Selective in vitro labeling of white blood cells using 99mTc-labeled liposomes

We describe a method by which endocytosis-based radiolabeling of WBC is achieved using 99mTc-liposomes of optimal size and charge, and of a composition that assures both in vitro (whole blood) and intracellular stability of the radiopharmaceutical. In our study, excellent in vitro stability of 99mTc-liposomes with 95% labeling efficiency was observed with >90% stability up to 6 h and a minimum of 85% after 24 h of incubation either in normal saline or serum. Total WBC labeling efficiency using 99mTc-liposomes determined by radio-thin layer chromatographic analysis was 30.6 +/- 2.21%, 20.89 +/- 1.31% for monocytes and 9.7 +/- 1.74% for polymorphonuclears. Negligible activity was bound to red blood cells. The procedure did not affect the cell viability and the separation of the free 99mTc-liposomes from the cells was done by centrifugation.