A new transgene reporter for in vivo magnetic resonance imaging

Abstract

We report a new platform technology for visualizing transgene expression in living subjects using magnetic resonance imaging (MRI). Using a vector, we introduced an MRI reporter, a metalloprotein from the ferritin family, into specific host tissues. The reporter is made superparamagnetic as the cell sequesters endogenous iron from the organism. In this new approach, the cells construct the MRI contrast agent in situ using genetic instructions introduced by the vector. No exogenous metal-complexed contrast agent is required, thereby simplifying intracellular delivery. We used a replication-defective adenovirus vector to deliver the ferritin transgenes. Following focal inoculation of the vector into the mouse brain, we monitored the reporter activity using in vivo time-lapse MRI. We observed robust contrast in virus-transduced neurons and glia for several weeks. This technology is adaptable to monitor transgene expression in vivo in many tissue types and has numerous biomedical applications, such as visualizing preclinical therapeutic gene delivery.

Theoretical MRI contrast model for exogenous T2 agents

“…1b and c) have interesting implications for experiments that express holoferritin protein via transgenes (2,7). First, because ferritin exhibits a pronounced linear T 2 relaxivity increase with increasing field strength, significantly less transgene expression is needed at high fields for contrast detection.…”

“…New generations of agents can often provide MRI contrast for specific cell types, detect the presence of specific molecules, such as enzymes and nucleic acids (1)(2)(3), and be responsive to physiology.…”

“…In addition, T 2 -type CAs are included in a new category of intracellular labeling approaches that utilize genetically-encoded metalloproteins (2,7). In this approach, metalloproteins from the ferritin family are expressed in specific host tissues.…”

Genetic inducible fate mapping in mouse: Establishing genetic lineages and defining genetic neuroanatomy in the nervous system

“…In the developing mouse nervous system, this will be limited to in vitro culture preparations or in situ whole embryo cultures. The advent of genetic magnetic resonance imaging contrast agents could allow fate mapped cells to be tracked in vivo for many days (Cohen et al, 2005;Genove et al, 2005;Deans et al, 2006).…”

Magnetic resonance imaging of viral particle biodistribution in vivo

“…[1][2][3] In addition, magnetic resonance imaging (MRI) has been successfully employed to visualize gene expression in vivo, 4,5 and more recently for detecting the presence of a ferritin marker gene after viral transduction in mouse brain in vivo. 6 With these advances in mind, a robust, preferably noninvasive and widely applicable method for detecting the actual vectors would be highly desirable. Conventional imaging techniques for assessing viral biodistribution, such as immunohistochemistry or polymerase chain reaction, are, albeit sensitive, highly laborious and lack the important non-invasive real-time option that would be required, especially for clinical work.…”