An in vitro study to compare 99mTc-stannous colloids and 99mTc-HMPAO for labelling human leukocytes

Aim Aim of the present study was to compare in vitro the labelling efficiency (LE) and cell viability (TBE) of autologous leukocytes labelled with 9 9 m Tc-SnF 2 and 9 9 m Tc-HMPAO, and to evaluate the quantity and quality of spontaneously released 9 9 m Tc (SR) from labelled cells at several time points after labelling. Methods. A total of 14 patients with different diseases and 18 normal subjects were included in this study. A blood sample was collected from each patient; purified autologous leukocytes were divided into 2 samples and labelled with 9 9 m Tc-SnF 2 and 9 9 m Tc-HMPAO. LE was evaluated at the end of labelling and TBE and SR were evaluated at 10 min and 1 h, 2 hand 4 h after labelling. Results. LE of 9 9 m Tc-SnF 2 -WBC was higher than 9 9 m Tc-HMPAO-WBC (61.2′18.7% and 43.3′11.3; p<0.0001) and we found an inverse correlation between blood glucose and labelling efficiency for both methods (p=0.02). Minimal differences were also observed between 2 methods after 10 min and 1 h, as far as the cell viability is concerned. The percentage of radioactivity spontaneously released from 9 9 m Tc-SnF 2 -WBC was significantly higher compared to 9 9 m Tc-HMPAO-WBC at each time point Radioactivity released from labelled cells was predominantly 9 9 m Tc-SnF 2 and 9 9 mTc-HMPAO with few free 99mTc (<20%). Conclusion. Both radiopharmaceuticals are not toxic for WBC. Labelling with 9 9 m Tc-SnF 2 give a higher LE than with 9 9 m Tc-HMPAO; however, radiolabelled colloids are more released from labelled cells over a period of 4 h. While 9 9 m Tc-HMPAO is physiological excreted into gastrointestinal tract, 9 9 m Tc-SnF 2 can be re-uptaken in vivo by reticulo-endothelial cells of liver and spleen. These findings suggest that 9 9 m Tc-SnF 2 -WBC might be better than 9 9 m Tc-HMPAO-WBC for studying inflammatory bowel diseases.