| Abstract: |
Types A and B Niemann-Pick disease (NPD) result from inherited deficiencies of the lysosomal hydrolase, acid sphingomyelinase (ASM; sphingomyelin cholinephosphohydrolase, EC 3.1.4.12). To evaluate the feasibility of somatic gene therapy for the treatment of these disorders, retroviral-mediated gene transfer was used to introduce the full-length ASM cDNA into cultured fibroblasts from two unrelated type A NPD patients. The ASM activities in these cells were <4% of mean normal levels, and, consequently, they accumulated ≈3-fold elevated levels of sphingomyelin. After retroviral-mediated transfer of the ASM cDNA, ASM activities in the NPD cells increased to levels up to 16-fold those found in normal fibroblasts. In addition, the sphingomyelin content was reduced to normal levels, indicating that the vector-encoded enzyme was properly targeted to lysosomes, where it was enzymatically active and able to degrade the accumulated substrate. In situ cell-loading studies also were undertaken to evaluate the effects of retroviral-mediated gene transfer on the pathology of NPD fibroblasts. When a pyrene derivative of sphingomyelin was introduced into the lysosomes of cultured fibroblasts from a type A NPD patient by using apolipoprotein E-mediated endocytosis, only ≈6% of the delivered substrate was degraded. In contrast, normal cells and NPD cells transduced (i.e., "corrected") by retroviral-mediated gene transfer could degrade ≈80% of the delivered sphingomyelin. These results provided further evidence that retroviral-mediated gene transfer may be used to correct the pathology of NPD cells. Cell-loading studies were also used to develop a selection system for discriminating between NPD cells and those transduced by retroviral-mediated gene transfer. This selection scheme was based on the fluorescence emission of intact NPD cells, which, when loaded with pyrene-labeled sphingomyelin, was 3- to 5-fold that of normal or transduced cells. As a consequence, the NPD and transduced cells could be efficiently sorted by flow cytometry with a fluorescence-activated cell sorter. In addition, the NPD cells could be selectively killed by photosensitization after irradiation with a long-wavelength UV light. These results should permit direct selection of ASM-expressing cells after retroviral-mediated gene transfer without the need to preselect for a cotransferred marker gene. (. |
| Keywords: |
controlled study; human cell; flow cytometry; cell survival; cells, cultured; enzyme activity; transfection; gene transfer; genetic vectors; skin; dna; reference values; gene therapy; fibroblasts; ultraviolet rays; radiation-sensitizing agents; metabolic disorder; moloney murine leukemia virus; cell killing; fibroblast culture; complementary dna; retrovirus; lysosome; sphingomyelin phosphodiesterase; sphingomyelin; niemann pick disease; niemann-pick diseases; sphingomyelins; somatic gene therapy; photosensitization; human; priority journal; article; support, non-u.s. gov't; support, u.s. gov't, p.h.s.; support, u.s. gov't, non-p.h.s.; lysosomal storage disease; photosensitized cell selection
|
