Exhausted CD8 T (Tex) cells in chronic viral infection and cancer have sustained co-expression of inhibitory receptors (IRs). Tex cells can be reinvigorated by blocking IRs, such as PD-1, but synergistic reinvigoration and enhanced disease control can be achieved by co-targeting multiple IRs including PD-1 and LAG-3. To dissect the molecular changes intrinsic when these IR pathways are disrupted, we investigated the impact of loss of PD-1 and/or LAG-3 on Tex cells during chronic infection. These analyses revealed distinct roles of PD-1 and LAG-3 in regulating Tex cell proliferation and effector functions, respectively. Moreover, these studies identified an essential role for LAG-3 in sustaining TOX and Tex cell durability as well as a LAG-3-dependent circuit that generated a CD94/NKG2+ subset of Tex cells with enhanced cytotoxicity mediated by recognition of the stress ligand Qa-1b, with similar observations in humans. These analyses disentangle the non-redundant mechanisms of PD-1 and LAG-3 and their synergy in regulating Tex cells.

Human CD8 tumor-infiltrating lymphocytes (TILs) with impaired effector functions and PD-1 expression are categorized as exhausted. However, the exhaustion-like features reported in TILs might stem from their activation rather than the consequence of T cell exhaustion itself. Using CRISPR-Cas9 and lentiviral overexpression in CD8 T cells from non-cancerous donors, we show that the T cell receptor (TCR)-induced transcription factor interferon regulatory factor 4 (IRF4) promotes cell proliferation and PD-1 expression and hampers effector functions and expression of nuclear factor κB (NF-κB)-regulated genes. While CD8 TILs with impaired interferon γ (IFNγ) production exhibit activation markers IRF4 and CD137 and exhaustion markers thymocyte selection associated high mobility group box (TOX) and PD-1, activated T cells in patients with COVID-19 do not demonstrate elevated levels of TOX and PD-1. These results confirm that IRF4+ TILs are exhausted rather than solely activated. Our study indicates, however, that PD-1 expression, low IFNγ production, and active cycling in TILs are all influenced by IRF4 upregulation after T cell activation.

Thymocyte selection-associated high-mobility group box (TOX) is a transcription factor that is crucial for T cell exhaustion during chronic antigenic stimulation, but its role in inflammation is poorly understood. Here, we report that TOX extracellularly mediates drastic inflammation upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection by binding to the cell surface receptor for advanced glycation end-products (RAGE). In various diseases, including COVID-19, TOX release was highly detectable in association with disease severity, contributing to lung fibroproliferative acute respiratory distress syndrome (ARDS). Recombinant TOX-induced blood vessel rupture, similar to a clinical signature in patients experiencing a cytokine storm, further exacerbating respiratory function impairment. In contrast, disruption of TOX function by a neutralizing antibody and genetic removal of RAGE diminished TOX-mediated deleterious effects. Altogether, our results suggest an insight into TOX function as an inflammatory mediator and propose the TOX-RAGE axis as a potential target for treating severe patients with pulmonary infection and mitigating lung fibroproliferative ARDS.

Rewiring exhausted CD8+ T (Tex) cells toward functional states remains a therapeutic challenge. Tex cells are epigenetically programmed by the transcription factor Tox. However, epigenetic remodeling occurs as Tex cells transition from progenitor (Texprog) to intermediate (Texint) and terminal (Texterm) subsets, suggesting development flexibility. We examined epigenetic transitions between Tex cell subsets and revealed a reciprocally antagonistic circuit between Stat5a and Tox. Stat5 directed Texint cell formation and re-instigated partial effector biology during this Texprog-to-Texint cell transition. Constitutive Stat5a activity antagonized Tox and rewired CD8+ T cells from exhaustion to a durable effector and/or natural killer (NK)-like state with superior anti-tumor potential. Temporal induction of Stat5 activity in Tex cells using an orthogonal IL-2:IL2Rβ-pair fostered Texint cell accumulation, particularly upon PD-L1 blockade. Re-engaging Stat5 also partially reprogrammed the epigenetic landscape of exhaustion and restored polyfunctionality. These data highlight therapeutic opportunities of manipulating the IL-2-Stat5 axis to rewire Tex cells toward more durably protective states.

Tox is a member of the high mobility group (HMG)-Box transcription factors and plays important roles in thymic T cell development. Outside of the thymus, however, Tox is also highly expressed by CD8 and CD4 T cells in various states of activation and in settings of cancer and autoimmune disease. In CD4 T cells, Tox has been primarily studied in T follicular helper (TFH) cells where it, along with Tox2, promotes TFH differentiation by regulating key TFH-associated genes and suppressing CD4 cytotoxic T cell differentiation. However, the role of Tox in other T helper (Th) cell subtypes is less clear. Here, we show that Tox is expressed in several physiologically-activated Th subtypes and its ectopic expression enhances the in vitro differentiation of Th2 and T regulatory (Treg) cells. Tox overexpression in unpolarized Th cells also induced the expression of several genes involved in cell activation (Pdcd1), cellular trafficking (Ccl3, Ccl4, Xcl1) and suppressing inflammation (Il10) across multiple Th subtypes. We found that Tox binds the regulatory regions of these genes along with the transcription factors BATF, IRF4, and JunB and that Tox-induced expression of IL-10, but not PD-1, is BATF-dependent. Based on these data, we propose a model where Tox regulates Th cell chemotactic genes involved in facilitating dendritic cell-T cell interactions and aids in the resolution or prevention of inflammation through the production of IL-10.

Thymocyte selection-associated high mobility group box protein (TOX) and members of the nuclear receptor 4A (NR4A) are known as transcription factors involved in T cell exhaustion.
To evaluate the mRNA expression of TOX and NR4A1-3 in CD8+ T cells in acute leukemia.
Blood samples were obtained from 21 ALL and 6 AML patients as well as 20 control subjects. CD8+ T cells were isolated using MACS. Relative gene expression of TOX and NR4A1-3 was then evaluated using qRT-PCR.
Comparison of mRNA expression of TOX in CD8+ T cells showed no significant difference among the study groups (p>0.05), while the expression of NR4A1 was significantly lower in AML patients than in the control group (p=0.0006). Also, the expression of NR4A2 and NR4A3 was significantly lower in both ALL (p=0.0049 and p=0.0005, respectively) and AML (p=0.0019 and p=0.0055, respectively) patients.
NR4As expressions were found to be lower in CD8+ T cells from patients with AML and ALL compared to controls, whereas the mRNA expression of TOX showed no significant difference. Although TOX and NR4As are associated with CD8+ T cell exhaustion in solid tumors, they might play different roles in acute leukemia, which requires further investigation.

BACKGROUND: Diagnosis of early mycosis fungoides (eMF) is challenging and often delayed as many of its clinical and histopathologic features may mimic various benign inflammatory dermatoses (BIDs). The products of the thymocyte selection-associated high mobility group box (TOX), twist family BHLH transcription factor 1 (TWIST1), signal transducer and activator of transcription 4 (STAT4), and special AT-rich sequence-binding protein 1 (SATB1) genes function as transcription factors and are involved in the pathogenesis of MF.
OBJECTIVE: We aim to determine the diagnostic value of TOX, TWIST1, STAT4, and SATB1 protein expressions in eMF.
METHODS: This non-randomized, controlled, prospective analytic study was conducted by performing immunohistochemistry staining with TOX, TWIST1, STAT4, and SATB1 polyclonal antibodies in lesional skin biopsies of eMF and BID patients. Nuclear staining of lymphocytes was compared between eMF and BIDs, and the capacity of these antibodies to predict eMF was determined.
RESULTS: Immunostainings with anti-TWIST1 showed an increase in protein expression (p = 0.003) and showed a decrease with anti-SATB1 antibodies in eMF compared to BIDs (p = 0.005) while anti-TOX and anti-STAT4 antibodies did not exhibit significant differences (p = 0.384; p = 0.150). Receiver operating characteristic analysis showed that immunohistochemical evaluations of TWIST1 and SATB1 protein expressions can differentiate eMF (area under the curve [AUC]: 0.728, 95% confidence interval [CI]: 0.605-0.851, p = 0.002; AUC: 0.686, 95% CI: 0.565-0.807, p = 0.013).
CONCLUSIONS: TWIST1 and SATB1 are potential diagnostic markers for the histologic diagnosis of eMF.

Unlike many other hematologic malignancies, Richter syndrome (RS), an aggressive B cell lymphoma originating from indolent chronic lymphocytic leukemia, is responsive to PD-1 blockade. To discover the determinants of response, we analyze single-cell transcriptome data generated from 17 bone marrow samples longitudinally collected from 6 patients with RS. Response is associated with intermediate exhausted CD8 effector/effector memory T cells marked by high expression of the transcription factor ZNF683, determined to be evolving from stem-like memory cells and divergent from terminally exhausted cells. This signature overlaps with that of tumor-infiltrating populations from anti-PD-1 responsive solid tumors. ZNF683 is found to directly target key T cell genes (TCF7, LMO2, CD69) and impact pathways of T cell cytotoxicity and activation. Analysis of pre-treatment peripheral blood from 10 independent patients with RS treated with anti-PD-1, as well as patients with solid tumors treated with anti-PD-1, supports an association of ZNF683high T cells with response.

The fundamental principle of immune checkpoint blockade (ICB) is to protect tumor-infiltrating T cells from being exhausted. Despite the remarkable success achieved by ICB treatment, only a small group of patients benefit from it. Characterized by a hypofunctional state with the expression of multiple inhibitory receptors, exhausted T (Tex) cells are a major obstacle in improving ICB. T cell exhaustion is a progressive process which adapts to persistent antigen stimulation in chronic infections and cancers. In this review, we elucidate the heterogeneity of Tex cells and offer new insights into the hierarchical transcriptional regulation of T cell exhaustion. Factors and signaling pathways that induce and promote exhaustion are also summarized. Moreover, we review the epigenetic and metabolic alterations of Tex cells and discuss how PD-1 signaling affects the balance between T cell activation and exhaustion, aiming to provide more therapeutic targets for applications of combinational immunotherapies.

Rationale: TOX is a DNA-binding factor required for the development of multiple immune cells and the formation of lymph nodes. However, the temporal regulation mode of TOX on NK cell development and function needs to be further explored. Methods: To investigate the role of TOX in NK cells at distinct developmental phases, we deleted TOX at the hematopoietic stem cell stage (Vav-Cre), NK cell precursor (CD122-Cre) stage and late NK cell developmental stage (Ncr1-Cre), respectively. Flow cytometry was used to detect the development and functional changes of NK cell when deletion of TOX. RNA-seq was used to assess the differences in transcriptional expression profile of WT and TOX-deficient NK cells. Published Chip-seq data was exploited to search for the proteins directly interact with TOX in NK cells. Results: The deficiency of TOX at the hematopoietic stem cell stage severely retarded NK cell development. To a less extent, TOX also played an essential role in the physiological process of NKp cells differentiation into mature NK cells. Furthermore, the deletion of TOX at NKp stage severely impaired the immune surveillance function of NK cells, accompanied by down-regulation of IFN-γ and CD107a expression. However, TOX is dispensable for mature NK cell development and function. Mechanistically, by combining RNA-seq data with published TOX ChIP-seq data, we found that the inactivation of TOX at NKp stage directly repressed the expression of Mst1, an important intermediate kinase in Hippo signaling pathway. Mst1 deficient at NKp stage gained the similar phenotype with Toxfl/flCD122Cre mice. Conclusion: In our study, we conclude that TOX coordinates the early mouse NK cell development at NKp stage by maintaining the expression of Mst1. Moreover, we clarify the different dependence of the transcription factor TOX in NK cells biology.