Why Do Cultured Transplanted Myoblasts Die in Vivo? DNA Quantification Shows Enhanced Survival of Donor Male Myoblasts in Host Mice Depleted of CD4+ and CD8+ Cells or NK1.1+ Cells

NK1 T cells are a specialized population of alpha/beta T cells that coexpress receptors of the NK lineage and have the unique potential to very rapidly secrete large amounts of cytokines, providing early help for effector cells and regulating the Th1 or Th2 differentiation of some immune responses. NK1 T cells express a restricted TCR repertoire made of an invariant TCR alpha chain, V alpha 14-J alpha 281, associated with polyclonal V beta 8, V beta 7, and V beta 2 TCR beta chains. NK1 T cells recognize the products of the conserved family of MHC class I-like CD1 genes, apparently in the absence of foreign antigens. Thus, this novel regulatory pathway, which straddles the innate and the adaptive immune systems, is unique in that its activation may not require associative recognition of antigen. Here, we review the specificity and function of mouse NK1 T cells, and we discuss the relationship of this lineage to mainstream T cells and NK cells.

An important corollary to the recent advances in our understanding of the primary cause of Duchenne muscular dystrophy, is the validation of genuine genetic homologues as animal models of the disease in which potential therapies can be tested. The persistent skeletal muscle necrosis that characterizes human Duchenne muscular dystrophy is also seen in the mdx mouse and is, in both, a consequence of a deficiency of dystrophin, probably within the muscle fibres themselves. As injected muscle precursor cells of one genotype can fuse with host muscle fibres of a different genotype and express the donor genes, we decided to test grafts of normal muscle precursor cells to see if they could induce synthesis of dystrophin in innately dystrophin-deficient mdx muscle fibres. We show that injected normal muscle precursor cells can fuse with pre-existing or regenerating mdx muscle fibres to render many of these fibres dystrophin-positive and so to partially or wholly rescue them from their biochemical defect.

Myoblast transplantation has been extensively studied as a gene complementation approach for genetic diseases such as Duchenne Muscular Dystrophy. This approach has been found capable of delivering dystrophin, the product missing in Duchenne Muscular Dystrophy muscle, and leading to an increase of strength in the dystrophic muscle. This approach, however, has been hindered by numerous limitations, including immunological problems, and low spread and poor survival of the injected myoblasts. We have investigated whether antiinflammatory treatment and use of different populations of skeletal muscle–derived cells may circumvent the poor survival of the injected myoblasts after implantation. We have observed that different populations of muscle-derived cells can be isolated from skeletal muscle based on their desmin immunoreactivity and differentiation capacity. Moreover, these cells acted differently when injected into muscle: 95% of the injected cells in some populations died within 48 h, while others richer in desmin-positive cells survived entirely. Since pure myoblasts obtained from isolated myofibers and myoblast cell lines also displayed a poor survival rate of the injected cells, we have concluded that the differential survival of the populations of muscle-derived cells is not only attributable to their content in desmin-positive cells. We have observed that the origin of the myogenic cells may influence their survival in the injected muscle. Finally, we have observed that myoblasts genetically engineered to express an inhibitor of the inflammatory cytokine, IL-1, can improve the survival rate of the injected myoblasts. Our results suggest that selection of specific muscle-derived cell populations or the control of inflammation can be used as an approach to improve cell survival after both myoblast transplantation and the myoblast-mediated ex vivo gene transfer approach.