99mTc-interleukin-2 scintigraphy in normal subjects and in patients with autoimmune thyroid diseases: a feasibility study

Purpose  Radiolabelled interleukin-2 is a radiopharmaceutical used for the study of chronic inflammatory processes. ¹²³I-labelled interleukin-2 has successfully been used in a large number of patients affected by several immune-mediated diseases. ¹²³I, however, is expensive and not readily available. We have, therefore, developed a method for labelling interleukin-2 with ^99mTc to high specific activity based on the use of an N₃S bifunctional chelating agent. In this paper, we describe the results obtained with ^99mTc-interleukin-2 in a series of eight normal subjects and of 12 patients with autoimmune thyroid diseases. Methods  Biodistribution, pharmacokinetics, haematological and systemic toxicity, radiation absorbed dose and in vivo targeting were studied. Results  Results showed rapid plasma clearance of ^99mTc-interleukin-2 with retention mainly in the kidneys. Biodistribution and kinetics were similar to that observed for ¹²³I-interleukin-2. No acute systemic toxicity was found; a small decrease in peripheral blood lymphocytes was observed in the first hours only in patients, but it was mild and transient. ^99mTc-interleukin-2 accumulated, to varying extents, in the thyroid of all patients affected by autoimmune thyroid diseases but not in the thyroid of normal subjects. The effective dose equivalent of a diagnostic activity of ^99mTc-interleukin-2 (185 MBq) was 1.35 mSv. No correlation was observed between thyroid autoantibodies and uptake of ^99mTc-interleukin-2. Conclusions  The use of ^99mTc-interleukin-2 is safe and simple; the favourable dosimetry and biodistribution and the rapid clearance make it potentially useful for the study of chronic inflammatory diseases such as autoimmune thyroid disease.