Overexpression of interleukin (IL)-7 leads to IL-15-independent generation of memory phenotype CD8+ T cells

Transgenic (TG) mice expressing a high copy number of interleukin (IL)-7 cDNA under the control of the major histocomaptability complex (MHC) class 11 promoter display a 10-20-fold increase in total T cell numbers, Here, we show, that the increase in T cell numbers in IL-7 TG mice is most apparent at the level of memory phenotype CD44(bi) CD 122(bi) CD8(+) cells. Based on studies with T cell receptor (TCR) TG mice crossed to IL-7 TG mice, increased levels of IL-7 may provide costimulation for TCR recognition of self-MHC ligands and thus Cause naive CD8(+) cells to proliferate and differentiate into memory phenotype cells. In addition, a marked increase in CD44(bi) CD122(bi) CD8(+) cells was found in IL-7 TG IL-15(-) mice. Since these cell are rare in normal IL-15(-) mice, the dependency of memory phenotype CD8(+), cells on IL-15 can be overcome by overexpression of IL-7.