C1.7 antigen expression on CD8(+) T cells is activation dependent: Increased proportion of C1.7(+)CD8(+) T cells in HIV-1-infected patients with progressing disease

The C1.7 Ag is a surface marker previously shown to be expressed on all NK cells and on a subset of CD8(+) T cells. We report in this study that C1.7 Ag expression on peripheral blood-derived CD8(+) T cells overlaps with acti vation markers S6F1(high) and CD29(high) and is reciprocally expressed with CD62L, C1.7 Ag expression can be induced in vitro on CD8(+) T cells by ant i-CD3 cross-linking, suggesting that C1.7 Ag is activation dependent. In co ntrast to NK cells, C1.7 Ag does not signal on CD8(+) T cells, nor does it induce redirected lysis upon ligation. The proportion of C1.7 Ag(+)CD8(+) T cells is increased in HIV-infected patients compared with healthy donors. In 69 HIV-infected patients, we observed a significant inverse correlation between the percentage of C1.7 Ag-expressing CD8(+) T cells and the absolut e CD4(+) T cell count. Two-year clinical follow-up of patients with initial CD4(+) T cell count of >400 cells/mm(3) and a normal proportion of C1.7 Ag (+)CD8(+) T cells revealed that these patients were clinically stable with minimal HIV-associated symptoms. In contrast, 10 of 12 patients with CD4+ T cell counts of >400 cells/mm(3) and an elevated proportion of C1.7 Ag(+)CD 8(+) T cells were symptomatic. ANOVA analysis of patients indicates that C1 .7 Ag is a better predictor of disease progression than CD4(+) count. Overa ll, our findings indicate that C1.7 Ag is the first described marker for ac tivated/memory CD8(+) T cells and a useful parameter for evaluating the lev el of CD8(+) T cell activation in vivo.