Background/introduction: T cell engagers (TCEs) are engineered immunotherapeutic molecules designed to direct the body’s immune system against tumour or infected cells by bridging T cells and their targets, triggering potent cytotoxic responses. Over the past decade, TCE-based therapies have gained momentum in oncology, resulting in several FDA approvals for haematologic malignancies and showing growing promise in solid tumours. Objective: This review elaborates on TCE mechanisms of action, emphasising their ability to activate T cells, target tumour antigens, and modulate the tumour microenvironment. Methods/results: We also delve into the clinical outcomes demonstrating TCE efficacy, alongside challenges such as cytokine release syndrome, antigen heterogeneity, and short half-lives. Recent advances in TCE design have incorporated multispecific constructs and conditional activation strategies and expansion in target molecules has enabled broadening applications to non-oncology indications like autoimmune and infectious diseases. Moreover, the use of artificial intelligence (AI) has also accelerated TCE discovery by identifying favourable epitope interactions, reducing immunogenicity risks, and enhancing overall design efficiency. Conclusions: Looking further, these advances open up a new era to redefine success for TCEs in both cancer and beyond, offering hope for more effective, safer immunotherapies.

Background Glioblastoma (GBM) almost invariably becomes resistant towards conventional treatment of radiotherapy and temozolomide (TMZ) chemotherapy, partly due to subpopulations of intrinsically resistant glioma stem-like cells (GSC). The oncolytic herpes simplex virus-1 G207 is a promising approach for GBM virotherapy although its efficacy in patients with GBM is often limited. Natural killer group 2 member D ligands (NKG2DLs) are minimally expressed by healthy cells but are upregulated by the DNA damage response (DDR) and in malignant cells with chronic DDR signaling, resulting in innate immune activation. Methods We have designed a bispecific T-cell engager (BiTE) capable of cross-linking CD3 on T cells with NKG2DL-expressing GBM cells. We then engineered the G207 virus to express the NKG2D BiTE and secrete it from infected cells. The efficacy of the free BiTE and BiTE delivered by G207 was evaluated in combination with conventional therapies in GBM cells and against patient-derived GSCs in the context of T-cell activation and target cell viability. Results NKG2D BiTE-mediated cross-linking of GBM cells and T cells causes antigen-independent T-cell activation, pro-inflammatory cytokine release, and tumor cell death, thereby combining direct viral oncolysis with BiTE-mediated cytotoxicity. Surface NKG2DL expression was further elevated on GBM cells following pretreatment with sublethal doses of TMZ and radiation to induce the DDR, increasing sensitivity towards G207-NKG2D BiTE and achieving synergistic cytotoxicity. We also demonstrate a novel strategy for targeting GSCs that are non-permissive to G207 infection but remain sensitive to NKG2D BiTE. Conclusions We propose a potential model for targeting GSCs in heterogeneous tumors, whereby differentiated GBM cells infected with G207-NKG2D BiTE produce NKG2D BiTE locally, directing T-cell cytotoxicity towards the GSC subpopulations in the tumor microenvironment.

Oncolytic viruses (OVs) provide the promise of tumor-selective cytotoxicity coupled with amplification of the therapeutic agent (the virus) in situ within the tumor improving its therapeutic index. Despite this promise, however, single agent-treatments have not been as successful as combination therapies, particularly combining with checkpoint inhibitor antibodies. The antibodies may be delivered by two approaches, either encoded within the OV genome to restrict antibody production to sites of active virus infection or alternatively given alongside OVs as separate treatments. Both approaches have shown promising therapeutic outcomes, and this leads to an interesting question of whether one approach is potentially better than the other. In this review, we provide a brief summary of the combination OV-antibody therapies that target tumor cells, tumor microenvironment and immune cells to help define key parameters influencing which approach is superior, thereby improving insight into the rational design of OV treatment strategies.

Nuclear receptor related-1 protein (Nurr1), coded by an early response gene, is involved in multiple cellular and physiological functions, including proliferation, survival, and self-renewal. Dysregulation of Nurr1 has been frequently observed in many cancers and is attributed to multiple transcriptional and post-transcriptional mechanisms. Besides, Nurr1 exhibits extensive crosstalk with many oncogenic and tumor suppressor molecules, which contribute to its potential pro-malignant behaviors. Furthermore, Nurr1 is a key player in attenuating antitumor immune responses. It not only potentiates immunosuppressive functions of regulatory T cells but also dampens the activity of cytotoxic T cells. The selective accessibility of chromatin by Nurr1 in T cells is closely associated with cell exhaustion and poor efficacy of cancer immunotherapy. In this review, we summarize the reported findings of Nurr1 in different malignancies, the mechanisms that regulate Nurr1 expression, and the downstream signaling pathways that Nurr1 employs to promote a wide range of malignant phenotypes. We also give an overview of the association between Nurr1 and antitumor immunity and discuss the inhibition of Nurr1 as a potential immunotherapeutic strategy.

Background: Colorectal liver metastasis (CRLM) is the terminal stage of colorectal cancer and remains largely resistant to immunotherapeutics, yet the underlying immune escape mechanisms remain poorly understood. Through novel observational methods focused on human living and fixed tissue, we profiled the spatial and molecular features of microsatellite stable (MSS) CRLM and the surrounding liver microenvironment. Methods: First, we re-purposed normothermic hepatic machine perfusion as a preclinical model of MSS CRLM, enabling delivery of labelled T-cells through physiological vascular routes into living, tumour-bearing human livers. Second, to dissect the liver microenvironment, we spatially map the transcriptomes of MSS CRLM and adjacent liver at single-cell resolution across ~ 1.9 million cells, and perform multiplexed immunofluorescence applying a19-marker panel to a validation cohort. Results: Whilst T-cells readily extravasated within the peri-tumoural liver, they failed to extravasate into MSS CRLM. Spatial analyses revealed a progressive shift in endothelial phenotypes across regions: from a non-inflamed state in normal liver, to a highly inflamed, peri-tumoural endothelium, and finally to an anergic, angiogenic endothelial population within CRLM characterised by reduced expression of adhesion molecules required for T-cell extravasation. CD4 T-cells that extravasate in the peri-tumoural liver are TCR-reactive yet exhausted, whereas CD4 T-cells within CRLM show stress responses, impaired cytokine gene expression and reduced TCR reactivity, residing within hypoxic niches. These divergent CD4 phenotypes are associated with distinct fibroblast-myeloid niches across peri-tumoural and tumour regions. Conclusion: Based on these observations, MSS CRLM impair T-cell extravasation and simultaneously drive intra-tumoural endothelial anergy, peri-tumoural T-cell exhaustion and an intra-tumoural T-cell stress response. Further mechanistic work is needed to validate these findings and guide the development of novel immunotherapeutics.

Purpose: Bispecific T cell engagers (BiTEs) have recently been approved as a locoregional immunotherapy for malignant ascites. Although ascites is recognised as a lipid-rich, immunosuppressive environment, the mechanisms by which ascites, particularly its lipid components, suppress antitumour immunity remain poorly understood. Here, we investigated the impact of ascites-associated lipids on T cell immunosuppression and assessed whether lipid modulation could enhance the efficacy of BiTE therapy. Experimental Design: Transcriptomic profiling was performed on T cells treated with acellular ascites fluid to identify gene expression signatures associated with ascites exposure. Functional assays were conducted to evaluate the effects of ascites-associated lipids on T cell activation and cytotoxicity. In parallel, T cells were cocultured with ovarian cancer cells and EpCAM-targeting BiTEs in the presence or absence of a lipid-removal agent to assess how lipid depletion affected BiTE efficacy. Results: T cells exposed to acellular ascites fluid exhibited an enriched transcriptomic signature associated with cholesterol efflux and incomplete fatty acid oxidation, which are metabolic features often found in exhausted T cells. These alterations converged on a metabolically imbalanced state linked to impaired plasma membrane signalling. Lipid removal from ascites selectively rescued CD137 expression but not CD25, and restored BiTE-mediated cytotoxicity, suggesting a differential impact of lipid metabolism on TCR complex-dependent versus cytokine-driven activation pathways. Conclusions: These findings identified lipid as a driver for T cell dysfunction in ovarian cancer ascites. Removal of ascites lipids restored T cell activation and augmented BiTE-mediated cytotoxicity, supporting a combination approach to potentiate BiTE therapy in malignant ascites. Translational Relevance: Malignant ascites represents a lipid-rich, immunosuppressive tumour microenvironment that is increasingly targeted by emerging T cell-based therapies. Although EpCAM-targeting bispecific T cell engagers (BiTEs) have recently been approved for malignant ascites and multiple similar BiTEs are in clinical development, the mechanisms by which ascites impairs T cell function and potentially limits therapeutic efficacy remain poorly understood. Using patient-derived ascites throughout, this study demonstrated that lipid metabolic reprogramming, rather than immune checkpoint upregulation, was a driver of T cell dysfunction. Importantly, we demonstrated that lipid removal from ascites rescued T cell function and restored BiTE efficacy, identifying a targetable metabolic barrier to immunotherapy. While EpCAM was used as a proof-of-concept target, we anticipate the metabolic insights and therapeutic strategies identified here will be equally applicable to other BiTE and CAR-T platforms, supporting a new combination approach for the treatment of malignant ascites.