Lentivirally-mediated stem cells to treat Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked condition in which muscle fibres degenerate due to the lack of the protein dystrophin. Stem cells, called satellite cells, within skeletal muscle do repair and regenerate lost fibres, but as the new fibres remain dystrophin-deficient, they continually break down, eventually leading to loss of muscle fibres and replacement by fat and connective tissue. If we want to use stem cells to treat DMD, these would have to be a type of stem cell that can be delivered via the blood system, as DMD affects all the muscles of the body. We propose to use stem cells derived from the patient themselves, so that they would not promote immunonological rejection. We aim to engineer these stem cells so that they have a heritable copy of the dystrophin gene. But the whole dystrophin gene is too large to fit into any viral vector. We will therefore engineer the dystrophin gene to be small enough to fit into a lentiviral vector, but large enough to contain as much as possible of the gene, to make it as functional as possible. Combining the best stem cell to regenerate skeletal muscle with the optimal dystrophin gene will pave the way for clinical trials to treat DMD.

Genetic correction of autologous stem cells is a potential therapy for Duchenne muscular dystrophy (DMD). However, key questions need to be resolved before this approach could be realistically used in DMD. These include the determination of the best stem cell and a safe lentivirus containing a dystrophin gene that is small enough to fit into the vector, yet large enough to code for a functional protein. We aim to design a safe lentiviral vector, coding for an effective dystrophin gene (opti-dystrophin). In parallel, we will compare the ability of induced pluripotent stem cells (iPS) and adult stem cells (AC133+ cells), firstly of mouse origin and then of human origin, to efficiently regenerate skeletal muscle and functionally reconstitute the satellite cell (muscle stem cell) pool following intra-arterial injection in an immunodeficient mouse model of DMD. We will then combine the optimised lentivirus with the most favourable stem cell of DMD origin and test this in our in vivo model. Solving these preclinical questions will allow us to plan for future clinical trials for DMD.