This study developed the TCRm Bi-NbTE platform, enabling efficient T cell redirection against intracellular tumor antigens such as WT1 and GPC3, offering an innovative strategy to overcome the target limitations of conventional T cell engagers and advancing CD3-based immunotherapy for solid tumors.
Literature Overview
The article titled 'TCR-mimic bispecific nanobody-based T cell engager targeting intracellular tumor antigens for cancer immunotherapy,' published in Signal Transduction and Targeted Therapy, systematically explores how nanobody technology can overcome the limitations of traditional T cell engagers (TCEs) in targeting intracellular tumor antigens. The authors developed a novel TCR-mimic (TCRm) bispecific nanobody-based T cell engager (TCRm Bi-NbTE), which simultaneously binds to CD3ε on T cells and peptide-MHC class I complexes (pMHC I), such as HLA-A2/WT1 and HLA-A2/GPC3, presented by HLA-A*02:01 on tumor cells. This design significantly expands the antigen repertoire accessible to TCEs, overcomes the structural instability and aggregation tendencies of traditional single-chain variable fragments (scFvs), and enables effective recognition of low-density pMHC complexes. The study confirms high specificity, potent anti-tumor activity, and favorable safety profiles through in vitro functional assays and multiple mouse xenograft models, including CDX and PDX systems.Background Knowledge
Although cancer immunotherapy has made significant progress, most T cell engager therapies are limited to cell surface antigens, while over 70% of tumor-specific proteins are intracellular or secreted, rendering them inaccessible to conventional BiTE-like drugs. This bottleneck severely restricts the applicability of immunotherapies, especially in solid tumors. Furthermore, existing scFv-based BiTE molecules suffer from structural instability and manufacturing challenges. While cell therapies like CAR-T can target intracellular antigens, they are complex and costly to produce and carry risks of off-target toxicity. Therefore, there is an urgent need for next-generation T cell engagers capable of effectively targeting intracellular tumor antigens. This study addresses this gap by leveraging nanobodies (VHH) to replace traditional scFvs and incorporating TCR-mimic (TCRm) antibodies that specifically recognize pMHC complexes, thereby constructing a modular, stable, and scalable bispecific platform. This approach avoids VH-VL domain mispairing and enables precise targeting of ideal tumor-associated antigens such as WT1 and GPC3, which are highly expressed in various malignancies but nearly absent in normal tissues—making them ideal immunotherapeutic targets. HLA-A2-restricted recognition further enhances the safety and specificity of the therapy.
Research Methods and Experiments
The authors used genetic engineering to fuse an anti-CD3ε nanobody with TCRm nanobodies specific for HLA-A2/WT1 or HLA-A2/GPC3 complexes via a flexible linker (Gly4Ser), creating the TCRm Bi-NbTE molecule. The protein was expressed in the E. coli BL21(DE3) system, purified from inclusion bodies, and refolded into functional form. Flow cytometry confirmed its binding specificity, showing that TCRm Bi-NbTE bound only to cells co-expressing HLA-A2 and the corresponding peptide, such as OVCAR3, HepG2, and peptide-pulsed T2 cells, but not to antigen-negative or HLA-mismatched cells. Bio-layer interferometry (BLI) revealed KD values in the 10⁻⁸ M range for both CD3ε and pMHC complexes, indicating high-affinity binding. ELISA confirmed simultaneous binding to both targets without steric hindrance.
In functional assays, the authors used a co-culture system of PBMC-derived T cells and tumor cells to assess T cell activation markers (CD25, CD69), degranulation (CD107a), proliferation (CFSE dilution), and cytokine secretion (IL-2, IFN-γ). TCRm Bi-NbTE induced strong antigen-dependent T cell activation and effector functions. In vitro cytotoxicity assays demonstrated dose-dependent killing of pMHC⁺ cells at an E:T ratio of 10:1, with no effect on pMHC⁻ cells. In vivo, NOD/SCID mice bearing CDX (HepG2-Luc, OVCAR3) or PDX models were injected intravenously with human PBMCs followed by TCRm Bi-NbTE treatment. The treatment group showed significant tumor growth inhibition and prolonged survival without notable toxicity. Histological analysis revealed increased T cell infiltration, reduced Ki-67 expression, and elevated apoptosis in tumors. Transcriptomic analysis showed upregulation of T cell activation and cytotoxicity-related genes, supporting the proposed mechanism of action.Key Conclusions and Perspectives
Research Significance and Prospects
This study marks a pivotal step forward in T cell engager technology toward targeting intracellular antigens. By integrating TCRm specificity with the advantages of nanobodies, the TCRm Bi-NbTE platform can be widely applied to various HLA-A*02:01-positive cancers, such as liver cancer, ovarian cancer, and leukemia, greatly expanding the targetable antigen landscape for immunotherapy. For drug development, this modular design allows rapid redirection to other pMHC complexes, accelerating new drug discovery. In clinical settings, patient selection can be guided by pMHC expression status to enable precision therapy. Moreover, this platform offers a new path toward universal 'off-the-shelf' immunotherapies, circumventing the high cost and long production timelines associated with personalized cell therapies. Future studies should further evaluate its safety and anti-tumor efficacy in humanized immune system models and explore combination therapies with PD-1/PD-L1 inhibitors.
Conclusion
This study successfully developed a nanobody-based bispecific T cell engager—TCRm Bi-NbTE—capable of specifically recognizing intracellular tumor antigen peptides presented by HLA-A*02:01, such as WT1 and GPC3, and effectively activating T cells to eliminate tumors. This innovative strategy overcomes the long-standing limitation of traditional T cell therapies to surface antigens, opening new avenues for treating both solid and hematological tumors. Its modular, stable, and scalable design enables rapid development of immunotherapeutics targeting diverse pMHC epitopes, offering strong clinical translational potential. At the laboratory level, this platform provides a new tool for studying T cell responses to pMHC complexes; clinically, it holds promise as an 'off-the-shelf' immunotherapy that could reduce treatment costs and benefit more patients. Particularly for refractory tumors expressing WT1 or GPC3, this technology may reshape current treatment paradigms and become a cornerstone of future precision immunotherapies. As more pMHC-specific nanobodies are developed, this platform could extend to a broad spectrum of cancers, ushering in a new era of personalized cancer immunotherapy.
