Abstract 6055: Discovery of epitope-selective anti-CD25 targeting therapeutic antibodies for effective Treg cell depletion in cancer using a novel AI/ML based platform

Therapeutic antibodies have contributed significantly to better clinical outcomes across multiple tumor types. However, there is still unmet clinical need in cancers with an immunosuppressive and stroma rich tumor microenvironment (TME). One key limitation in early antibody discovery is immunodominance - an evolutionary bias toward specific epitopes that steer antibody selection away from potentially high-efficacy epitopes. Our integrated computational and laboratory approach to antibody discovery enabled us to build focused epitope embodiments of structural epitopes. These epitope embodiments, called Meso-scale Engineered Molecules (MEMs), are used in antibody selection to steer hits toward intended epitopes. CD25 (IL2Rα) is highly expressed on regulatory T-cells (Tregs) that drive immunosuppression in the TME. Depletion of Tregs can restore anti-tumor T effector (Teff) function in the TME, by increasing the Teff/Treg ratio, especially when combined with checkpoint-inhibitors. Using our epitope-selective antibody discovery platform, we built MEMs that embody eight CD25 structural epitopes outside the CD25:IL-2 interface. Through in vitro selection, several high-affinity (median KD = 25 nM) anti-CD25 antibodies from each of the eight intended CD25 epitopes were identified and confirmed to be on epitope by cross-blocking assays and in-epitope alanine mutations. Several conventional- and epitope-selective anti-CD25 clones were converted to human IgG1 and tested in in vitro assays. As a result, these antibodies bound specifically to CD25+ cells, preserve IL-2 signaling via pSTAT5 assays and elicited potent ADCC activity using human effector cells, superior to benchmark antibodies. These studies show that our integrated computational and laboratory platform improves the antibody discovery process, producing clones with biological function and improved therapeutic efficacy. Citation Format: Phung Gip, Bing Li, Angeles Estelles, Hanako Daino-Laizure, Oleg Gurinovich, Piotr Zalicki, Kevin Hauser, Alex Taguchi, Christian Barrett, Andrew Morin, Jordan Willis, Mohan Srinivasan, Isaac Bright, Matt Greving. Discovery of epitope-selective anti-CD25 targeting therapeutic antibodies for effective Treg cell depletion in cancer using a novel AI/ML based platform [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6055.