Cutting edge:: Cytolytic effector function in human circulating CD8+ T cells closely correlates with CD56 surface expression

Recent data suggest that human effector CD8(+) T cells express a distinct CD27(-)CD45RA(high) (CD57(+)CD28(-)CD11a(high)) phenotype, Here, we propose that CTL effector function correlates better with CD56 (neuronal cell adhesion molecule (NCAM)) surface expression. CD56 was absent on cord blood CD8(+) T cells, but was expressed by 4-30% of freshly isolated circulating CD8(+) T cells from 15 adults. Dramatic oligoclonal expansions in 3/3 individuals were confined to the CD56(+) subset of CD8(+) T cells. The CD56(+) subset generally contained high amounts of intracellular perforin and granzyme B. Finally, direct cytolytic capacity was closely restricted to the CD56(+)(CD45RA(high)) cells, better than to CD27(-)CD45RA(high) cells in 5/5 individuals analyzed. Thus, the phenotype corresponding to the circulating effector CD8(+) T cell pool may be simplified and more precisely defined by the use of just two surface markers: CD8 and CD56.