Activating a collaborative innate-adaptive immune response to control breast and ovarian cancer metastasis
Many cancers recruit monocytes/macrophages and polarize them into tumor-associated macrophages (TAMs). TAMs promote tumor growth and metastasis and inhibit cytotoxic T cells. Yet, macrophages can also kill cancer cells after polarization by e.g., lipopolysaccharide (LPS, a bacteria-derived toll-like receptor 4 [TLR4] agonist) and interferon gamma (IFN{gamma}). They do so via nitric oxide (NO), generated by inducible NO synthase (iNOS). Altering the polarization of macrophages could therefore be a strategy for controlling cancer. Here, we show that monophosphoryl lipid A (MPLA, a derivative of LPS) with IFN{gamma} activated macrophages isolated from metastatic pleural effusions of breast cancer patients to kill the corresponding patients cancer cells in vitro. Importantly, intratumoral injection of MPLA with IFN{gamma} not only controlled local tumor growth but also reduced metastasis in mouse models of luminal and triple negative breast cancers. Furthermore, intraperitoneal administration of MPLA with IFN{gamma} reprogrammed peritoneal macrophages, suppressed metastasis, and enhanced the response to chemotherapy in the ID8-p53-/- ovarian carcinoma mouse model. The combined MPLA+IFN{gamma} treatment reprogrammed the immunosuppressive microenvironment to be immunostimulatory by recruiting leukocytes, stimulating type I interferon signaling, decreasing tumor-associated (CD206+) macrophages, increasing tumoricidal (iNOS+) macrophages, and activating cytotoxic T cells through macrophage-secreted interleukin 12 (IL-12) and tumor necrosis factor (TNF). Both macrophages and T cells were critical for the anti-metastatic effects of MPLA+IFN{gamma}. MPLA and IFN{gamma} are already used individually in clinical practice, so our strategy to engage the anti-tumor immune response, which requires no knowledge of unique tumor antigens, may be ready for near-future clinical testing.