Deep sequencing and flow cytometric characterization of expanded effector memory CD8+CD57+ T cells frequently reveals T-cell receptor Vβ oligoclonality and CDR3 homology in acquired aplastic anemia

Oligoclonal expansion of CD8(+)CD28(-) lymphocytes has been considered indirect evidence for a pathogenic immune response in acquired aplastic anemia. A subset of CD8(+)CD28(-) cells with CD57 expression, termed effector memory cells, is expanded in several immune-mediated diseases and may have a role in immune surveillance. We hypothesized that effector memory CD8(+)CD28(-)CD57(+) cells may drive aberrant oligoclonal expansion in aplastic anemia. We found CD8(+)CD57(+) cells frequently expanded in the blood of aplastic anemia patients, with oligoclonal characteristics by flow cytometric V beta usage analysis: skewing in 1-5 V beta families and frequencies of immunodominant clones ranging from 1.98% to 66.5%. Oligoclonal characteristics were also observed in total CD8(+) cells from aplastic anemia patients with CD8(+)CD57(+) cell expansion by T-cell receptor deep sequencing, as well as the presence of 1-3 immunodominant clones. Oligoclonality was confirmed by T-cell receptor repertoire deep sequencing of enriched CD8(+)CD57(+) cells, which also showed decreased diversity compared to total CD4(+) and CD8(+) cell pools. From analysis of complementarity-deter-mining region 3 sequences in the CD8(+) cell pool, a total of 29 sequences were shared between patients and controls, but these sequences were highly expressed in aplastic anemia subjects and also present in their immunodominant clones. In summary, expansion of effector memory CD8(+) T cells is frequent in aplastic anemia and mirrors V beta oligoclonal expansion. Flow cytometric V beta usage analysis combined with deep sequencing technologies allows high resolution characterization of the T-cell receptor repertoire, and might represent a useful