Expression of S100A8 and S100A9 in AML. (A) S100A8 and S100A9 RNA expression in patients with AML in the Leucegene cohort. Each dot represents 1 patient: orange, myelomonocytic and monocytic AML; blue, undifferentiated M0 and M1 AML. (B) S100A8/A9 concentration in plasma of patients with AML (n = 6) and healthy controls (n = 10) measured by ELISA. (C) S100A8/A9 plasma concentrations in control and MLL-ENL or H9M1 AML mice (control, n = 5; AML, n = 3). (D) Concentrations of heterodimeric S100A8/A9 and homodimeric S100A8 and S100A9 in plasma of control or H9M1 AML mice at death (n = 3). (E) Correlation of plasma S100A8/A9 concentration with percentage of leukemic cells in peripheral blood (PB) of H9M1 secondary recipients during leukemia progression. (F) Schematic representation of the in vivo experiments. (G) S100A8/A9 concentrations in plasma at death of WT, S100A8KO, and S100A9KO recipient mice receiving WT AML cell transplants (n = 6). (H) Kaplan-Meier survival curves of mice (WT, S100A8KO, or S100A9KO) receiving 2 × 10⁶ BM cell transplants from WT C57BL/6-expressing H9M1. (I) Intracellular flow cytometry analyses of S100A8 and S100A9 expression in BM, PB, and spleen of H9M1 AML mice (left). Ly6G and c-kit marker expression in AML S100A⁺ and S100A⁻ subpopulations (right). Data are represented as the mean ± standard error of the mean. Two-tailed Student t tests were used to assess statistical significance from 2 independent experiments. *P < .05; **P < .01; ****P < .0001. ns, not significant; RPKM, reads per kilobase of transcript per million.