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Abstract Background EGFR and/or HER2 expression in pancreatic cancers is correlated with poor prognoses. We generated homodimeric (EGFRxEGFR or HER2xHER2) and heterodimeric (EGFRxHER2) T cell-engaging bispecific antibodies (T-BsAbs) to direct polyclonal T cells to these antigens on pancreatic tumors. Methods EGFR and HER2 T-BsAbs were constructed using the 2 + 2 IgG-[L]-scFv T-BsAbs format bearing two anti-CD3 scFvs attached to the light chains of an IgG to engage T cells while retaining bivalent binding to tumor antigens with both Fab arms. A Fab arm exchange strategy was used to generate EGFRxHER2 heterodimeric T-BsAb carrying one Fab specific for EGFR and one for HER2. EGFR and HER2 T-BsAbs were also heterodimerized with a CD33 control T-BsAb to generate ‘tumor-monovalent’ EGFRxCD33 and HER2xCD33 T-BsAbs. T-BsAb avidity for tumor cells was studied by flow cytometry, cytotoxicity by T-cell mediated 51Chromium release, and in vivo efficacy against cell line-derived xenografts (CDX) or patient-derived xenografts (PDX). Tumor infiltration by T cells transduced with luciferase reporter was quantified by bioluminescence. Results The EGFRxEGFR, HER2xHER2, and EGFRxHER2 T-BsAbs demonstrated high avidity and T cell-mediated cytotoxicity against human pancreatic ductal adenocarcinoma (PDAC) cell lines in vitro with EC50s in the picomolar range (0.17pM to 18pM). They were highly efficient in driving human polyclonal T cells into subcutaneous PDAC xenografts and mediated potent T cell-mediated anti-tumor effects. Both EGFRxCD33 and HER2xCD33 tumor-monovalent T-BsAbs displayed substantially reduced avidity by SPR when compared to homodimeric EGFRxEGFR or HER2xHER2 T-BsAbs (∼150-fold and ∼6000-fold respectively), tumor binding by FACS (8.0-fold and 63.6-fold), and T-cell mediated cytotoxicity (7.7-fold and 47.2-fold), while showing no efficacy against CDX or PDX. However, if either EGFR or HER2 was removed from SW1990 by CRISPR-mediated knockout, the in vivo efficacy of heterodimeric EGFRxHER2 T-BsAb was lost. Conclusion EGFR and HER2 were useful targets for driving T cell infiltration and tumor ablation. Two arm Fab binding to either one or both targets was critical for robust anti-tumor effect in vivo. By engaging both targets, EGFRxHER2 heterodimeric T-BsAb exhibited potent anti-tumor effects if CDX or PDX were EGFR+HER2+ double-positive with the potential to spare single-positive normal tissue.

The role of T cells in controlling human cancers is well known. Their success requires continued persistence in vivo and efficient trafficking to tumor sites, requirements shared by other effectors such as Natural Killer (NK) cells. To date, cytokine IL2 remains the only clinically approved cytokine therapy available to expand, maintain, and activate these effector lymphoid cells, but toxicities can be severe. Cytokine IL15 offers similar T cell proliferation and activation properties, but without the unwanted side-effects seen with IL2. Several IL15-cytokine fusion proteins have been developed to improve their in vivo function, typically exploiting the IL15Rα to complex with IL15, to extend serum half-life and increase affinity for IL15β receptor on immune cells. Here we describe a novel IL15 complex incorporating the full-length IL15Rα to complex with wild type IL15 to form spontaneous trimers of dimers (6 IL15 + 6 IL15Rα) during co-expression, resulting in a substantial increase in serum half-life and enhancement of in vivo cytokine effect on IgG or T cell engaging antibody-dependent cell-mediated cytotoxicities, when compared to alternative strategies.

T-cell-based therapies have emerged as one of the most clinically effective ways to target solid and non-solid tumors. HER2 is responsible for the oncogenesis and treatment resistance of several human solid tumors. As a member of the HER family of tyrosine kinase receptors, its over-activity confers unfavorable clinical outcome. Targeted therapies directed at this receptor have achieved responses, although development of resistance is common. We explored a novel HER2/CD3 bispecific antibody (HER2-BsAb) platform that while preserving the anti-proliferative effects of trastuzumab, it recruits and activates non-specific circulating T-cells, promoting T cell tumor infiltration and ablating HER2(+) tumors, even when these are resistant to standard HER2-targeted therapies. Its in vitro tumor cytotoxicity, when expressed as EC50, correlated with the surface HER2 expression in a large panel of human tumor cell lines, irrespective of lineage or tumor type. HER2-BsAb-mediated cytotoxicity was relatively insensitive to PD-1/PD-L1 immune checkpoint inhibition. In four separate humanized mouse models of human breast cancer and ovarian cancer cell line xenografts, as well as human breast cancer and gastric cancer patient-derived xenografts (PDXs), HER2-BsAb was highly effective in promoting T cell infiltration and suppressing tumor growth when used in the presence of human peripheral blood mononuclear cells (PBMC) or activated T cells (ATC). The in vivo and in vitro antitumor properties of this BsAb support its further clinical development as a cancer immunotherapeutic.