Tracking Cell-targeting Ligands and Viruses by Optical Imaging

Determining where ligands and viruses distribute in vivo is normally an exhaustive process requiring that the animals be sacrificed and their tissues and organs be extracted for enzymatic assays or be sectioned to identify the specific cell types that were transduced. These assays are quite laborious requiring that one actually section the whole animal to be certain of the tissue localization of the vector and to ensure that ligand or vector delivery into very unexpected sites would not be missed. Given the labor involved in these traditional assays, we have recently optimized fluorescence and luciferase luminescence imaging to track ligands, vector particles, and gene delivery in vivo. While luciferase imaging is now accepted as an excellent approach to track vector delivery or to assess tumor burden non-invasively from luciferase-expressing cancer cells, this technology cannot track the targeting ligands we are interested in since they do not carry transgenes. Likewise, even in vectors, luciferase imaging only allows us to identify where cells are that were successfully transduced by the vector. This provides zero information on 1) where all of the the virions actually went, 2) where the unsuccesful vectors went, and 3) if any of the vectors actually made it to the tumor without transducing it. Given this, we are now applying near infrared fluorescence imaging to track ligands and vectors in vivo and are combining this with luciferase imaging to track successful virus and vector delivery in small animals. These imaging approaches are being applied for all of our gene therapy, vaccine, and cancer projects.