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For the first time, scientists at the University of Wisconsin-Madison have made early retina structures containing proliferating neuroretinal progenitor cells using induced pluripotent stem (iPS) cells derived from human blood.

And in another advance, the retina structures showed the capacity to form layers of cells—as the retina does in normal human development—and these cells possessed the machinery that could allow them to communicate information. (Light-sensitive photoreceptor cells in the retina along the back wall of the eye produce impulses that are ultimately transmitted through the optic nerve and then to the brain, allowing you to see.)

Put together, these findings suggest that it is possible to assemble human retinal cells into more complex retinal tissues, all starting from a routine patient blood sample.

Many applications of laboratory-built human retinal tissues can be envisioned, including using them to test drugs and study degenerative diseases of the retina such as retinitis pigmentosa, a prominent cause of blindness in children and young adults. One day, it may also be possible replace multiple layers of the retina in order to help patients with more widespread retinal damage.

"We don't know how far this technology will take us, but the fact that we are able to grow a rudimentary retina structure from a patient's blood cells is encouraging, not only because it confirms our earlier work using human skin cells, but also because blood as a starting source is convenient to obtain," says David Gamm, MD, pediatric ophthalmologist and senior author of the study. "This is a solid step forward."

In 2011, the Gamm laboratory at the Waisman Center created structures from the most primitive stage of retinal development using embryonic stem cells and stem cells derived from human skin. While those structures generated the major types of retinal cells, including photoreceptors, they lacked the organization found in more mature retina.

This time, the team, led by Gamm, assistant professor of ophthalmology and visual sciences in the UW School of Medicine and Public Health, and postdoctoral researcher and lead author Joseph Phillips, used their method to grow retina-like tissue from iPS cells derived from human blood gathered via standard blood draw techniques.

In their study, about 16% of the initial retinal structures developed distinct layers. The outermost layer primarily contained photoreceptors, whereas the middle and inner layers harbored intermediary retinal neurons and ganglion cells, respectively. This particular arrangement of cells is reminiscent of what is found in the back of the eye.

Further, work by Phillips showed that these retinal cells were capable of making synapses, a prerequisite for them to communicate with one another.

The iPS cells used in the study were generated through collaboration with Cellular Dynamics International (CDI) of Madison, Wisconsin, which pioneered the technique to convert blood cells into iPS cells. CDI scientists extracted a type of blood cell called a T-lymphocyte from the donor sample, and reprogrammed the cells into iPS cells. Cellular Dynamics International was founded by UW-Madison stem cell pioneer James Thomson.

"We were fortunate that CDI shared an interest in our work. Combining our lab's expertise with that of CDI was critical to the success of this study," added Gamm.

The results were published in an online issue of Investigative Ophthalmology & Visual Science.

Science
Vol. 335 no. 6073 p. 1153
DOI: 10.1126/science.335.6073.1153-b

Newsmakers

Bioethicist Leaves Texas Stem Cell Bank

Controversial bioethicist Glenn McGee resigned last week from a Texas company that banks adult stem cells for use in medical treatments.

McGee drew attention last month for serving as editor-in-chief of the American Journal of Bioethics (AJOB) while working since December for CellTex Therapeutics in Houston. The company licenses technology from a South Korean company, RNL Bio, that treats people with various medical conditions with adult stem cells processed from the patients' own fat cells. Such treatments have not been approved for routine use by U.S. regulators. Critics suggested that McGee's employment with CellTex posed a conflict of interest with his AJOB duties.

Last week, Nature reported that CellTex has allegedly been paying a physician in Texas to inject patients with stem cells prepared by CellTex, probably illegally. Later that day, McGee announced his departure from CellTex on Twitter. “Enough,” he wrote, adding: “I am preparing timely, lengthy, pointed comments on the whole matter.”

New Stem Cells Could Aid Transplant Studies

April 6, 2012

Researchers have generated a new type of human stem cell that can develop into numerous types of specialized cells, including functioning pancreatic beta cells that produce insulin. Called endodermal progenitor (EP) cells, the new cells show two important advantages over embryonic stem cells and induced pluripotent stem cells: they do not form tumors when transplanted into animals, and they can form functional pancreatic beta cells in the laboratory.

"Our cell line offers a powerful new tool for modeling how many human diseases develop," says study leader Paul Gadue, a stem cell biologist in the Center for Cellular and Molecular Therapeutics at The Children's Hospital of Philadelphia. "Additionally, pancreatic beta cells generated from EP cells display better functional ability in the laboratory than beta cells derived from other stem cell populations."

In addition to producing beta cells, the researchers also directed EP cells to develop into liver cells and intestinal cells--both of which normally develop from the endoderm tissue layer early in human development.

Gadue and colleagues are publishing their study today, April 6, in the journal Cell Stem Cell.

The researchers manipulated two types of human stem cells — embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) — to become EP cells. Because both stem cell populations proliferate in great numbers and potentially generate all types of tissue, they offer enormous promise for scientists to precisely control cell development, both for the study of basic biology and for future cell-based treatments.

ESCs are derived from human embryos, typically unused embryos from fertility treatments that are donated for research purposes, while iPSCs are engineered from human somatic cells, such as skin cells or blood cells. Researchers have learned how to reprogram somatic cells to become pluripotent. Like ESCs, iPSCs are able to develop into many other types of human cells. However, when undifferentiated ESCs or iPSCs are transplanted in animal studies, they form teratomas, tumors containing many different cell types. Therefore, it has been critical that any cell type generated from ESCs or iPSCs and used for transplantation is stringently purified to exclude undifferentiated cells with tumor-forming potential.

In the current study, the researchers used signaling molecules called cytokines to steer ESCs and iPSCs into becoming EP cells, committed to developing into endoderm, one of the three tissue layers found in early human development. The EP cells have nearly unlimited potential for growth in the laboratory.

Both in cell cultures and when transplanted into animals, the study team showed that EP cells can differentiate into multiple cell types, representing those found in the liver, pancreas and intestine. Importantly, undifferentiated EP cells did not form teratomas in the team's transplantation studies.

In cell culture, the researchers differentiated the EP cells into beta cells--insulin-expressing cells similar to those found in the pancreas. Those engineered beta cells passed an important test--when stimulated by glucose, they were able to release insulin, a function that is impaired or absent in patients with diabetes. While the cells achieved only 20 percent of normal function, this result is an improvement over that seen in similar cells derived directly from ESCs or iPSCs, which typically respond very poorly or not at all to glucose.



Gadue stressed that these promising early results are only the first steps in researching EP cells. Further work may focus on taking cells from individual patients with genetic forms of diabetes or liver disease to derive EP cell lines. The EP cell lines can then be used to model the development and progression of the patient's disease and discover new therapies for that particular disease.

Finally, although applying this science to cell therapy is years away from practical clinical use, EP cells may offer a powerful starting point for developing tissue replacement treatments, such as supplying beta cells for diabetes patients or hepatocytes (liver cells) for patients with liver disease. "While more work is needed to characterize EP cells, they may offer a potential source of safe, abundant cells for future diabetes treatments," says Gadue.

Source: The Children's Hospital of Philadelphia

 

Organ replacement regenerative therapy is purported to enable the replacement of organs damaged by disease, injury or ageing in the foreseeable future. A research group led by Professor Takashi Tsuji (Professor in the Research Institute for Science and Technology, Tokyo University of Science, and Director of Organ Technologies Inc.) has provided a proof-of-concept for bioengineered organ replacement as a next stage of regenerative therapy.

Reporting in Nature Communications, the group demonstrated that bioengineered hair follicle germ reconstructed from adult epithelial stem cells and dermal papilla cells can regenerate fully functional hair follicle and hair growth. Their bioengineered follicles showed restored hair cycles and piloerection through the rearrangement of follicular stem cells and their niches. The bioengineered hair follicle also developed the correct structures and formed proper connections with surrounding host tissues such as the epidermis, arrector pili muscle and nerve fibers. This study thus reveals the potential applications of adult tissue-derived follicular stem cells as a bioengineered organ replacement therapy.

This was collaborative research with Lecturer Tarou Irié and Professor emertius Tetsuhiko Tachikawa (Department of Oral Pathology, Showa University School of Dentistry, Japan), Professor Akio Sato (Department Regenerative Medicine, Plastic and Reconstructive Surgery, Kitasato University School of Medicine, Japan) and Associate Professor Akira Takeda (Department of Plastic and Aesthetic Surgery, Kitasato University School of Medicine, Japan).

Full article on research2

Source:
Tokyo University of Science via ResearchSEA

New Method Generates Cardiac Muscle Patches from Stem Cells

Featured In: Academia News | Cardiovascular

Tuesday, June 19, 2012

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A cutting-edge method developed at the University of Michigan Center for Arrhythmia Research successfully uses stem cells to create heart cells capable of mimicking the heart’s crucial squeezing action.

The cells displayed activity similar to most people’s resting heart rate. At 60 beats per minute, the rhythmic electrical impulse transmission of the engineered cells in the U-M study is 10 times faster than in most other reported stem cell studies.

An image of the electrically stimulated cardiac cells is displayed on the cover of the current issue of Circulation Research, a publication of the American Heart Association.

For those suffering from common, but deadly, heart diseases, stem cell biology represents a new medical frontier.

The U-M team of researchers is using stem cells in hopes of helping the 2.5 million people with an arrhythmia, an irregularity in the heart’s electrical impulses that can impair the heart’s ability to pump blood.

“To date, the majority of studies using induced pluripotent stem cell-derived cardiac muscle cells have focused on single cell functional analysis,” says senior author Todd J. Herron, Ph.D., an assistant research professor in the Departments of Internal Medicine and Molecular & Integrative Physiology at the U-M.

“For potential stem cell-based cardiac regeneration therapies for heart disease, however, it is critical to develop multi-cellular tissue like constructs that beat as a single unit,” says Herron.

Their objective, working with researchers at the University of Oxford, Imperial College and University of Wisconsin, included developing a bioengineering approach, using stem cells generated from skin biopsies, which can be used to create large numbers of cardiac muscle cells that can transmit uniform electrical impulses and function as a unit.

Furthermore, the team designed a fluorescent imaging platform using light emitting diode (LED) illumination to measure the electrical activity of the cells.

“Action potential and calcium wave impulse propogation trigger each normal heart beat, so it is imperative to record each parameter in bioengineered human cardiac patches,” Herron says.

Authors of the study note that the velocity of the engineered cardiac cells, while faster than previous reports, it is still slower than the velocity observed in the beating adult heart.

Still the velocity is comparable to commonly used rodent cells, and authors suggest human cardiac patches could be used rather than rodent systems for research purposes.

The new method can be readily applied in most cardiac research laboratories and opens the door for the use of cardiac stem cell patches in disease research, testing of new drug treatments and therapies to repair damaged heart muscle.

Source: University of Michigan

 

Science
Vol. 336 no. 6088 p. 1488
DOI: 10.1126/science.336.6088.1488

Stem Cell Hope for Vision, Brain

Bone marrow transplants have been used for decades, but research presented last week in Yokohama, Japan, at the annual meeting of the International Society for Stem Cell Research (ISSCR) confirmed that scientists are making progress at developing more innovative stem cell therapies.

A research team from the RIKEN Center for Developmental Biology in Kobe presented animal studies indicating that stem cells created from a person's own cells could be turned into retinal cells that treat a form of age-related macular degeneration. And StemCells Inc. of Newark, California, reported encouraging results from transplants of human neural stems into four infants with Pelizaeus-Merzbacher disease (PMD), a progressive and fatal disorder in which a genetic mutation inhibits the normal growth of myelin, a protective material that envelopes nerve fibers in the brain.

In the clinical trial conducted by researchers at the University of California, San Francisco, magnetic resonance imaging taken 18 months after the transplants indicated the formation of new myelin around axons, and clinical observations of treated infants indicated that their motor functions remained stable or enjoyed modest gains. The company is planning larger trials; an official says that if the therapy proves efficacious, it could lead to treatments for multiple sclerosis, cerebral palsy, and Alzheimer's disease. http://scim.ag/primestem

Lab-engineered muscle implants restore function in animals

Posted In: R&D Daily | Biology | Biotechnology | Genetic Engineering | Medical Technology | Technology | Biology | Biotechnology | Biotechnology | Scientific & Medical Instrumentation

Monday, July 16, 2012


New research shows that exercise is a key step in building a muscle-like implant in the lab with the potential to repair muscle damage from injury or disease. In mice, these implants successfully prompt the regeneration and repair of damaged or lost muscle tissue, resulting in significant functional improvement.

"While the body has a capacity to repair small defects in skeletal muscle, the only option for larger defects is to surgically move muscle from one part of the body to another. This is like robbing Peter to pay Paul," said George Christ, Ph.D., a professor at Wake Forest Baptist Medical Center's Institute for Regenerative Medicine. "Rather than moving existing muscle, our aim is to help the body grow new muscle."

In the current issue of Tissue Engineering Part A, Christ and team build on their prior work and report their second round of experiments showing that placing cells derived from muscle tissue on a strip of biocompatible material—and then "exercising" the strip in the lab—results in a muscle-like implant that can prompt muscle regeneration and significant functional recovery. The researchers hope the treatment can one day help patients with muscle defects ranging from cleft lip and palate to those caused by traumatic injuries or surgery.

For the study, small samples of muscle tissue from rats and mice were processed to extract cells, which were then multiplied in the lab. The cells, at a rate of 1 million per square centimeter, were placed onto strips of a natural biological material. The material, derived from pig bladder with all cells removed, is known to be compatible with the body.

Next, the strips were placed in a computer-controlled device that slowly expands and contracts—essentially "educating" the implants on how to perform in the body. This cyclic stretching and relaxation occurred three times per minute for the first five minutes of each hour for about a week. In the current study, the scientists tried several different protocols, such as adding more cells to the strips during the exercise process.

The next step was implanting the strips in mice with about half of a large muscle in the back (latissimus dorsi) removed to create functional impairment. While the strips are "muscle-like" at the time of implantation, they are not yet functional. Implantation in the body—sometimes referred to as "nature's incubator"—prompts further development.

The goal of the project was to speed up the body's natural recovery process as well as prompt the development of new muscle tissue. The scientists compared four groups of mice. One group received no surgical repair. The other groups received implants prepared in one of three ways: one was not exercised before implantation, one was exercised for five to seven days, and one had extra cells added midway through the exercise process. The results showed that exercising the implants made a significant difference in both muscle development and function.

"The implant that wasn't exercised, or pre-conditioned, was able to accelerate the repair process, but recovery then stopped," said Christ. "On the other hand, when you exercise the implant, there is a more prolonged and extensive functional recovery. Through exercising the implant, you can increase both the rate and the magnitude of the recovery."

A variety of laboratory tests were used to measure results. A test of muscle force at two months, for example, showed that animals who received the implants with extra cells added had a threefold increase in absolute force compared to animals whose muscle damage was not repaired. The force-producing capacity of muscle is what determines the ability to perform everyday tasks.

"If these same results were repeated in humans, the recovery in function would clearly be considered significant," said Christ. "Within two months after implantation, the force generated by the repaired muscle is 70% that of native tissue, compared to 30% in animals that didn't receive repair."

The results also showed that new muscle tissue developed both in the implant, as well as in the area where the implant and native tissue met, suggesting that the implant works by accelerating the body's natural healing response, as well as by prompting the growth of new muscle tissue.

The researchers hope to evaluate the treatment in patients who need additional surgery for cleft lip and palate, a relatively common birth defect where there is a gap in muscle tissue required for normal facial development. These children commonly undergo multiple surgeries that involve moving muscle from one location to another or stretching existing muscle tissue to cover the tissue gap. The implant used in the current research is almost exactly the size required for these surgeries.

"As a surgeon I am excited about the advances in tissue-engineered muscle repair, which have been very promising and exciting potential in the surgical correction of both functional and cosmetic deformities in cleft lip and cleft palate" said Phillip N. Freeman, M.D., D.M.D., associate professor of Oral and Maxillofacial Surgery at the University of Texas Health Science Center at Houston. "Current technology does not address the inadequate muscle volume or function that is necessary for complete correction in 20 to 30% of cases. With this innovative technology there is the potential to make significant advances in more complete corrections of cleft lip and cleft palate patients."

The technology was originally developed under the Armed Forces Institute of Regenerative Medicine (AFIRM) with funding from the Department of Defense and the National Institutes of Health. The sponsor of the current research was the Telemedicine & Advanced Technology Research Center. A longer-term goal is to use the implant—in combination with other tissue-engineered implants and technologies being developed as part of AFIRM—to treat the severe head and facial injuries sustained by military personnel. For example, AFIRM-sponsored projects under way to engineer bone, skin and nerve may one day be combined to make a "composite" tissue.

 

Muscle Cell Grafts Keep Broken Hearts from Breaking Rhythm

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Researchers have made a major advance in efforts to regenerate damaged hearts. They discovered that transplanted heart muscle cells, grown from stem cells, electrically couple and beat in sync with the heart’s own mucle. The grafts also reduced the incidence of arrhythmias (irregular heart rhythms) in a guinea pig model of myocardial infarction (commonly known as a heart attack).

This finding from University of Washington-led research is reported in the Aug. 5 issue of Nature.

The paper’s senior author, Dr. Michael Laflamme, said, “These results provide strong evidence that human cardiac muscle cell grafts meet physiological criteria for true heart regeneration. This supports the continued development of human embryonic stem cell-based heart therapies for both mechanical and electrical repair of the heart.”

During a myocardial infarction the flow of oxygen-rich blood to the heart muscle is interrupted by formation of a clot, causing death of the down-stream heart muscle and its eventual replacement by scar tissue. This can cause mechanical problems with filling and emptying the heart, and it can also interfere with the electrical signals that pace the heartbeat.

In this study, the guinea pigs’ hearts had an injury to the left ventricle, the thick walled lower chamber in the heart that pumps oxygenated blood to the body. The injury left a scar and thinned the ventricle, which showed both reduced pump function and greater susceptibility to arrhythmias.

Injured hearts that received the human cardiac muscle cell grafts showed partial re-muscularization of the scarred left ventricle.

Consistent with previous studies, tests showed that the injured hearts with the human cardiac cell grafts had improved mechanical function.

More surprisingly, these hearts showed fewer arrhythmias than did injured hearts without such grafts.

“We showed a couple years ago that transplanting human embryonic stem cell-derived heart muscle cells improves the pumping activity of injured hearts,” said Dr. Michael Laflamme, UW associate professor of pathology and a member of the UW Center for Cardiovascular Biology and the Institute for Stem Cell & Regenerative Medicine.

“In this recent paper,” he explained, “we show that the transplantation of these cells also reduces the incidence of arrhythmias [heart rhythm disturbances].”

Laflamme and Dr. Charles E. Murry, UW professor of pathology, bioengineering and medicine, Division of Cardiology, were the senior authors of the paper. The lead authors were Drs. Yuji Shiba and Sarah Fernandes in the UW Department of Pathology. Shiba is also from the Department of Cardiovascular Medicine at Shinshu University in Japan.

Because arrhythmias are a major cause of death in patients after a heart attack, Laflamme pointed out, this effect might be clinically useful if proven successful in large animal models as well.

Scientists had been worried that transplanting heart muscle cells derived from embryonic stem cells would promote arrhythmias.

“Instead, they suppress arrhythmias, at least in the guinea pig model,” Laflamme and his team were pleased to discover.

While Laflamme and Murry had previously shown that transplanting these types of cell grafts improved pump function in injured hearts, Laflamme noted that it had not been previously determined if the grafts actually coupled and fired synchronously with heart’s original muscle.

There was the possibility, he suggested, that they exerted their beneficial effects indirectly, perhaps by releasing signaling molecules, rather than by forming new force-generating units.

“In our study, we discovered that the heart cell grafts do, in fact, couple to the guinea pig hearts,” he said.

The research team found the heart cell grafts electrically coupled in all of the normal, uninjured hearts into which they were transplanted, and in the majority of the injured hearts.

The researchers were able to observe this coupling by transplanting human heart muscle cells that were genetically modified to flash every time they fired. By correlating this optical signal from the graft cells with the electrocardiogram – electrical signals from the recipient heart – the researchers were able to determine whether cell grafts were electrically coupled with the animal’s heart.

Source: University of Washington

 

Aging heart cells rejuvenated by modified stem cells

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Damaged and aged heart tissue of older heart failure patients was rejuvenated by stem cells modified by scientists, according to research presented at the American Heart Association’s Basic Cardiovascular Sciences 2012 Scientific Sessions.

The study is simultaneously published in the Journal of the American College of Cardiology.

The research could one day lead to new treatments for heart failure patients, researchers said.

“Since patients with heart failure are normally elderly, their cardiac stem cells aren’t very healthy,” said Sadia Mohsin, Ph.D., one of the study authors and a post-doctoral research scholar at San Diego State University’s Heart Institute in San Diego, Cal. “We modified these biopsied stem cells and made them healthier. It is like turning back the clock so these cells can thrive again.”

Modified human stem cells helped the signaling and structure of the heart cells, which were biopsied from elderly patients. Researchers modified the stem cells in the laboratory with PIM-1, a protein that promotes cell survival and growth.

Cells were rejuvenated when the modified stem cells enhanced activity of an enzyme called telomerase, which elongates telomere length. Telomeres are “caps” on the ends of chromosomes that facilitate cell replication. Aging and disease results when telomeres break off.
“There is no doubt that stem cells can be used to counter the aging process of cardiac cells caused by telomere degradation,” Mohsin said.

The technique increased telomere length and activity, as well as increasing cardiac stem cell proliferation, all vital steps in combating heart failure.

While human cells were used, the research was limited to the laboratory. Researchers have tested the technique in mice and pigs and found that telomere lengthening leads to new heart tissue growth in just four weeks.

“Modifying aged human cardiac cells from elderly patients adds to the cell’s ability to regenerate damaged heart muscle, making stem cell engineering a viable option,” Mohsin said. “This is an especially exciting finding for heart failure patients. Right now we can only offer medication, heart transplantation or stem cell therapies with modest regenerative potential, but PIM-1 modification offers a significant advance for clinical treatment.”

Source: American Heart Association

Science
Vol. 336 no. 6088 p. 1488
DOI: 10.1126/science.336.6088.1488

Stem Cell Hope for Vision, Brain

Bone marrow transplants have been used for decades, but research presented last week in Yokohama, Japan, at the annual meeting of the International Society for Stem Cell Research (ISSCR) confirmed that scientists are making progress at developing more innovative stem cell therapies.

Figure
CREDIT: NISSIM BENVENISTY

A research team from the RIKEN Center for Developmental Biology in Kobe presented animal studies indicating that stem cells created from a person's own cells could be turned into retinal cells that treat a form of age-related macular degeneration. And StemCells Inc. of Newark, California, reported encouraging results from transplants of human neural stems into four infants with Pelizaeus-Merzbacher disease (PMD), a progressive and fatal disorder in which a genetic mutation inhibits the normal growth of myelin, a protective material that envelopes nerve fibers in the brain.

In the clinical trial conducted by researchers at the University of California, San Francisco, magnetic resonance imaging taken 18 months after the transplants indicated the formation of new myelin around axons, and clinical observations of treated infants indicated that their motor functions remained stable or enjoyed modest gains. The company is planning larger trials; an official says that if the therapy proves efficacious, it could lead to treatments for multiple sclerosis, cerebral palsy, and Alzheimer's disease. http://scim.ag/primestem

 

Human stem cells restore hearing in gerbil study

Posted In: Strange But True | Biology | Biotechnology | Gene Therapy | Medical Technology | Stem Cell Research | Biology | University of California, San Francisco

By Malcolm Ritter, Associated Press

Thursday, September 13, 2012

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NEW YORK (AP)—For the first time, scientists have improved hearing in deaf animals by using human embryonic stem cells, an encouraging step for someday treating people with certain hearing disorders.

"It's a dynamite study (and) a significant leap forward," said one expert familiar with the work, Dr. Lawrence Lustig of the University of California, San Francisco.

The experiment involved an uncommon form of deafness, one that affects fewer than 1% to perhaps 15% of hearing-impaired people. And the treatment wouldn't necessarily apply to all cases of that disorder. Scientists hope the approach can be expanded to help with more common forms of deafness. But in any case, it will be years before human patients might benefit.

Results of the work, done in gerbils, were reported online Wednesday in the journal Nature by a team led by Dr. Marcelo Rivolta of the University of Sheffield in England.

To make the gerbils deaf in one ear, scientists killed nerve cells that transmit information from the ear to the brain. The experiment was aimed at replacing those cells.

Human embryonic stem cells can be manipulated to produce any type of cell. Using them is controversial because they are initially obtained by destroying embryos. Once recovered, stem cells can be grown and maintained in a lab and the experiment used cells from lab cultures.

The stem cells were used to make immature nerve cells. Those were then transplanted into the deaf ears of 18 gerbils.

Ten weeks later, the rodents' hearing ability had improved by an average of 46%, with recovery ranging from modest to almost complete, the researchers reported.

And how did they know the gerbils could hear in their deafened ears? They measured hearing ability by recording the response of the brain stem to sound.

The gerbils were kept on medication to avoid rejecting the human cells, much like people who get transplants of human organs, Rivolta said. But that might not be necessary if the procedure proceeds to people, he said. Scientists may be able to work with stem cells that closely match a patient, or even use a different technology to make the transplanted cells from a patient's own tissue, he said.

Rivolta's team also reported making immature versions of a second kind of inner-ear cell. Transplants of those cells might be able to treat far more cases of hearing loss. But the team has not yet tested these in animals, Rivolta said.

Yehoash Raphael of the University of Michigan, who didn't participate in the work, said it's possible the stem cell transplants worked by stimulating the gerbils' own few remaining nerve cells, rather than creating new ones. But either way, "this is a big step forward in use of stem cells for treating deafness," he said.