BIOLOGICAL CONSEQUENCES OF THE HETEROGENEOUS IRRADIATION OF LYMPHOCYTES DURING TC-99M HEXAMETHYLPROPYLENE AMINE OXIME WHITE BLOOD-CELL LABELING

Technetium-99m hexamethylpropylene amine oxime (Tc-99m-HMPAO) labellin g of white blood cells, routinely used for the detection of infection, results in the incorporation of radioactivity by polymorphonuclear le ucocytes and also lymphocytes and can induce cell lesions in the latte r case. The aim of this study was therefore to acquire data on the mor phological and functional status of labelled lymphocytes present in th e Tc-99m-HMPAO leucocyte mixture and to determine the cellular consequ ences of labelling. The mean radioactivity associated with lymphocytes was 325+/-10.8 kBq/10(6) lymphocytes under standard labelling conditi ons. Microautoradiographic studies showed that labelling was heterogen eous (4% intensely labelled cells), which prevented calculation of the mean absorbed dose. The frequency of chromosomal aberrations (dicentr ics and rings) in the labelled lymphocytes for 380 kBq/10(6) cells was 1.08+/-0.09 but no abnormality was observed in the unlabelled control lymphocytes. The plating efficiency of labelled lymphocytes was reduc ed, as compared with that for control cells, but some lymphocytes were still able to form clones and were still ''alive'' by radiobiological definition. It is therefore suggested that lymphocytes should be remo ved from Tc-99m-HMPAO cell preparations before administration to patie nts.