The road to memory: an early rest for the long journey.

Central memory T lymphocytes were reported to develop after acute but not chronic infection, which prompted this feasibility study on generating long-term CD8 T cells ex vivo, by applying a culture condition that simulates an acute infection. During 35 d of culture, naive T cells (CD45RA(+), CD127(+), CCR7(+), CD62L(+), CXCR3(+)) first developed into effector T cells (CD45RA(+/-), CD127(+/-), CCR7(+/-), CD62L(+), CXCR3(+)), followed by three intermediate stages: intermediate T cells 1 (CD45RO(+), CD127(+/-), CCR7(+), CD62L(+), CXCR3(+)), intermediate T cells 2 (CD45RO(+), CD127(-), CCR7(-), CD62L(+), CXCR3(+)), and intermediate T cells 3 (CD45RO(+/-), CD127(+), CCR7(+), CD62L(-), CXCR3(+)) before reverting to stable CD45RA(+) central memory T cells (CD45RA(+), CD127(+), CCR7(+), CD62L(+), CXCR3(+)). If both anti-CD3 and the inflammatory milieu persisted beyond day 10, intermediate T cells 2 gradually developed into effector memory T cells (CD45RO(+), CD127(-), CCR7(-), CD62L(-), CXCR3(+)). Furthermore, intermediate T cells 2 or effector memory T cells, when cultured in persistent inflammatory cytokines devoid of anti-CD3, were converted to central memory T cells (CD45RO(+), CCR7(+), CD62L(+)). Overall, these results support ex vivo memory-like T lymphocyte production and favor a developmental pathway including both divergent and linear relationships.