Positron emission tomography: measurement of transgene expression

Noninvasive and repetitive imaging of transgene expression can play a pivotal role in the development of gene therapy strategies, as it offers investigators a means to determine the effectiveness of their gene transfection protocols. In the last decade, imaging of transgene expression using positron emission tomography (PET) or single-photon emission computed tomography (SPECT) has received considerable attention and as a result several imaging methods have now been evaluated in animals. As a typical example of noninvasive imaging of transgene expression, this article describes the principles of monitoring the expression of the herpes simplex virus type 1 thymidine kinase gene with PET, using the ganciclovir analog 9-(3-[18F]fluoro-1-hydroxy-2-propoxy)methylguanine as the tracer. In addition to a description of the execution of the PET scan and data analysis, the types of transgene animal models that are applied and the principal limitations of the imaging technique are summarized. Finally, several indirect approaches to image transgenes via a linked reporter gene are discussed.