Stem Cell Meeting Opens in Tucson

Tucson, Ariz., March 9, 2002 — More than 30 investigators from the United States, France, Italy and Great Britain met yesterday for the opening sessions of a two-day workshop on the possible applications of stem cells to the treatment of muscular dystrophy.

Stem cells are "undifferentiated" cells — cells that haven't yet chosen a developmental path and (at least in theory) have the potential to go where they're needed. In the last few years, scientists have noted that there are stem cells present in the body throughout life that can probably give rise to almost any tissue.

The morning sessions reflected much progress since the Muscular Dystrophy Association held its first stem cell workshop in 2000.

At that time, it had only recently been discovered that cells from the bone marrow could migrate to muscle and contribute to muscle tissue. Several investigators on Friday reported isolating particular types of cells in bone marrow and at least one type of cell in muscle that appears to be a muscle stem cell.

Many reported efforts to isolate bone marrow stem cells from a donor and inject the cells into a host animal. In all studies, the bone marrow cells entered muscle in extremely small numbers and usually required some sort of stimulus to do so, such as a severe chemical injury or irradiation of the muscle.

The afternoon sessions were devoted to an examination of bone marrow transplantation in diseases other than muscular dystrophies. The procedure is well established for cancers of the bone marrow or blood cells and for genetic disorders that result in deficiencies of the immune system. In these disorders, the replacement of the defective blood cells with donated bone marrow cells (which directly supply the immune system) has a solid rationale and is usually considered worth the risks associated with the procedure.

A more recent application of bone marrow transplantation has been in the experimental treatment of a bone disorder known as osteogenesis imperfecta. This disease is somewhat analogous to muscular dystrophy, in that a genetic flaw results in the production of bone cells that are fragile and prone to fracture, just as muscle cells that carry a genetic flaw are apparently prone to damage.

There is evidence that some bone marrow cells can make bone, but, so far, evidence from animal experiments suggests that very few bone marrow cells ever incorporate into muscle.

At the end of the first day, the consensus of the experts was that more work needs to be done to understand the basic biology of muscle-forming stem cells and to answer key questions about bone marrow transplantation from a healthy donor. This procedure carries considerable risk and, at this point, questionable benefit.

Among questions to be explored were:

• What types of bone marrow cells must be isolated before considering a transplant?
• How can these cells be positively identified?
• What signals cause stem cells to be attracted to muscle, and how can these signals be amplified?
• How can such cells be targeted to muscles and coaxed to integrate (engraft) into the existing muscle tissue?
• How much, if any, immunosuppression or destruction of the recipient's own bone marrow must be implemented prior to performing a bone marrow transplant in people with muscular dystrophy?
• At what point in the disease process should a bone marrow transplant be performed to balance risks with possible benefits?