The development of technetium-99m-labelled interleukin-2: A new radiopharmaceutical for the in vivo detection of mononuclear cell infiltrates in immune-mediated diseases

We describe here a new method for labelling interleukin-2 (IL-2) in high specific activity with Tc-99m for in vivo studies in man. Labelling was performed via a two-step reaction using an N3S bifunctional chelating agent. To optimise the reaction, factors affecting the incorporation of Tc-99m into the N3S ligand were studied. The conjugation of the preformed N3S chelate ligand to IL-2 was then similarly optimised. Various strategies for purifying the Tc-99m-IL-2 were explored including size exclusion, ion exchange, and several modes of reversed-phase chromatography. The radiochemical purity of the purified protein was determined by HPLC, ITLC, TCA precipitation, and SDS-PAGE. The receptor binding capacity of Tc-99m-IL-2 was studied. Biodistribution studies in normal mice were performed with Tc-99m-IL-2 purified using different techniques or labelled after prolonged storage and compared to I-125-IL-2. (C) 1997 Elsevier Science Inc.