Identification of cellular and signaling signatures of the Lckhi subpopulations. (A) BCR-signaling profiles differ between Lckhi and Lck−/low subpopulations. Cells from group C CLL patients were left unstimulated or triggered with anti-human IgM/IgG. Graphs show pCD79a, pERK, and pAKT levels at steady state (−) and after BCR triggering (+) among Lck−/low, Lckhi, and corresponding T cells, as indicated. The Wilcoxon matched-pair test (dotted line) was used for comparisons between unstimulated samples and the Student t test (solid line) for comparison of responses to BCR crosslinking (n = 8; mean ± SEM; *P < .05; **P < .005; ***P < .0005). Lck−/low cells from group A and B CLL patients respond to BCR crosslinking in a similar fashion as the Lck−/low subpopulation from group C, as shown in supplemental Figure 1C. CD79a total protein expression in different subsets is also shown in supplemental Figure 1C. (B) Lckhi subsets display a hyperactivated phenotype. PBMCs from group C CLL patients were stained with CD3, CD19, pERK and each of Lck, CD38, CD69, and Ki-67. Graphs display the expression levels of CD38, CD69, and Ki-67 in the Lckhi, Lck−/low subsets and T cells as indicated. The right graph shows the percentage of Ki-67+ cells within the Lckhi and Lck−/low subpopulations (n = 11; Student t test; mean ± SEM; **P < .01; ***P < .001). Supplemental Figure 1D-E shows a detailed analysis of a representative experiment. (C) Evaluation of the presence of Lckhi subsets within proliferative (CXCR4dim/CD5bright) and resting (CXCR4bright/CD5dim) CLL fractions. Cells from group C patients were stained for CD19, CD5, CXCR4, and Lck. The CD19+CD5+ populations were analyzed in 2D FACS plots of CXCR4 vs CD5 (a) and of Lck vs CD19 (b). Top rows, The CXCR4dim/CD5bright and CXCR4bright/CD5dim fractions were defined in (a) as 5% of the cells lying on the 2 extremes of the plots, as previously described.24 Each fraction shown as a 2D FACS plot of Lck vs CD19 was used to calculate the relative proportions of Lck−/low and Lckhi subpopulations within the CXCR4bright/CD5dim (a1) and CXCR4dim/CD5bright (a2) compartments, respectively. The graph on the right shows collective data. Bottom row, The Lckhi subset from (b) is represented in a 2D FACS plot of CXCR4 vs CD5 (b1). The gates demarcating the CXCR4bright/CD5dim and CXCR4dim/CD5bright fractions from (a) were applied to (b1) to reveal the distribution of Lckhi cells within the respective fractions and the dominant intermediate population. The graph on the right shows collective data (n = 8; Wilcoxon matched-pair test; *P < .05; **P < .005).