Abstract 1631: Leveraging off-the-shelf T cells to enhance bispecific T cell engager therapy efficacy in patients with suboptimal T cell responses

Abstract Bispecific T cell engagers (BiTEs) have showed potent antitumor activity in hematologic malignancies but are often limited by T-cell dysfunction in patients. To overcome this challenge, we developed an off-the-shelf immunotherapy platform using healthy donor-derived multi-virus-specific T cells (mVSTs) as effectors for BiTE-mediated redirection. These memory-derived mVSTs recognize cytomegalovirus (CMV) and Epstein-Barr virus (EBV) antigens, exhibit central and effector memory phenotypes, and carry minimal graft-versus-host disease (GVHD) risk, providing a bankable, and functional T-cell source.mVSTs were expanded from CMV/EBV-seropositive donors and evaluated in multiple myeloma and lymphoma models. Two BiTE-loading strategies were tested: pre-incubation with T cells (armored) or direct addition to co-culture. mVSTs alone exhibited minimal cytotoxicity, whereas BCMAxCD3 BiTE-redirected mVSTs mediated robust tumor lysis in both approaches (89.8 ± 1.7% and 88.7 ± 0.4%, respectively at 72h and E:T 1:4) and expanded ≥3-fold versus no-BiTE controls. Both loading methods triggered robust activation, with marked upregulation of CD137 and CD25 and substantial increases in effector cytokines. In Raji lymphoma models, CD19×CD3 and CD20×CD3 BiTEs produced 48-52% cytotoxicity with armored mVSTs, and direct BiTE addition further enhanced killing to 73-74% with a comparable activation profile. Collectively, BiTE-redirected mVSTs exhibit potent cytotoxicity, robust activation, and strong effector cytokine release across myeloma and lymphoma targets, validating their function as an effective, off-the-shelf T-cell platform. A single donor-derived mVST source can be paired with multiple BiTEs to address tumor heterogeneity or antigen-loss relapse without engineering. These data support the feasibility and translational promise of combining BiTEs with healthy donor-derived mVSTs to generate scalable, non-engineered allogeneic T-cell immunotherapies for diverse malignancies. Citation Format: Saghar Pahlavanneshan, Stephen J. Forman, Xiuli Wang, . Leveraging off-the-shelf T cells to enhance bispecific T cell engager therapy efficacy in patients with suboptimal T cell responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1631.