Noninvasive molecular imaging to detect transgene expression of lentiviral vector in nonhuman primates

Noninvasive imaging of a reporter gene is a new and promising technique to quantify transgene expression after gene therapy. This study was performed to demonstrate visualization of lentiviral-marked cells by PET.We transduced nonhuman primate CD34+ hematopoietic cells with a lentiviral vector expressing a PET reporter gene, the mutant viral herpes simplex virus type 1-thymidine kinase (HSV1-sr39tk) gene. 1-(2-Fluoro-2-deoxy-beta-D-arabinofuranosyl)-76Br-5-bromouracil (76Br-FBAU) was used as the substrate for the viral tk enzyme. Upon phosphorylation, 76Br-FBAU was retained by cells and imaged by PET. The long half-life of 76Br, 16.2 h, permitted us to perform extended pharmacokinetic and imaging studies.76Br-FBAU was retained in vascular tissues of the animals with transplanted tk lentiviral vector-transduced CD34+ cells. Elimination of 76Br-FBAU was through renal and hepatic excretion.Noninvasive molecular imaging using PET will help us, in the future, to define the contribution and distribution of cells and their progeny to tissue repair and development.