cancers Review Recruitment and Expansion of Tregs Cells in the Tumor Environment—How to Target Them? Justine Cinier 1,†, Margaux Hubert 1,†, Laurie Besson 1, Anthony Di Roio 1 ,Céline Rodriguez 1, Vincent Lombardi 2, Christophe Caux 1,‡ and Christine Ménétrier-Caux 1,*,‡ 1 University of Lyon, Claude Bernard Lyon 1 University, INSERM U-1052, CNRS 5286 Centre Léon Bérard, Cancer Research Center of Lyon (CRCL), 69008 Lyon, France;
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[email protected] (M.H.);
[email protected] (L.B.);
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[email protected] (C.C.) 2 Institut de Recherche Servier, 125 Chemin de Ronde, 78290 Croissy-sur-Seine, France;
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[email protected] † Co-first authorship. ‡ Co-last authorship. Simple Summary: The immune response against cancer is generated by effector T cells, among them cytotoxic CD8+ T cells that destroy cancer cells and helper CD4+ T cells that mediate and support the immune response. This antitumor function of T cells is tightly regulated by a particular subset of CD4+ T cells, named regulatory T cells (Tregs), through different mechanisms. Even if the complete inhibition of Tregs would be extremely harmful due to their tolerogenic role in impeding autoimmune diseases in the periphery, the targeted blockade of their accumulation at tumor sites or their targeted Citation: Cinier, J.; Hubert, M.; depletion represent a major therapeutic challenge. This review focuses on the mechanisms favoring Besson, L.; Di Roio, A.; Rodriguez, C.; Treg recruitment, expansion and stabilization in the tumor microenvironment and the therapeutic Lombardi, V.; Caux, C.; strategies developed to block these mechanisms.