Induction of cytotoxic CD8(+)CD56(+) T cells from human thymocytes by interleukin-15

CD8(+)CD56(+) cells isolated from human peripheral blood lymphocytes have b een shown recently to represent a population of cytotoxic active T cells. H owever, it is not known if these cells are intrathymically or extrathymical ly developed or how these cells are influenced by growth factors. In the pr esent study, we investigated the effects of interleukin-2 (IL-2) and IL-15 on human thymocytes with respect to development of CD8(+)CD56(+) T cells. F reshly isolated thymocytes contain few CD8(+)CD56(+) cells, but the number of these cells increases significantly when thymocytes are grown in the pre sences of IL-15 or IL-2. However, IL-15 induced a significantly higher frac tion of CD8(+)CD56(+) cells compared with IL-2. Thus, although IL-2 and IL- 15 are known to have a number of redundant functions, we here demonstrate t hat IL-15 is superior to IL-2 in inducing CD8(+)CD56(+) T cells from cultur es of thymocytes. The majority of the IL-15-grown CD8(+)CD56(+) cells were CD45R0(+), representing a memory phenotype, and showed high expression of t he IL-15R-complex and high numbers of CD69(+) cells. Moreover, cytotoxic ac tivity was confined to this cell population.