Memory phenotype CD8⁺ T cells with innate function selectively develop in the absence of active Itk

T cells with a memory-like phenotype and possessing innate immune function have been previously identified as CD8⁺CD44^hi cells. These cells rapidly secrete IFN-γ upon stimulation with IL-12/IL-18 and are involved in innate responses to infection with Listeria monocytogenes. The signals regulating these cells are unclear. The Tec kinase Itk regulates T cell activation and we report here that a majority of the CD8⁺ T cells in Itk null mice have a phenotype of CD44^hi similar to memory-like innate T cells. These cells are observed in mice carrying an Itk mutant lacking the kinase domain, indicating that active Tec kinase signaling suppresses their presence. These cells carry preformed message for and are able to rapidly produce IFN-γ upon stimulation in vitro with IL-12/IL-18, and endow Itk null mice the ability to effectively respond to infection with L. monocytogenes or exposure to lipopolysaccharides by secretion of IFN-γ. Transfer of these cells rescues the ability of IFN-γ null mice to reduce bacterial burden following L. monocytogenes infection, indicating that these cells are functional CD8⁺CD44^hi T cells previously detected in vivo. These results indicate that active signals from Tec kinases regulate the development of memory-like CD8⁺ T cells with innate function.