This article could not have been written three years ago because the technology did not exist. Shinya Yamanaka of Kyoto University had not announced his findings (Cell, 2006) and many observers thought it might not be possible to confer (embryonic) stem cell-like attributes to an adult cell. Others had tried and failed. Today, after additional advancements at Harvard and the University of Wisconsin, we are looking at what may be a new approach toward treating a variety of major diseases – one that uses an individual’s own transformed adult cells as a means of regenerative therapy – and bypasses use of embryonic stem cells.

Yasuhiro Ikeda, D.V.M., Ph.D. invites us into his lab in Mayo Clinic’s Guggenheim Building. He removes a reservoir slide tray from an incubator. There, beneath the microscope, we see heart muscle-like cells, beating. Originally adult skin cells, they are fascinating symbols of pluripotency, the potential to become many different cell types. They have been transformed from adult cells to undifferentiated stem cell-like cells – induced pluripotent stem (iPS) cells – and then into the specialized cells of heart muscle. Mayo Clinic sees iPS cells as a major resource in its regenerative medicine efforts.

After graduating from the University of Tokyo, Dr. Ikeda began his career as a small animal veterinarian. People would bring their cats to him at the university clinic for infectious diseases. That went well – for a while.

“After about a year I became allergic to cats. I couldn’t be in the same room with them. I didn’t even have to touch them for my eyes to start watering.”

Fortunately for Mayo Clinic, Dr. Ikeda’s career “plan B” was to go into medical research.

“I decided to help people instead,” he smiles. His work with feline viruses led him to study viral vectors at the University of London where he met Mayo’s Stephen Russell, M.D., Ph.D., who recruited him into the Department of Molecular Medicine in Minnesota. When he read about the revolutionary iPS technology, he dove into the arduous task of translating this technology for novel cell therapy applications.

Techniques and Teratomas

What makes the adult cell “return” to a “pluripotent” stem cell form? They must be exposed to the right combination of genetic factors (also called pluripotent or “stemness” factors). Dr. Ikeda introduced the genetic factors Oct3/4, Sox2, Klf4 and c-Myc to transform skin cells into iPS cells, the artificial stem cells. iPS cells have several potential advantages. They can be created from the patient they will be used to treat, thus avoiding the need for anti-rejection drugs that are essential in non-self transplants. And they are available in almost unlimited number, unlike embryonic cell lines. Still, iPS cells are not without their own set of problems.

In addition to finding the right stimulations to redirect the iPS cells into therapeutic cells there is the careful process to avoid teratomas…the development of tumors once the cells are reintroduced and begin to transform arbitrarily into many irrelevant cell types. One way to avoid this is through careful selection.

“Before transplanting the therapeutic cells, we make sure to choose only completely differentiated cells,” says Dr. Ikeda. Limiting the genes that are used at the very start of the process also seems to help avoid tumors. Another approach is to program into the process a form of “self destruct” or cell death for those cells that don’t differentiate.

The goal is to advance iPS technology so it can become a viable platform for regenerating cells to treat a variety of diseases – Type 1 diabetes, heart disease, spinal cord injury, and more. The problems are multiple – each condition or organ is different and cells differentiate based on exposure to unique proteins. More needs to be learned about these particular mechanisms. Still earlier in the process, researchers aren’t sure how efficiently skin cells from elderly patients or patients on multiple medications can be transformed into iPS cells and then differentiated into therapeutic cells. As Dr. Ikeda and his colleagues work out the best options, they are advancing practical collaborations, including regenerative medicine projects focusing on diabetes and heart disease.

Toward a Diabetes Solution

“We are about to begin biopsies on 25 participants with Type 1 diabetes,” says Mayo endocrinologist Yogish Kudva, M.B.B.S. “This is very important research and many patients realize that.”

Dr. Kudva admits that many of his patients are “very enthusiastic” about the research project to regenerate insulin-producing cells from their skin cells. Their transformed cells will be implanted not in their bodies, but initially in animals. This proof of principle study is a first step to evaluate the functionality of the iPS-derived insulin-producing cells. If all goes well research will eventually move toward a human trial – Dr. Kudva nods to an estimate of “at least a couple of years.” Ultimately, the goal is to use iPS cells as a means of eliminating Type 1 diabetes.

With Type 1 diabetes – in which the pancreas produces no or little insulin – a person is much more likely to experience kidney failure. Diabetes in all forms accounts for 43 percent of new cases of kidney failure (end-stage renal disease or ESRD). Roughly half of all those with Type 1 diabetes develop ERSD. Treatment includes kidney and pancreas transplants, with the accompanying risk of surgery, rejection and other complications, not to mention the difficulty of obtaining appropriate organs. Transplanting pancreatic islet cells to produce more insulin is limited due to the difficulty finding an appropriate match and the availability of donor organs.

Dr. Kudva underscores the potential patient benefit: If regenerative medicine, in the form of iPS cell therapy, can prompt the body to produce appropriate levels of insulin, then more people can be helped and the demand for transplant organs will lessen.

Repairing Hearts

Across the street, another collaborator has already shown what iPS cells can do. Andre Terzic, M.D., Ph.D., working with Timothy Nelson, M.D., Ph.D., used cells provided by Dr. Ikeda to regenerate damaged heart tissue in mice. They reported their findings in the journal Circulation online (2009). When they transplanted the “reprogrammed” iPS cells into mice that had experienced infarction (a heart attack), the new cells engrafted after two weeks. After four weeks they were improving the structure and function of the heart. According to Dr. Terzic, the iPS cells restored heart muscle performance, stopped any further structural damage and regenerated tissue at the damaged site. And all this without the looming threat of cell rejection and without the use of limited embryonic stem cell lines.

Dr. Terzic and his team have also worked in recent years to successfully and significantly reduce the threat of teratomas developing as part of cardiac regeneration.

“This lays the groundwork for translational applications,” says Dr. Terzic, who now talks of “customized, on-demand, cardiovascular regenerative medicine.”

He reminds visitors that once someone has suffered a heart attack, they may regain their health, but their heart never regains its previous potential. Part of it remains scarred, essentially useless. If the experience in mice can be replicated in humans, not only would the heart repair itself, even the scar would disappear.

Again, as with the diabetes study, we are years from a possible therapy, but Dr. Ikeda says the various projects they have underway generate knowledge almost every week, adding to the foundations of regenerative and individualized medicine.

“We want to develop a safe and robust method of generating patient-specific iPS cells,” he says. “We have much work to do to develop this platform. But we are very excited by the unlimited potential of iPS technology.”
Stay tuned.

— Bob Nellis, September 2009