TC-99M AND IN-111 DOUBLE-LABELING OF GRANULOCYTES FOR KINETIC AND CLINICAL-STUDIES

A new technique of labelling granulocytes with both technetium-99m hexamethylpropylene amine oxime (HMPAO) and indium-lll in a single protocol was developed in order to exploit the advantages of each radiolabel in clinical and investigative studies. Fourteen patients were included in this prospective study. Granulocytes were labelled with both In-111-tropolonate and Tc-99m-HMPAO. In vitro shape change assay and in vivo distribution and recovery studies were performed to assess the activation of and damage to these cells due to the labelling procedure. The comparative kinetics of In-111 and Tc-99m in the blood, liver, spleen, and bone marrow were studied by blood sampling and dual radionuclide imaging early (1 h) and late (24 h) after injection. The functional integrity of the double-labelled granulocytes and the feasibility of the technique were investigated in 14 patients with a painful prosthetic hip due to causes other than infection. The efficiency of double labelling was 63% (SD 14%) for In-111 and 39% (SD 12%) for Tc-99m-HMPAO. In vitro granulocyte activation and ex vivo recovery values were comparable to those from single radionuclide labelling. No artefactual granulocyte sequestration was seen in the lungs or liver. The radioactivity was distributed between the liver, spleen and bone marrow and, to a lesser extent, the lung. Early Tc-99m counts in the liver, spleen and bone marrow, in relation to background, were significantly higher than In-111 counts while the reverse was seen in late images. Furthermore, circulating ''free'' Tc-99m was significantly higher than free In-111 at 24 h. Organ Tc-99m counts, expressed in relation to the activity in early images, decreased in the spleen, increased in the liver and remained unchanged in bone marrow whereas In-111 counts increased in the bone marrow and liver, and decreased in the spleen. Granulocytes can be labelled with both In-111 and Tc-99m-HMPAO in a single protocol without cross-chelation, cellular activation or damage. By favourably exploiting their kinetics for early and late imaging, double-labelled granulocytes may be useful in several clinical and investigative situations.