IL-7 and IL-15 instruct the generation of human memory stem T cells from naive precursors

Long-living memory stem T cells (T-SCM) with the ability to self-renew and the plasticity to differentiate into potent effectors could be valuable weapons in adoptive T-cell therapy against cancer. Nonetheless, procedures to specifically target this T-cell population remain elusive. Here, we show that it is possible to differentiate in vitro, expand, and gene modify in clinically compliant conditions CD8(+) T-SCM lymphocytes starting from naive precursors. Requirements for the generation of this T-cell subset, described as CD62L(+)CCR7(+)CD45RA(+)CD45R0(+)IL-7R alpha(+)CD95(+), are CD3/CD28 engagement and culture with IL-7 and IL-15. Accordingly, T-SCM accumulates early after hematopoietic stem cell transplantation. The gene expression signature and functional phenotype define this population as a distinct memory T-lymphocyte subset, intermediate between naive and central memory cells. When transplanted in immunodeficient mice, gene-modified naive-derived T-SCM prove superior to other memory lymphocytes for the ability to expand and differentiate into effectors able to mediate a potent xenogeneic GVHD. Furthermore, gene-modified T-SCM are the only T-cell subset able to expand and mediate GVHD on serial transplantation, suggesting self-renewal capacity in a clinically relevant setting. These findings provide novel insights into the origin and requirements for T-SCM generation and pave the way for their clinical rapid exploitation in adoptive cell therapy. (Blood. 2013; 121(4): 573-584)