Abstract 4969: TIGIT pathway phenotyping sheds light on promising strategies to restore anti-tumor immunity
Authors: Wald Noémie , Mercier Marjorie , Cuende Julia , Nyawouame Florence , Prasad Shruthi , Brouwer Margreet , Houthuys Erica , Marie-Cardine Anne , Bagot Martine , Driessens Grégory , Bodo Véronique , Hoofd Catherine 
Published: August 2019

Abstract
TIGIT is a T cell co-inhibitory receptor recently described as a key checkpoint driving tumor cell immunosuppression. It is predominantly expressed on CD4+ Tregs, CD8+ T cells and NK cells from healthy individuals but further upregulated in cancer patients where it frequently co-expresses with exhaustion markers such as PD-1. TIGIT cognate receptors are members of the poliovirus receptors, among which CD155 has the highest affinity for TIGIT. They are expressed on antigen presenting cells but also on tumor cells which provides a strong rationale for blocking TIGIT as a therapeutic approach to reverse T or NK cell dysfunction linked with cancer progression.
To substantiate the importance of TIGIT as an immunotherapy target, we used flow cytometry and immunohistochemistry (IHC) to extensively characterize TIGIT and CD155 expression in both healthy donors and cancer patients.
We initially confirmed TIGIT expression on multiple immune subsets from healthy donors. Similar flow cytometry analysis performed on matched circulating and tumor-infiltrating immune populations from 15 cancer patients highlighted the global overexpression of TIGIT associated with cancer. Interestingly, ex vivo polyfunctional analysis of cytokine release strongly supported the immunosuppressed character of infiltrated TIGIT positive CD4+ and CD8+ T cells. Finally, combining receptor density with frequency of positive cells led to the interesting observation that tumor-infiltrating Tregs represents the population with the highest TIGIT expression, confirming the opportunity to preferentially target that suppressive population within the tumor microenvironment. These findings on Tregs were further confirmed by IHC. TIGIT was expressed in 10 out of the 11 lung adenocarcinoma tissues analysed. Both Tregs and CD8+ T cells express TIGIT, with Tregs showing a higher proportion of TIGIT+ cells.
Finally, direct expression of TIGIT on tumor cells was also found on several haematological malignancies, opening the door for anti-TIGIT therapies to act directly on tumor cells besides revigoration of the immune system.
The presence of TIGIT ligands within the tumor microenvironment was also assessed and confirmed using both flow cytometry and IHC. CD155 expression was analysed by IHC in both normal individuals (n=90) and cancer patient tissues from 9 different cancer indications (n=284). In cancer tissues, CD155 is mostly expressed by tumor cells, ranging from a median percentage of 50 % for pancreatic cancer to 2 % for cervix cancer. Cancer samples with the highest CD155 expression are pancreatic, prostate, kidney, gastric and colon cancers. CD155 expression is always lower in normal tissues compared to their cancer counterparts except for lung.
Together, these data strongly support the relevance of targeting TIGIT in immuno-oncology and pave the way to select the ideal indications where patients could benefit from such a therapy.
Citation Format: Noémie Wald, Marjorie Mercier, Julia Cuende, Florence Nyawouame, Shruthi Prasad, Margreet Brouwer, Erica Houthuys, Anne Marie-Cardine, Martine Bagot, Grégory Driessens, Véronique Bodo, Catherine Hoofd. TIGIT pathway phenotyping sheds light on promising strategies to restore anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4969.