Transplantation of Myoblasts to Duchenne Muscular Dystrophy (DMD) Patients

Duchenne Muscular Dystrophy (DMD) is a degenerative disease of genetic origin, due to a mutation in the gene coding for the protein dystrophin. This mutation leads to deficiency of dystrophin in the myofibers, causing progressive muscle degeneration by the following mechanism: (1) dystrophin deficiency leads to myofibers being very vulnerable to muscle contraction-relaxation, causing frequent damage and necrosis of myofibers; (2) necrosis is followed by myofiber regeneration, as long as the regenerative capacity of muscle is not exhausted; (3) when the regenerative capacity of the muscle is exhausted, myofibers become atrophic and are ultimately lost; (4) fibrosis and fat infiltration replace the lost myofibers. This progressive muscle destruction takes place in most muscles of the limbs and trunk, leading to progressive loss of muscle strength, musculotendinous contractures, restrictive respiratory insufficiency and premature death between 17 and 30 years.

The transplantation of myoblasts obtained from a healthy donor is a potential treatment of DMD. Following intramuscular injection, donor myoblasts fuse with the myofibers of the patient, introducing the normal dystrophin gene in them. In a previous Phase 1A clinical trial, the investigators proved that transplantation of myoblasts grown from the muscle biopsy of a healthy donor introduced the normal dystrophin gene in the DMD myofibers, with the consequent expression of the normal dystrophin mRNA and restoration of the dystrophin protein in several myofibers.

The aim of this Phase I/II of the clinical trial is to investigate whether the transplantation of normal myoblasts throughout one muscle (in this case, the extensor carpi radialis) of DMD patients is safe and will improve the strength of that muscle. The patients will be transplanted with myoblasts grown from the muscle biopsy of a healthy donor. Thirty million myoblasts will be injected per cm cube in a progressively higher volume of muscle (i.e., 3, 6 and 9 cm cube). The contralateral muscle will be injected with saline as a control. The patients and the investigators will be blind to the side injected with cells. The strength of both muscles will be measured at 3 months post transplant to verify if myoblast transplantation increased muscle strength. If there is no significant strength increase, the protocol will be terminated immediately for that patient. If there is a significant strength increase, the patient will be maintained under immunosuppression until 6 months and the muscle strength will be re-evaluated.

The objectives of this Phase I/II clinical trial with DMD patients are thus:

Primary objective:

To evaluate the safety of a procedure of high-density injections of donor myoblasts throughout a muscle (under immunosuppression by tacrolimus).

Secondary objectives:

1. To evaluate whether myoblast transplantation resulted in the presence of dystrophin-positive myofibers of donor origin.
2. To evaluate whether myoblast transplantation improved the muscle strength or prevent or slowed down the progression of the muscle weakness as shown by the following parameters: 2.1) Increase of the voluntary strength of the subject's wrist extension done by the extensor carpi radialis 12 or 24 weeks after myoblast transplantation compared with the pre-transplant values of the same muscle. 2.2) Reduction of the fatigue of the voluntary strength of the subject's wrist extension done by the extensor carpi radialis 12 or 24 weeks after myoblast transplantation compared with the pre-transplant fatigue values of the same muscle. 2.3) Reduce the progression of the muscle weakness in the myoblast injected muscle compared with the control contralateral muscle.
3. To verify the long term effectiveness of the tacrolimus immunosuppression to control acute rejection in myoblast transplantation (by examining the presence of muscle fibers expressing normal dystrophin and the absence of specific immune responses)