TOX reinforces the phenotype and longevity of exhausted T cells in chronic viral infection.

Cytotoxic T cells are essential mediators of protective immunity to viral infection and malignant tumours and are a key target of immunotherapy approaches. However, prolonged exposure to cognate antigens often attenuates the effector capacity of T cells and limits their therapeutic potential1-4. This process, known as T cell exhaustion or dysfunction1, is manifested by epigenetically enforced changes in gene regulation that reduce the expression of cytokines and effector molecules and upregulate the expression of inhibitory receptors such as programmed cell-death 1 (PD-1)5-8. The underlying molecular mechanisms that induce and stabilize the phenotypic and functional features of exhausted T cells remain poorly understood9-12. Here we report that the development and maintenance of populations of exhausted T cells in mice requires the thymocyte selection-associated high mobility group box (TOX) protein13-15. TOX is induced by high antigen stimulation of the T cell receptor and correlates with the presence of an exhausted phenotype during chronic infections with lymphocytic choriomeningitis virus in mice and hepatitis C virus in humans. Removal of its DNA-binding domain reduces the expression of PD-1 at the mRNA and protein level, augments the production of cytokines and results in a more polyfunctional T cell phenotype. T cells with this deletion initially mediate increased effector function and cause more severe immunopathology, but ultimately undergo a massive decline in their quantity, notably among the subset of TCF-1+ self-renewing T cells. Altogether, we show that TOX is a critical factor for the normal progression of T cell dysfunction and the maintenance of exhausted T cells during chronic infection, and provide a link between the suppression of effector function intrinsic to CD8 T cells and protection against immunopathology.

Targeting Tumor-Associated Sialic Acids using Chimeric Switch Receptors based on Siglec-9 Enhances the Antitumor Efficacy of Engineered T Cells.

Cancer exploits different mechanisms to escape T-cell immunosurveillance, including overexpression of checkpoint ligands, secretion of immunosuppressive molecules, and aberrant glycosylation. Herein, we report that IFNγ, a potent immunomodulator secreted in the tumor microenvironment, can induce α2,6 hypersialylation in cancer cell lines derived from various histologies. We then focused on Siglec-9, a receptor for sialic acid moieties, and demonstrated that the Siglec-9+ T-cell population displayed reduced effector function. We speculated that Siglec-9 in primary human T cells can act as a checkpoint molecule and demonstrated that knocking out Siglec-9 using a CRISPR/Cas9 system enhanced the functionality of primary human T cells. Finally, we aimed to augment cancer-specific T-cell activity by taking advantage of tumor hypersialylation. Thus, we designed several Siglec-9-based chimeric switch receptors (CSRs), which included an intracellular moiety derived from costimulatory molecules (CD28/41BB) and different hinge regions. In an antigen specific context, T cells transduced with Siglec-9 CSRs demonstrated increased cytokine secretions and upregulation of activation markers. Moreover, T cells equipped with specific Siglec-9 CSRs mediated robust antitumor activity in a xenograft model of human tumors. Overall, this work sheds light on tumor evasion mechanisms mediated by sialylated residues and exemplifies an approach to improve engineered T cell-based cancer treatment.

A TIGIT-based chimeric co-stimulatory switch receptor improves T-cell anti-tumor function.

BACKGROUND: Tumors can employ different mechanisms to evade immune surveillance and function. Overexpression of co-inhibitory ligands that bind to checkpoint molecules on the surface of T-cells can greatly impair the function of latter. TIGIT (T cell immunoreceptor with Ig and ITIM domains) is such a co-inhibitory receptor expressed by T and NK cells which, upon binding to its ligand (e.g., CD155), can diminish cytokine production and effector function. Additionally, the absence of positive co-stimulation at the tumor site can further dampen T-cell response. METHODS: As T-cell genetic engineering has become clinically-relevant in the recent years, we devised herein a strategy aimed at enhancing T-cell anti-tumor function by diverting T-cell coinhibitory signals into positive ones using a chimeric costimulatory switch receptor (CSR) composed of the TIGIT exodomain fused to the signaling domain of CD28. RESULTS: After selecting an optimized TIGIT-28 CSR, we co-transduced it along with tumor-specific TCR or CAR into human T-cells. TIGIT-28-equipped T-cells exhibited enhanced cytokine secretion and upregulation of activation markers upon co-culture with tumor cells. TIGIT-28 enhancing capability was also demonstrated in an original in vitro model of T-cell of hypofunction induction upon repetitive antigen exposure. Finally, we tested the function of this molecule in the context of a xenograft model of established human melanoma tumors and showed that TIGIT-28-engineered human T-cells demonstrated superior anti-tumor function. CONCLUSION: Overall, we propose that TIGIT-based CSR can substantially enhance T-cell function and thus contribute to the improvement of engineered T cell-based immunotherapy.

T-cells "à la CAR-T(e)" - Genetically engineering T-cell response against cancer.

The last decade will be remembered as the dawn of the immunotherapy era during which we have witnessed the approval by regulatory agencies of genetically engineered CAR T-cells and of checkpoint inhibitors for cancer treatment. Understandably, T-lymphocytes represent the essential player in these approaches. These cells can mediate impressive tumor regression in terminally-ill cancer patients. Moreover, they are amenable to genetic engineering to improve their function and specificity. In the present review, we will give an overview of the most recent developments in the field of T-cell genetic engineering including TCR-gene transfer and CAR T-cells strategies. We will also elaborate on the development of other types of genetic modifications to enhance their anti-tumor immune response such as the use of co-stimulatory chimeric receptors (CCRs) and unconventional CARs built on non-antibody molecules. Finally, we will discuss recent advances in genome editing and synthetic biology applied to T-cell engineering and comment on the next challenges ahead.

Targeting Multiple Tumors Using T-Cells Engineered to Express a Natural Cytotoxicity Receptor 2-Based Chimeric Receptor.

Recent developments in cancer treatment are demonstrating the increasing and powerful potential of immunotherapeutic strategies. In this regard, the adoptive transfer of tumor-specific T-lymphocytes approaches can lead to tumor regression in cancer patients. More recently, the use of T-cells genetically engineered to express cancer-specific receptors such as the anti-CD19 chimeric antigen receptor (CAR) continues to show promise for the treatment of hematological malignancies. Still, there is a crucial need to develop efficient CAR-T cell approaches for the treatment of solid tumors. It has been shown that other lymphocytes such as natural killer (NK) cells can demonstrate potent antitumor function-nonetheless, their use in immunotherapy is rather limited due to difficulties in expanding these cells to therapeutically relevant numbers and to suppression by endogenous inhibitory mechanisms. Cancer recognition by NK cells is partly mediated by molecules termed natural cytotoxicity receptors (NCRs). In the present study, we hypothesize that it is possible to endow T-cells with an NK recognition pattern, providing them with a mean to recognize tumor cells, in a non-MHC restricted way. To test this, we genetically modified human T-cells with different chimeric receptors based on the human NCR2 molecule and then assessed their antitumor activity in vitro and in vivo. Our results show that expression in primary lymphocytes of an NCR2-derived CAR, termed s4428z, confers T-cells with the ability to specifically recognize heterogeneous tumors and to mediate tumor cytotoxicity in a mouse model. This study demonstrates the benefit of combining tumor recognition capability of NK cells with T cell effectiveness to improve cancer immunotherapy.