Activation of the transcription factor NFAT5 in the tumor microenvironment enforces CD8+ T cell exhaustion.

Persistent exposure to antigen during chronic infection or cancer renders T cells dysfunctional. The molecular mechanisms regulating this state of exhaustion are thought to be common in infection and cancer, despite obvious differences in their microenvironments. Here we found that NFAT5, an NFAT family transcription factor that lacks an AP-1 docking site, was highly expressed in exhausted CD8+ T cells in the context of chronic infections and tumors but was selectively required in tumor-induced CD8+ T cell exhaustion. Overexpression of NFAT5 in CD8+ T cells reduced tumor control, while deletion of NFAT5 improved tumor control by promoting the accumulation of tumor-specific CD8+ T cells that had reduced expression of the exhaustion-associated proteins TOX and PD-1 and produced more cytokines, such as IFNÉ£ and TNF, than cells with wild-type levels of NFAT5, specifically in the precursor exhausted PD-1+TCF1+TIM-3-CD8+ T cell population. NFAT5 did not promote T cell exhaustion during chronic infection with clone 13 of lymphocytic choriomeningitis virus. Expression of NFAT5 was induced by TCR triggering, but its transcriptional activity was specific to the tumor microenvironment and required hyperosmolarity. Thus, NFAT5 promoted the exhaustion of CD8+ T cells in a tumor-selective fashion.

Inflammatory B cells correlate with failure to checkpoint blockade in melanoma patients.

The understanding of the role of B cells in patients with solid tumors remains insufficient. We found that circulating B cells produced TNFα and/or IL-6, associated with unresponsiveness and poor overall survival of melanoma patients treated with anti-CTLA4 antibody. Transcriptome analysis of B cells from melanoma metastases showed enriched expression of inflammatory response genes. Publicly available single B cell data from the tumor microenvironment revealed a negative correlation between TNFα expression and response to immune checkpoint blockade. These findings suggest that B cells contribute to tumor growth via the production of inflammatory cytokines. Possibly, these B cells are different from tertiary lymphoid structure-associated B cells, which have been described to correlate with favorable clinical outcome of cancer patients. Further studies are required to identify and characterize B cell subsets and their functions promoting or counteracting tumor growth, with the aim to identify biomarkers and novel treatment targets.

LAG-3 and PD-1+LAG-3 inhibition promote anti-tumor immune responses in human autologous melanoma/T cell co-cultures.

Despite the success of immunotherapy using checkpoint blockade, many patients with solid tumors remain refractory to these treatments. In human cancer, the experimental options to investigate the specific effects of antibodies blocking inhibitory receptors are limited and it is still unclear which cell types are involved. We addressed the question whether the direct interaction between T cells and tumor cells can be enforced through blocking a set of inhibitory receptors including PD-1, TIM-3, BTLA and LAG-3, blocked either individually or in dual combinations with the anti-PD-1 antibody, and to determine the condition that induces maximal T cell function preventing tumor cell proliferation. Using short-term Melan-A-specific or autologous re-stimulations, checkpoint blockade did not consistently increase cytokine production by tumor-derived expanded T cells. We next set up a 5-day co-culture assay with autologous melanoma cell lines and expanded tumor infiltrating T cells, originating from tumor specimens obtained from 6 different patients. Amongst all combos tested, we observed that blockade of LAG-3 alone, and more strongly when combined with PD-1 blockade, enforced T cell responses and tumor cell growth control. The combination of anti-LAG-3 plus anti-PD-1 acted through CD8 T cells and led to increased IFNγ production and cytotoxic capacity. Our results show that LAG-3 and PD-1 are regulating the direct interaction between tumor cells and autologous T cells, suggesting that therapy effects may be promoted by enhanced access of the corresponding blocking reagents to the tumor microenvironment.

CD40 Agonist Restores the Antitumor Efficacy of Anti-PD1 Therapy in Muscle-Invasive Bladder Cancer in an IFN I/II-Mediated Manner.

Bladder cancer is one of the most common malignancies and has poor prognosis for patients with locally advanced, muscle-invasive, disease despite the efficacy of immune checkpoint blockade. To develop more effective immunotherapy strategies, we studied a genetic mouse model carrying deletion of Tp53 and Pten in the bladder, which recapitulates bladder cancer tumorigenesis and gene expression patterns found in patients. We discovered that tumor cells became more malignant and the tumor immune microenvironment evolved from an inflammatory to an immunosuppressive state. Accordingly, treatment with anti-PD1 was ineffective, but resistance to anti-PD1 therapy was overcome by combination with a CD40 agonist (anti-CD40), leading to strong antitumor immune responses. Mechanistically, this combination led to CD8+ T-cell recruitment from draining lymph nodes. CD8+ T cells induced an IFNγ-dependent repolarization toward M1-like/IFNß-producing macrophages. CD8+ T cells, macrophages, IFN I, and IFN II were all necessary for tumor control, as demonstrated in vivo by the administration of blocking antibodies. Our results identify essential cross-talk between innate and adaptive immunity to control tumor development in a model representative of anti-PD1-resistant human bladder cancer and provide scientific rationale to target CD40 in combination with blocking antibodies, such as anti-PD1/PD-L1, for muscle-invasive bladder cancer.

Analysis of cancer cell-intrinsic immune regulation in response to CD8+ T cell attack.

Immunotherapies against cancer continue to improve, but many cancers show primary or secondary resistance. Novel research strategies are necessary to reach a comprehensive understanding of the underlying mechanisms. There is increasing evidence that T cells themselves provoke immune escape of cancer cells. In this chapter we describe a co-culture system to analyze the dynamic interplay between T cells and cancer cells. Using human melanoma cell lines and T cell clones, we obtained reproducible and comparable results despite the high heterogeneity of tumor cells. We show the feasibility of differential protein and gene expression analysis of melanoma cells isolated from our culture system. Thus, the system allows quantifying broadly the differential gene expression in melanoma cells upon interaction with T cells, revealing immune-related reactions in cancer cells. Many parts of this chapter were previously published in an original paper and are reproduced here for this book.

T cell-induced CSF1 promotes melanoma resistance to PD1 blockade.

Colony-stimulating factor 1 (CSF1) is a key regulator of monocyte/macrophage differentiation that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). We show that CSF1 is expressed in human melanoma, and patients with metastatic melanoma have increased CSF1 in blood compared to healthy subjects. In tumors, CSF1 expression correlated with the abundance of CD8+ T cells and CD163+ TAMs. Human melanoma cell lines consistently produced CSF1 after exposure to melanoma-specific CD8+ T cells or T cell-derived cytokines in vitro, reflecting a broadly conserved mechanism of CSF1 induction by activated CD8+ T cells. Mining of publicly available transcriptomic data sets suggested co-enrichment of CD8+ T cells with CSF1 or various TAM-specific markers in human melanoma, which was associated with nonresponsiveness to programmed cell death protein 1 (PD1) checkpoint blockade in a smaller patient cohort. Combination of anti-PD1 and anti-CSF1 receptor (CSF1R) antibodies induced the regression of BRAFV600E -driven, transplant mouse melanomas, a result that was dependent on the effective elimination of TAMs. Collectively, these data implicate CSF1 induction as a CD8+ T cell-dependent adaptive resistance mechanism and show that simultaneous CSF1R targeting may be beneficial in melanomas refractory to immune checkpoint blockade and, possibly, other T cell-based therapies.

Broad and Conserved Immune Regulation by Genetically Heterogeneous Melanoma Cells.

Although mutations drive cancer, it is less clear to what extent genetic defects control immune mechanisms and confer resistance to T-cell-based immunotherapy. Here, we studied the reactions of malignant and benign melanocyte lines to cytotoxic CD8+ T cells (CTL) using flow cytometry and gene expression analyses. We found rapid and broad upregulation of immune-regulatory genes, essentially triggered by CTL-derived IFNγ and augmented by TNFα. These reactions were predominantly homogenous, independent of oncogenic driver mutations, and similar in benign and malignant cells. The reactions exhibited both pro- and antitumorigenic potential and primarily corresponded to mechanisms that were conserved, rather than acquired, by mutations. Similar results were obtained from direct ex vivo analysis of the tumor microenvironment. Thus, immune regulation in the tumor landscape may often be driven by conserved mechanisms, which may explain why T-cell-based immunotherapy can provide durable benefits with relatively infrequent escape. Cancer Res; 77(7); 1623-36. ©2017 AACR.