An IgG3-IL-2 fusion protein has higher affinity than hrIL-2 for the IL-2R alpha subunit: Real time measurement of ligand binding

The alpha subunit of the interleukin-2 (IL-2) receptor (IL-2Rα)³ has the highest individual affinity for IL-2 and is the only subunit not known to bind other cytokines. The interactions between IL-2 and IL-2Rα studied in cell binding assays have revealed a number of factors which may vary significantly in different cell lines used for these assays in different laboratories. In order to avoid the problems associated with cellular assays we used an optical biosensor to examine the interaction between IL-2Rα and hrIL-2. Real-time measurement of association and dissociation resulted in a calculated K(D) of 1.9 x 10^-7 M for this interaction. We then examined the IL-2Rα binding of a potentially bivalent IgG3-IL2 fusion protein previously shown to have a higher affinity than hrIL-2 for the high affinity IL-2R but not the intermediate affinity IL-2R. Biosensor measurements of association and dissociation of IgG3-IL2 to IL-2Rα yielded a similar association rate but a decreased dissociation rate compared to hrIL-2, resulting in a K(D) of 5.3 x 10^-8 M. This system is applicable to the numerous IL-2 mutants with different affinities and activities and is generalizable to other cytokine/receptor interactions. Copyright (C) 1996 Elsevier Science Ltd.