Researchers Reveal New Prospects
for Treating Muscular Dystrophy

Immunofluorescence image showing the stem-cell induced tissue replacement in mouse muscle cells. The green represents muscle fibers that were built thanks to stem cells with the corrected gene. The opposite leg of the mouse did not receive the new treatment described in this study. Without treatment with stem cells carrying a corrected version of the gene, the muscle building seen in the above image (and visualized by the green muscle fibers) barely occurred. Image © Science

Inside a glass-clad building in Milan on Thursday, 10 July, Giulo Cossu from the Scientific Institute San Raffaele and Roberto Bottinelli from the University of Pavia described, to a room full of journalists, a mouse study that may lead to new prospects for treating muscular dystrophy (MD). The researchers injected stem cells carrying a corrected version of a gene involved in muscle building into the bloodstreams of mice suffering from a condition comparable to one type of muscular dystrophy that afflicts humans. This work appears on-line today at the Science Express web site, Science's rapid, electronic publishing system.

The authors caution that more research must be done before researchers consider applying these findings to humans. Nonetheless, their results provide a possible new direction for efforts that have met largely with frustration thus far.

Cossu and his team found that the engineered stem cells can cross from the bloodstream into muscle tissue. There, they seem to take on a new identity, helping to generate new muscle fibers in mice with MD-like symptoms.

MD is a collection of disorders caused by genetic defects that lead to increasing muscle weakness over time. These disorders currently have no cure.

"Although these results are exciting, we have not cured the mice," Cossu said in an interview that preceded the press conference. "We believe this is a significant step toward therapy, but the question that keeps me awake at night is whether this will work in larger animals."

Cossu's team conducted its experiments on mice with the same genetic defect that causes one form of MD in humans. If the same stem cells, called "mesoangioblasts," can be collected from human MD patients, and if the cells have the same versatility they do early in life, they may offer a new avenue for treating the disease.

The approach Cossu and his colleagues are envisioning would involve collecting mesoangioblasts from a patient's blood vessels, genetically "correcting" the cells in the laboratory, allowing them to multiply, and then injecting the cells back into the patient's bloodstream. The cells would then migrate to the patient's muscles, and begin producing healthy muscle cells.

Because the cells would be from the patient's own body, his or her immune system wouldn't reject them.

Trying to find a therapy for MD "has been a long and frustrating series of exploits," said Cossu.

"There is this problem of delivering the cells, or in the case of gene therapy, the viral vector, to all of the muscles. If you could go through the circulatory system, you would have a way to homogeneously deliver the cells or the vector to all the muscle fibers," he said.

Praise from Science International Editor

After Cossu and Bottinelli had spoken to journalists in Milan at the morning press conference on 10 July, senior editor Peter Stern, of Science International, gave a few concluding remarks, which Cossu translated, phrase by phrase, into Italian.

After Stern had applauded the Italian scientists for "a beautiful piece of basic research," Cossu stopped translating to give a short statement of his own in Italian. The room full of reporters laughed as he confessed his embarrassment at having to translate such a complimentary statement about his own research.

However, Cossu did relay Stern's concluding remarks, including words of recognition for the "real translators" in the room.

"I'd like to thank all the members of the news media who joined us today," Stern said. "Journalists are so critical to the accurate translation of science to a much larger world."

Senior author Bottinelli stood in a hallway in Cossu's lab after the press conference and described how pleased he was with the multidisciplinary collaboration that had led to this Science paper.

"Science is progressing at such a fast rate thanks to our ability as scientists to exchange information and ideas, Bottinelli said. "Many times, scientists already have the techniques needed to investigate the questions that your research has prompted you to ask."

He explained that Cossu's lab had raised mice capable of partially reversing processes of physical deterioration associated with muscular dystrophy. These mice had built muscle fibers after they were treated with stem cells carrying the corrected version of an important gene. But Cossu needed a way to analyze the new muscles and investigate their function, and for this he turned to Bottinelli and his colleagues at the University of Pavia.

"Our collaboration has been wonderful," said Bottinelli, whose lab used its muscle analysis techniques to investigate experimental results with potentially exciting and far-reaching implications.

Questions Remain to be Answered

Cossu noted that several key issues must be answered before such a therapy can be developed for humans, according to the Science authors.

First, these particular stem cells are fairly new to scientists. Cossu and his colleagues discovered them approximately a year ago, and are still learning how to identify them and how they function in the body. Thus far, Cossu's team has only isolated human mesoangioblasts from fetal blood vessels.

More research is also needed for the "genetic correction" step of the therapy, which involves inserting the healthy version of a gene into the stem cell. The lentivirus Cossu used for delivering the gene in his mouse study provided the efficiency the researchers needed, but poses serious safety concerns for humans. Whether the safer retrovirus would be up to the task must still be determined.

When Cossu and his colleagues first identified mesoangioblasts last year, they determined that these cells could differentiate into a variety of cell types, including blood, bone, muscle, and connective tissue. They also found that the cells migrated outside the blood vessel, in response to inflammation.

For the current study, the researchers injected mesoangioblasts into the arteries of mice lacking the alpha sarcoglycan gene. This gene is one of several that, when defective, cause a type of MD called limb-girdle muscular dystrophy.

The researchers detected a significant portion of the normal mesoangioblasts in the muscles downstream of the injected artery. They also experimented with genetically modified mesoangioblasts, restoring healthy versions of alpha sarcoglycan gene to the cells. Three months after a single injection, they found healthy alpha sarcoglycan proteins in the muscles of the treated mice.

When Cossu's group examined the mice, they found that the treated muscles contained larger and more numerous and apparently normal muscle fibers. The treated animals were also able to walk on a rotating wheel for longer than untreated animals, although not as long as healthy mice.

"I'm convinced this is an important result, but this is still not the therapy — for the mice or for patients," Cossu said.

Following the press conference, the Cossu lab opened itself to TV news journalists, who captured the researchers on-camera as they described their findings in their native habitat. In the background, the lab's espresso machine hummed, and bench scientists continued to wield their pipettes.

—Daniel Kane and Kathy Wren

10 July 2003