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-2R alpha)(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-2R alpha studied in cell binding assays have revealed a number of f actors which may vary significantly in different cell lines used for t hese assays in different laboratories. In order to avoid the problems associated with cellular assays we used an optical biosensor to examin e the interaction between IL-2R alpha and hrIL-2. Real-time measuremen t 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-2R alpha bind ing 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 associ ation and dissociation of IgG3-IL2 to IL-2R alpha yielded a similar as sociation rate but a decreased dissociation rate compared to hrIL-2, r esulting 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) 1 996 Elsevier Science Ltd