CD163⁺ tumor‐associated macrophage accumulation in breast cancer patients reflects both local differentiation signals and systemic skewing of monocytes

Abstract

Objectives The accumulation of tumor‐associated macrophages (TAMs) is correlated with poor clinical outcome, but the mechanisms governing their differentiation from circulating monocytes remain unclear in humans. Methods Using multicolor flow cytometry, we evaluated TAMs phenotype in 93 breast cancer (BC) patients. Furthermore, monocytes from healthy donors were cultured in the presence of supernatants from dilacerated primary tumors to investigate their differentiation into macrophages (MΦ) in vitro. Additionally, we used transcriptomic analysis to evaluate BC patients’ blood monocytes profiles. Results We observed that high intra‐tumor CD163‐expressing TAM density is predictive of reduced survival in BC patients. In vitro, M‐CSF, TGF‐β and VEGF from primary tumor supernatants skewed the differentiation of healthy donor blood monocytes towards CD163highCD86lowIL‐10high M2‐like MΦ that strongly suppressed CD4+ T‐cell expansion via PD‐L1 and IL‐10. In addition, blood monocytes from about 40% of BC patients displayed an altered response to in vitro stimulation, being refractory to type‐1 MΦ (M1‐MΦ) differentiation and secreting higher amounts of immunosuppressive, metastatic‐related and angiogenic cytokines. Aside from showing that monocyte transcriptome is significantly altered by the presence of BC, we also demonstrated an overall metabolic de‐activation in refractory monocytes of BC patients. In contrast, monocytes from sensitive BC patients undergoing normal M1‐MΦ differentiation showed up‐regulation of IFN‐response genes and had no signs of metabolic alteration. Conclusion Altogether, our results suggest that systemic factors skew BC patient blood monocytes towards a pro‐metastatic profile, resulting in the accumulation of further polarised CD163high TAMs resembling type‐2 MΦ (M2‐MΦ) in the local BC microenvironment. These data indicate that monitoring circulating monocytes in BC patients may provide an indication of early systemic alterations induced by cancer and, thus, be instrumental in the development of improved personalised immunotherapeutic interventions.

Systemic Reprogramming of Monocytes in Cancer

“…Classical monocytes isolated from breast cancer patients also exhibit altered response to inflammatory stimuli, as indicated by their impaired secretion of TNFα and IL-1β in response to bacterial lipopolysaccharide (88,115). In addition, classical monocytes from lymphoma and breast cancer patients showed reduced responsiveness to IFNγ as indicated by the lower levels of STAT1 phosphorylation following stimulation (98,116).…”

“…Furthermore, the cancer-induced transcriptional profiles show considerable interpatient heterogeneity within a given cancer type, uncovering patient subsets with differential reprogramming (19,115). Specifically, greatly differing monocyte reprogramming (>1,000 differentially expressed genes) could be observed between pancreatic cancer patients in which immunosuppressive monocytes emerged and patients whose monocytes remained non-suppressive (19).…”

“…Specifically, greatly differing monocyte reprogramming (>1,000 differentially expressed genes) could be observed between pancreatic cancer patients in which immunosuppressive monocytes emerged and patients whose monocytes remained non-suppressive (19). Among breast cancer patients, differential responsiveness of monocytes to IFNγ+GM-CSF stimulation was associated with distinct gene expression profiles, including differential expression of genes linked to the IFN response (115).…”

“…Accordingly, classical monocytes from non-small cell lung cancer patients showed enhanced migration toward cancer cells, however, the underlying mechanisms remain to be determined (96). Intriguingly, multiple studies from breast cancer patients showed the downregulation of HIF1A expression in monocytes, suggesting that cancer may impair their response to hypoxia (88,113,115). Monocytes also exhibited cancer-induced changes in the expression of numerous metabolic genes in several tumor types (19,114,115).…”

“…Intriguingly, multiple studies from breast cancer patients showed the downregulation of HIF1A expression in monocytes, suggesting that cancer may impair their response to hypoxia (88,113,115). Monocytes also exhibited cancer-induced changes in the expression of numerous metabolic genes in several tumor types (19,114,115). Namely, immunosuppressive monocytes in pancreatic cancer showed upregulation of genes involved in fatty acid and lipoprotein metabolism (CD36, LYPLA1, CERS5) ATP metabolism (ATP5F1C, ATP5MC2, SDHB), glucose metabolism (PDK4, GXYLT1), and amino acid metabolism (ERICH1, GLS, CTSC, ARG1, NAT2, UST, OXR1) when compared to non-immunosuppressive monocytes (19).…”