Development of a CCR8 monoclonal antibody to block CCR8 signaling and to abolish the immunosuppressive function of Treg for the treatment of cancers.

e14506 Background: The tumor microenvironment (TME) contains regulatory T (Treg) cells, which play a critical role in immunosuppression and are thus an attractive target for cancer therapy. The ideal approach would be to inhibit Tregs within tumors while sparing those in peripheral and normal tissues. Tumor-associated Tregs express the chemokine receptor CCR8, which is involved in the induction, expansion, migration, and immunosuppression of Tregs, making targeted inhibition of CCR8 signaling a potential therapeutic strategy against cancer. Methods: We have developed IPG0521, a monoclonal antibody antagonist of CCR8, and characterized its properties, including signaling blocking, chemotaxis, species cross-reactivity, anti-tumor efficacy, and synergistic antitumor effect with PD1 antibody. Single-cell RNA sequencing with CD45+ cells isolated from tumors treated with or without IPG0521 was also employed for profiling the mechanism of the antitumor effect of IPG0521 in the murine H22 cancer model. Results: IPG0521 inhibits receptor-mediated signaling and chemotaxis in Treg cells with a single-digit nanomolar IC50. It is cross-reactive in five species: mouse, rat, dog, monkey, and human. IPG0521 has shown excellent anti-tumor efficacy in several murine syngeneic cancer models, and its anti-tumor effect is enhanced when combined with a PD-1 antibody. Its sustained anti-tumor efficacy has been demonstrated in the murine H22 cancer model via even withdrawing the antibody during the study. The results of deep single-cell RNA sequencing on tumor-infiltrating lymphocytes (TILs) showed that the transcriptional profiles of these Treg cells could be distinguished into three distinct subsets based on molecular, functional, and immunosuppressive properties. These subsets were defined as the Treg_Foxp3 high subset, which exhibited low immunosuppression, the Treg_Foxp3 mild subset, which demonstrated mild immunosuppression, and the Treg_Foxp3 low subset, which had high proliferation. IPG0521 treatment resulted in a significant increase in the Treg_ Foxp3 high subset and a significant decrease in the Treg _ Foxp3 mild subset while no change in the Treg_ Foxp3 low subset, indicating a reduction in Treg immunosuppression. This change in Treg cells also altered the composition of other immune cells, including a significant increase in neutrophils and natural killer (NK) cells, which ultimately inhibited tumor growth. Conclusions: IPG0521 has potent anti-tumor effects in multiple tumor types, including lung, liver, and breast cancers, in both syngeneic and immune-humanized mouse models. It inhibits Tregs immunosuppression and activates CD8+ T cells to achieve its anti-tumor effects. These results support the development of IPG0521, which is currently under IND filing, as a novel therapeutic agent for the treatment of cancers.