Another delivery method for both viral and non-viral vectors is ex vivo transduction of target cells that are then reintroduced into the patient (6). This delivery mechanism was first used by Rosenberg et al. in the initial human gene therapy trial when human tumor infiltrating cells were transduced with retroviral constructs and reinfused in metastatic melanoma patients (1). The advantage of this delivery method is that there is more control of the transduced cell and higher transduction efficiencies can be achieved in the target tissue. Disadvantages included difficulties in targeting the reinfused cells to specific anatomic locations as well as possible contamination with reintroduced biologic agents. Current research efforts are evaluating ex vivo transduction of stem and progenitor cells which may lead to more sustained gene expression and better tissue targeting.
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