Molecular dissection of the interactions of an antitumor interleukin-2-derived mutein on a phage display-based platform.

A mutein with stronger antitumor activity and lower toxicity than wild-type human interleukin-2 (IL-2) has been recently described. The rationale behind its design was to reinforce the immunostimulatory potential through the introduction of four mutations that would selectively disrupt the interaction with the IL-2 receptor alpha chain (thought to be critical for both IL-2-driven expansion of T regulatory cells and IL-2-mediated toxic effects). Despite the successful results of the mutein in several tumor models, characterization of its interactions was still to be performed. The current work, based on phage display of IL-2-derived variants, showed the individual contribution of each mutation to the impairment of alpha chain binding. A more sensitive assay, based on the ability of phage-displayed IL-2 variants to induce proliferation of the IL-2-dependent CTLL-2 cell line, revealed differences between the mutated variants. The results validated the mutein design, highlighting the importance of the combined effects of the four mutations. The developed phage display-based platform is robust and sensitive, allows a fast comparative evaluation of multiple variants, and could be broadly used to engineer IL-2 and related cytokines, accelerating the development of cytokine-derived therapeutics.