Background T-cell engaging bispecific antibodies have been successful in hematological malignancies in part due to the accessibility of both T-cells and target cancer cells. However, their potential in solid tumors is limited by challenges such as tissue penetration and T-cell activation within the immunosuppressive tumor microenvironment (TME). Traverse Biotech is developing TB-Bs1, a CD3xROR2 bispecific antibody generated using the DuoBody^(R) platform, an established platform that has led to four FDA-approved bispecific antibodies. TB-Bs1 is produced through controlled Fab Arm Exchange, resulting in a bispecific antibody with pharmacokinetic properties comparable to wild type IgG1.

TB-Bs1 targets the Receptor Tyrosine Kinase-like Orphan Receptor 2 (ROR2), a non-canonical Wnt-binding receptor expressed during embryogenesis that is upregulated in select cancers, often correlating with poor prognosis. Immunohistochemistry analysis shows significant ROR2 expression in multiple primary solid tumors, including sarcomas, ovarian cancer, non-small cell lung cancer (NSCLC) and colon cancer. TB-Bs1 is the first highly specific ROR2 engaging antibody with a low-affinity anti-CD3 T-cell engaging arm. Preliminary in vitro data demonstrates TB-Bs1 dose-dependent T-cell mediated cytotoxicity against multiple ROR2-expressing human cancer cell lines. We are now evaluating ROR2 as a CD3 T-cell engager target in vivo for ROR2-expressing tumors, with a proof-of-concept study in humanized NSG™ mice bearing NCI-H1650 orthotopic tumors.

Methods We established a humanized mouse model to evaluate the efficacy of TB-Bs1. Using NCI-H1650 human lung adenocarcinoma and human donor-derived peripheral blood monocytes (PBMCs) engrafted in NSG™ mice. Treatments include a human IgG isotype control, and 9 additional groups receiving hPBMCs from either donor 2 or donor 4 followed by intravenous treatment with TB-Bs1 at weekly doses ranging from 0.1 mg/kg to 10 mg/kg. Primary endpoints are tumor volume reduction and T-cell-mediated cytotoxicity. Flow cytometry will assess human T-cell engraftment and ROR2 expression on tumor cells. Graft-versus-host disease and body weight changes will be monitored throughout the study.

Results Immunohistochemistry analysis showed ROR2 incidence between 25% and 100% in various solid tumor indications. We have confirmed that TB-Bs1 can effectively direct human CD3+T cells to kill ROR2-expressing tumor cells in vitro. Now, we now investigate whether our in vivo study will further demonstrate TB-Bs1 has anti-tumor efficacy of ROR2+ tumor cells in our established humanized mouse model.

Conclusions This study aims to validate ROR2 as a target in cancer immunotherapy and provide a therapeutic proof-of-concept for T-cell engager therapy in a preclinical humanized mouse model of a ROR2-positive tumor.