Imaging of Mesenchymal Stem Cell Transplant by Bioluminescence and PET

Department of Nuclear Medicine/Radiology, University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Journal of Nuclear Medicine (Impact Factor: 6.16). 01/2008; 48(12):2011-20. DOI: 10.2967/jnumed.107.043166
Source: PubMed


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.
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.
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.
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.

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    • "According to Lebond et al. (2009), the mean engraftment rate after systemic delivery is in a range of 0.01–0.1 %. However, imaging studies of labeled mesenchymal stem cells show that following intravenous delivery most of the cells home into the lung (Love et al. 2007). Yan et al. (2007) conclude that systemic administration of mesenchymal stem cells shortly after lung injury results in adequate engraftment, but their application at a later time might initiate fibrotic changes. "
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    • "It is noteworthy that there are no experimental data using stem cells transduced with an fl-mrfp-ttksr39 gene construct driven by a constitutive cytomegaloviral (CMV) promoter. Several studies have reported epigenetic silencing of CMV promoter after longitudinal passage of stem cells [16] [17]. Thus, we speculated whether the lentiviral-mediated overexpression of fl-mrfp-ttksr39 TF driven by the CMV promoter would induce aberrant characteristics or alter differentiation capacity of stem cells. "
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