Current HER2-targeted therapies have markedly improved the outcome of cancer patients with HER2 overexpressing tumors. However, these patients may eventually relapse or develop treatment resistance. In addition, HER2-low patients that are not eligible for treatment constitute a significant portion of the breast cancer patients. To address these unmet needs, we have developed a novel HER2-targeting T cell engager, SAR443216. This is a trispecific antibody with binding sites for HER2, CD3 and CD28, and containing a mutated IgG4-Fc which lacks effector functions. CD28 binding contributes to T cell activation, including activation of IL-2 and NFκB pathways, as well as induction of anti-apoptotic protein, Bcl-xL. In the presence of HER2-positive cancer cells, SAR443216 is able to activate primary human CD4 and CD8 T cells, resulting in T cell proliferation and secretion of cytokines and granzyme B. Moreover, it has potent in vitro T cell-dependent cellular cytotoxicity (TDCC) against a panel of HER2-expressing cancer cell lines, including those that are HER2-low. The potency of in vitro TDCC is largely correlated with HER2 surface expression in the target cells. Finally, in a HER2-low breast cancer xenograft model, SAR443216 also exhibited significant anti-tumor activity in immuno-deficient NSG mice reconstituted with primary human T cells. Thus, SAR443216 represents a promising new drug for cancer patients with HER2-expressing tumors, including those who are currently ineligible for stand-of-care therapy.

Citation Format: Wenwen Sha, Sri Vadde, Zhili Song, Edward Seung, Zhen Xing, Liqing Chen, Virna Cortez-Retamozo, Sukhvinder Sidhu, Dinesh Bangari, Lan Wu, Ronnie Wei, Zhi-yong Yang, Gary Nabel, Vasiliki Pelekanou, Michele Sanicola-Nadel, Serena Masciari, Dmitri Wiederschain, Lily Pao. SAR443216, a novel trispecific T cell engager with potent T cell-dependent cytotoxicity for HER2-low tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1825.