Abstract 5627: Anti-TIGIT biomarker study: Inhibition of TIGIT induces loss of Tregs from tumors and requires effector function for tumor growth inhibition

The immune checkpoint co-inhibitory receptor TIGIT (T cell immunoreceptor with Ig ITIM domain) is expressed on regulatory T cells (Tregs) and on activated CD4+ T, CD8+ T, and NK cells. We have reported that by blocking TIGIT activity with an IgG2a anti-TIGIT antibody (313R12), CD8+ and CD4+ Tcells and NK cells were activated, resulting in dose-dependent tumor growth inhibition (TGI) in multiple syngeneic mouse models. To explore the pharmacodynamics (PD) and mechanism of action of tumor growth inhibition (TGI) by anti-TIGIT antibodies, we examined the kinetics of immune cell frequency and activation in tumor by flow cytometry, qPCR and immunohistochemistry (IHC). We performed in vivo time course studies in the CT26.WT colon carcinoma model using weekly dosing at 0.1, 0.5 and 12.5 mg/kg anti-TGIT. Mice were sacrificed at 24 hours, 7 days and 14 days after the first dose for biomarker analysis. After 24 hours of treatment, Tregs in the tumor decreased and this reduction of Tregs was sustained at 7 and 14 days. Markers of immune cell activation and exhaustion such as CD69, PD1 and intracellular cytokines were modulated during the course of the study, suggesting a more cytotoxic intratumoral environment after 313R12 treatment. In addition, CD226, a binding partner of TIGIT, was significantly upregulated in T cells, Tregs and NK cells throughout the study, reflecting a feedback loop activated by inhibiting TIGIT activity. The anti-TIGIT antibody used in these studies, 313R12, is effector function competent and is able to induce cell-mediated cytotoxic effector functions upon binding. In order to determine whether effector function is necessary for anti-TIGIT antibody activity, we compared 313R12 with an effector function-deficient molecule, 313R13, in CT26.WT tumors. After 7 days, only 313R12 showed significant TGI compared to control-treated animals, suggesting that effector function is required for efficacy. While the effector function-deficient molecule 313R13 was able to similarly induce some changes in PD biomarkers, including immune cell activation, it required a higher dose than 313R12 to do so. To develop biomarkers for anti-TIGIT, we used microarray analyses to identify anti-TIGIT gene signatures in tumors and blood from multiple syngeneic models. In addition, we developed multiplexed IHC panels (e.g., TIGIT+CD8, TIGIT+FOXP3) to quantify expression of TIGIT and TIGIT ligand-positive immune cells in the tumor and surrounding stroma, and we profiled a panel of 80 human tumors with these panels. In summary, we examined the effects of anti-TIGIT antibodies on preclinical mouse models. Biomarker analysis demonstrated loss of Tregs and activation of T cells and NK cells, as well as effector function, as part of the mechanism of action of the molecule. We have also identified biomarkers that can be used for PD and potential predictive analysis in clinical trial samples. Citation Format: Gretchen M. Argast, Belinda Cancilla, Fiore Cattaruzza, Pete Yeung, Erwan le Scolan, Rose Harris, Reyhaneh Lahmy, Alayne Brunner, Min Wang, Gilbert O9Young, Earth Light Lowe, Fumiko Axelrod, Jorge Monteon, Jennifer Elechko, Andrew Lam, MingHong Xie, Austin Gurney, John Lewicki, Ann Kapoun. Anti-TIGIT biomarker study: Inhibition of TIGIT induces loss of Tregs from tumors and requires effector function for tumor growth inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5627.