Stemming the tide of disease

Jerusalem’s stem cell research center is making strides in the fledgling field.

Stem cells (photo credit: Associated Press)
Stem cells
(photo credit: Associated Press)
TO VISIT THE HUMAN Embryonic Stem Cell Research Center at Hadassah Ein Kerem Medical Center in Jerusalem is to glimpse the seam line between scientific inquiry and its actualization.
Since its establishment in 2003, the research center has gained a sterling world reputation in research on embryonic stem cells. It has produced innovative studies on the development of cell lines, the analysis of the use of stem cells in models of diseases, and controlled inducement of differentiation of stem cells. It recently counted among its many breakthroughs a method for culturing stem cells “in suspension” in a medium (not attached to any surface), which had been assumed impossible because it was thought to lead to uncontrollable cell differentiation. The discovery paves the way for the creation of bulk cultures.
“The significance is that stem cells can be grown in large bioreactors and industrial-scale tanks under finely controlled conditions,” explains center head Dr. Benjamin Reubinoff, an associate professor of obstetrics and gynecology.
“That will be necessary if stem cells are to be made available in the quantities needed to treat millions of people around the world.”
But perhaps most exciting is the sense that, after a decade of hearing about the potential of stem cell therapy to change dramatically the way human disease is treated, and perhaps even to enable the replacement of our worn body parts as easily as new car parts are installed, stem cells are on the cusp of their first clinical trials. The past 10 years have been devoted to basic research, and there are as yet no fully approved treatments using embryonic stem cells. Without clinical trials, there is no way of knowing whether or not stem cell therapy can live up to the tremendous promise that has accompanied its development.
The road from a headline laboratory discovery to a treatment your local doctor can casually prescribe is a very long one, fraught with many hurdles. Even transitioning from the laboratory to the earliest clinical trials is a major challenge.
“We call it ‘crossing death valley,’” says Reubinoff, “and not only because of the tech-nical difficulties involved. It is typically too risky a stage for commercial investors to put their money behind it yet, and at the same time there is no government funding to perform these studies in academia, because they are no longer in the area of basic science research.”
Despite all the risks and difficulties, Reubinoff’s group, through a start-up company established to apply its scientific research, has found the funding it needs and is moving full speed ahead.
EMBRYONIC STEM CELLS ARE cells with a remarkable property: they are pluripotent, meaning that they have the “potential” to become any cell in the body. The cells with which we are familiar in our bodies – blood cells, skin cells, the beating cells of the heart muscle, the insulin-producing cells of the pancreas and so on – are each specialized for their task in keeping the body healthy. But since we all start life as a single cell, immediately after conception, and all our cells come from that initial cell by the process of cell division, there must be cells that are unspecialized but can, under the right conditions, be turned into any mature cell. These are embryonic stem cells.
Stems cells derived from embryos have another remarkable property, which is their capability for infinite self-renewal in culture yet still retaining a normal genetic pattern. Their infinite self-renewal capacity, along with their potential to be turned into any cell, has given rise to the hope that their use can usher in a new age in medical treatment. Since nearly all disease and injury ultimately involve damaged or malfunctioning body cells, replacing damaged cells with healthy cells is a fitting solution.
Though still in the theoretical stages, the vision of stem cell researchers is that eventually “banks” of mass-produced and infinitely fresh stem cell-derived differentiated progeny will be available for therapeutic use. Then if your pancreas is damaged or malfunctioning, for instance, your doctor would in theory take some new young and healthy stem cell-derived pancreas cells, and transplant them directly into you.
The conditions that researchers are currently looking into treating with stem cells include neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, multiple sclerosis, cerebrovascular accidents, spinal cord injuries, as well as heart failure and diabetes.
The number of patients that could potentially benefit from transplantation of stem cells is overwhelming. For example, there are over 16 million patients worldwide with neurodegenerative disorders and over 120 million diabetic patients. Moreover, transplantation of genetically modified stem cells may finally facilitate gene therapy because the modified stem cells would be an ideal “vector” for expressing new genes in target organs.
Before all that can happen, however, scientists have a long way to go in understanding exactly how stem cells can be induced into differentiating into a particular type of desired cell, how they can be efficiently mass produced and stored, and how they can safely be transplanted into humans. There are still more unknowns than knowns in this young field, even before taking into account safety issues.
E VERY HUMAN BEING IS essentially created from the pluripotent stem cells of the embryo, and these stem cells, called human embryonic stem cells, may be derived from embryos.
“We derive stem cells from human embryos, but only from embryos that developed in culture for five to six days after fertilization,” says Reubinoff. “This is done, of course, only after we receive full authorization from the parents, and there is stringent oversight over all of this by an ethics panel of the Ministry of Health.”
Reubinoff and his staff shy away from discussing controversies, which are most pronounced in the United States, surrounding the use of embryonic cells for medical research.
After the Clinton administration permitted research into embryonic stem cells, as long as the embryos were not expressly created for experimentation, president George W. Bush applied a new policy limiting federal funding to be used only for the study of human embryonic stem cells lines that were in existence in 2001, not new ones. Although President Barack Obama removed these restrictions in 2009, federal regulators continue to restrict funding for studies on human embryonic stem cells in the US, due to limiting Congressional provisions.
There is no comparable controversy in Israel, which gives Israeli researchers an advantage. The use of five-day old embryos for medical studies from the standpoint of Jewish religious tradition is less controversial than it is in many Christian theological traditions. In addition, Israel is a world center for in vitro fertilization (IVF) treatment of infertility. Each IVF treatment typically creates a cohort of fertilized embryos. The best quality embryos are implanted into a womb and brought to full term. The others are frozen for future fertility treatments. In the case that the parents have completed their family planning and the frozen embryos are no longer needed for further fertility treatments, they may elect to donate the embryos for research, or to discard them.
Not all stem cell research involves the use of human embryos. There are also adult stem cells; in 2006 it was discovered that it is possible to take mature stem cells and “reprogram” them into induced pluripotent stem cells, which have many properties similar to embryonic stem cells. Reubinoff notes, however, that there are differences between embryonic stem cells and induced pluripotent stem cells. “These differences are still being studied,” he says. “Perhaps one day we will come to the conclusion that adult cells can be used in place of embryonic cells, but for now, we need to continue to study both, to learn what can be accomplished with each of them, as well as to consider whether both are safe for use in human treatment.”
REUBINOFF BRINGS AN IMpressive professional portfolio to his position of director of the embryonic stem cell research center. He completed his medical degree at the Hebrew University of Jerusalem in 1989, and subsequently conducted his internship and residency in Obstetrics and Gynecology, also at the Hadassah Medical School in Jerusalem. In 1999, he earned a PhD in Developmental Biology at Monash University in Australia. While at Monash, Reubinoff was part of a team from Hadassah, Monash and the National University of Singapore that worked on, among other things, the development of human embryonic cell lines – only the second group in the world to do so. On his return to Israel, as a pioneer in the field, he helped move the state to the forefront in embryonic stem cell research.
Indeed, under Reubinoff’s direction, the Hadassah research center group was the first to document that under specific conditions, human embryonic stem cells can be induced to differentiate into a mixture of mature cells, including muscle and nerve cells. The center was also the first to develop nearly fully homogenous populations of neural precursors, which were successfully transplanted into the brains of newborn mice and responded to host brain signals. Researchers at Hadassah hope that these advancements can pave the way for the development of more specialized nerve cells for the treatment of various neurological disorders such as Parkinson’s disease or multiple sclerosis, especially after they showed, for the first time, that transplanting stem-cell derived neural precursor cells induces functional recovery from Parkinson’s in animals.
Reubinoff tells The Report that the current focus of his staff, in collaboration with Prof.
Tamir Ben-Hur of the Neurology Department, is on possible applications of stem cell therapies for neurological diseases, such as multiple sclerosis, Parkinson’s and ALS, and, with Prof.
Eyal Banin of the Ophthalmology Department, on treating age-related macular degeneration (AMD). “AMD is a disease that affects about 30 percent of people above the age of 70 in the Western world, and about 8 percent of them become legally blind because of loss of vision in the center of their visual field,” Reubinoff explains. “It is caused by degeneration of the retinal pigmented cell layer, which then damages the adjacent photoreceptive cells” MOVING THE TRANSITION from research to clinical trials involves several major hurdles. For one thing, most existing human embryonic stem cell lines were developed for research purposes and are likely unsuitable for clinical transplantation.
These cell lines have not been established under appropriate quality assurance conditions. A stem cell line is essentially a family of cells cultured in laboratories, all of which originated from a parent group of stem cells from a single embryo. All the cells within a single cell line carry identical genetic material. They typically get the nutrients they need from mouse embryonic fibroblasts (a form of “feeder cells”), and therefore, may potentially transfer mouse pathogens to human recipients. A lot of work is required to develop new, animal-free cell lines that will be suitable for clinical transplantation.
“The majority of existing stem cell lines were derived for research purposes alone,” says Reubinoff. “For human use, we need to develop stem cell lines grown under more tightly monitored conditions and using reagents that are animal-free.”
In addition, protocols for ensuring that human embryonic stem cells are directed into differentiating into a pure culture of a single cell type, such as a cardiac cell or a neuron, instead of a mixture of different types of cells, must be developed and improved.
Hadassah team member Malkiel Cohen has been studying this problem as part of his doctoral research. “Essentially, we are trying to mimic in the lab the way cells develop and differentiate in embryos,” explains Cohen. “In my research, I identified two main factors that control the development of stem cells uniformly into neural cells.” Cohen is shy about taking credit for his work, and when asked about his plans for the near future, he says only that he has been accepted to a post-doctoral fellowship at “a private institute in the Boston area,” which, after some prompting, he reveals to be the Massachusetts Institute of Technology.
The Hadassah team has also published a paper on a novel protocol for directing stem cells to differentiate into retinal pigmented cells.
“When transplanted into the eyes of rats, these pigmented retinal cells rescue the function of the adjacent photoreceptor cells, significantly delaying loss of vision,” says Reubinoff. “We chose to concentrate on treatment of this disease for early clinical trials, because there is proof of concept in patients that replacing the degenerating pigmented cells with more healthy ones can improve visual function. In addition, the eye affords easy access for follow-up, and since it is a relatively confined organ, dissemination of the transplanted cells to affect other parts of the body is less likely.”
The directed differentiation of human embryonic stem cells into retinal pigmented cells has been a focus of the work of Hanita Khaner, also a team member, who for the past two years has also been working on what is known as “translational research” – the steps involved in transitioning from animal testing of stem cell therapies to human clinical trials.
In order to cross that “death valley” of the biomedical industry, in 2006 the Hadassah team established the start-up Cell Cure Neurosciences Ltd. The basic research it has conducted has been sufficiently impressive to attract private funding, but the amount of work involved is massive, says Khaner.
“When I started, I thought that within two to three months I would translate the basic research protocols for getting embryonic stem cells to differentiate into retinal pigmented cells to protocols that will be suitable for use in clinical trials, but it took 18 months,” she tells The Report. “This involves using clinical grade cell lines instead of research grade lines, and replacing animal-derived reagents with high quality human or recombinant reagents, which is not trivial. Different protocols and reagents need to be developed for human use.”
The Hadassah team now hopes that it will be ready for clinical human trials involving retinal cells in about two years. Getting there will involve many safety studies. If implanted cells include undifferentiated stem cells, instead of a uniform mass of retinal pigmented cells, there is a danger of tumors developing. Avoiding this is a safety-critical issue.
Another aspect of stem cell research that the Hadassah team is tackling is graft rejection, which is a common outcome of the grafting of mature cells or tissues between two genetically unrelated individuals. The team is studying the immune response that is provoked by human embryonic stem cells as the basis for the development of strategies to avoid immunological rejection.
Reubinoff relates a vision for overcoming rejection by establishing “banks” filled with a large variety of stem cell lines. Transplant rejection is due to the immune system of the recipient discerning transplanted cells as foreign, based on what is known as the serotype of the transplanted cells. The closer the serotype of the donor is to that of the recipient, the less likely the transplant will be rejected.
“If we can create banks from enough different stem cell lines, with sufficiently different markers,” says Reubinoff, “then we could cover the majority of the population. It is only a vision right now, but work is already beginning to establish these banks, which could have a large impact.”