Figure 1. Phenotypic plasticity of malignant T cells in CTCL cells. By activating STAT5, IL-2 and IL-15 play a major role in inducing FoxP3 expression and a development of Treg phenotype. Activation of STAT3 leads to IL-17, IL-10, PD-L1 and SOCS-3 expression fostering the TH17 phenotype and immune evasion by diverse, FoxP3-independent mechanisms. Targeting of the key cell signaling nodes may modulate the cytokine-dependent CTCL cell phenotype and, consequently, exert a therapeutic effect.