Cytokine heterogeneity and plasticity are characteristic features of CD4+ IL-17+ T cells , , and IL-17+ CD8+ T cell plasticity has been investigated in mouse studies. Adoptive transfer of in vitro generated and sorted IL-17+ CD8+ T cells, IFN-γ+ CD8+ T cells and IL-17+ IFN-γ+ CD8+ T cells to C3HAhigh mice, which express haemagglutinin as a self antigen, resulted in a persistence of IL-17+ CD8+ T cells and IL-17+ IFN-γ+CD8+T cells but a loss of IFN-γ+ CD8+ T cells in recipient lungs after 7 days . Adoptive transfer of IL-17-polarised premelanosome protein-1 specific CD8+ T cells to mice with melanoma led to a conversion of the IL-17+ CD8+ T cells towards an IFN-γ+ CD8+ T cell phenotype from days 5–11, with a small presence of dual-producing CD8+ T cells . The most significant IFN-γ expression was observed within transferred IL-17+ CD8+ T cells, indicating plasticity of these cells in vivo. Culture of naive CD8+ T cells from IL-17A-EGFP reporter mice with IL-12 resulted in an IFN-γ+ cell subset within EGFP+ cells, confirming that IL-17+ IFN-γ+ CD8+ T cells can derive from IL-17+ CD8+ T cells in vivo . A recent study utilising reporter IL-17A-YFP mice investigated the in vivo cytokine profile of CD8+ YFP+ T cells 7 and 21 days post-allogeneic stem cell transplant . Cytokine profile heterogeneity with expression of IL-13, IL-22, TNF-α, GM-CSF and IFN-γ and minimal IL-10 expression was observed at day 7, and at 21 days CD8+ YFP+ cells possessed a pro-inflammatory cytokine profile, predominantly co-expressing IFN-γ, TNF-α and GM-CSF.