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Targeting A Scavenger Receptor On Tumor-associated Macrophages Activates Tumor Cell Killing By Natural Killer Cells

Silke Eisinger, Dhifaf Sarhan, Vanessa F. Boura, Itziar Ibarlucea-Benitez, Sofia Tyystjärvi, Ganna Oliynyk, Marie Arsenian-Henriksson, David Lane, Stina L. Wikström, Rolf Kiessling, Tommaso Virgilio, Santiago F. Gonzalez, Dagmara Kaczynska, Shigeaki Kanatani, Evangelia Daskalaki, Craig E. Wheelock, Saikiran Sedimbi, Benedict J. Chambers, Jeffrey V. Ravetch, Mikael C. I. Karlsson

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Tumor-associated macrophages (TAMs) can have protumor properties, including suppressing immune responses, promoting vascularization and, consequently, augmenting tumor progression. To stop TAM-mediated immunosuppression, we use a novel treatment by injecting antibodies specific for scavenger receptor MARCO, which is expressed on a specific subpopulation of TAMs in the tumor. We now report the location of this TAM as well as the pleiotropic mechanism of action of anti-MARCO antibody treatment on tumor progression and further show that this is potentially relevant to humans. Using specific targeting, we observed decreased tumor vascularization, a switch in the metabolic program of MARCO-expressing macrophages, and activation of natural killer (NK) cell killing through TNF-related apoptosis-inducing ligand (TRAIL). This latter activity reverses the effect of melanoma cell-conditioned macrophages in blocking NK activation and synergizes with T cell-directed immunotherapy, such as antibodies to PD-1 or PD-L1, to enhance tumor killing. Our study thus reveals an approach to targeting the immunosuppressive tumor microenvironment with monoclonal antibodies to enhance NK cell activation and NK cell-mediated killing. This can complement existing T cell-directed immunotherapy, providing a promising approach to combinatorial immunotherapy for cancer.