IL-15 mimics T cell receptor crosslinking in the induction of cellular proliferation, gene expression, and cytotoxicity in CD8⁺memory T cells

<jats:p>Generation of CD8<jats:sup>+</jats:sup>memory T cells requires antigenic stimulation through T cell receptor (TCR); however, maintenance of CD8<jats:sup>+</jats:sup>memory T cells seems to be mediated by cytokines, such as IL-15, in a TCR-independent manner. Compared with the TCR-induced activation, less is known about the mechanisms of IL-15 action. We report here a comparative and kinetic analysis of the responses of memory phenotype CD8<jats:sup>+</jats:sup>T cells to IL-15 or TCR (anti-CD3) stimulation<jats:italic>in vitro</jats:italic>. These two stimuli induce highly similar responses in memory phenotype CD8<jats:sup>+</jats:sup>T cells as measured by cellular proliferation, gene expression changes, synthesis of effector molecules (IFNγ, tumor necrosis factor β, granzyme B, and perforin), and induction of cytotoxicity. From 189 genes/expressed sequence tags (ESTs) whose expression changed in CD8<jats:sup>+</jats:sup>memory T cells after IL-15 and anti-CD3 stimulation identified by cDNA microarray analysis, 77% of the genes/ESTs exhibit a highly similar pattern of expression between IL-15 and anti-CD3-treated cells, and only 16% and 7% of the genes/ESTs are differentially expressed in response to IL-15 and anti-CD3 treatments, respectively. These results show that IL-15 and anti-CD3 stimulation induced remarkably similar gene expression and effector function. Thus, IL-15 acts not only as a crucial growth factor but also as an antigen-independent activator of effector functions for CD8<jats:sup>+</jats:sup>memory T cells.</jats:p>