MDA RESEARCH FEATURED AT NATIONAL GENE THERAPY MEETING

This June, with notebooks in tow, about 2,000 researchers, clinicians, graduate students, technicians and postdoctoral assistants descended upon Washington, D.C., for the second annual American Society of Gene Therapy meeting.

Attendees from diverse areas of research were united in their enthusiasm for developing gene therapy technology to fight human disease. MDA, for the second year in a row, was a sponsor of the meeting. (For an update on MDA's progress in gene therapy for muscular dystrophy, see the Special Report in this issue.)

The goal of gene therapy is to correct hereditary diseases by providing patients' cells with healthy copies of the gene that's defective. The most promising way to deliver healthy genes is to use a disabled virus as a carrier, or vector.

Although in many ways they're ideally suited for delivering therapeutic genes, modified viruses have also presented some difficulty because of their tendency to attract unwanted attention from the immune system. Many of the reports at the society's meeting concerned improvements in different versions of gene therapy viral vectors.

Other interesting findings the scientists discussed included the discovery of cells in the bone marrow that can migrate into muscle and become new muscle cells, and the ability of utrophin, a molecule similar to dystrophin, to completely compensate for the lack of dystrophin in mice.

MDA grantee James Wilson, who heads the Institute for Human Gene Therapy at the University of Pennsylvania in Philadelphia, is the current president of the society.

Highlights of the meeting included the following key talks by MDA grantees:

• Jeffrey Chamberlain, University of Michigan, reported that the new "gutted" adenoviral (AV) vectors for gene therapy in Duchenne muscular dystrophy (DMD) seem to evade detection by the immune system and have persisted in the muscles of animals for up to a year. In addition to continuing with preclinical testing of the gutted AV vector, Chamberlain has also designed a super-gutted AV vector that contains the dystrophin gene and the gene for a protein called MyoD.
  
  Preliminary experiments in mice indicate that the MyoD protein can cause fibroblasts, another type of cell found in muscle, to fuse into pre-existing muscle cells. The genes in this latest vector can be turned off and on in response to an oral drug.
  
  
• Andrea Amalfitano, Duke University Medical Center, presented data on his version of the AV vector, developed originally in Chamberlain's lab. Amalfitano's vector differs from the "gutted" AV vector in that only two sets of viral genes are removed rather than the entire viral genome.
  
  This version of the AV vector doesn't attract attention from the immune system when injected into muscle and may be safer for human therapy because it doesn't require a fully functional "helper virus" in its manufacture. Amalfitano is interested in using his AV vector in the treatment of DMD and Pompe's disease.
  
  
• Hansell Stedman, University of Pennsylvania, described an innovative way to deliver an adeno-associated virus (AAV) vector carrying the gene for delta sarcoglycan (one of the genes that, when defective, leads to limb-girdle muscular dystrophy) into many muscles at once in a rodent through injection into the bloodstream. Normally, the AAV vector can't pass through the lining of the blood vessels into the muscles. Stedman used a combination of chemicals to make "tiny temporary holes" in the blood vessel walls to allow the gene therapy vector to escape into the muscle.
  
  
• Emanuela Gussoni, who works in the laboratory of MDA grantee Louis Kunkel at Children's Hospital in Boston, described the isolation of a very primitive population of cells from bone marrow in mice that are capable of maturing into many different types of cells, including muscle.
  
  When primitive "stem" cells taken from a healthy donor mouse were injected into the bloodstream of a mouse that lacked dystrophin, some of the stem cells migrated into the muscle compartment and merged with muscle cells, where they produced dystrophin (the protein that's missing in DMD and flawed in Becker muscular dystrophy). The use of stem cells that migrate to areas of the body where they're needed may prove to be a useful way to distribute therapeutic genes.
  
  
• Kay Davies, University of Oxford in England, reported that the full-length gene for utrophin, when introduced into mice that lack dystrophin via gene therapy, can reverse the symptoms of muscular wasting. Davies' group, in collaboration with OSI Pharmaceuticals, is now looking for small-molecule drugs that may increase the production of utrophin in people with DMD or BMD, making gene therapy unnecessary.
  
  

RECRUITMENT BEGINS FOR POMPE'S DISEASE TRIAL

Duke University researchers led by MDA grantee Y.T. Chen are beginning a combined phase 1 and 2 clinical trial to test enzyme replacement therapy for Pompe's disease (acid maltase deficiency) in infants. Phase 1 refers to safety and phase 2 to effectiveness, and this trial is a combination of both kinds of testing.

Pompe's disease is caused by mutations in the gene for an enzyme called acid maltase that's critical for breaking down glycogen into glucose (sugar). When glycogen can't be broken down, harmful levels accumulate in the cells of the skeletal, heart and lung muscles. The disease is most severe in its infantile form.

Chen's group is manufacturing an immature form of an enzyme that they previously found is taken up more efficiently than the mature form by the muscle after injection into the bloodstream.

The phase 1 and 2 trial is expected to last for six months and involve three infants. If successful, it will be extended to a larger, phase 3 trial, and clinical trials for older children will be planned.

For more information on trial enrollment, see the listing for this trial on the MDA Web site (under Research; Active Clinical Trials). Or call Jennifer Sullivan, a genetic counselor in the Division of Medical Genetics at Duke University Medical Center in Durham, N.C., at (919) 684-2036.

RESEARCH PROVIDES LEAD FOR POSSIBLE SMA TREATMENT

The differences between two similar, adjacent genes could offer a clue to a treatment for spinal muscular atrophy.

MDA researchers were involved in the 1995 discovery that defects in a gene known as SMN (survival of motor neurons) cause this disease. SMA affects the nerve cells that control movement -- the motor neurons.

Scientists later found that people have multiple copies of the SMN gene. The varying degrees of weakness and paralysis in different forms of SMA depend on the precise genetic defects in an individual's SMN genes.

Some researchers believe that the severity of SMA is related, in part, to how many copies of the gene called SMN-C (also called SMN-2) are present in a person with a flawed SMN-T (also called SMN-1) gene. The two genes lie close to each other on chromosome 5.

Extra copies of SMN-C seem to offer some protection against defects in SMN-T. However, the protein produced from SMN-C isn't as good at helping nerve cells develop and survive as that normally produced from SMN-T.

Now, two MDA-supported researchers have found the precise difference between the two genes and say it may be possible to convert an SMN-C to an SMN-T gene, thereby correcting the motor neuron problem in SMA.

Elliot Androphy of the New England Medical Center and Tufts University School of Medicine in Boston, Arthur Burghes of Ohio State University and colleagues say they've found a tiny difference between these two genes that causes the cells to process them differently when producing the SMN-C and SMN-T proteins. A gene therapy strategy that targets this tiny difference could change the way motor neurons process SMN-C genes so that they produce the more helpful SMN-T protein molecules instead. This strategy could correct the motor neuron problem in SMA, the researchers suggest.

Androphy was on a team that published the first results in the May issue of the Proceedings of the National Academy of Sciences. Androphy and Burghes authored a second paper on the subject in the July issue of Human Molecular Genetics.

NEW WHEELCHAIR BOASTS GYROS, FOUR-WHEEL DRIVE

By rearing up and balancing on two wheels, a four-wheeled chair goes through sand, over curbs, and up and down stairs. It also features a lift to allow users to reach high counters and hold eye-level conversations with standing adults.

Recently featured on NBC's "Dateline" and in other media reports, this wheelchair, manufactured by Johnson & Johnson, isn't science fiction: It's currently undergoing clinical trials to gain Food and Drug Administration approval.

Named the INDEPENDENCE™ 3000 IBOT™ Transporter, the chair relies on gyroscopes, electronic sensors and the ability to switch between four wheels and two to traverse uneven terrain. The chair climbs and descends stairs by moving one pair of wheels past the other and placing them on a higher or lower stair, says a spokesperson for Johnson & Johnson.

The chair was originally developed by Dean Kamen, president of DEKA Research & Development, who got the idea after observing a man at a shopping mall who was having difficulties with an ordinary wheelchair.

Johnson & Johnson hopes to be able to offer the wheelchair by late 2000. The cost will be prohibitive at $20,000 to $25,000, but the company plans to lobby the insurance industry to pay for the chair on the principle that it significantly improves quality of life for users.

For more information, call the company hotline at (888) IND-3000 or visit the IBOT Web site at www.jnj.com/news_finance/89.htm.

ANTIBIOTIC MAY HELP SOME DMD PATIENTS

Up to 15 percent of people with Duchenne muscular dystrophy (DMD) could be helped by an antibiotic medication that's been on the market to treat infections for many years.

MDA grantees H. Lee Sweeney, Elisabeth Barton-Davis and Laurence Cordier at the University of Pennsylvania School of Medicine found that the drug gentamicin allowed mice with a DMD-like disorder to make the protein dystrophin. Dystrophin is the protein that's missing but needed in people with DMD.

In a study published in the Aug. 15 issue of the Journal of Clinical Investigation, the research team found that gentamicin has an unusual property: It allows cells to ignore an abnormal signal to stop making dystrophin, and to go ahead and make the protein.

These abnormal signals, which are genetic mutations, are called premature stop codons, and they're responsible for a lack of dystrophin in an estimated 5 to 15 percent of people with DMD. (The signals also occur in other genetic diseases.)

In the mice the researchers tested, those that received gentamicin injections made enough dystrophin to improve their muscle function and the sturdiness of their muscle cell membranes. Loss of muscle function and membrane fragility also occur in people with DMD.

The researchers will join forces with neurologist Jerry Mendell, MDA clinic codirector at Ohio State University, to study the drug in a small group of children with DMD who have premature stop codons. If the drug proves helpful, larger numbers of children should be genetically tested to see if they have premature stop codons, the researchers say.

Sweeney and Mendell caution that proper dosage of gentamicin in DMD hasn't been determined and that the drug can damage kidneys and cause hearing loss. They advise doctors and families to wait for the results of the human trials before attempting treatment with gentamicin. The trials will test procedures to reduce toxicity.

Only a small percentage of people with DMD have stop codons, and this can only be determined by a genetic test. The researchers note that gentamicin will not help those whose disorder results from other types of mutations in the dystrophin gene.

Gentamicin is unlikely to help people with Becker muscular dystrophy, the researchers say, because that disorder is generally caused by a different type of mutation.