to perform the first transplant means we've taken the "first step," not "zero steps." There's no time to wait. This time, for sure, we want to speed things up even more to deliver this treatment to patients.

-I imagine that patients in the chronic phase and their families also have high expectations. What is the outlook for treatment?

Okano: We are, of course, also advancing research for the chronic phase. For the chronic phase, we use neural progenitor cells derived from iPS cells with slightly different characteristics than those for the subacute phase. We are steadily preparing with Professor Nakamura and his team to be able to start an investigator-initiated clinical trial in two to three years.

Nakamura: After this clinical trial was reported, I received a letter from the family of a chronic-phase patient saying, "My father, who had given up, started working hard on his rehabilitation again after hearing this news." I was happy that it has become a ray of hope not only for subacute patients but also for chronic-phase patients, and I feel an even greater sense of responsibility than before.

What I always tell people at public lectures and other events is, "Please continue to work hard at rehabilitation to maximize your remaining functions." Some patients with spinal cord injuries and their families misunderstand, thinking that "iPS cells are magic cells, and with them, my legs will suddenly start moving again," but that's completely wrong. Cell transplantation is just one piece of the puzzle for spinal cord regeneration. And rehabilitation is another essential piece. In preparation for the realization of regenerative medicine, I want them to work hard on their daily rehabilitation to maintain the muscle strength, physical stamina, and mental fortitude to receive it.

-What are the challenges for the practical application of regenerative medicine?

Okano: In the future, to "implement regenerative medicine in society," meaning to provide iPS cell-derived cells throughout the country, we will need to develop a platform for mass-culturing cells and build large-scale cell culture facilities. It is impossible for universities to handle this alone, nor will it work if we just hand it over to companies. In other words, "medical-engineering collaboration" and "industry-academia collaboration," where we in academia and industry work together as one, are essential.

Therefore, in addition to our research work, both Professor Nakamura and I are now focusing on initiatives to promote regenerative medicine as a nation in various forums, including the Japanese Society for Regenerative Medicine. Furthermore, as the demand for regenerative medicine increases and a system for sufficient supply is established, a certain degree of cost reduction should naturally follow.

Nakamura: For regenerative medicine to become a widespread and accessible treatment for every patient, we must be able to provide better, faster, and cheaper options. To achieve this, it is important not only for science to advance but also for industry and academia to work together with a sense of speed.

-What is the "future of regenerative medicine" that you envision?

Okano: Regenerative medicine using iPS cells currently targets many diseases that significantly impair QOL or have no cure, but eventually, it will be widely used for common diseases as well. At that point, I believe the direction will be to enhance treatment effects by combining it with other therapies, such as boosting the effects of existing drugs or improving the effectiveness of rehabilitation.

Nakamura: What I'm aiming for with regenerative medicine is for people to "live healthily and die suddenly." What I mean is, while medical advances have extended lifespans, there are many cases where organs and systems can't keep up. This includes dementia and stroke in the neurological field, and lower back pain and knee joint pain in the orthopedic field. If regenerative medicine can cover these areas, more people should be able to live as themselves until the very end, rather than being bedridden or requiring nursing care. I believe that contributing to such a society is the goal of regenerative medicine.

-By the way, having researched together for 20 years, what do you each think of the other as a researcher?

Nakamura: Professor Okano is a world-class neuroscientist, so I have complete respect for him. What's particularly amazing? For example, when we went to the ICM (Paris Brain Institute) together, Professor Okano could have an engaging conversation with researchers from any field. I was truly amazed by the breadth and depth of his knowledge, wondering how he could be so knowledgeable even about things outside his specialty. People at academic conferences often say to me, "How can you work with such a sharp guy as Okano for decades?" I just reply, "I do it on pure spirit!" (laughs).

Okano: I don't think there are many orthopedic surgeons with as much passion as Professor Nakamura. And I was in surgery with him the other day, and he is truly a skilled surgeon. I have complete trust in his "passionate heart" and "god-like hands." Well, maybe Professor Nakamura and I have been able to work together for over 20 years because we have slightly different personalities (laughs).

Nakamura: Shinzo Koizumi, a former President of Keio, left behind the words, "Practice makes the impossible possible," using sports as an example. But through my research with Professor Okano, I've come to feel that "science makes the impossible possible." After all, we have now taken a step forward and realized something that was thought to be impossible just a few decades ago. I want to work even harder from now on.

-Once again, what do you find attractive about the Keio University School of Medicine?

Okano: The Keio University School of Medicine has advocated for the "unity of basic and clinical medicine" since its establishment, and true to that philosophy, the barriers are really low. It's rare to find a university where both Translational Research, which connects basic research to the development of new diagnostic and therapeutic methods, and Reverse Translational Research, which feeds clinical problems and diagnoses back into basic research, can be done so smoothly. I think it's an excellent environment.

Nakamura: I agree. In fact, Professor Okano has been working on spinal cord regeneration from a basic research standpoint, while I have been working from a clinical standpoint. Our partnership is also an embodiment of the spirit of the Keio University School of Medicine, isn't it?

Okano: And what's interesting is that, for example, in our Department of Physiology, clinicians come from various departments, not just orthopedic surgery but also neurosurgery and neurology. The formation of a community among clinicians allows us to form a "group strategy" against diseases, so to speak, and the perspectives and testing methods of doctors from other departments often prove useful. Not only are the barriers between basic and clinical medicine low, but the barriers between clinical departments are also low. I think it's a great university.

-Do you have a message for the younger generation aspiring to study medicine?

Okano: The desire to break new ground in a field no one has explored with science, and the desire to save people suffering from incurable diseases. I believe these two things have been the driving force behind my continued research. No matter what era lies ahead, new intractable diseases will always emerge. Even if we conquer cancer and dementia, another disease will appear. At that time, I hope you will be scientists and doctors who have a challenging spirit and who strive to develop treatments using the full extent of human wisdom.

Nakamura: There are three words I often share with medical students and young orthopedic surgeons. First, what's important is Passion. You could also call it a strong desire or a dream. With that passion, you create a Vision. What do you want to be in 10 years? To achieve that, specify what you want to be in five years, and in three years. And then, what you must do now to achieve that vision is Action. "Passion, Vision, Action"—people who are serious about this don't make excuses even if they fail. Even if they hit rock bottom, they will always grasp something there and crawl back up, having grown bigger.

Also, I want you to find something that you can proudly say, "I did this during my university years." It can be studying, club activities, or any other activity. Devote yourself to it with all your might, tackle it head-on. I believe that attitude will surely be rewarded in the future. I hope young students will come to the Keio University School of Medicine with big dreams.

Hideyuki Okano

Graduated from the Keio University School of Medicine in 1983. After positions at the Keio University School of Medicine's Department of Physiology, Osaka University's Institute for Protein Research, Johns Hopkins University in the U.S., and the University of Tokyo's Institute of Medical Science, he became a professor of molecular neurobiology in the Institute of Basic Medical Sciences at the University of Tsukuba in 1994. In 1997, he became a professor in the Department of Neuroscience, Osaka University Graduate School of Medicine. Since 2001, he has been a professor in the Department of Physiology at the Keio University School of Medicine, and since 2017, he has served as the Graduate School of Medicine Dean at Keio University (both positions current). He has received numerous awards, including the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology, the Inoue Prize for Science, the Medal with Purple Ribbon, the Baelz Prize, the Takamine Memorial Daiichi Sankyo Prize, and the Uehara Prize.

Masaya Nakamura

Graduated from the Keio University School of Medicine in 1987. After positions at the Keio University School of Medicine's Department of Orthopedic Surgery and Georgetown University in the U.S., he became an assistant professor at the Keio University School of Medicine in 2000. After serving as a part-time lecturer at Kyoto University's Institute for Frontier Medical Sciences, a part-time lecturer at Hoshi University's Department of Pharmacology, and an associate professor at the Keio University School of Medicine's Department of Orthopedic Surgery, he became a full professor in 2015 (current position). He has received numerous awards, including the Japanese Orthopaedic Association's Academic Encouragement Award, the Baelz Prize, and the Japanese Society for Regenerative Medicine Award.

This article was originally published on the Keio University School of Medicine and Graduate School of Medicine website.

*Affiliations and titles are as of the time of the interview.