Background: Immunotherapy using checkpoint blockade antibodies that target effector cell inhibitory receptors, like PD-1 and CTLA-4, have elicited some dramatic and durable responses in several tumor types. Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a cell-surface protein expressed by immune cells and tumor cells, and it can inhibit T cell function similar to PD-1 and CTLA-4. CEACAM1 is also a potent inhibitor of natural killer (NK) cell function; binding between CEACAM1 on NK cells and CEACAM1 or CEACAM5 on tumor cells inhibits activation signaling by NKG2D, which prevents NK cell cytolysis and permits tumor cells to evade NK killing.

NEO-201 is a novel humanized IgG1 monoclonal antibody (mAb) that was derived from an immunogenic preparation of tumor-associated antigens (TAAs) from pooled allogeneic colon tumor tissue extracts. It reacts against a wide variety of human carcinoma cell lines and tumor tissues, but is largely non-reactive against normal tissues. NEO-201 binds to members of the CEACAM family, and can activate innate immune mechanisms such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) to kill tumor cells. This investigation was designed determine whether NEO-201 blocks the CEACAM1 inhibitory pathway to restore antitumor functionality to NK cells.

Methodology: In vitro assays using human tumor cell lines were conducted to identify CEACAM family members bound by NEO-201. Functional assays were conducted to assess the ability of NEO-201 to potentiate the in vitro killing of tumor cells by the NK cell line NK-92, which expresses CEACAM1 and lacks CD16 and the ability to mediate ADCC.

Results: NEO-201 was found to react with distinct variants of CEACAM5 and CEACAM6, but not with CEACAM1 or CEACAM8. Expression profiling revealed that various NEO-201+ cell lines expressed differing levels of the native forms of CEACAM5/6 vs. the NEO-201-reactive variant forms of these molecules. Functionally, NEO-201 treatment augmented the cytolytic activity of NK-92 cells against NEO-201+ tumor cells in proportion to their level of CEACAM5 expression (average increase of 2-fold), but not against NEO-201+ cells that only expressed CEACAM6.

Conclusions: This study demonstrates that NEO-201 is reactive against a tumor-associated variant of CEACAM5/6, and provides evidence that this antibody can block the interaction between tumor cell CEACAM5 and NK cell CEACAM1 to reverse CEACAM1-dependent inhibition of NK cytotoxicity. Experiments are in progress to determine the involvement of NK cell CEACAM1 and/or other checkpoint pathways in this mechanism of action. These results suggest that NEO-201 may potentially reverse CEACAM1-dependent immunosuppression of NK cells in patients whose tumors express the NEO-201-reactive variant of CEACAM5.

Citation Format: Justin M. David, Massimo Fantini, Christina M. Annunziata, Philip M. Arlen, Kwong Y. Tsang. The neoantigen-targeting antibody NEO-201 enhances NK cell-dependent killing of tumor cells through blockade of the inhibitory CEACAM5/CEACAM1 immune checkpoint pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3821.