Reprogramming the immune environment in breast cancer via dendritic cells.
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Breast cancer is the most common cancer among American women. The current therapies are not curative for some forms of breast cancer, especially breast cancers that do not express the growth factor and hormone receptors and metastatic cancers. Recently, immunotherapy become an anticipated option for breast cancer. Before approaching immunotherapy, it is important to firstly understand how is the immune microenvironment regulated in breast cancer to determine how it could be modulated for therapy. The human breast cancer microenvironment displays features of T helper 2 (Th2) immunity which promotes tumor development. Here we show that human breast cancer cells produce thymic stromal lymphopoietin (TSLP). Breast tumor supernatants, in a manner dependent on TSLP, induce expression of OX40L on dendritic cells (DCs). OX40L⁺ DCs are found in primary breast tumor infiltrates. OX40L⁺ DCs drive development of inflammatory Th2 cells producing interleukin 13 and tumor necrosis factor in vitro. Antibodies neutralizing TSLP or OX40L inhibit breast tumor growth and interleukin 13 production in a humanized mouse model of breast cancer. Thus, breast cancer cell-derived TSLP, by inducing OX40L expression on DCs, contributes to the Th2 immunity conducive to breast tumor development. In order to reprogram the inflammatory pro-tumor Th2 (iTh2) into anti-tumor Th1 microenvironment, we tested the impact of targeting the innate receptors on DCs to render the resistant to tumor environment. We show that intratumoral delivery of β-glucan, a natural ligand for dectin-1 expressed on DCs, blocks the generation of iTh2 cells leading to decreased IL-13 in the tumor microenvironment and prevents breast cancer development in vivo. β-glucan inhibits OX40L expression on tumor-associated DCs which is due to a block in STAT6 phosphorylation. β-glucan-treated DCs, when exposed to breast cancer supernatant, secrete higher levels of IL-12p70 and do not expand iTh2 cells thereby enabling the T helper 1 cells secreting IFN-γ. β-glucan exposed DCs expand CD8⁺ T cells that express CD103, a ligand for E-cadherin. These CD8+ T cells, which produce higher IFN-γ, Granzyme A and Granzyme B, accumulate in the tumors leading to enhanced tumor necrosis in vivo. DC reprogramming by β-glucan is dependent upon dectin-1 engagement. The ligand of TLR7/8 (CL075) and TLR3 (polyI:C) show the same effect in Th2 response inhibition but no effect on the functions of CD8 T cells. Taken together, our data demonstrate that exploiting pattern recognition receptors on tumor-infiltrating DCs enables cancer rejection.