Diagnostic Magnetoelectroporation: improved labeling of neural stem cells and leukocytes for cellular magnetic resonance imaging using a single FDA-approved agent Piotr Walczak, MD, a Jesus Ruiz-Cabello, PhD, a Dorota A. Kedziorek, MD, a Assaf A. Gilad, PhD, a Sopo Lin, a Bradley Barnett, BA, a Lu Qin, BA, b Hyam Levitsky, MD, b Jeff W.M. Bulte, PhD a, 4 a Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, and Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland b Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland Received 3 October 2005; accepted 15 January 2006 Abstract Cellular magnetic resonance imaging (MRI) relies on the use of intracellular contrast agents, primarily iron oxide compounds. Several techniques have been used to efficiently shuttle iron oxides into nonphagocytic cells, but all methods used until now require a prolonged incubation of cells. We hypothesized that instant magnetic labeling of cells could be achieved using electroporation. Neural stem cells (NSCs) and leukocytes from spleen and lymph nodes were suspended in a ferumoxide labeling solution, loaded into cuvettes, and subjected to electromechanical permeabilization using electroporation. Magnetically labeled cells were assayed for labeling efficiency, as well as for potential toxicity or altered function. To confirm the method’s applicability to detect cells, MRI experiments were performed at 11.7 T. Magnetoelectroporation of NSCs, as demonstrated by Prussian blue staining, anti-dextran immunostaining, and a quantitative iron uptake assay, proved to be an efficient intracellular magnetic labeling method. Leukocytes including lymphocytes, which are notoriously difficult to label because of their membrane properties and small cytoplasmic volume, also demonstrated a pronounced uptake of ferumoxide. MRI experiments showed that labeled NSCs could be visualized as single cells and cell clusters in gelatin phantoms, and as proliferating cell masses in mouse brain. We have developed a convenient technique for instant magnetic labeling of cells. Because magnetoelectroporation allows the use of ferumoxides approved by the US Food and Drug Administration without additional agents, it has excellent potential for clinical translation. D 2006 Published by Elsevier Inc. Key words: Magnetic labeling; Electroporation; Magnetic resonance imaging; Cell tracking; Superparamagnetic iron oxide Magnetic resonance (MR) cell tracking is a novel technique that provides unique information about the distribution and migration of transplanted cells within a living organism. In vivo longitudinal studies are ideally suited to address the dynamics and the true extent of cellular migration. In addition, MR imaging (MRI) provides the opportunity for real-time correlation of cell localization with measured physiologic outcomes. The successful appli- cation of MR cellular imaging at a preclinical level contributes to the development of new cell-based therapeutic 1549-9634/$ – see front matter D 2006 Published by Elsevier Inc. doi:10.1016/j.nano.2006.01.003 Piotr Walczak is the recipient of the 2005 AANM First Annual Meeting First Place Young Investigator Award. This research is supported by National Institutes of Health Grant RO1 NS045062. JRC was funded by a fellowship from the Spanish Ministry bPrograma de Movilidad del Profesorado.Q BB is a Howard Hughes Medical Institute research training fellow. The authors are grateful to Mary McAllister for editorial assistance. 4 Corresponding author. Department of Radiology and Institute for Cell Engineering, Johns Hopkins University School of Medicine, 217 Traylor Building, 720 Rutland Avenue, Baltimore, Maryland. E-mail address: jwmbulte@mri.jhu.edu (J.W.M. Bulte). Nanomedicine: Nanotechnology, Biology, and Medicine 2 (2006) 89– 94 www.nanomedjournal.com