Preclinical characterization and efficacy of 4R9, a novel immune checkpoint blockade targeting CEACAM1 for cancer therapy.

Abstract

e14155 Background: CEACAM1 is one of the several immune checkpoint receptors expressed on T cells that mediate suppression of inflammatory T cell response. It is known that CEACAM1-CEACAM1 homophilic interaction induces downregulation of ZAP70 phosphorylation in response to T cell receptor (TCR) stimulation. Also, CEACAM1 is highly expressed on non-small cell lung cancer (NSCLC) and its expression correlated with cancer progression and poor prognosis. We developed a fully human monoclonal antibody 4R9, human CEACAM1-targeting antibody. Methods: T cell activation of 4R9 was determined by NFAT-luciferase reporter assay with CEACAM1 overexpressing Jurkat stable cells. In vitro efficacy of 4R9 was examined using NK-mediated tumor cell killing assay. The anti-tumor efficacy of 4R9 alone or in combination was studied in vivo in a humanized mouse model engrafted with NSCLC patient-derived tumor xenografts. Results: Anti-CEACAM1 antibody 4R9 binds to CEACAM1 overexpressed in HEK293 or Jurkat cells but not to other CEA family members. 4R9 blocks CEACAM1-CEACAM1 homophilic interaction by binding to N domain of CEACAM1. CEACAM1-CEACAM1 homophilic interaction induced downregulation of ZAP70 phosphorylation in response to TCR stimulation in CEACAM1 overexpressing Jurkat stable cell line, which was rescued by 4R9 resulting in augmentation of NFAT activity and IL-2 expression. NK cell-mediated tumor lysis was increased by 4R9 in a CEACAM1 expression-dependent manner. Out of 49 NSCLC tumor tissues, 20 cases exhibited dominant expression of CEACAM1 over PD-L1 with 6 cases showing > 50% of CEACAM1 positivity. In a single mouse trial using NSCLC PDX-huNSG mouse model, 4R9 (20 mpk, 2qW) suppressed tumor progression more than 30% as monotherapy (10/19) as well as in combination (16/22) with pembrolizumab (5 mpk, 2qW). Moreover, PDX of adenocarcinoma origin with more than 50% of CEACAM1 expression were more efficiently prohibited for progression with 4R9, suggesting potential therapeutic use of 4R9 in patients with NSCLC. Conclusions: Anti-CEACAM1 antibody blocked CEACAM1-mediated negative regulation and restored T/NK cell activities. Different expression patterns of CEACAM1 compared with PD-L1 and efficacies in a single mouse trial support the rationale for developing anti-CEAEAM1 antibody as cancer therapeutics.