T-cell clones in persons carrying CLL-like MBL. (A) PB T lymphocytes from a representative case (VB0902) are subdivided, based on CD4 and CD8 expression, in 4 subpopulations: CD8⁺ (gate A), CD4^lowCD8^high (gate B), CD4^highCD8^low (gate C), and CD4⁺ (gate D). (B) CD8⁺ T lymphocytes (gated through A) of subject VB0902 show a restricted expression of TRBV2 (35.7%, upper right quadrant). (C) T-cell subpopulations in case VB1002. (D) CD4^highCD8^low T lymphocytes in this second subject (gated through C) show restricted expression for distinct TRBV chain (TRBV9, 24.8%, upper left; and TRBV16, 38.9%, lower right), indicating the presence of 2 distinct clones. In the TCR-Vβ repertoire kit each tube includes a FITC-conjugated mAb, a PE-conjugated mAb, and a third mAb derived from a balanced mixture of a PE- and a FITC-conjugated form. Because of the mutually exclusive expression of each TRBV gene, the “virtual” double-positive population on the upper left quadrant represents a third different TRBV domain.