Will gene therapy trump factor treatment in hemophilia?

Centre for Haemostasis & Thrombosis, Guy's & St Thomas' NHS Foundation Trust, 1st Floor North Wing, St Thomas' Hospital, Westminster Bridge Road, London, SE1 7EH, UK. .
Expert Review of Hematology (Impact Factor: 2.07). 02/2013; 6(1):43-8. DOI: 10.1586/ehm.12.70
Source: PubMed


Hemophilia treatment is entering a new phase, with the exciting possibility of gene therapy promising a cure. Novel gene transfer strategies are being considered for patients with inhibitors.Improvement of factor-replacement therapy is being aggressively pursued with long-acting factor concentrates, many of which are in clinical trials. Whether gene therapy will be safe and cost effective to eventually supersede factor-replacement therapy is yet to be determined. It is hoped that with the profusion of clinical trial programs in hemophilia care, it will eventually provide affordable treatment to many patients who currently cannot access adequate treatment in the developing countries.

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    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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