RADIOLABELED MIXED LEUKOCYTES AND PURE GRANULOCYTES WITH STABILIZED TC-99(M)-EXAMETAZIME

Although the methylene blue stabilizer extends the shelf Life of Tc-99 (m)-exametazime to 4-6 h after reconstitution, the dark blue appearanc e of the mixture of stabilized Tc-99(m)-exametazime and blood componen ts makes it impossible to separate out the leukocyte button. The aim o f this study was to assess the feasibility of using stabilized Tc-99(m )-exametazime to radiolabel mixed leukocytes separated by Volex sedime ntation with hypotonic lysis (VL) and pure granulocytes isolated by a single-density Ficoll-Hypaque gradient with hypotonic lysis (FL). Isol ated cells from 40-ml and 80-ml donor blood samples were mixed with 0. 5 ml stabilized Tc-99(m)-exametazime (similar to 925 MBq Tc-99(m) and 62.5 mu g exametazime) and incubated at room temperature for 15 min. A fter incubation, two dilution steps with 3 ml and 9 ml of 12.6% ACD/NS (anticoagulant citrate dextrose, solution A USP, mixed with 0.9% NaCl , v/v) were conducted to dilute the dark blue mixture and to remove an y unbound Tc-99(m) activity. With the addition of 9 mi of 12.6% ACD/NS solution to the 1-ml bottom portion from the first dilution, the supe rnatant of the centrifuged preparation was clear enough to be withdraw n. The overall labelling efficiency (LE) of labelled leukocytes and gr anulocytes was 87.1 +/- 4.9% and 87.7 +/- 6.2%, respectively (n = 12 e ach). Overall, radiolabelled cells (n = 12) from the 80-ml blood sampl es (LE = 90.3 +/- 2.8%) had an similar to 6% higher labelling efficien cy than from the 40-ml blood samples (LE = 84.5 +/- 6.0%) and also had a slightly better in vitro stability compared to the 40-ml samples. T he in vitro stability studies showed that only similar to 2% (n = 48) Tc-99(m) activity was eluted each hour from the radiolabelled leukocyt es or granulocytes for the 40-ml or 80-ml blood samples during the 6-h evaluation period. Cell viability of all labelled leukocyte samples w as confirmed by the trypan blue staining technique. In conclusion, mix ed leukocytes separated by the VL method and pure granulocytes isolate d by the FL method can be effectively labelled with stabilized Tc-99(m )-exametazime with the use of the 'double dilution' technique. ((C) 19 98 Lippincott Williams & Wilkins).