Evaluation of Two Internalizing Carcinoembryonic Antigen Reporter Genes for Molecular Imaging

PURPOSE: The objective of this article is to develop internalizing positron emission tomography (PET) reporter genes for tracking genetically modified T cells in vivo. PROCEDURES: The transmembrane and cytoplasmic domains of the human transferrin receptor (TfR) and CD5 were each fused to the carcinoembryonic (CEA) minigene N-A3 and expressed in Jurkat T cells. Internalization was evaluated by confocal microscopy or by intracellular uptake of (125)I-labeled anti-CEA scFv-Fc. Reporter gene-transfected Jurkat xenografts in mice were analyzed by immunohistochemistry (IHC) and imaged by PET using (124)I- or (64)Cu-scFv-Fc as tracers. RESULTS: Surface expression of TR(1–99)-NA3 was lower than that of NA3-CD5. Both reporter genes were internalized following binding of the anti-CEA antibody fragment. IHC of tumors showed strong staining of NA3-CD5, whereas TR(1–99)-NA3 stained weakly. Specific targeting of TR(1–99)-NA3 or NA3-CD5 was shown by PET in xenografted mice. CONCLUSIONS: The in vivo imaging studies suggest a potential application of the internalizing form of CEA (N-A3) as a PET reporter gene.