title: Using C-arm x-ray imaging to guide local reporter probe delivery for tracking stem cell engraftment.
abstract: Poor cell survival and difficulties with visualization of cell delivery are major problems with current cell transplantation methods. To protect cells from early destruction, microencapsulation methods have been developed. The addition of a contrast agent to the microcapsule also could enable tracking by MR, ultrasound, and X-ray imaging. However, determining the cell viability within the microcapsule still remains an issue. Reporter gene imaging provides a way to determine cell viability, but delivery of the reporter probe by systemic injection may be hindered in ischemic diseases. In the present study, mesenchymal stem cells (MSCs) were transfected with triple fusion reporter gene containing red fluorescent protein, truncated thymidine kinase (SPECT/PET reporter) and firefly luciferase (bioluminescence reporter). Transfected cells were microencapsulated in either unlabeled or perfluorooctylbromide (PFOB) impregnated alginate. The addition of PFOB provided radiopacity to enable visualization of the microcapsules by X-ray imaging. Before intramuscular transplantation in rabbit thigh muscle, the microcapsules were incubated with D-luciferin, and bioluminescence imaging (BLI) was performed immediately. Twenty-four and forty-eight hours post transplantation, c-arm CT was used to target the luciferin to the X-ray-visible microcapsules for BLI cell viability assessment, rather than systemic reporter probe injections. Not only was the bioluminescent signal emission from the PFOB-encapsulated MSCs confirmed as compared to non-encapsulated, naked MSCs, but over 90% of injection sites of PFOB-encapsulated MSCs were visible on c-arm CT. The latter aided in successful targeting of the reporter probe to injection sites using conventional X-ray imaging to determine cell viability at 1-2 days post transplantation. Blind luciferin injections to the approximate location of unlabeled microcapsules resulted in successful BLI signal detection in only 18% of injections. In conclusion, reporter gene probes can be more precisely targeted using c-arm CT for in vivo transplant viability assessment, thereby avoiding large and costly systemic injections of a reporter probe.
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Dorota A
authors.initials: DA
authors.lastname: Kedziorek
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Meiyappan
authors.initials: M
authors.lastname: Solaiyappan
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States. ; 2. Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Piotr
authors.initials: P
authors.lastname: Walczak
authors.affiliation: 3. Center for Applied Medical Imaging, Corporate Technology, Siemens Corporation, Baltimore, Maryland, United States.
authors.forename: Tina
authors.initials: T
authors.lastname: Ehtiati
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Yingli
authors.initials: Y
authors.lastname: Fu
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States. ; 2. Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Jeff W M
authors.initials: JW
authors.lastname: Bulte
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States. ; 3. Center for Applied Medical Imaging, Corporate Technology, Siemens Corporation, Baltimore, Maryland, United States.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Shea
authors.affiliation: 4. Pattern Recognition Lab, University of Erlangen, Erlangen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Brost
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States. ; 5. Department of Radiology, Hannover Medical School, Hannover, Germany.
authors.forename: Frank K
authors.initials: FK
authors.lastname: Wacker
authors.affiliation: 1. Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States.
authors.forename: Dara L
authors.initials: DL
authors.lastname: Kraitchman
mesh_terms: D000818:Animals; D017930:Genes, Reporter; D049409:Luciferases, Firefly / Q000032:analysis / Q000235:genetics; D008163:Luminescent Measurements; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics; D045164:Mesenchymal Stem Cell Transplantation / Q000379:methods*; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D057054:Molecular Imaging / Q000379:methods*; D011817:Rabbits; D013937:Thymidine Kinase / Q000032:analysis / Q000235:genetics; D014057:Tomography, X-Ray Computed / Q000379:methods*; D000097573:Red Fluorescent Protein
chemical_list: D049409:Luciferases, Firefly; D008164:Luminescent Proteins; D013937:Thymidine Kinase; D000097573:Red Fluorescent Protein
keywords: bioluminescence; c-arm CT; mesenchymal stem cells; microencapsulation; probe targeting.; reporter gene