A novel peptide-MHC-based T cell engager synergizes with tumor-targeted IL-12 for immunotherapy of solid tumors.

Conventional CD3-targeting bispecific T cell engagers (BiTEs) have shown limited efficacy in solid tumors, largely due to the highly immunosuppressive tumor microenvironment (TME) and systemic T cell activation-associated toxicity. To address this challenge, we developed a peptide-MHC class I-based T cell engager platform that selectively redirects a specific subset of CD8+ T cells to tumor cells. Using the model ovalbumin (OVA) system, we engineered fusion proteins comprising an OVA peptide-H-2Kᵇ complex linked to an anti-HER2 nanobody (OVA-αHER2), enabling simultaneous engagement of OVA-specific T cells and HER2-expressing tumor cells and inducing potent tumor cell killing in vitro. To overcome the immunosuppressive TME, we further combined a HER2-targeted IL-12 fusion protein with OVA-αHER2, achieving synergistic anti-tumor responses in a mouse B16-HER2 solid tumor model. This treatment enhanced both systemic and intratumoral OVA-specific CD8+ T cell responses, accompanied by increased IFN-γ production in the TME. Together, these findings establish a modular immunotherapy strategy that integrates recruitment of a specific CD8+ T cell subset with localized cytokine-mediated immune reprogramming, providing a potential approach for HER2-positive solid tumors.