A CD3 x FRα T-cell engaging bispecific antibody for efficient killing of ovarian cancer cells with minimal cytokine release.

e18050 Background: Ovarian Cancer (OvCa) is the leading cause of gynecologic cancer mortality in women. Since the introduction of platinum-based chemotherapy there has been little change in the prognosis of OvCa patients, with < 30% overall survival in advanced disease, creating an urgent medical need for novel therapies. Few ovarian epithelium-specific surface proteins are suited for Ab targeting. However, studies have shown folate receptor α (FRα) to be highly over-expressed in OvCa; expression level and stage correlate, and FRα is absent or minimally expressed in normal tissues. However, naked Ab therapy has shown limited efficacy while CAR-T therapy has been plagued by toxicity and limited efficacy. ADCs have demonstrated some activity but present the risk of toxin-mediated side effects. Using Teneobio’s unique antibody discovery platform, we have developed a CD3 x FRα T-BsAb that retains the potent cytotoxicity of other T-cell redirecting therapies but with significantly reduced cytokine release. Methods: Antibodies targeting CD3 and FRα were generated via immunization of our proprietary transgenic animals. Candidate antibodies were selected by repertoire deep sequencing of B-cells from draining lymph nodes, high-throughput gene assembly, recombinant expression, and functional screening. Bispecific antibodies targeting CD3 and FRα were assembled and evaluated for their ability to selectively activate primary human T-cells and mediate killing of FRα+ tumor cells in vitro and in vivo. T-cell activation surface markers, cytokine production and tumor cell cytotoxicity were measured. Results: Primary human T-cells were activated only in the presence of both the CD3 x FRα T-BsAb and FRα (either recombinant or cell-surface protein). Potent and selective cytotoxicity against FRα+ tumor cells was observed in co-cultures of primary human T-cells and OvCa tumor cell lines. Strikingly, our T-BsAb mediated comparable tumor cell cytotoxicity to CD3 x FRα T-BsAbs containing a high affinity anti-CD3 domain but with significantly reduced cytokine production. Our Ab showed preliminary evidence of tumor growth inhibition in xenograft models of OvCa in vivo. Conclusions: We have created a novel CD3 x FRα T-BsAb that mediates T-cell killing of FRα+ tumor cells with minimal production of cytokines. This molecule may improve safety, efficacy, and offer opportunities for combination therapy to treat OvCa.