99mTc-Interleukin-2

Excerpt

Interleukin-2 (IL-2) is a T-cell growth factor secreted by T lymphocytes (1). It stimulates the growth and differentiation of T cells, B cells, NK cells, LAK cells, monocytes, macrophages, and oligodendrocytes (2-4). Three subunits (α, β, and γ) of the IL-2 receptor (IL-2R) have been identified. The α subunit has low affinity and normally expresses very low levels in resting lymphocytes (5). The high-affinity receptor is expressed mainly on activated T cells and macrophages (6) when the α, β, and γ subunits associate together (7). Activated cells are found in infiltrating tumors, inflammatory tissues, and autoimmune tissues.

[¹²³I]IL-2 has been developed as a single-photon emission computed tomography (SPECT) tracer for imaging activated immune cells in tumors and pathological tissues (8-10). However, ¹²³I is a cyclotron radionuclide and therefore is expensive and not readily available. On the other hand, the ready availability and low cost of ^99mTc led to the development of ^99mTc-IL-2 for studying activated cells in tissues and tumors (11).