Suicide induced by cytolytic activity controls the differentiation of memory CD8+ T lymphocytes

Cytotoxic T lymphocytes (CTL) confer protection against intracellular pathogens, yet the mechanism by which some escape activation induced cell death (AICD) and give rise to long-lived memory cells is unclear. We studied the differentiation of transgenic TCR CD8(+) cells into CTL and memory cells using a novel system that allowed us to control cytolytic activity. The perforin/granzyme granules used to lyse targets induced the apoptosis of CTL in a fratricide-independent manner. After adoptive transfer to antigen-free mice, the ability of CTL to give generate memory cells was determined. We found that the extent of cytolysis by a common pool of CTL controlled the differentiation into memory cells, which were only generated under conditions of minimal cytolytic activity. Thus, the differentiation of naive CD8(+) cells into memory cells may not depend on the presence on a subset of committed CTL precursors, but rather is controlled by the extent of granule-mediated cytolysis.