Oncolytic Virus-Delivered CEACAM6/CD3 BiTEs Combine with PD-1 Blockade to Achieve Synergistic Anticancer Efficacy

Systemic administration of bispecific T‑cell engagers (BiTEs) targeting CEACAM6 has shown therapeutic potential but is limited by on‑target/off‑tumor toxicity and short serum half‑life. To overcome these challenges, we engineered an oncolytic herpes simplex virus (oHSV) that delivers and locally produces anti‑CEACAM6/CD3 BiTE directly within the tumor microenvironment (oHSV‑anti‑CEA6/CD3). In immunocompetent mouse models of colon (CT26) and breast (4T1) cancer, a single intratumoral injection of oHSV‑anti‑CEA6/CD3 promoted tumor regression, increased infiltration of CD8⁺CD44⁺ T cells both locally and systemically, and induced durable antitumor immunity. When combined with PD‑1 blockade, this localized BiTE‑arming strategy synergistically enhanced therapeutic efficacy, leading to superior tumor control and long‑term immunological memory without additional toxicity. Mechanistically, the virus exerts a dual action: direct oncolysis and sustained in situ BiTE production, enabling targeted T‑cell activation and tumor elimination while avoiding systemic BiTE exposure. Unlike previous reports of BiTE‑armed oncolytic viruses or simple combinations with immune checkpoint inhibitors, our approach leverages the oHSV platform to achieve spatiotemporally controlled T‑cell redirection coupled with virus‑mediated innate immune stimulation. This work provides a safe, effective, and readily translatable strategy for solid tumor immunotherapy.