A human memory T-cell subset with stem cell-like properties

Immunological memory is thought to depend upon a stem cell-like, self-renewing population of lymphocytes capable of differentiating into effector cells in response to antigen re-exposure. Here we describe a long-lived human memory T-cell population that displays enhanced self-renewal and multipotent capacity to derive central memory, effector memory and effector T cells. These cells, specific for multiple viral and self-tumor antigens, were found within a CD45RO(−), CCR7(+), CD45RA(+), CD62L(+), CD27(+), CD28(+) and IL-7Rα(+) T-cell compartment characteristic of naïve T cells. However, they expressed increased levels of CD95, IL-2Rβ, CXCR3, and LFA-1, and exhibited numerous functional attributes distinctive of memory cells. Compared to known memory populations, these lymphocytes displayed increased proliferative capacity, more efficiently reconstituted immunodeficient hosts and mediated superior anti-tumor responses in a humanized mouse model. The identification of a human stem cell-like memory T-cell population is of direct relevance to the design of vaccines and T-cell therapies.