MO1 accumulation characterized CMML and a CMML-like subgroup of MDS. MDS and CMML, including CMML-0, CMML-1, and CMML-2, are defined according to the WHO classification. “CMML-like” MDS indicates MDS with a fraction of classical CD14⁺⁺CD16⁻ monocytes (called MO1) ≥94% of total monocytes. (A-F) Comparison of the fraction of MO1 among peripheral blood monocytes (A), WBC count (B), platelet count (C), absolute monocyte count (D), monocyte fraction in WBC differential count (E), and bone marrow monocytes (F) in the 5 studied groups. *P < .05; **P < .01; ***P < .001; Student t test. (G-L) CD14 vs CD16 dot plots showing the monocyte subset repartition in peripheral blood (MO1: CD14⁺⁺CD16⁻; MO2: CD14⁺CD16⁺; MO3: CD14^lowCD16⁺). Characteristic profile observed in CMML patients (G), CMML with normal subset repartition (H), CMML patient in inflammatory condition showing the “bulbous” profile with an increased MO2 population (I), example of a CMML patient before (J), during (K), and after (L) occurrence of a chondritis (C-reactive protein [CRP] values are indicated below the dot plots). (M) CMML-free evolution of MDS patients with (“CMML-like MDS”, n = 16) or without (“other MDS”, n = 28) classical monocyte accumulation at diagnosis (MO1 ≥ 94%). Monocytosis up to 1 × 10⁹/L and monocyte percentage ≥10% were assessed by 2 consecutive CBC; P = .005, log-rank test. (N) Absolute monocyte count repartition in 192 healthy blood donors (median of age: 51; range: 19-99) with median value of 0.49 × 10⁹/L (lower 95 confidence interval [CI]: 0.49; upper 95 CI: 0.53 × 10⁹/L). (O) Linear regression of absolute monocyte count related to age in 192 controls (monocyte count = 0.002038*age + 0.4037).