Yosra Messai

Cutting Edge: Hypoxia-Induced Nanog Favors the Intratumoral Infiltration of Regulatory T Cells and Macrophages via Direct Regulation of TGF-β1

Emerging evidence suggests a link between tumor hypoxia and immune suppression. In this study, we investigated the role of hypoxia-induced Nanog, a stemness-associated transcription factor, in immune suppression. We observed that hypoxia-induced Nanog correlated with the acquisition of stem cell–like properties in B16-F10 cells. We further show that Nanog was selectively induced in hypoxic areas of B16-F10 tumors. Stable short hairpin RNA–mediated depletion of Nanog, combined with melanocyte differentiation Ag tyrosinase-related protein-2 peptide-based vaccination, resulted in complete inhibition of B16-F10 tumor growth. Nanog targeting significantly reduced immunosuppressive cells (regulatory T cells and macrophages) and increased CD8+ T effector cells in tumor bed in part by modulating TGF-β1 production. Additionally, Nanog regulated TGF-β1 under hypoxia by directly binding the TGF-β1 proximal promoter. Collectively, our data establish a novel functional link between hypoxia-induced Nanog and TGF-β1 regulation and point to a major role of Nanog in hypoxia-driven immunosuppression.

The multifaceted role of autophagy in tumor evasion from immune surveillance

While autophagy is constitutively executed at basal level in all cells, it is activated in cancer cells in response to various microenvironmental stresses including hypoxia. It is now well established that autophagy can act both as tumor suppressor or tumor promoter. In this regard, several reports indicate that the tumor suppressor function of autophagy is associated with its ability to scavenge damaged oxidative organelles, thereby preventing the accumulation of toxic oxygen radicals and limiting the genome instability. Paradoxically, in developed tumors, autophagy can promote the survival of cancer cells and therefore operates as a cell resistance mechanism. The consensus appears to be that autophagy has a dual role in suppressing tumor initiation and in promoting the survival of established tumors. This has inspired significant interest in applying anti-autophagy therapies as an entirely new approach to cancer treatment. While much remains to be learned about the regulation and context-dependent biological role of autophagy, it is now well established that modulation of this process could be an attractive approach for the development of novel anticancer therapeutic strategies. In this review, we will summarize recent reports describing how tumor cells, by activating autophagy, manage to resist the immune cell attack. Data described in this review strongly argue that targeting autophagy may represent a conceptual realm for new immunotherapeutic strategies aiming to block the immune escape and therefore providing rational approach to future tumor immunotherapy design.

Crosstalk between CTC, Immune System and Hypoxic Tumor Microenvironment

Accumulating evidence indicate that the behavior of tumorigenic cells is highly influenced by their microenvironment. In this regard, microenvironmental hypoxia plays a determinant role in the emergence of CTC (circulating tumor cells) and CSC (cancer stem cells). CTCs are believed to be indicators of residual disease and thus pose an increased risk of metastasis. In spite of being rare and exposed to immune attack, these cells are capable to escape the immune system of the host. Although CTC play a pivotal role in the metastatic cascade and their prognostic impact has been repeatedly demonstrated, little is known about their escape mechanisms to immune system of the host. Therefore a better knowledge of the immunogenicity of these cells and their cross talk with immune killer cells as well as with tumor microenvironment may represent an exciting new immunotherapy opportunity. In this chapter, we will discuss how hypoxia is involved in the regulation of tumor progression and induction of EMT and cancer stem cell like features. We will also illustrate the relationship between hypoxia and CTC and review how CTC interact with the cells of immune system (both innate and adaptive) in terms of their survival and EMT phenotype. We will attempt to outline how hypoxic stress may confer resistance to CTC by giving them EMT and CSC like phenotype. Finally we will discuss whether the inhibition of hypoxic signaling pathways in different compartments of the solid tumor microenvironment will have an impact on CTC number, resistant phenotype and CTC lysis by immune effectors.

Emerging Role of Hypoxia-Induced Autophagy in Cancer Immunotherapy

Cytotoxic T-lymphocytes (CTLs) are central effectors to eliminate cancer cells in an antigen- and cell contact-dependent manner, and induce long-lasting tumor regression. However, CTLs often fail to eradicate established tumors, likely as a consequence of failed infiltration and/or a locally immunosuppressive and metabolically perturbed tumor microenvironment. In fact, tumor cell growth in vivo is not only influenced by CTL-tumor cell recognition and tumor susceptibility to cell-mediated death, but also by the complex and highly dynamic tumor microenvironment, providing important clues to tumor development and progression. Besides the development of cancer vaccines, recent years have also seen the emergence of novel cancer immunotherapies based on our increasing knowledge of T cell molecules that regulate T cell responses. This has resulted in the development of several monoclonal antibody (mAb)-based therapies, such as anti-CTLA-4 or anti-PD-1, which have recently shown clinical benefits in several cancers. Accumulating experimental and clinical evidence indicates that multiple mechanisms suppressing the antitumor immune functions are directly developed in the tumor microenvironment. Recently, attention has focused on the mechanisms by which tumor microenvironmental hypoxia alters tumor transcriptional profiles to modulate glycolysis, proliferation, survival, and invasion. This chapter will summarize the recent progress in understanding the influence of tumor microenvironment, in particular hypoxia-induced autophagy, on the tumor survival mechanisms, and subsequently the quality of the antitumor response.

Role of ITPR1/HIF-2{alpha} axis in protecting renal cancer cells against natural killer cells.

417 Background: Clear cell renal cell carcinomas frequently display inactivation of VHL gene leading to increased level of hypoxia inducible factors (HIFs). The specific role of VHL mutations and selective activation of HIF-2 alpha in modulating RCC susceptibility to cytotoxic immune response remains largely unknown. Methods: In this study, we used 786-0 RCC VHL-mutated cell line selectively induces HIF-2 alpha stabilization.Chromium release cytotoxicity assay was regularly used to evaluate tumor target cells sensitivity to NK-mediated lysis. Confocal microscopy was aso used to analyse immunologic synapse formation and for autophagy studies. Immunochemistry staining using RCC tissue microarrays was performed to evaluate HIF-2 alpha and ITPR1 expression in RCC patients. Results: We demonstrated that the RCC cell line 786-0 with mutated VHL was resistant to NK-mediated lysis as compared to the VHL-corrected cell line (WT7). This resistance was found to require HIF-2α stabilization. Based on global gene expr...

Hypoxic Stress: A Key Regulator of the Antitumor Cytotoxic Response Linking Immune Resistance to Immune Suppression

The tumor microenvironment is a complex network of tumor cells, immune cells, stromal cells and extracellular matrix accomplishing proliferation, migration, and dissemination of tumor cells. The reactivity of the immune system towards the growing tumor determines its capacity to reject the tumor, but this reactivity is increasingly appearing to be critically dependent on tumor microenvironmental factors. These factors include secreted molecules, type of infiltrating cells, and metabolic component such as hypoxia. Microenvironmental hypoxia is a prominent feature of solid tumors and is involved in fostering the neoplastic process and in modulation of immune reactivity. It results from inadequacies between the tumor microcirculation and the oxygen demands of the growing tumor mass, which leads to a lowering of oxygen partial pressure and a metabolic switch towards glycolysis [1]. Tumor hypoxia is a negative prognostic and predictive factor due to many effects on the selection of hypoxiasurviving clones [2], activation of the expression of genes involved in apoptosis inhibition [3], angiogenesis [4], invasiveness and metastasis [5], epithelial-to-mesenchymal transition [6], and loss of genomic stability [7]. Accumulating evidence indicates that tumor hypoxia is also involved in loss of immune reactivity either by decreasing tumor cell sensitivity to cytotoxic effectors or promoting immunosuppressive mechanisms [8].