Identification of a macrophage activation threshold associated with malignant transformation and the sensing of candidate "danger signals"

Abstract Cancer immunosurveillance is based on the recognition of changes brought by malignant transformation of normal cells, leading to their elimination, immunoediting, or escape. The ability of immune cells to sense changes associated with malignant transformation as early as possible is likely to be important for the successful outcome of cancer immunosurveillance. In this process, the immune system faces a trade-off between elimination of cells harboring premalignant or malignant changes, and autoimmune pathologies. We hypothesized that the immune system has therefore evolved a threshold for distinguishing normal from abnormal cells, perhaps similar to a pathogen recognition threshold at which macrophages distinguish non-dangerous from dangerous microbes. We co-cultured human macrophages with a unique set of genetically related human cell lines that recapitulate breast cancer development: MCF10A (immortalized); MCFneoT (hyperplasia); MCFT1 (atypical hyperplasia); MCFCA1 (invasive cancer). Using cytokines-based assays, we found that the threshold for macrophage activation was between MCFNeoT and MCFT1, with macrophages co-cultured with the atypical hyperplasia and invasive cancer cell lines showing an inflammatory cytokine response. This response was accompanied by an increase in macrophage migration, phagocytosis and capacity to infiltrate MCFT1 spheroids. We are currently validating candidates for “danger signals” that will be shared by MCFT1 and MCFCA1 but absent or expressed at low level in the early state of premalignancy. Using proteomic and transcriptomic approaches, we identified 13 surface or secreted molecules corresponding to this definition, some of which are well-known tumor-associated antigens.