In addition to cytotoxic lymphocytes and natural killer (NK) cells (House et al., 2015), perforin-dependent cytotoxicity is also seen in CD4+FOXP3+ regulatory T cells (Tregs), which show aberrant, T helper-like IFNγ secretion in MS patients (Dominguez-Villar et al., 2011). Here, FOXP3 is linked to myeloid sarcoma.