CD4 and cancer: Research on the role of DOT1L in various cell types is of utmost importance as 1) the extrapolation of its significant impacts on various immune cell subsets, e.g. CD4+ T cells (33), 2) the realisation that the attempt to inhibit DOT1L in cancer cells with systemically acting small molecule inhibitors (SMIs) also has a profound effect on other cells (128), and 3) the scientific challenges that coincide with research on epigenetic modifiers, in particular DOT1L.