It is well established that transforming growth factor (TGF)-β, IL-6, IL-1β, IL-21 and IL-23 can promote IL-17+ CD4+ T cell differentiation in humans , , ,  and mice , , , . Since IL-17+ CD8+ T cells have a similar cytokine profile to IL-17+ CD4+ T cells, this provides a rationale for applying IL-17+ CD4+ T cell polarising conditions to induce or expand IL-17+ CD8+ T cells. Table 1 summarises the in vitro culture conditions reported thus far to expand human or mouse IL-17+ CD8+ T cells and IL-17+ interferon (IFN)-γ+ dual producing CD8+ T cells. A limited number of human IL-17+ CD8+ T cell differentiation studies are published to date compared to those in mice. One study reported that human IL-17+ CD8+ T cells were induced upon culture of naïve CD8+ T cells with recombinant TGF-β, IL-6, IL-1β, IL-23 and α-IFN-γ mAb for 5 days, followed by IL-2 addition for a further 4 days . However, a representative figure showed 0.11% of IL-17+ CD8+ T cells indicating that only a limited percentage of these cells was induced. Another protocol involved culturing human bulk CD8+ T cells with TGF-β and IL-6 for 3 days . IL-17+ CD8+ T cell induction frequencies were not reported, but low IL-17 levels were detected by ELISA.