Imaging gene expression in human mesenchymal stem cells: from small to large animals.
OBJECTIVE
To evaluate the feasibility of reporter gene imaging in implanted human mesenchymal stem cells (MSCs) in porcine myocardium by using clinical positron emission tomography (PET)-computed tomography (CT) scanning.


METHODS
Animal protocols were approved by the Institutional Administrative Panel on Laboratory Animal Care. Transduction of human MSCs by using different doses of adenovirus that contained a cytomegalovirus (CMV) promoter driving the mutant herpes simplex virus type 1 thymidine kinase reporter gene (Ad-CMV-HSV1-sr39tk) was characterized in a cell culture. A total of 2.25 x 10(6) transduced (n = 5) and control nontransduced (n = 5) human MSCs were injected into the myocardium of 10 rats, and reporter gene expression in human MSCs was visualized with micro-PET by using the radiotracer 9-(4-[fluorine 18]-fluoro-3-hydroxymethylbutyl)-guanine (FHBG). Different numbers of transduced human MSCs suspended in either phosphate-buffered saline (PBS) (n = 4) or matrigel (n = 5) were injected into the myocardium of nine swine, and gene expression was visualized with a clinical PET-CT. For analysis of cell culture experiments, linear regression analyses combined with a t test were performed. To test differences in radiotracer uptake between injected and remote myocardium in both rats and swine, one-sided paired Wilcoxon tests were performed. In swine experiments, a linear regression of radiotracer uptake ratio on the number of injected transduced human MSCs was performed.


RESULTS
In cell culture, there was a viral dose-dependent increase of gene expression and FHBG accumulation in human MSCs. Human MSC viability was 96.7% (multiplicity of infection, 250). Cardiac FHBG uptake in rats was significantly elevated (P < .0001) after human MSC injection (0.0054% injected dose [ID]/g +/- 0.0007 [standard deviation]) compared with that in the remote myocardium (0.0003% ID/g +/- 0.0001). In swine, myocardial radiotracer uptake was not elevated after injection of up to 100 x 10(6) human MSCs (PBS group). In the matrigel group, signal-to-background ratio increased to 1.87 after injection of 100 x 10(6) human MSCs and positively correlated (R(2) = 0.97, P < .001) with the number of administered human MSCs.


CONCLUSIONS
Reporter gene imaging in human MSCs can be translated to large animals. The study highlights the importance of co-administering a "scaffold" for increasing intramyocardial retention of human MSCs.
Molecular Imaging Program at Stanford, Department of Radiology and Bio-X Program, Stanford University School of Medicine, James H. Clark Center, 318 Campus Dr, Stanford, CA 94305-5427, USA.
Jürgen K
JK
Willmann
Ramasamy
R
Paulmurugan
Martin
M
Rodriguez-Porcel
William
W
Stein
Todd J
TJ
Brinton
Andrew J
AJ
Connolly
Carsten H
CH
Nielsen
Amelie M
AM
Lutz
Jennifer
J
Lyons
Fumiaki
F
Ikeno
Yoriyasu
Y
Suzuki
Jarrett
J
Rosenberg
Ian Y
IY
Chen
Joseph C
JC
Wu
Alan C
AC
Yeung
Paul
P
Yock
Robert C
RC
Robbins
Sanjiv S
SS
Gambhir
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods / Q000662:veterinary*; D017930:Genes, Reporter / Q000502:physiology*; D006801:Humans; D045164:Mesenchymal Stem Cell Transplantation / Q000379:methods*; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000000981:diagnostic imaging* / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000662:veterinary*; D020543:Proteome / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D020543:Proteome