FOXP3 and neoplasm: Although this concept and process of cellular conversion and/or plasticity among CD4+FoxP3+ TReg cells remains controversial (Rubtsov et al., 2010), it is clear that the biological properties of CD4 TReg cells and their subpopulations are heterogeneous and influenced by the tumor environment in which they infiltrate (Hamann, 2012; Sainz-Perez et al., 2012).