In vitro human leukocyte labeling with ⁶⁴Cu: an intraindividual comparison with ¹¹¹In-oxine and ¹⁸F-FDG☆

Abstract 

We investigated labeling human leukocytes [white blood cells (WBCs)] in vitro with copper-64 (Cu) comparing labeling efficiency, viability and stability of Cu-WBCs with ¹¹¹In-oxine (In) WBCs and ¹⁸F-FDG (FDG) WBCs.

Methods

Leukocytes from 10 volunteers were labeled with Cu, In and FDG. Forty milliliters of venous blood was collected and leukocyte separation was performed according to standard methods. In-WBCs and FDG-WBCs were labeled according to published methods. For Cu-WBCs, tropolone initially was used as a single chelating agent. Because of poor intracellular Cu retention (54±4% at 3 h and 24±5% at 24 h), the fluorinated, membrane-permeable divalent cation chelator quin-MF was added. WBCs were incubated in 5 ml saline containing 100 μl of 1mM quin-MF/AM in 2% dimethyl sulfoxide and 74–185 MBq Cu-tropolone for 45 min at 37°C. Labeling efficiencies; in vitro cellular viabilities at 1, 3 and 24 h; and in vitro stabilities at 1, 2, 3, 4 and 24 h (except FDG-WBCs) were determined.

Results

Mean Cu-WBCs (87±4%) and In-WBCs (86±4%) labeling efficiencies were comparable and were significantly higher than FDG-WBCs (60±19%, P<.001). Cell viabilities, similar at 1 h, were significantly higher for ⁶⁴Cu-WBCs at 3 and 24 h. Intracellular retention of activity was always significantly higher for In-WBCs than for Cu-WBCs and FDG-WBCs. At 24 h, intracellular retention was 88±4% for In-WBCs and 79±6% for Cu-WBCs.

Conclusion

Cu-WBC labeling efficiency and viability were comparable or superior to In-WBCs and significantly higher than FDG-WBCs. Although significantly more activity eluted from Cu-WBCs than from In-WBCs, Cu-WBC probably is adequate for imaging. These data suggest that further investigation of in vitro copper-64-labeled leukocytes for PET imaging of infection is warranted.

Keywords: ⁶⁴Cu, ¹⁸F-FDG, ¹¹¹In-oxine, Infection imaging, Labeled leukocytes, PET