Abstract 6075: The combination of an EpCAMx4-1BB bispecific antibody with PD-1 blockade exhibits antitumor activity in a murine tumor model unresponsive to each individual antibody

Abstract Activation of the costimulatory receptor 4-1BB and blockade of the PD1/PD-L1 axis can augment immune responses through distinct mechanisms. DuoBody®-EpCAMx4-1BB (BNT314/GEN1059) is an investigational Fc-silenced bispecific antibody (bsAb) designed to boost antitumor immune responses via EpCAM-dependent 4-1BB agonist activity. We previously showed that combining DuoBody-EpCAMx4-1BB with PD-(L)1 blockade potentiated T-cell effector functions in vitro compared to single treatments1. Furthermore, combining an EpCAMx4-1BB bsAb with PD-1 blockade exhibited potent antitumor activity in vivo in the immunogenic MC38 tumor model. Here we further investigated this combination in ex vivo tumor-infiltrating lymphocyte (TIL) assays using resected human colorectal cancer (CRC) specimens and in vivo using the less immunogenic B16F10 tumor model. DuoBody-EpCAMx4-1BB promoted CD8+ T-cell and NK-cell expansion in human TIL assays, whereas pembrolizumab alone had minimal effect. Combined treatment with both antibodies further enhanced CD8+ T-cell expansion in three of six specimens tested. The combination of an Fc-silenced bsAb targeting human EpCAM and mouse 4-1BB (hEpCAMxm4-1BB) with anti-mouse PD-1 showed robust antitumor activity in mice bearing human EpCAM-expressing B16F10 tumors. This was evidenced by significantly delayed tumor outgrowth and prolonged survival compared to both single treatments and a nonbinding control antibody, whereas hEpCAMxm4-1BB or anti-PD-1 as single treatments showed no antitumor activity compared to the control. Furthermore, combination treatment led to complete tumor regression in 2 of 11 mice. Flow cytometry analysis of the peripheral blood of tumor-bearing mice showed that hEpCAMxm4-1BB treatment enhanced CD8+ T-cell and NK-cell activation and proliferation, and frequencies of CD8+ T cells with an effector phenotype. The pharmacodynamic effects on CD8+ T cells were further potentiated by the combination with anti-PD-1, whereas anti-PD-1 alone had no effect. NK-cell activation and proliferation was modestly further enhanced by combination treatment, compared to hEpCAMxm4-1BB alone. In addition, the combination significantly enhanced CD4+ T-cell activation and proliferation, compared to each single treatment. In conclusion, combining Fc-silenced hEpCAMxm4-1BB bsAb with PD-1 blockade exhibited antitumor activity in vivo in a model unresponsive to each single treatment, suggesting synergistic effects of the combination. The immunomodulatory activity of EpCAMx4-1BB bsAb in mice and in human CRC TIL cultures was further potentiated in combination with PD-1 blockade. These data provide preclinical rationale for the clinical evaluation of DuoBody-EpCAMx4-1BB in combination with PD-1/PD-L1 checkpoint blockade. 1 Fellermeier-Kopf et al, J Immunother Cancer 2024; 12(S2): A833. Citation Format: Andrea Imle, Sina Fellermeier-Kopf, Andreea Ioan-Facsinay, Lena Wiedmann, Maren Köhne, Aras Toker, Annieck M. Diks, Tahamtan Ahmadi, Alexander Muik, Kristel Kemper, Özlem Türeci, Esther Breij, Ugur Sahin. The combination of an EpCAMx4-1BB bispecific antibody with PD-1 blockade exhibits antitumor activity in a murine tumor model unresponsive to each individual antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6075.