Abstract A77: Efficient targeting of HER-2-positive cancers by Antibody-Coupled T cell Receptor (ACTR) engineered autologous T cells

HER2 gene amplification occurs in 20-30% of aggressive breast and gastric cancer diagnoses, often signifying poor prognosis. The current standard of care for HER2 amplified cancer is the HER2 targeting antibody trastuzumab with chemotherapy. In the setting of HER2 amplified breast cancer, the combination of HER2 targeting antibodies trastuzumab and pertuzumab with the chemotherapeutic docetaxel is the frontline therapy. Despite the success of targeting the HER2 pathway, there are still many patients who are refractory or relapse following HER2 targeting regimens. Outside of the setting of HER2 overexpression or gene amplification, targeting HER2-positive cancers has thus far been ineffective. Engineered autologous T-cells, including chimeric antigen receptors (CARs) and high affinity T-cell receptors (TCRs), have gained attention recently due to their potent efficacy, with overall response rates reaching 80% and examples of long lasting remissions, particularly in advanced lymphoma and leukemia. However, initial clinical attempts to target HER2-amplified breast cancer with CAR-T cell therapy met with either acute toxicities or lack of efficacy. The Antibody-Coupled T-cell Receptor (ACTR) platform is a universal, engineered T cell therapy technology developed to mediate anti-tumor activity in combination with tumor-targeting antibodies. The ACTR chimeric construct is composed of the high-affinity CD16 (FCGR3A) V158 variant with the signaling domains from CD3z and 4-1BB. ACTR is designed to engage the Fc domain of human IgG1 antibodies when opsonized to the cognate target cells and deliver an activation signal to the engineered T cells. ACTR T cells combined with either HER2 targeting trastuzumab or pertuzumab exhibited potent cytotoxic activity, cytokine response and proliferation on a HER2 amplified tumor cell lines. ACTR activity was specific to antibody treated cells, and had little activity on HER2 low or negative tumor lines. Furthermore, the effectiveness of ACTR T cells in a non-amplified HER2 (HER2 low) setting was tested in the presence of a combination of trastuzumab and pertuzumab. This multi-antibody combination increased the cytotoxicity by ACTR T cells, whereas trastuzumab or pertuzumab as single antibody combinations with ACTR had little effect, suggesting a potential therapeutic approach for this disease setting with high unmet medical need. Importantly, the ACTR platform decouples the targeting moiety from the engineered T cell allowing for an antibody dose response which may spare cytotoxicity on normal cells. The specific response to HER2 positive tumor cells in the presence of trastuzumab, pertuzumab or the combination of HER2 directed antibodies demonstrates the potential therapeutic activity of ACTR T cells and supports consideration of clinical testing of ACTR T cells in HER2-positive cancers. Furthermore, combining multiple targeting antibodies to achieve greater potency and efficacy is unique to the ACTR technology and demonstrates the potential for such activity across many other tumor targets and tumor targeting antibodies. Citation Format: Casey B. Judge, Rachel DeBarge, Eugene Choi, Katie O9Callaghan, Lindsay Edwards, Birgit Schultes, Seth Ettenberg, Heather A. Huet. Efficient targeting of HER-2-positive cancers by Antibody-Coupled T cell Receptor (ACTR) engineered autologous T cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A77.