TCRm Bi-NbTE nanobody engager targets intracellular antigens, suppressing tumor growth in xenograft models.

T cell engagers (TCEs) have revolutionized cancer immunotherapy, yet their efficacy is often limited by the inaccessibility of intracellular tumor antigens. Conventional bispecific TCEs, typically constructed from single-chain variable fragments (scFvs), suffer from structural instability and are restricted to extracellular targets. This creates a critical gap, as many potent tumor antigens reside within cells. Developing stable, targeted engagers for these internal antigens is crucial for expanding effective immunotherapies and overcoming current treatment limitations.

Researchers established a modular bispecific VHH-VHH immunotherapeutic platform, developing a first-in-class TCRm Bi-NbTE nanobody-based T cell engager. This platform simultaneously engages CD3ε on T cells and tumor-specific peptide-MHC class I (pMHC I) complexes, using HLA-A2/WT1126-134 or HLA-A2/GPC3144-152 as examples. Functional analyses were conducted in vitro and in vivo using multiple mouse xenograft models, including both cell-derived xenograft (CDX) and patient-derived xenograft (PDX) models. The primary endpoints assessed were tumor growth suppression, survival prolongation, and T cell infiltration.

In vitro and in vivo functional analyses confirmed that the TCRm Bi-NbTE platform exhibits exceptional specificity for tumor-specific pMHC I complexes. The nanobody potently induced antigen-restricted T cell activation, leading to selective lysis of pMHC I⁺ tumor cells while crucially sparing antigen-negative cells, demonstrating a high degree of precision. This targeted action is critical for minimizing off-target effects.

In multiple mouse xenograft models, encompassing both cell-derived (CDX) and patient-derived (PDX) models, TCRm Bi-NbTE significantly suppressed tumor growth, prolonged survival, and enhanced T cell infiltration.

These therapeutic effects were observed across various models, indicating broad applicability. Importantly, the treatment was well-tolerated, with no reported treatment-related adverse effects, suggesting a favorable safety profile in these preclinical models.