RT Journal Article
SR Electronic
T1 Interleukin 2 (IL-2) Variants Engineered for Increased IL-2 Receptor α-Subunit Affinity Exhibit Increased Potency Arising from a Cell Surface Ligand Reservoir Effect
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 864
OP 869
DO 10.1124/mol.66.4.864
VO 66
IS 4
A1 Balaji M. Rao
A1 Ian Driver
A1 Douglas A. Lauffenburger
A1 K. Dane Wittrup
YR 2004
UL http://molpharm.aspetjournals.org/content/66/4/864.abstract
AB Proliferation of activated T cells and CD56 bright natural killer (Cytokine Growth Factor Rev13:169-183, 1995OpenUrl) cells caused by interleukin-2 (IL-2) has been exploited in IL-2-based therapies for the treatment of metastatic renal cell carcinoma and melanoma (J Clin Oncol13:688-696, 1995OpenUrlAbstract/FREE Full Text; J Clin Oncol17: 2105-2116, 1999OpenUrlAbstract/FREE Full Text). In this study, we demonstrate the potentially improved therapeutic value of IL-2 variants engineered to gain 15- to 30-fold increased affinity for the IL-2 receptor α-subunit (IL-2Rα). A novel pulsed bioassay was used to more closely approximate the rapid systemic clearance pharmacokinetics of cytokines such as IL-2, compared with conventional static bioassays. In this assay, mutants with increased affinity for IL-2Rα exhibit significantly increased activity for T-cell proliferation, whereas static bioassays not only fail to reveal the increased activity resulting from enhanced IL-2Rα affinity (false negatives), but also suggest improved activity for another mutant without enhanced activity in the pulsed assay (false positive). Our studies on the mechanism leading to increased activity of IL-2 mutants with increased IL-2Rα affinity suggest that cell-surface IL-2Rα acts as a ligand reservoir for the IL-2 mutants. This leads to increased cell-surface persistence of the IL-2 mutants with increased IL-2Rα affinity in cell-surface ligand reservoirs and consequently increased integrated growth signal. Furthermore, a mathematical model predicts increased persistence of cell surface-bound IL-2 in vivo for enhanced IL-2Rα-binding IL-2 mutants, suggesting potentially improved therapeutic value of allowing cellular capture of ligands in persistent cell-surface reservoirs. Finally, our findings emphasize the critical choice of appropriate bioassays to evaluate engineered proteins and other drugs.