Anti-TIGIT Antibodies Promote Immune Activation Relevant to Targeting Stem-Like and Tumor-Specific T Cells in Combination with Anti-Pd-1

TIGIT is an inhibitory receptor expressed primarily on NK and T cell subsets, and binding to its cognate receptor ligand, CD155, results in multiple mechanisms of immunosuppression. Blocking the TIGIT-CD155 interaction in the context of cancer promotes anti-tumor immunity. We characterized cellular subsets that TIGIT blockade may impact and the pharmacology of two anti-TIGIT antibodies - representing functional (AB308) and non-functional (AB154) Fc domain classes - undergoing clinical evaluation. Surrogate antibodies were leveraged to interrogate TIGIT biology in mouse syngeneic tumor models. Human tumor-infiltrating lymphocytes from a variety of cancer types expressed appreciable levels of TIGIT on relevant immune populations, including Tregs and CD8+ T cells with tumor reactive or pre-dysfunctional stem-like phenotypes. Both antibodies potently bound TIGIT and blocked the TIGIT-CD155 interaction as well as displayed the predicted phenotypes in terms of Fcγ receptor (FcγR) engagement. In line with FcγRIII binding, AB308 demonstrated a capacity to induce ADCC against TIGIT-expressing target cells. Combination of anti-TIGIT antibodies with other therapeutic approaches that promote T cell activation resulted in enhanced immune responses. In mice, while combining Fc-silent or Fc-enabled anti-mouse TIGIT antibody with anti-PD-1 resulted in greater tumor growth inhibition than with anti-PD-1 alone, the activity of Fc-enabled anti-TIGIT was associated with intratumoral Treg depletion. These data provide a rationale for combination with immune-activating agents and support ongoing clinical evaluation of AB154 and AB308 with biomarker strategies focused on understanding the role of Fc functionality.