Journal
CANCER RESEARCH
Volume 77, Issue 15, Pages 4158-4170Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/0008-5472.CAN-16-2212
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Funding
- NIH [R01 CA196657, U01 CA141468, U54 CA209971, T32 AI007290, F32 CA189408]
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Pancreatic ductal adenocarcinoma (PDAC) after complete surgical resection is often followed by distant metastatic relapse for reasons that remain unclear. In this study, we investigated how the immune response at secondary sites affects tumor spread in murine models of metastatic PDAC. Early metastases were associated with dense networks of CD11(-)CD11c(+)MHC-II(+)CD24(+)CD64(low)F4/80(low) dendritic cells (DC), which developed from monocytes in response to tumor-released GM-CSF. These cells uniquely expressed MGL2 and PD-L2 in the metastatic microenvironment and preferentially induced the expansion of T regulatory cells (Treg) in vitro and in vivo. Targeted depletion of this DC population in Mgl2(DTR) hosts activated cytotoxic lymphocytes, reduced Tregs, and inhibited metastasis development. Moreover, blocking PD-L2 selectively activated CD8 T cells at secondary sites and suppressed metastasis, suggesting that the DCs use this particular pathway to inhibit CD8 T-cell-mediated tumor immunity. Phenotypically similar DCs accumulated at primary and secondary sites in other models and in human PDAC. These studies suggest that a discrete DC subset both expands Tregs and suppresses CD8 T cells to establish an immunosuppressive microenvironment conducive to metastasis formation. Therapeutic strategies to block the accumulation and immunosuppressive activity of such cells may help prevent PDAC progression and metastatic relapse after surgical resection. (C)2017 AACR.
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