CD28 and B-cell chronic lymphocytic leukemia: To gain insight into the functional characteristics of the three clinically significant T-cell subpopulations identified in this study, PBMCs from a randomly selected subset of 30 CLL patients in the discovery cohort were stimulated using anti-CD3/CD28 microbeads and analysed for the expression of seven different cytokines using a modified CyTOF antibody panel (Supplementary Table S2).