Defective capacity of CD8+ memory T cells developed from absence of IL‐12 priming for secondary expansion

In vivo CD8+ T cell responses consist of three main phases, namely: (i) a proliferation phase consisting of effector T cell clonal expansion, (ii) a contraction (transition) phase leading to the transition from the large population of effector T cells to a smaller population of long‐lived memory T (Tm) cells, and (iii) a maintenance phase involving Tm cell survival in the host. Recently, it has also been shown that IL‐12 priming during in vitro Ag stimulation changes properties of CD8+ T cells such as downregulation of CD69, alteration in the distribution of lipid rafts, a decrease in T cell receptor structural avidity and cytolytic activity. However, the potent functional property of CD8+ Tm cells without IL‐12 priming for secondary expansion upon Ag reencounter is still unclear.In this study, we attempted to clarify the role of IL‐12 by transferring the CD8+ effector T cells into wild‐type C57BL/6 and IL‐12 gene KO mice, respectively. Our findings showed that IL‐12 priming is important not only in CD8+ T cell clonal expansion in the proliferation phase, but also in generation of CD8+ Tm cells with the capacity of secondary expansion upon antigen re‐encounter. However, IL‐12 signaling is neither involved in CD8+ effector T cell survival in the transition phase nor in the CD8+ Tm cell's secondary expansion in recall responses.