(A) HO-1 staining (in red) combined with DAPI costaining showing nuclei (in blue) visualized in tumor slices by immunofluorescence in F4/80⁺ myeloid cells (in green) in an EG7-OVA tumor 21 days after tumor inoculation in a WT mouse. Scale bar: 5 μm. (B) Flow cytometry plots pregated on live CD11b⁺ cells indicate 12 days after tumor inoculation the proportion of HO-1–producing cells among different tumor-infiltrating myeloid cell subtypes: the CD11b^hiLy6G⁺ neutrophils (PMN), the CD11b^hiLy6G^–Ly6C^hiMHCII^– monocytes (I), the CD11b^hiLy6G^–Ly6C^hiMHCII⁺ cells (II), and the CD11b^hiLy6G^–Ly6C^loMHCII⁺ TAMs (III). Horizontal bars indicate median ± interquartile range (n = 6). (C) Representative histograms indicating by MFI the level of expression of the specified markers in HO-1⁺ (blue) versus HO-1^– (red) TAMs. (D) Representative flow cytometry plots of the accumulation of immature myeloid cells compatible with myeloid-derived suppressor cell phenotype (CD11b^hiLy6C⁺Ly6G^– and CD11b^hiLy6C^intLy6G⁺ summarized as CD11b⁺Gr1⁺ cells) in the bone marrow (BM) and spleen from tumor-bearing WT mice. Data representative of 3 independent experiments. Each point represents an individual mouse. Horizontal bars indicate median ± interquartile range (E) HO-1 expression measured by flow cytometry among CD11b⁺Gr1⁺ cells from bone marrow, spleen, and EG7-OVA tumor from tumor-bearing WT mice, compared with tumor-free WT mice (naive). Horizontal bars indicate median ± interquartile; n = 3 (naive), and n = 6 (tumor-bearing group). Statistical analysis was performed with Mann-Whitney U test. ***P < 0.001; ****P < 0.0001.