Mass cytometric analysis resolves CLL heterogeneity. (A) Schematic representation of the experimental strategy with PB samples from 20 patients with CLL collected at screening and during weekly venetoclax dose escalation. (B) Lymphocyte counts (cells per liter) during venetoclax dose escalation in each patient. (C) UMAP projection of PB cells (subsampling of 2000 cells per each sample) from patients with CLL (n = 18 VEN patients plus n = 2 VEN+IBR patients, 6 timepoints) and healthy donors colored by the following clusters: B cells (C1), CLL cells (C2-5), T cells (C6-C12), NK cells (C14), and myeloid cells (C15:C30). (D) UMAP plots colored by expression levels of the indicated markers used to identify the major immune cell populations. (E) UMAP plots of a patient with CLL (CLL27) and healthy donor with B/CLL clusters circled. IBR, ibrutinib; NKT, natural killer T; Scr, screening.