Abstract 599: Pharmacodynamic biomarkers for anti-TIGIT treatment and prevalence of TIGIT expression in multiple solid tumor types
Authors: Cattaruzza Fiore , Yeung Pete , Wang Min , Brunner Alayne , Scolan Erwan Le , Cain Jennifer , Argast Gretechen , O'Young Gilbert , Liu YuWang , Cancilla Belinda , Gurney Austin , Hoey Tim , Lewicki John , Kapoun Ann 
Published: July 2017

Abstract
TIGIT (T cell immunoreceptor with Ig ITIM domain) is a co-inhibitory receptor and its signaling axis inhibits T cell and Natural Killer (NK) cell activity in the healthy immune system. In tumors TIGIT is highly expressed on a subset of dysfunctional T and NK cells and of highly suppressive regulatory T cells (Treg). Loss of TIGIT signaling enhances NK cell activity, CD4+ T cell priming and CD8+ T cell effector functions, suggesting a role in anti-tumor immunity. We have developed an anti-TIGIT blocking antibody that shows potent antitumor efficacy in in multiple syngeneic mouse models, including CT26WT colon, B16F10 melanoma and 4T1 breast cancer. Dose-dependent (12.5-0.1 mg/Kg) single agent efficacy was demonstrated in established tumors, and pharmacodynamic (PD) biomarkers in blood and in tumors were identified.
Consistent with TIGIT’s role as a co-inhibitory receptor, anti-TIGIT promoted a dose-dependent increase in activation of CD8+ and CD4+ tumor infiltrating leukocytes (TIL) and NK cells, as shown by increased staining of IFN-γ and CD69 by flow cytometry, when compared to controls. Anti-TIGIT also increased CD4 and CD8 T cell frequency in the tumor, measured by immunohistochemistry (IHC). Furthermore, anti-TIGIT caused an increase in splenic NK cell cytotoxicity, which correlated with dose and efficacy.
To identify gene expression biomarkers in tumor and in blood, we used microarray analysis, and found similar immune gene changes between the two tissues. As expected, anti-TIGIT increased the expression of genes associated with CD8+ T cells, CD4+ T cells, and NK cells. Markers indicative of cytotoxic activity and Th1 response were also induced by anti-TIGIT. The microarray data were validated by qRT-PCR and results were consistent with flow cytometry and cytotoxicity results, and underlie the mechanism of action of anti-TIGIT.
We have developed an IHC assay to evaluate TIGIT expression patterns in tumor and the associated stroma and TILs. Using this assay, we profiled 17 tumor types to evaluate patterns of TIGIT expression. Expression was high on immune cells in the stroma and on TILs in 8 tumor types, while it was generally low on tumor cells. TIGIT expression was also low on tumor cells in a panel of 27 PDX models. Consistent with the IHC results, analysis of 33 tumor types in the TCGA by RNA-Seq showed a good correlation of the expression levels of TIGIT and T cell markers, suggesting that TIGIT is mostly expressed on immune cells in tumors.
In conclusion, we have identified PD biomarkers for anti-TIGIT in tumors and in surrogate tissues in syngeneic mouse models. Analysis of the biomarkers demonstrates activation of T cells and NK cells upon inhibition of TIGIT signaling. These biomarkers can be used in the clinic to demonstrate target engagement. In addition, we have profiled the expression of TIGIT in multiple solid tumor types and characterized prevalence of TIGIT-positive cells.
Citation Format: Fiore Cattaruzza, Pete Yeung, Min Wang, Alayne Brunner, Erwan Le Scolan, Jennifer Cain, Gretechen Argast, Gilbert O'Young, YuWang Liu, Belinda Cancilla, Austin Gurney, Tim Hoey, John Lewicki, Ann Kapoun. Pharmacodynamic biomarkers for anti-TIGIT treatment and prevalence of TIGIT expression in multiple solid tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 599. doi:10.1158/1538-7445.AM2017-599