Induction of a distinct CD8 Tnc17 subset by transforming growth factor-β and interleukin-6

Cross-talk between TGF-β and IL-6 has been shown to direct the differentiation of CD4⁺ cells into special IL-17-secreting cells, which are termed Th17 cells. In this study, we demonstrated that TGF-β and IL-6 could stimulate CD8⁺ cells to differentiate into noncytotoxic, IL-17-producing cells in MLC. These IL-17-producing CD8⁺ cells exhibit a unique granzyme B^-IFN-γ-IL-10- phenotype. The mRNA level of Th2/T cytotoxic 2 (Tc2) transcription factors GATA3 and Th1/Tc1 transcription factors T-box expressed in T cell (T-bet) as well as its target H2·O-like homeobox (Hlx) is decreased in CD8⁺ cells from TGF-β- and IL-6-treated MLC. In addition, these CD8⁺ cells display a marked up-regulation of retinoic acid-related orphan receptor-γt, a key IL-17 transcription factor. These results demonstrate that the existence of an IL-17-producing CD8⁺ subset belongs to neither the Tc1 nor the Tc2 subset and can be categorized as a T noncytotoxic 17 (Tnc17) subset.