Xenotransplantation in immunodeficient mouse strains such as NOD/SCID has proven to be a valuable assay for human hematopoietic stem cells. Mucopolysaccharidosis type VII (MPS VII) mice are beta-glucuronidase (GUSB) deficient and serve as a model for the lysosomal storage disease Sly Syndrome. Normally, GUSB is expressed ubiquitously in all cell types, but MPS VII mice lack detectable enzyme activity in all tissues. Backcrossing the MPS VII mutation to NOD/SCID mice has produced the NOD/SCID/MPS strain. NOD/SCID/MPS mice retain the capability to support sustained production of lymphoid and myeloid progeny from transplanted human hematopoietic stem cells. Since the engrafted human cells constitutively express GUSB from the endogenous gene, transplanted mice can be analyzed by several sensitive, enzyme-based assays. A fluorogenic substrate specific for GUSB activity allows identification of human cells by flow cytometry, a method independent of human surface markers like the widely utilized CD45 antigen. Additionally, a biochemical assay on homogenized tissues of transplanted mice allows for quantitative analysis of the distribution of enzyme activity in whole organs. Furthermore, a simple histochemical staining procedure on frozen sections of organs of transplanted mice allows in situ localization of single human cells. In preliminary studies, sublethally irradiated NOD/SCID/MPS mice were transplanted intravenously with 1 X 10° mobilized human peripheral blood CD34+ cells at 4 weeks of age. GUSB positive human cells were present in sections of bone marrow, spleen, lymph nodes, thymus, liver, lungs, kidneys, heart, and brain of animals at 2, 5, and 8 weeks post-transplant. High numbers of cells were detected in organs not usually analyzed in most transplant studies such as the liver and lungs. Interestingly, at both 5 and 8 weeks post-transplant, the total liver GUSB activity was found to be substantially higher than that of all other organ systems analyzed, including a calculation of the total bone marrow activity. The enzyme-specific assays of the NOD/SCID/MPS mouse offer tremendous advantages to the study of trafficking of hircin celis as well as the investigation of stem cell plasticity in vivo. This mouse strain will also allow future gene therapy studies aimed at the correction of human MPSVII hematopoietic stem cells.
|Issue number||11 PART I|
|State||Published - Dec 1 2000|