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

Unlabelled: 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-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.

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.