Abstract
Gene therapy using recombinant adeno-associated virus vectors (rAAV) is generally considered safe. During the course of a study designed to determine the long-term efficacy of rAAV-mediated gene therapy initiated in newborn mice with the lysosomal storage disease, mucopolysaccharidosis type VII (MPSVII), a significant incidence of hepatocellular carcinomas and angiosarcomas was discovered. A hepatocellular carcinoma was first detected in a 35-week-old mouse and by 72 weeks of age, three out of five rAAV-treated MPSVII mice had similar lesions. These types of tumors had not been seen previously in long-term studies of MPSVII mice using recombinant enzyme or bone marrow transplantation. In an attempt to ascertain whether mouse strain or GUSB expression confers susceptibility to tumor formation, we histopathologically examined untreated normal mice of the same strain, untreated MPSVII mice, and normal mice overexpressing human GUSB for the presence of tumors and increased hepatocyte replication. The results of these studies do not indicate that MPSVII mice or mice overexpressing human GUSB are susceptible to tumor formation; however, the number of animals examined is too small to draw definitive conclusions. Results from quantitative PCR performed on the tumor samples suggest that the tumors are probably not caused by an insertional mutagenesis event followed by the clonal expansion of a transformed cell. In a separate study, a relatively large group of mice injected with varying doses and types of rAAV vectors had no evidence of hepatic or vascular tumors. Although the mechanism of tumor formation is currently unknown, the tumorigenic potential of rAAV vectors must be rigorously determined in long-term in vivo studies.
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Acknowledgements
Many thanks to Dr Ronald Marks who assisted with the statistical comparisons, Amy Pourier for technical support for the real-time PCR assays and Dr Kathy Ponder for assistance with BrdU labeling. This work was funded by grants from the NIDDK DK58327 (NM, TF), the NHLBI HL59412 (NM, TF), NIDDK 27726 (JEB), and NIDDK 53920 (MSS). Many thanks to Barry Byrne, Alfred Lewin, and Philip Laipis for contributing retrospective data.
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Donsante, A., Vogler, C., Muzyczka, N. et al. Observed incidence of tumorigenesis in long-term rodent studies of rAAV vectors. Gene Ther 8, 1343–1346 (2001). https://doi.org/10.1038/sj.gt.3301541
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DOI: https://doi.org/10.1038/sj.gt.3301541
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