α_Eβ₇ integrin interaction with E-cadherin promotes antitumor CTL activity by triggering lytic granule polarization and exocytosis

Various T cell adhesion molecules and their cognate receptors on target cells promote T cell receptor (TCR)–mediated cell killing. In this report, we demonstrate that the interaction of epithelial cell marker E-cadherin with integrin α_E(CD103)β₇, often expressed by tumor-infiltrating lymphocytes (TILs), plays a major role in effective tumor cell lysis. Indeed, we found that although tumor-specific CD103⁺ TIL-derived cytotoxic T lymphocyte (CTL) clones are able to kill E-cadherin⁺/intercellular adhesion molecule 1⁻ autologous tumor cells, CD103⁻ peripheral blood lymphocyte (PBL)-derived counterparts are inefficient. This cell killing is abrogated after treatment of the TIL clones with a blocking anti-CD103 monoclonal antibody or after targeting E-cadherin in the tumor using ribonucleic acid interference. Confocal microscopy analysis also demonstrated that α_Eβ₇ is recruited at the immunological synapse and that its interaction with E-cadherin is required for cytolytic granule polarization and subsequent exocytosis. Moreover, we report that the CD103⁻ profile, frequently observed in PBL-derived CTL clones and associated with poor cytotoxicity against the cognate tumor, is up-regulated upon TCR engagement and transforming growth factor β1 treatment, resulting in strong potentiation of antitumor lytic function. Thus, CD8⁺/CD103⁺ tumor-reactive T lymphocytes infiltrating epithelial tumors most likely play a major role in antitumor cytotoxic response through α_Eβ₇–E-cadherin interactions.