Abstract 5092: Non-IL-2 blocking Treg-depleting anti-human CD25 mAb primes potent anti-tumor immunity and synergizes anti-tumor effects of anti-PD-1 in a novel hIL-2RA knockin model
Authors: He Daniel 
Published: April 2023

Abstract
The therapeutic effects for cancer immunotherapy are largely hampered by intratumoral CD4+CD25+ regulatory T cells (Tregs) which leads to poor outcome in many cancer patients upon treatment of immune checkpoint inhibitors. Moreover, the balance between effector T (Teff) cells and Treg cells in the tumor microenvironment (TME) impacts on tumor progression and anti-tumor immunity. Depleting tumor-infiltrating Tregs by selectively targeting CD25 to reduce the ratios of regulatory to effector T cells (Treg/Teff) without disturbing IL-2 signalling is a promising strategy to advance anti-tumor immunity. Hence, we evaluated the in vivo anti-tumor effects of Non-IL-2 blocking Treg-depleting anti-hCD25 mAb versus IL-2-blocking anti-hCD25 mAb (Basiliximab) in an engineered hCD25 (IL-2RA) knockin mouse model.Firstly, we developed the genetically engineered CD25 (IL-2RA) humanized mouse model by ES cell targeting, in which mouse Cd25 exons 2-6 are replaced by human counterparts corresponding to the extracellular domain leaving the intracellular regions intact. Then, we performed flow cytometry analysis to confirm the surface expression of hCD25 on naive Treg cell from peripheral blood and spleen in homozygous hCD25 knockin mice. In addition, we found the hCD25 expression is upregulated on activated Treg cell derived from splenocytes for both heterozygous and homozygous hCD25 knockin mice. Furthermore, the female homozygous hCD25 knockin mice subcutaneously engrafted with MC38 syngeneic tumors received two different therapeutic anti-CD25 mAb treatment in parallel and we found the Non-IL-2 blocking Treg-depleting anti-human CD25 mAb (anti-hCD25NB) displayed more potent anti-tumor response compared to IL-2-blocking Treg-depleting anti-human CD25 mAb (anti-hCD25BL), supporting that keeping IL-2 signaling on effector T cells are required to enhance effector activation and anti-tumor immunity. Notably, the study groups treated with anti-hCD25NB plus anti-mPD-1 showed synergistic therapeutic effects as expected. As a matter of fact, both CD4+CD25+ T cells and CD4+CD25+FoxP3+ Treg cells reduced significantly upon treatment of anti-hCD25NB and anti-hCD25BL in spleen and tumors, but no big change in the number of CD4+FoxP3+ Treg cells.Likewise, anti-hCD25NB in combination with anti-mPD-1 leads to more significant CD4+CD25+ Treg depletion in spleen and tumors along with increased CD8+Granzyme B+ cytotoxic T cells.Collectively, our CD25 (IL-2RA) humanized mouse provides a powerful model to assess the in vivo preclinical therapeutic effects of CD25+ Treg-depleting antibodies for cancer immunotherapy.
Citation Format: Daniel He. Non-IL-2 blocking Treg-depleting anti-human CD25 mAb primes potent anti-tumor immunity and synergizes anti-tumor effects of anti-PD-1 in a novel hIL-2RA knockin model. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5092.