Pathogen-induced inflammatory environment controls effector and memory CD8 ⁺ T cell differentiation

In response to infection, CD8 ⁺ T cells integrate multiple signals and undergo an exponential increase in cell numbers. Simultaneously, a dynamic differentiation process occurs, resulting in the formation of short-lived effector cells (SLECs; CD127 ^low KLRG1 ^high) and memory precursor effector cells (CD127 ^highKLRG1 ^low) from an early effector cell that is CD127 ^lowKLRG1 ^low in phenotype. CD8 ⁺ T cell differentiation during vesicular stomatitis virus infection differed significantly than during Listeria monocytogenes infection with a substantial reduction in early effector cell differentiation into SLECs. SLEC generation was dependent on Ebi3 expression. Furthermore, SLEC differentiation during vesicular stomatitis virus infection was enhanced by administration of CpG-DNA, through an IL-12-dependent mechanism. Moreover, CpG-DNA treatment enhanced effector CD8 ⁺ T cell functionality and memory subset distribution, but in an IL-12-independent manner. Population dynamics were dramatically different during secondary CD8 ⁺ T cell responses, with a much greater accumulation of SLECs and the appearance of a significant number of CD127 ^highKLRG1 ^high memory cells, both of which were intrinsic to the memory CD8 ⁺ T cell. These subsets persisted for several months but were less effective in recall than memory precursor effector cells. Thus, our data shed light on how varying the context of T cell priming alters downstream effector and memory CD8 ⁺ T cell differentiation.