Abstract 578: Discovery and characterization of novel antagonistic antibodies that bind with high affinity to human, cynomolgus, and murine TIGIT, an immune checkpoint receptor
Authors: Piasecki Julia C. , Brasel Kenneth , Rosler Robert , Klucher Kevin M. , Peterson Scott R. 
Published: July 2017

Abstract
TIGIT is a recently identified coinhibitory immune checkpoint receptor expressed on NK, effector T, and regulatory T cells. In the oncology setting, TIGIT is upregulated on tumor infiltrating immune cells and is co-expressed with exhaustion markers including PD-1, TIM-3 and LAG-3 on infiltrates. TIGIT binds at least two ligands, CD155 and CD112, which are expressed on antigen presenting cells and other tissues, including tumor cells. These ligands also bind the activating receptor CD226, often co-expressed with TIGIT, creating a network that modulates adaptive and innate immune response in a manner analogous to the CD28-CTLA4-CD80-CD86 network. The absence of TIGIT signaling, resulting from genetic deficiency or blockade, enhances anti-tumor immunity in murine models, suggesting that disruption of TIGIT signaling may have clinical utility. To explore this concept, yeast antibody display was used to identify fully human, anti-TIGIT antibodies that block binding to ligands. Multiple rounds of selection with human and mouse TIGIT protein were performed to promote species cross-reactivity, diversity and affinity. A pool of 695 unique clones were screened for binding to TIGIT protein; 65 clones were then selected for further evaluation. Of the 65, 63 competed with CD155 for binding to TIGIT in a ForteBio screen. Fifty-three clones bound cyno TIGIT and 25 bound TIGIT from all three species (human, cyno, mouse). Antibodies bound endogenous TIGIT on primary T cells and blocked binding of ligands to cell surface expressed TIGIT in a dose dependent manner. Twelve clones showed functional activity in a TIGIT blockade bioassay and showed synergy with anti-PD-1 antibody in a PD-1/TIGIT combination bioassay. Activity in the bioassays correlated with affinity for recombinant and cell surface expressed TIGIT. Based on species cross-reactivity, binding affinity and activity in the bioassays, a lead candidate antibody was selected and produced as mouse IgG1 and IgG2a chimeras for testing in mouse tumor models. The chimeric antibodies behaved similarly to the parent clone in vitro exhibiting high affinity for TIGIT, competition with ligand for binding to TIGIT, and functional blockade of CD155-TIGIT interaction. Evaluation of the chimeric anti-TIGIT candidates alone and in combination with anti-PD-1 antibody in mouse syngeneic tumor models is ongoing, and results will be reported at the meeting. Antibody mediated blockade of coinhibitory immunoreceptors has proven clinically efficacious and supports the development of antibodies that target TIGIT. The unique human, non-human primate, and murine cross-reactive TIGIT-specific antibodies described here offer a simplified preclinical development path and the functional activity of these molecules supports their consideration as candidates for therapeutic development.
Citation Format: Julia C. Piasecki, Kenneth Brasel, Robert Rosler, Kevin M. Klucher, Scott R. Peterson. Discovery and characterization of novel antagonistic antibodies that bind with high affinity to human, cynomolgus, and murine TIGIT, an immune checkpoint receptor [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 578. doi:10.1158/1538-7445.AM2017-578