Development and evaluation of a radiolabelling agent for white blood cell scans

Radiolabelled autologous leukocytes have been used for the clinical diagnosis of inflammation and infection. To develop a stable and efficient radiopharmaceutical for labelling leukocytes, we prepared a novel radioiodinated cell-penetrating peptide, ¹²⁵I-TAT, using a bi-functional linker. ¹²⁵I-TAT was stable for two days under three different temperature conditions of -20 °C, 4 °C, and 40 °C, with its radiochemical purity remaining over 99%. Iodinated TAT was non-toxic to leukocytes with an IC₅₀ value of over 100 μM. The labelling efficiency of ¹²⁵I-TAT using 1ｘ10⁷ cells ranged from 27% to 53% when the three leukocyte cell lines were pre-treated with DMSO. This is comparable to the labelling efficiency recommended by the guideline for conventional labelling agents using 2ｘ10⁸ cells. Radioiodinated cell-penetrating peptide may be an improved radiopharmaceutical for white blood cell scans by further optimization.