^99mTc Labelled Human Leukocytes

Abstract

A new method of human leukocyte labelling is described. 20 ml of human blood are allowed to sediment in a dextran solution and the remaining red blood cells are removed using NH₄Cl. The leukocyte-rich suspension is incubated with a Sn-pyrophosphate solution, and then labelled, using 20 mCi ^99mTc pertechnetate. Labelling efficiency is about 30%. Functional activity was shown to be satisfactory: (1) appearance under electron microscopy was quite normal; (2) Klebsiella ingestion, zymosan-stimulated oxygen consumption and iodination were similar in labelled and unlabelled cells, and (3) chemotaxis revealed no alteration in cell migration.

Direct Cell Radiolabeling for in Vivo Cell Tracking with PET and SPECT Imaging

“…Being able to image autologous WBCs is a useful method to diagnose infections/inflammation. Linhart et al explored this concept in vitro, showing radiolabeling yields of 30% and satisfactory functional activity tests (e.g., chemotaxis) postradiolabeling . Kelbaek et al refined this methodology for WBC radiolabeling, exploring different amounts of Sn salts (SnF 2 and SnP 2 O 7 ), and confirming retainment of cell function after radiolabeling…”

“…The first clinical study of radiolabeled leukocytes already acknowledged the issue of labeling mixed cell populations, noting a much higher accumulation of radioactivity in the spleen of patients injected with 111 In-labeled cells containing large numbers of erythrocytes compared to the patient who was administered an erythrocyte-depleted preparation . The stannous pyrophosphate labeling method for 99m Tc suffers from the same drawback, as it efficiently labels residual erythrocytes in WBC preparations . This realization led early investigators in the field to evaluate the selectivity of various radiotracers for leukocytes over erythrocytes, although the radiotracers initially found to be the most efficient for cell labeling were not selective .…”

“…Cell functionality assays will depend on the cell type and the main function that is expected from the cell population. For neutrophils and eosinophils, chemotaxis, phagocytosis, ROS production, or granule-release assays can be used. , More recently, measuring HMGB1, an endogenous marker of cellular damage, has been suggested . For lymphocytes, cytokine secretion (e.g., IFNγ for CD4 or CD8 T cells, IL-10 for Tregs), phenotyping and proliferation assays are typically desirable.…”