Silencing Fc Domains in T cell–Engaging Bispecific Antibodies Improves T-cell Trafficking and Antitumor Potency

Silencing Fc domains of bispecific antibodies (BsAbs) improves T-cell trafficking and antitumor effects in GD2+ and HER2+ tumor systems and two mouse models. Future BsAb designs that inactivate Fc domains could improve antitumor efficacy and limit organ toxicities. Bispecific antibodies (BsAb) that engage T cells bind to tumor cells via a tumor-associated antigen and to T cells through surface CD3. BsAbs have promising antitumor properties in vivo. Here, we describe the effects of Fc silencing on BsAb-driven T-cell trafficking to solid tumors. We used BsAbs specific for disialoganglioside GD2 or oncoprotein ErbB2 (HER2) and built on the IgG(L)-scFv platform with or without Fc silencing. We studied the kinetics of T-cell infiltration from blood into solid tumor masses when driven by these BsAbs. We also investigated the therapeutic efficacy of these BsAbs in two mouse models: immunodeficient mice xenografted with patient-derived GD2+ neuroblastoma or HER2+ breast cancer, and human CD3ϵ transgenic mice implanted with a GD2+ murine tumor. BsAbs built with intact Fc domain were unable to drive T cells to tumor, thereby failing to achieve an antitumor effect in mice. T cells became sequestered in lungs by myeloid cells or depleted in circulation. In contrast, when Fc function was silenced by N297A ± K322A mutations, T cells were able to infiltrate into subcutaneous solid tumors, a prerequisite for successful therapy outcome.