The aryl hydrocarbon receptor suppresses immunity to oral squamous cell carcinoma through immune checkpoint regulation.

Immune checkpoint inhibitors represent some of the most important cancer treatments developed in the last 20 y. However, existing immunotherapy approaches benefit only a minority of patients. Here, we provide evidence that the aryl hydrocarbon receptor (AhR) is a central player in the regulation of multiple immune checkpoints in oral squamous cell carcinoma (OSCC). Orthotopic transplant of mouse OSCC cells from which the AhR has been deleted (MOC1AhR-KO) results, within 1 wk, in the growth of small tumors that are then completely rejected within 2 wk, concomitant with an increase in activated T cells in tumor-draining lymph nodes (tdLNs) and T cell signaling within the tumor. By 2 wk, AhR+ control cells (MOC1Cas9), but not MOC1AhR-KO cells up-regulate exhaustion pathways in the tumor-infiltrating T cells and expression of checkpoint molecules on CD4+ T cells (PD-1, CTLA4, Lag3, and CD39) and macrophages, dendritic cells, and Ly6G+ myeloid cells (PD-L1 and CD39) in tdLNs. Notably, MOC1AhR-KO cell transplant renders mice 100% immune to later challenge with wild-type tumors. Analysis of altered signaling pathways within MOC1AhR-KO cells shows that the AhR controls baseline and IFNγ-induced Ido and PD-L1 expression, the latter of which occurs through direct transcriptional control. These observations 1) confirm the importance of malignant cell AhR in suppression of tumor immunity, 2) demonstrate the involvement of the AhR in IFNγ control of PD-L1 and IDO expression in the cancer context, and 3) suggest that the AhR is a viable target for modulation of multiple immune checkpoints.

A cell-based drug delivery platform for treating central nervous system inflammation.

Mesenchymal stem cells (MSCs) are promising candidates for the development of cell-based drug delivery systems for autoimmune inflammatory diseases, such as multiple sclerosis (MS). Here, we investigated the effect of Ro-31-8425, an ATP-competitive kinase inhibitor, on the therapeutic properties of MSCs. Upon a simple pretreatment procedure, MSCs spontaneously took up and then gradually released significant amounts of Ro-31-8425. Ro-31-8425 (free or released by MSCs) suppressed the proliferation of CD4+ T cells in vitro following polyclonal and antigen-specific stimulation. Systemic administration of Ro-31-8425-loaded MSCs ameliorated the clinical course of experimental autoimmune encephalomyelitis (EAE), a murine model of MS, displaying a stronger suppressive effect on EAE than control MSCs or free Ro-31-8425. Ro-31-8425-MSC administration resulted in sustained levels of Ro-31-8425 in the serum of EAE mice, modulating immune cell trafficking and the autoimmune response during EAE. Collectively, these results identify MSC-based drug delivery as a potential therapeutic strategy for the treatment of autoimmune diseases. KEY MESSAGES: MSCs can spontaneously take up the ATP-competitive kinase inhibitor Ro-31-8425. Ro-31-8425-loaded MSCs gradually release Ro-31-8425 and exhibit sustained suppression of T cells. Ro-31-8425-loaded MSCs have more sustained serum levels of Ro-31-8425 than free Ro-31-8425. Ro-31-8425-loaded MSCs are more effective than MSCs and free Ro-31-8425 for EAE therapy.

How the AHR Became Important in Cancer: The Role of Chronically Active AHR in Cancer Aggression.

For decades, the aryl hydrocarbon receptor (AHR) was studied for its role in environmental chemical toxicity i.e., as a quirk of nature and a mediator of unintended consequences of human pollution. During that period, it was not certain that the AHR had a "normal" physiological function. However, the ongoing accumulation of data from an ever-expanding variety of studies on cancer, cancer immunity, autoimmunity, organ development, and other areas bears witness to a staggering array of AHR-controlled normal and pathological activities. The objective of this review is to discuss how the AHR has gone from a likely contributor to genotoxic environmental carcinogen-induced cancer to a master regulator of malignant cell progression and cancer aggression. Particular focus is placed on the association between AHR activity and poor cancer outcomes, feedback loops that control chronic AHR activity in cancer, and the role of chronically active AHR in driving cancer cell invasion, migration, cancer stem cell characteristics, and survival.

Author Correction: Control of tumor-associated macrophages and T cells in glioblastoma via AHR and CD39.

In the version of this article initially published, author Alexandre Prat's surname was misspelled. The error has been corrected in the HTML and PDF versions of the article.

Control of tumor-associated macrophages and T cells in glioblastoma via AHR and CD39.

Tumor-associated macrophages (TAMs) play an important role in the immune response to cancer, but the mechanisms by which the tumor microenvironment controls TAMs and T cell immunity are not completely understood. Here we report that kynurenine produced by glioblastoma cells activates aryl hydrocarbon receptor (AHR) in TAMs to modulate their function and T cell immunity. AHR promotes CCR2 expression, driving TAM recruitment in response to CCL2. AHR also drives the expression of KLF4 and suppresses NF-κB activation in TAMs. Finally, AHR drives the expression of the ectonucleotidase CD39 in TAMs, which promotes CD8+ T cell dysfunction by producing adenosine in cooperation with CD73. In humans, the expression of AHR and CD39 was highest in grade 4 glioma, and high AHR expression was associated with poor prognosis. In summary, AHR and CD39 expressed in TAMs participate in the regulation of the immune response in glioblastoma and constitute potential targets for immunotherapy.

Detection of aryl hydrocarbon receptor agonists in human samples.

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor with important functions in the immune response and cancer. AHR agonists are provided by the environment, the commensal flora and the metabolism. Considering AHR physiological functions, AHR agonists may have important effects on health and disease. Thus, the quantification of AHR agonists in biological samples is of scientific and clinical relevance. We compared different reporter systems for the detection of AHR agonists in serum samples of Multiple Sclerosis (MS) patients, and assessed the influence of transfection methods and cell lines in a reporter-based in vitro assay. While the use of stable or transient reporters did not influence the measurement of AHR agonistic activity, the species of the cell lines used in these reporter assays had important effects on the reporter readings. These observations suggest that cell-specific factors influence AHR activation and signaling. Thus, based on the reported species selectivity of AHR ligands and the cell species-of-origin effects that we describe in this manuscript, the use of human cell lines is encouraged for the analysis of AHR agonistic activity in human samples. These findings may be relevant for the analysis of AHR agonists in human samples in the context of inflammatory and neoplastic disorders.

Sphingosine 1-phosphate receptor modulation suppresses pathogenic astrocyte activation and chronic progressive CNS inflammation.

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the CNS that causes disability in young adults as a result of the irreversible accumulation of neurological deficits. Although there are potent disease-modifying agents for its initial relapsing-remitting phase, these therapies show limited efficacy in secondary progressive MS (SPMS). Thus, there is an unmet clinical need for the identification of disease mechanisms and potential therapeutic approaches for SPMS. Here, we show that the sphingosine 1-phosphate receptor (S1PR) modulator fingolimod (FTY720) ameliorated chronic progressive experimental autoimmune encephalomyelitis in nonobese diabetic mice, an experimental model that resembles several aspects of SPMS, including neurodegeneration and disease progression driven by the innate immune response in the CNS. Indeed, S1PR modulation by FTY720 in murine and human astrocytes suppressed neurodegeneration-promoting mechanisms mediated by astrocytes, microglia, and CNS-infiltrating proinflammatory monocytes. Genome-wide studies showed that FTY720 suppresses transcriptional programs associated with the promotion of disease progression by astrocytes. The study of the molecular mechanisms controlling these transcriptional modules may open new avenues for the development of therapeutic strategies for progressive MS.

Metabolic control of type 1 regulatory T cell differentiation by AHR and HIF1-α.

Our understanding of the pathways that regulate lymphocyte metabolism, as well as the effects of metabolism and its products on the immune response, is still limited. We report that a metabolic program controlled by the transcription factors hypoxia inducible factor-1α (HIF1-α) and aryl hydrocarbon receptor (AHR) supports the differentiation of type 1 regulatory T cell (Tr1) cells. HIF1-α controls the early metabolic reprograming of Tr1 cells. At later time points, AHR promotes HIF1-α degradation and takes control of Tr1 cell metabolism. Extracellular ATP (eATP) and hypoxia, linked to inflammation, trigger AHR inactivation by HIF1-α and inhibit Tr1 cell differentiation. Conversely, CD39 promotes Tr1 cell differentiation by depleting eATP. CD39 also contributes to Tr1 suppressive activity by generating adenosine in cooperation with CD73 expressed by responder T cells and antigen-presenting cells. These results suggest that HIF1-α and AHR integrate immunological, metabolic and environmental signals to regulate the immune response.