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Despite the promise of immunotherapy for cancer treatment, nearly 80% of patients fail to respond to checkpoint inhibitor (CPI) therapy. Regulatory T cells (Tregs), which inhibit immune responses in the tumor microenvironment via multiple suppressive mechanisms, have been proposed to play a key role in those patients who are not responding to CPI therapy. Therefore, targeted depletion of Tregs should promote more effective antitumor immunity. CCR8 is a chemokine receptor that is selectively expressed on highly activated human tumor-resident Tregs, and these intratumoral CCR8+ Tregs have been shown to drive immunosuppression that leads to poor prognosis for cancer patients. Here, we demonstrate that CCR8 is highly expressed on intratumoral FoxP3+ Treg cells in multiple cancers and is absent on other major immune cell populations in tumor microenvironment including effector T cells, conventional CD4 T cells, B cells, NK cells, some FoxP3+ cells, and myeloid cells. Importantly, no CCR8 protein expression was observed on any peripheral human leukocyte subset examined. These results provide strong rationale for targeting CCR8 as a cancer immunotherapy by selectively depleting the most suppressive intratumoral Treg cells. We have developed a humanized therapeutic antibody, ZL-1218, that binds to human CCR8 with high affinity and specificity and can induce potent ADCC activity enabling strong NK cell-mediated killing of CCR8-expressing Tregs. We show that in human CCR8 knock-in mouse models bearing syngeneic tumors, ZL-1218 reduces intratumoral Treg cells and thus elicits significant tumor growth inhibition in a dose-dependent manner. We have recently explored the potential for ZL-1218 in combination immunotherapy, examining the enhanced antitumor activity when ZL-1218 is combined with anti-PD-1. Using human dissociated tumor samples, we further observed that different tumor types may induce different CCR8 expression levels on intratumoral Tregs leading to multiple, distinct CCR8+ subsets in various indications. We are currently exploring the significance of these distinct populations and the impact of ZL-1218-mediated depletion of both CCR8 high- and CCR8 low-expressing subsets in multiple indications. Together, these data support the advancement of ZL-1218 into clinical evaluation as a novel therapeutic candidate to treat human solid tumors. Citation Format: Jing Zhang, Wenhua Shi, Min Chen, Xinchuan Dai, Hongshui Liu, Shou Li, Lina Wang, Bee-Chun Sun, Monica You, Vivian Morton, Qiuping Ye, Lishan Kang, Bing Wan, Peter Brams, David I. Bellovin. ZL-1218, a novel anti-CCR8 antibody, exerts potent antitumor effect by depleting intratumoral regulatory T cells [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 3590. |
