Inhibition of Human Tumor-Infiltrating Lymphocyte Effector Functions by the Homophilic Carcinoembryonic Cell Adhesion Molecule 1 Interactions

Abstract

Efficient antitumor immune response requires the coordinated function of integrated immune components, but is finally exerted by the differentiated effector tumor-infiltrating lymphocytes (TIL). TIL cells comprise, therefore, an exciting platform for adoptive cell transfer (ACT) in cancer. In this study, we show that the inhibitory carcinoembryonic Ag cell adhesion molecule 1 (CEACAM1) protein is found on virtually all human TIL cells following preparation protocols of ACT treatment for melanoma. We further demonstrate that the CEACAM1 homophilic interactions inhibit the TIL effector functions, such as specific killing and IFN-γ release. These results suggest that CEACAM1 may impair in vivo the antitumor response of the differentiated TIL. Importantly, CEACAM1 is commonly expressed by melanoma and its presence is associated with poor prognosis. Remarkably, the prolonged coincubation of reactive TIL cells with their melanoma targets results in increased functional CEACAM1 expression by the surviving tumor cells. This mechanism might be used by melanoma cells in vivo to evade ongoing destruction by tumor-reactive lymphocytes. Finally, CEACAM1-mediated inhibition may hinder in many cases the efficacy of TIL ACT treatment of melanoma. We show that the intensity of CEACAM1 expression on TIL cells constantly increases during ex vivo expansion. The implications of CEACAM1-mediated inhibition of TIL cells on the optimization of current ACT protocols and on the development of future immunotherapeutic modalities are discussed.

Novel Immunotherapy for Malignant Melanoma with a Monoclonal Antibody That Blocks CEACAM1 Homophilic Interactions

“…This was in line with our findings that CEACAM1 protects melanoma cells and inhibits both activated NK cells (17) and activated T cells (19,20,24). Furthermore, we have recently shown an unusually high percentage of CEACAM1 þ circulating lymphocytes in the peripheral blood of patients with melanoma, as compared with healthy donors (24).…”

“…We have previously shown that CEACAM1 homophilic interactions inhibit natural killer (NK) cell-mediated killing, independently of MHC class I recognition (16)(17)(18). We have further shown that CEACAM1 inhibits effector functions of TILs, such as cytotoxicity and IFNg release (19). Moreover, we found that an IFNg-driven upregulation of CEACAM1 on melanoma cells surviving TIL-mediated attack renders them even more resistant (20).…”

“…It has a strong prognostic value (23) implying on its clinical mechanistic importance. Mechanistically, CEACAM1 protects melanoma cells by inhibiting effector functions of NK cells (13,17,24) and T cells (19,20) in a homophilic manner. Indeed, blocking of CEACAM1 homophilic interactions with polyclonal antibodies enhanced the killing of CEACAM1 þ melanoma cells by NK and T cells (17,19).…”

“…Mechanistically, CEACAM1 protects melanoma cells by inhibiting effector functions of NK cells (13,17,24) and T cells (19,20) in a homophilic manner. Indeed, blocking of CEACAM1 homophilic interactions with polyclonal antibodies enhanced the killing of CEACAM1 þ melanoma cells by NK and T cells (17,19). Here, we present MRG1, a CEACAM1-specific, highaffinity mAb that efficiently blocks CEACAM1 homophilic interactions and renders CEACAM1 þ melanoma cells more susceptible to elimination by T cells in an antigenrestricted, dose-dependent manner (Supplementary Figs.…”

“…Cytotoxicity measurements were based on carboxyfluorescein succinimidyl ester (CFSE) labeling of target cells and costaining with propidium iodide (PI) after 6 hours of incubation with the effector cells as previously described (19). Blocking with MRG1 was carried out by preincubation of either effectors or targets for 1 hour on ice at the indicated concentrations.…”