Conclusions Different strategies can be considered to impair Treg cell fitness in cancers. care. However, only a fraction of patients display durable responses to these treatments, and a deeper understanding of the cellular and mechanisms orchestrating immune responses to tumors is usually mandatory for the discovery of novel therapeutic targets. Among the most scrutinized immune cells, Forkhead Box Protein P3 (Foxp3)+ Regulatory T cells (Treg cells) are central inhibitors of protective anti-tumor immunity. These tumor-promoting functions render Treg cells attractive immunotherapy targets, and multiple strategies are being developed to inhibit their recruitment, survival, and function in the tumor microenvironment. In this context, it is critical to decipher the complex and multi-layered molecular mechanisms that shape and stabilize the Treg cell transcriptome. Here, we provide a global view of the transcription factors, and their upstream signaling pathways, involved in the programming of Treg cell homeostasis and functions LMD-009 in cancer. We also evaluate the feasibility and safety of novel therapeutic approaches aiming at targeting specific transcriptional regulators. and after the ablation of Treg cells in young and adult mice [2,3,4,5]. In addition, through their multiple mechanisms of suppression, Treg cells are involved in the inhibition of a wide variety of immune responses, ranging from contamination to cancer immunity . Studies conducted in preclinical murine models have established the deleterious function of Treg cells in cancer. Indeed, genetic and antibody-mediated depletion of Treg cells enhances tumor immunity and reduces tumor burden in many settings [7,8]. These conclusions have been largely confirmed in cancer patients, where the accumulation of Treg cells in the blood and tumor tissues is generally indicative of poor prognosis, though several exceptions, such as colorectal cancer, have been identified . Because of this deleterious facet, the development of therapies aiming at modulating Treg recruitment, accumulation, and function in the tumor microenvironment is an area of extensive investigation in the field of malignancy immunotherapy. As a prominent example, anti-Cytotoxic T-Lymphocyte-Associated Protein 4 (CTLA-4) antibodies, the first approved checkpoint-blockade therapy for cancer, were shown to exert their beneficial effects in cancer by decreasing Treg cells in mouse models , though the relevance of this mechanism in patients is still under debate [11,12]. The effect of Programmed Death-1 (PD-1) blockade on Treg cells and its contribution to therapeutic efficacy is also under scrutiny (reviewed in ). Interestingly, it was suggested that PD-1 inhibition on Treg cells may contribute to the hyperprogressive disease observed in a number of patients with gastric LMD-009 cancer . Together, this demonstrates the central role of Treg cells in cancer immunotherapy. Cutting-edge technologies now provide scientists with the ability to comprehend the complexity of Treg cell populations and their molecular regulation to highlight additional therapeutic targets. 2. An Overview of Treg Cell Subsets and Their Transcriptional Regulation The presence of different flavors of Treg cells underlies their large panel of LMD-009 functions. First, Treg cells can either develop in the thymus (tTreg) or differentiate in peripheral lymphoid tissues from na?ve conventional (Tconv) cells (pTreg cells and their in vitro relatives, iTreg). To date, whether these two populations rely on shared or distinct transcription factor activity remains unclear. The proper development of Treg cells relies on a large number of transcriptional and epigenetic regulators, either for their survival or for the expression of Foxp3 or its stabilization. These mechanisms have been largely deciphered elsewhere [15,16], and we will therefore focus our review around the transcriptional regulation of mature Foxp3+ Treg cells. Treg cell subsets can also be defined based on their activation status. Whereas na?ve-like Resting cells (rTreg) are primarily found in lymphoid tissues, engagement of the T-Cell Receptor (TCR) and its co-stimulation partner CD28, as well as members of the Tumor Necrosis Factor Receptor SuperFamily (TNFRSFs), drives the maturation of rTreg cells to a highly immunosuppressive Activated subset (aTreg cells, also known as effector eTreg cells) . aTreg cells migrate to non-lymphoid tissues, where they maintain Rabbit Polyclonal to NT tissue homeostasis and potently suppress ongoing immune responses. In particular, aTreg cells are highly abundant in the tumor microenvironment and express a large panel of immune checkpoints (i.e., inhibitory and stimulatory surface receptors), making their regulation an important aspect in the development of immune checkpoint-blockade therapies.