Imaging of Mesenchymal Stem Cell Transplant by Bioluminescence and PET

Abstract

Dynamic measurements of infused stem cells generally require animal euthanasia for single-time-point determinations of engraftment. In this study, we used a triple-fusion reporter system for multimodal imaging to monitor human mesenchymal stem cell (hMSC) transplants. Methods: hMSCs were transduced with a triple-fusion reporter, fluc-mrfp-ttk (encoding firefly luciferase, monomeric red fluorescent protein, and truncated herpes simplex virus type 1 sr39 thymidine kinase) by use of a lentiviral vector. Transduced cells were assayed in vitro for the expression of each functional component of the triple-fusion reporter. Transduced and control hMSCs were compared for their potential to differentiate into bone, cartilage, and fat. hMSCs expressing the reporter were then loaded into porous, fibronectin-coated ceramic cubes and subcutaneously implanted into NOD-SCID mice along with cubes that were loaded with wild-type hMSCs and empty cubes. Mice were imaged repeatedly over 3 mo by bioluminescence imaging (BLI), and selected animals underwent CT and PET imaging. Results: Osteogenic, adipogenic, and chondrogenic potential assays revealed retained differentiation potentials between transduced and wild-type hMSCs. Signals from the cubes loaded with reporter-transduced hMSCs were visible by BLI over 3 mo. There was no signal from the empty or wild-type hMSC-loaded control cubes. PET data provided confirmation of the quantitative estimation of the number of cells at one spot (cube). Cubes were removed from some animals, and histologic evaluations showed bone formation in cubes loaded with either reporter-transduced or wild-type hMSCs, whereas empty controls were negative for bone formation. Conclusion: The triple-fusion reporter approach resulted in a reliable method of labeling stem cells for investigation in small-animal models by use of both BLI and small-animal PET imaging. It has the potential for translation into future human studies with clinical PET.

Intravascular cell replacement therapy for stroke

“…Several imaging modalities, including MR imaging, 10,31,33,37 bioluminescence imaging, 84 PET, 23,57 and in vivo fluorescence microscopy, 93 have been used to track stem cells in vivo. Of these methods, however, only MR imaging and PET are practicable for clinical use.…”

Comparison of red-shifted firefly luciferase Ppy RE9 and conventional Luc2 as bioluminescence imaging reporter genes for <italic>in vivo</italic> imaging of stem cells

“…Bioluminescence imaging (BLI) has been widely used for in vivo tracking of transplanted stem cells, including hematopoietic, 1 embryonic, 2 mesenchymal, 3 and neural stem cells. 4,5 Introduced expression of luciferase enables researchers to observe luminescence upon injection of its substrates and therefore to monitor the survival, migration, or differentiation of stem cells over time with high sensitivity.…”

Imaging Gene Expression in Human Mesenchymal Stem Cells: From Small to Large Animals

“…Recently, molecular imaging approaches such as positron emission tomography (PET) using reporter gene imaging and dedicated small-animal micro-PET imaging systems have been used as promising noninvasive, objective, and quantitative techniques to assess location, survival, and engraftment of stem cells after intramyocardial transplantation in small animals (mice and rats) (23)(24)(25). In reporter gene imaging, reporter genes such as the mutant form of the gene encoding herpes simplex virus 1 thymidine kinase (HSV1-sr39tk) (26)(27)(28) are introduced into stem cells via a vector (eg, a recombinant adenovirus) before intramyocardial cell transplantation.…”