Cutting edge: Phenotypic characterization and differentiation of human CD8⁺ T cells producing IL-171

Although IL-17-producing CD8⁺ T cells (Tc17 cells) have recently been identified, the detailed information about these cells still remains unclear. In this article we describe a study investigating the phenotype and differentiation of human Tc17 cells. Human Tc17 cells were detected in a minor population of CD8⁺ T cells and were predominantly found in CD27 ^-/+ CD28⁺CD45RA^- memory subsets. They also expressed CCR6 and a high level of CCR5. Though most Tc17 cells produced IFN-γ, a small part of the Tc17 cell population was IFN-γ negative in some individuals. Analysis of the in vitro induction of Tc17 cells showed that these cells were induced from the CD27⁺ CD28 ⁺CD45RA⁺ naive subset and that they expressed the CD27^-CD28⁺CD45RA^- and CCR6⁺ phenotype. These results together indicate that Tc17 cells have a unique phenotype and suggest that they differentiate from the same precursors that differentiate into IFN-γ-producing CD8⁺ T cells.