Omer Aras MD, Presenter: Nothing to Disclose

Marcelino Bernardo, Abstract Co-Author: Nothing to Disclose

Dawn Betters PhD, Abstract Co-Author: Nothing to Disclose

Michael Kruhlak PhD, Abstract Co-Author: Nothing to Disclose

Richard W Childs MD, Abstract Co-Author: Nothing to Disclose

Joseph Alan Frank MD, Abstract Co-Author: Nothing to Disclose

Peter L. Choyke MD, Abstract Co-Author: Researcher, Koninklijke Philips Electronics NV Researcher, General Electric Company Researcher, Siemens AG Researcher, F. Hoffmann-La Roche Ltd Researcher, iCAD, Inc

Noriko Sato MD, Abstract Co-Author: Nothing to Disclose

The aim of this study is to explore the feasibility of using Ferumoxytol, a Food and Drug Administration (FDA) approved ultrasmall superparamagnetic iron oxide (USPIO), for labeling and magnetic resonance imaging (MRI) of human natural killer (NK) cells.

Human NK cells (CD3-/CD56+) isolated from PBMC and expanded in vitro were labeled with Ferumoxytol alone, Ferumoxytol with protamine sulfate (PS) or Ferumoxytol with PS and heparin (H) mixture. H was used to examine if it enhance the labeling. In each labeling condition, increasing concentrations of Ferumoxytol (equivalent to iron concentrations of 0–100 µg/mL) were used. The presence of USPIO in NK cells was confirmed by Prussian blue staining. The effects of the labeling on cell viability were examined by Trypan blue staining. To determine the MRI detection threshold of labeled NK cells in vitro, titration experiments with different numbers of labeled cells were performed using a clinical 3 T MRI system.

A labeling efficiency of >99% was achieved after incubating NK cells with 100 µg/mL of USPIO for 2 h either in the presence of PS (40µg/mL) or in the presence of the PS (40µg/mL)-H (2U/mL) mixture. No significant cell death was observed with either method. In vitro MRI of labeled NK cells revealed that both USPIO-PS and USPIO-PS-H mixture labeling methods resulted in a significant but similar signal intensity (SI) loss on T2*WI sequences (48% and 46%, respectively) (Figure1A). USPIO alone only showed minimum SI loss (5%) but no visible Prussian blue staining (Figure1B). While 10 6 cells/mL resulted in strong SI loss, as few as 105 cells/mL could also be detected in vitro relative to unlabeled cells by using this approach.

The results of this study indicate that: (1) human NK cells could be effectively labeled with either USPIO-PS or USPIO-PS-H mixtures. (2) Optimized NK cell labeling was achieved with a USPIO concentration of 100 µg/mL and an incubation time of 2 hr without posing significant adverse effects on the viability of cells; (3) While macrophages have been shown to take up USPIOs, to the best of our knowledge, this is the first study showing effective labeling of NK cells with USPIO.

NK cells can be successfully labeled in vitro with an FDA approved USPIO and this method may enable imaging of innate immune responses and MRI-based tracking of human NK cells in patients with cancer.

Aras, O, Bernardo, M, Betters, D, Kruhlak, M, Childs, R, Frank, J, Choyke, P, Sato, N, Human Natural Killer (NK) Cells Labeling with Ultrasmall Superparamagnetic Iron Oxide (USPIO)-Ferumoxytol and Their Appearance on Magnetic Resonance Imaging.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034434.html