Molecular imaging of endothelial progenitor cell engraftment using contrast-enhanced ultrasound and targeted microbubbles.
OBJECTIVE
Imaging methods to track the fate of progenitor cells after their delivery would be useful in assessing the efficacy of cell-based therapies. We hypothesized that contrast-enhanced ultrasound (CEU) using microbubbles targeted to a genetically engineered cell-surface marker on endothelial progenitor cells (EPCs) would allow the targeted imaging of vascular engraftment.


RESULTS
Rodent bone marrow-derived EPCs were isolated, cultured, and transfected to express the marker protein, H-2Kk, on the cell surface. Non-transfected EPCs and EPCs transfected with either null plasmid or Firefly luciferase served as controls. Control microbubbles (MB(C)) and microbubbles targeted to H-2Kk expressed on EPCs (MB(H-2Kk)) were constructed. Binding of targeted microbubbles to EPCs was assessed in vitro using a parallel plate flow chamber system. CEU imaging of EPC-targeted microbubbles was assessed in vivo using subcutaneously implanted EPC-supplemented Matrigel plugs in rats. In flow chamber experiments, there was minimal attachment of microbubbles to plated control EPCs. Although numbers of adhered MB(C) were also low, there was greater and more diffuse attachment of MB(H-2Kk) to plated H-2Kk-transfected EPCs. Targeted CEU demonstrated marked contrast enhancement at the periphery of the H-2Kk-transfected EPC-supplemented Matrigel plug for MB(H-2Kk,) whereas contrast enhancement was low for MB(C). Contrast enhancement was also low for both microbubbles within control mock-transfected EPC plugs. The signal intensity within the H-2Kk-transfected EPC plug was significantly greater for MB(H-2Kk) when compared with MB(C).


CONCLUSIONS
Microbubbles targeted to a genetically engineered cell-surface marker on EPCs exhibit specific binding to EPCs in vitro. These targeted microbubbles bind to engrafted EPCs in vivo within Matrigel plugs and can be detected by their enhancement on CEU imaging.
Kuliszewski
Michael A
MA
Division of Cardiology, Keenan Research Centre in the Li Ka Shing Knowledge Institute, 7-052 Bond Wing, St Michael's Hospital, 30 Bond Street, Toronto, Ontario, Canada M5B 1W8.
Fujii
Hiroko
H
Liao
Christine
C
Smith
Alexandra H
AH
Xie
Aris
A
Lindner
Jonathan R
JR
Leong-Poi
Howard
H
D000818:Animals; D003094:Collagen; D003287:Contrast Media; D004338:Drug Combinations; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism / Q000637:transplantation*; D006085:Graft Survival; D049452:Green Fluorescent Proteins / Q000235:genetics; D006183:H-2 Antigens / Q000235:genetics; D007797:Laminin; D049409:Luciferases, Firefly / Q000235:genetics; D045423:Microbubbles; D018919:Neovascularization, Physiologic; D011509:Proteoglycans; D051381:Rats; D011916:Rats, Inbred F344; D033581:Stem Cell Transplantation; D014162:Transfection; D014463:Ultrasonography / Q000379:methods*
D003287:Contrast Media; D004338:Drug Combinations; D006183:H-2 Antigens; C024755:H-2K(K) antigen; D007797:Laminin; D011509:Proteoglycans; C485184:enhanced green fluorescent protein; C059485:matrigel; D049452:Green Fluorescent Proteins; D003094:Collagen; D049409:Luciferases, Firefly