Researchers to push frontiers of stem cell studies

Steve Fisch Photography

Renee Reijo Pera joined the Stanford faculty this year, coming from UC-San Francisco, to lead work at the Institute for Stem Cell Biology and Regenerative Medicine.

Stanford's stem cell institute has been ramping up its research program for the world-class effort needed to create new human embryonic stem cell lines, a crucial step to developing treatments for diabetes, Parkinson's disease, Alzheimer's disease and many other disorders.

Over the past year, the Institute for Stem Cell Biology and Regenerative Medicine has gathered momentum from several sources, including newly remodeled space off campus, a handful of new grants from California's $3 billion stem cell institute, and the arrival of top-notch researchers including Renee Reijo Pera, PhD, professor of obstetrics and gynecology, to lead the efforts.

Reijo Pera, who came to Stanford in May, said recent advances from other universities would provide encouragement and new ideas for Stanford researchers engaged in the effort to create new stem cell lines. The recent work by researchers in Wisconsin and Japan, who reprogrammed adult skin cells to behave like embryonic stem cells, is one good example. "It's a very exciting time to be working in this field," she said. "There's a great mystery about the best ways of creating these cell lines in humans and in how to work with the cells."

Embryonic stem cells have the ability to become any type of cell in the body. With this great potential, many researchers believe they could be used to replace cells damaged by injury or disease.

Another use for the cells, less often cited but a potentially major source of medical advances, is as a research tool. Studying embryonic stem cells derived from an adult genetically predisposed to a disease, for example, could reveal how that disease develops or lead to new ways of treating the disease when it occurs.

For any of these future benefits to pan out, researchers need access to more types of human embryonic stem cell lines. The ones that are currently available are difficult to work with in the lab and often have genetic abnormalities. The available cells also all come from embryos left over after couples underwent in vitro fertilization, or IVF. These aren't the best source of stem cell lines, in part because the cells reflect the mostly Caucasian genetics of people who visit IVF clinics.

The cells from IVF embryos may also trigger an immune reaction when used as a therapy, because they are not identical to the person being treated. An ideal situation would be to create new embryonic stem cell lines from the adult cell of a person undergoing treatment.

Until recently, that's been possible only in animals such as mice and sheep. But the recent human success from researchers in Japan and Wisconsin gives Reijo Pera hope that Stanford can pursue advances in this area as well.

Researchers at the School of Medicine are pursuing three different approaches in an effort to create the new embryonic stem cells researchers need to tap the full potential of the field.

IVF embryos

Despite the lack of genetic diversity in leftover IVF embryos, Reijo Pera said, they still constitute one major thrust of efforts to create new stem cell lines at Stanford. Julie Baker, PhD, assistant professor of genetics, has spent several years pursuing those very stem cell lines in collaboration with Barry Behr, PhD, associate professor of obstetrics and gynecology, and Eric Chiao, PhD, a research associate.

Together, they've created four new embryonic stem cell lines from IVF embryos that would otherwise have been discarded. Baker recently received a grant from the California Institute for Regenerative Medicine to extend that work to include embryos known to be predisposed to Downs syndrome, cystic fibrosis or muscular dystrophy. Baker hopes stem cell lines created from these embryos will be a valuable research tool for people trying to understand how to treat these genetic diseases.

Transferring the cell's nucleus

Despite these advances with IVF embryos, a major unmet goal of stem cell research is to create stem cells that are genetically identical to a specific person. One way of going about this is called nuclear transfer. In this technique, researchers remove the nucleus from an egg, replace it with the nucleus from a person's adult body cell, then stimulate that egg to develop as if it had been fertilized. After a few days, researchers can remove embryonic stem cells that carry exactly the same DNA as the adult cell that provided the nucleus. This technique would allow researchers to create stem cells from people with known genetic predispositions to diseases, or to create cells that could be used in therapies.

So far this technique hasn't worked in humans, and that's not for lack of trying. In 2004 researchers in South Korea announced success with nuclear transfer in humans, but last year that finding was revealed to be fraudulent. Since then, a few papers have been published that provide some ideas for new ways of going about the research.

The recent Nature paper by James Byrne, PhD, and his colleagues at Oregon Health Sciences University reported a major milestone—nuclear transfer producing two new embryonic stem cell lines in monkeys—which is a significant step toward achieving nuclear transfer in humans. Until that paper, the barrier to carrying out nuclear transfer in primates seemed so significant some researchers argued it couldn't be done.

"That puts what James is doing in perspective because his is the first primate stem cell line created through nuclear transfer," said Reijo Pera. "Now people can't argue that it can't be done."

Byrne moved to Stanford in July and is now a postdoctoral scholar working with Reijo Pera, and she hopes to adopt some of the techniques that made the Oregon team successful in monkeys. Byrne said the key to his success was in how he and his Oregon colleagues removed the nucleus from the egg. Past efforts had involved using a microscope that exposed the egg to damaging ultraviolet light. Once the group tried a different type of microscope to see and then remove the nucleus, their success rate skyrocketed.

"The next obvious step is to try this same technique in humans," Byrne said.

Reijo Pera said that another recent Nature paper points the way to overcoming a second obstacle to nuclear transfer in humans: acquiring eggs. The process of nuclear transfer requires human eggs, which have been a source of logistical and ethical concerns. Women are reluctant to undergo the often painful and time-consuming procedure to harvest eggs, simply for research purposes. Those who do go through the processes of harvesting eggs for IVF generally don't have any eggs left over after the procedure. That begs the question of where to get human eggs for nuclear transfer experiments.

But there may be an alternative. According to new work in mice by stem cell researchers at Harvard, it may be possible to use eggs that had failed to fertilize properly during IVF. These eggs, which begin to divide but then quickly stop, would normally be thrown out. It turns out that researchers were able to use such eggs to carry out nuclear transfer and generate new stem cell lines in mice.

"Working with Stanford's IVF clinic we have a chance to make use of these otherwise rejected eggs," Reijo Pera said. "That's a big advantage to being at Stanford."

Between alternate sources for eggs and a fresh approach to how they remove the egg's nucleus in preparation to receive an adult nucleus, she thinks her group might have a chance at succeeding where others have failed to create human stem cell lines using nuclear transfer.

Reprogramming adult cells

The announcement Nov. 20 that researchers in Wisconsin and Japan had reprogrammed adult human skin cells to act like embryonic stem cells reignites another path creating new stem cell lines. This approach avoids the need for human eggs and doesn't generate embryos, eliminating what, to some, are ethically troubling elements of nuclear transfer.

At Stanford, Thomas Wandless, PhD, assistant professor of chemical and systems biology, has a CIRM grant to investigate ways of reprogramming adult human cells and to better understand what's happening to the nuclei of adult cells when they get reprogrammed to an embryonic state.

Each of these techniques of generating embryonic stem cells involves different challenges and possible benefits, according to Reijo Pera. "For now we're betting on all approaches," she said.