Abstract 5308: Therapeutical antibody against CD25 mediating depletion of regulatory T cells without interruption of IL-2 signaling enhances antitumor immunity

Abstract

Abstract Regulatory T cell or suppressor T cell in tumor diminishes immune response to immunotherapy. CD25, the high-affinity receptor subunit for interleukin (IL)-2, is highly expressed on Treg and considered a selective target for Treg depletion. However, CD25 is also expressed on activated effector T cells (Teff), and antibodies against CD25 with blocking IL-2 signaling have limited antitumor activity. Here we developed a humanized antibody against CD25 (H3F1-4V2) without blocking IL-2 signaling. This antibody was derived from hybridoma of mice immunized with CD25-mFc. Two CD25 antibodies Daclizumab and RG6292 were applied as reference antibodies, and Daclizumab blocked IL-2 signaling, and RG6292 did not block IL-2 signaling. H3F1-4V2 had higher affinity to 293T cells overexpressing human CD25 than Daclizumab (EC50=0.4nM vs 0.45nM), with lower Kd (0.88nM vs 1.5nM). Because of high affinities, H3F1-4V2 and Daclizumab both efficiently depleted Treg from PBMC in vitro, while RG6292 depleted Treg with weaker ability because of low affinity to CD25. In the Teff, downstream signaling of IL-2 was analyzed, and Daclizumab significantly decreased pSTAT5, while RG6292 and H3F1-4V2 kept the pSTAT5 level intact. PBMC was cultured in the presence of CD25 antibodies, and Daclizumab inhibited T cell proliferation (ki67+%) and activation (Granzyme B+%), but not for RG6292 and H3F1-4V2. At last, these CD25 antibodies were tested in humanized mice whose CD25 was replaced with human CD25, and MC38 tumor cells were transplanted into these mice.H3F1-4V2 completely suppressed tumor growth, while RG6292 also suppressed tumor growth with weaker efficiency and Daclizumab had little effect on tumor growth. These results suggested H3F1-4V2 was the best candidate targeting CD25 for cancer therapy. Citation Format: Hao Peng, Shuangshuang Hu, Yuli Li, li Ding, Jinying Ning, Guojin Wu. Therapeutical antibody against CD25 mediating depletion of regulatory T cells without interruption of IL-2 signaling enhances antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5308.