To prevent glioblastoma (GBM) escape via antigen loss, Choi et al. designed CART.BiTE cells that express a CAR specific for EGFRvIII (a tumor-specific antigen expressed in many GBM tumors) and secrete a bispecific T cell engager against EGFR (overexpressed in GBM, but also expressed in normal tissues). Intracranially-delivered CART.BiTE cells cleared heterogeneous GBM tumors in mice. BiTEs redirected both CAR T cells and bystander T cells to tumor cells, and activation via CAR and BiTE together led to a less exhausted TCM phenotype. CART.BiTE cells did not cause toxicities in a human skin graft model.
Chimeric antigen receptor (CAR)-T-cell therapy for solid tumors is limited due to heterogeneous target antigen expression and outgrowth of tumors lacking the antigen targeted by CAR-T cells directed against single antigens. Here, we developed a bicistronic construct to drive expression of a CAR specific for EGFRvIII, a glioblastoma-specific tumor antigen, and a bispecific T-cell engager (BiTE) against EGFR, an antigen frequently overexpressed in glioblastoma but also expressed in normal tissues. CART.BiTE cells secreted EGFR-specific BiTEs that redirect CAR-T cells and recruit untransduced bystander T cells against wild-type EGFR. EGFRvIII-specific CAR-T cells were unable to completely treat tumors with heterogenous EGFRvIII expression, leading to outgrowth of EGFRvIII-negative, EGFR-positive glioblastoma. However, CART.BiTE cells eliminated heterogenous tumors in mouse models of glioblastoma. BiTE-EGFR was locally effective but was not detected systemically after intracranial delivery of CART.BiTE cells. Unlike EGFR-specific CAR-T cells, CART.BiTE cells did not result in toxicity against human skin grafts in vivo.