A comparison of two 99Tcm leucocyte labelling techniques

Full text: 111In-oxine labelled leucocytes are routinely used for the diagnosis of various inflammatory conditions. The search for a good 99Tcm labelling agent continues in order to prevent the radio-toxicity effects to lymphocytes caused by the high radiation dose from 111In decay. 99Tcm-HMPAO, a lipophilic, neutral molecule, has a leucocyte labelling mechanism similar to that of 111In-oxine (Passive Diffusion).Granulocytes are preferentially labelled with 99Tcm-HMPAO. Another method for labelling leucocytes with 99Tcm has been achieved with the polycationic, hydrophilic molecule, Modified Poly-lysine (MPL). Most mammalian cells have negatively charged surfaces which electrostatically attract cationic 99Tcm-MPL. Surface adsorption followed by internalisation by endocytosis leads to cell labelling. The entire mechanism is termed non-specific adsorptive endocytosis. The aim of this study was to compare the in vitro stability of the 99Tcm-leucocyte label prepared with 99Tcm-MPL to that prepared with 99Tcm-HMPAO. Leucocytes were isolated from venous blood using the 2% methyl cellulose sedimentation method. Half of the leucocytes were incubated in 99Tcm-HMPAO (1.5 GBq, 1 mL) for 15 minutes, the remaining leucocytes were incubated in 99Tcm- MPL (1.5 GBq, 1 mL) for 45 minutes. The labelling stability of the leucocytes was determined by incubation at room temperature in serum for 120 minutes. 99Tcm-MPL labels all components of the leucocyte population equally well and its improved labelling efficiency and stability may have application in studying the trafficking of T-lymphocytes in adoptive immunotherapy. Copyright (2000) The Australian and New Zealand Society of Nuclear Medicine Inc