Volker Morath, Katja Fitschle, Linda Warmuth, Markus Anneser, Sarah Dötsch, Milica Zivanic, Luisa Krumwiede, Philipp Bösl, Tarik Bozoglu, Stephanie Robu, Susanne Kossatz, Christian Kupatt, Markus Schwaiger, Katja Steiger, Dirk Busch, Arne Skerra, Wolfgang A. Weber

Seeing is believing: Imaging of cell and gene therapies using a novel PET reporter gene system

Advanced Therapy Medicinal Products (ATMPs), such as cell and gene therapies necessitate a reliable diagnostic method to image transgenes quantitatively. We developed a novel positron emission tomography (PET) reporter gene system consisting of a membrane-anchored Anticalin binding protein (DTPA-R) and a corresponding radiohybrid ligand [¹⁸F]F-DTPA•terbium. The simple design of the reporter protein yields high receptor densities of up to ~1×106 receptors per cell, small gene size and high affinity binding of [¹⁸F]F-DTPA. The physical detection limit for Jurkat^DTPA-R is 500 cells. [¹⁸F]F-DTPA showed a high tumor uptake of 22.1 %ID/g in PC3^DTPA-R xenografts compared to 0.2 %ID/g for a DTPA-R negative tumor  90 min p.i. (ratio = 125) and cleared nearly exclusively via the renal route . The reporter system allowed the quantitative, depth-independent imaging of gene therapy with AAV9 viral vectors with a linear dose-to-signal relation. Expansion and migration of CD19-CAR-T cells in a systemic Raji animal model was monitored over a four-week therapy, demonstrating a linear relationship between PET signal and CAR-T cell number. Furthermore, immunohistochemistry of these animals confirmed that PET imaging allowed identification of CAR-T infiltration into individual vertebrae. Our novel & proprietary reporter gene system is a promising tool to elevate the understanding of cell and gene therapies and support the development of precision medicine.