Original Article

European Journal of Nuclear Medicine and Molecular Imaging

, Volume 36, Issue 1, pp 104-114

Recombinant carcinoembryonic antigen as a reporter gene for molecular imaging

  • Vania KenanovaAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles
  • , Bhaswati BaratAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles
  • , Tove OlafsenAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles
  • , Arion ChatziioannouAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles
  • , Harvey R. HerschmanAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles
  • , Jonathan BraunAffiliated withDepartment of Pathology and Laboratory Medicine, David Geffen School of Medicine at the University of California Los Angeles
  • , Anna M. WuAffiliated withCrump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at the University of California Los Angeles Email author 

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Abstract

Purpose

Reporter genes can provide a way of noninvasively assessing gene activity in vivo. However, current reporter gene strategies may be limited by the immunogenicity of foreign reporter proteins, endogenous expression, or unwanted biological activity. We have developed a reporter gene based on carcinoembryonic antigen (CEA), a human protein with limited normal tissue expression.

Methods

To construct a CEA reporter gene for PET, a CEA minigene (N-A3) was fused to the extracellular and transmembrane domains of the human FcγRIIb receptor. The NA3-FcγRIIb recombinant gene, driven by a CMV promoter, was transfected in Jurkat (human T cell leukemia) cells. Expression was analyzed by flow cytometry, immunohistochemistry (IHC), and microPET imaging.

Results

Flow cytometry identified Jurkat clones stably expressing NA3-FcγRIIb at low, medium, and high levels. High and medium NA3-FcγRIIb expression could also be detected by Western blot. Reporter gene positive and negative Jurkat cells were used to establish xenografts in athymic mice. IHC showed staining of the tumor with high reporter gene expression; medium and low N-A3 expression was not detected. MicroPET imaging, using an anti-CEA 124I-labeled single-chain Fv-Fc antibody fragment, demonstrated that only high N-A3 expression could be detected. Specific accumulation of activity was visualized at the N-A3 positive tumor as early as 4 h. MicroPET image quantitation showed tumor activity of 1.8 ± 0.2, 15.2 ± 1.3, and 4.6 ± 1.2 percent injected dose per gram (%ID/g) at 4, 20, and 48 h, respectively. Biodistribution at 48 h demonstrated tumor uptake of 4.8 ± 0.8%ID/g.

Conclusion

The CEA N-A3 minigene has the potential to be used as a reporter gene for imaging cells in vivo.

Keywords

T cells CEA reporter gene Jurkat xenograft 124I-labeled scFv-Fc antibody fragment MicroPET/microCT imaging