IntroductionMucopolysaccharidosis type IH (MPS-IH, Hurler syndrome) is an autosomal recessive disorder resulting from defects in the gene encoding the lysosomal enzyme ␣-L-iduronidase (IDUA). This leads to ineffective degradation of the glycosaminoglycans (GAGs) heparan sulfate and dermatan sulfate. Individuals with very low levels of IDUA present in infancy and early childhood as a consequence of the deleterious accumulation of these GAGs in different organ systems, including the central nervous system, reticuloendothelial system, and the skeleton. Such severely affected patients usually die within the first decade. 1,2 Current therapy for MPS-IH focuses on allogeneic bone marrow transplantation from an unaffected, HLA-compatible donor. This provides normal, enzyme-competent leukocytes that secrete IDUA that can be taken up by enzyme-deficient cells via mannose-6-phosphate receptors. 3 The utility of this approach is significantly limited by the availability of donors and significant toxicity of the intense immunosuppressive conditioning therapy that the recipient requires for donor hemopoiesis to become established without rejection. Even where donor hemopoiesis is fully established (ie, all hemopoietic cells have normal enzyme levels), symptoms (particularly defects in the skeleton and central nervous system) are incompletely and variably corrected. 4,5 Mesenchymal stem cells (MSCs) are multipotent progenitors that can be isolated from bone marrow and are capable of contributing to multiple mesenchymal tissues in vivo. [6][7][8][9][10] In this paper we demonstrate, for the first time, retroviral gene transfer leading to correction of these MSCs in an inherited disorder. Furthermore, there is maintenance of the proliferative and multilineage differentiation potential of these modified cells, and they are able to cross-correct non-gene-modified cells.Numerous studies have demonstrated the presence of donor mesenchymal cells in multiple tissues following transplantation, and MSCs injected into brain are able to differentiate into nerve cells. Taken with these, our data indicate that MSCs may prove a better target than hematopoietic stem cells in the context of gene therapy of multisystem, lysosomal storage disorders.
Study design Isolation and culture of MSCsBone marrow samples were obtained from MPS-IH patients and unaffected individuals aged from 0 to 18 years, following informed parental consent and approval from the local research ethics committee. MSCs were isolated and cultured as previously described. 11 For differentiation assays, cells were plated at 5 ϫ 10 3 per well in 6-well plates in growth medium with either osteogenic 12 or adipogenic 13 supplements. For differentiation along the neuronal lineage, cells were preincubated for 24 hours in Dulbecco modified Eagle medium/20% fetal calf serum/1 mM -mercapotethanol and then switched into Dulbecco modified Eagle medium/5 mM -mercapotethanol. 14 Mineralized bone was stained by the von Kossa technique, 15 and adipocytes were stained using oil-red-O. 16 N...