Abstract Glioblastoma (GBM) is a devastating disease with an extremely poor prognosis. Immune therapy with T cells engineered to express chimeric antigen receptors (CARs), represents a promising alternative to conventional therapy, but responses have been limited to date due to heterogeneous target antigen expression and the emergence of immune escape following treatment with CAR T cells directed at a single target. This was observed in clinical studies with CART-EGFRvIII, wherein EGFRvIII-targeted T cells successfully localized to the brain tumor microenvironment, but ultimately failed to prevent disease progression—with post-treatment specimens demonstrating high levels of wild-type EGFR despite reduced expression of EGFRvIII. To help address this therapeutic barrier, we developed a novel CAR construct engineered for local delivery of bispecific T-cell engagers (BiTEs) that target residual tumor. Specifically, EGFRvIII-targeted CAR T cells were engineered to secrete BiTEs against wild-type EGFR, which is not expressed in normal brain but frequently amplified in GBM, recurrent disease and other cancers. Our results demonstrate that human T cells are efficiently transduced with the dual CART.BiTE transgene, and that modified cells successfully secrete biologically active EGFR-specific BiTEs that not only redirect CAR T cells but also recruit and activate untransduced bystander T cells against wild-type EGFR. Recapitulating clinical data, EGFRvIII CAR T cells were unable to completely treat tumors with heterogenous EGFRvIII expression, leading to outgrowth of EGFRvIII-negative, EGFR-positive recurrence. Conversely, CART.BiTE cells mediated potent antitumor efficacy in the setting of heterogeneous tumors and EGFRvIII antigen loss. In these models, infusion of CART.BiTE cells yielded extended survival and cured mice with even late-stage, established intracerebral tumors, including those derived from glioma cell lines and patient-derived glioma neurosphere cultures. Unlike CAR T cells directly targeting EGFR, which caused on-target toxicity against human skin grafts in vivo, secreted BiTE-EGFR was locally effective at exceedingly low concentrations that did not mediate immune responses against healthy human tissue. These results demonstrate that CARs and BiTEs can be combined strategically to mitigate the impact of antigen heterogeneity in GBM, and also provide a unique T-cell-based delivery method for BiTEs to tumors in the brain. Citation Format: Bryan D. Choi, Xiaoling Yu, Ana P. Castano, Amanda A. Bouffard, William T. Curry, Bob S. Carter, Marcela V. Maus. BiTE-armored CARs overcome antigen escape in EGFRvIII-targeted therapy for glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-066.