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. Methods: 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- β-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. Results: 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. Conclusion: 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.