A new technique for the radiolabelling of mixed leukocytes with zirconium-89 for inflammation imaging with positron emission tomography

Mixed leukocyte (white blood cells [WBCs]) trafficking using positron emission tomography (PET) is receiving growing interest to diagnose and monitor inflammatory conditions. PET, a high sensitivity molecular imaging technique, allows precise quantification of the signal produced from radiolabelled moieties. We have evaluated a new method for radiolabelling WBCs with either zirconium-89 (89Zr) or copper-64 (64Cu) for PET imaging. Chitosan nanoparticles (CNs) were produced by a process of ionotropic gelation and used to deliver radiometals into WBCs. Experiments were carried out using mixed WBCs freshly isolated from whole human blood. WBCs radiolabelling efficiency was higher with [89Zr]-loaded CN (76.8 ± 9.6% (n = 12)) than with [64Cu]-loaded CN (26.3 ± 7.0 % (n = 7)). [89Zr]-WBCs showed an initial loss of 28.4 ± 5.8% (n = 2) of the radioactivity after 2 h. This loss was then followed by a plateau as 89Zr remains stable in the cells. [64Cu]-WBCs showed a loss of 85 ± 6% (n = 3) of the radioactivity after 1 h, which increased to 96 ± 6% (n = 3) loss after 3 h. WBC labelling with [89Zr]-loaded CN showed a fast kinetic of leukocyte association, high labelling efficiency and a relatively good retention of the radioactivity. This method using 89Zr has a potential application for PET imaging of inflammation.