Abstract A137: PD-L1 antibodies induce macrophage phenotypic and functional activation

Background: The ability of PD-L1 signaling to alter tumor metabolism and stem cell properties has been previously established. However, the effects of PD-L1 signaling on other cells that express PD-L1, including tumor-associated macrophages, has not been previously investigated. It is also unknown how treatment with PD-L1 targeted antibodies may affect macrophage function. Purpose: These studies were designed to investigate the effects of PD-L1 antibodies on macrophage phenotype and function. Studies were done using in vitro assays of murine bone marrow-derived macrophages, as well as human monocyte-derived macrophages. Experimental Methods: Murine bone marrow-derived macrophages were generated by non-adherent culture in M-CSF. The cells were then plated in tissue culture plates and incubated with anti-murine PD-L1 antibodies (or with isotype-matched antibodies), and the effects on macrophage phenotype, proliferation, activation, antigen presentation, and tumor killing were assessed. Study Results: Following incubation with PD-l1 antibodies, we observed remarkable phenotypic changes in bone marrow-derived macrophages. These included physical changes including increased cell size and spreading, and increased proliferation and survival as measured by EdU incorporation and MTT assay. Macrophages incubated with PD-L1 antibodies spontaneously upregulated production of inflammatory cytokines and upregulated co-stimulatory molecule expression, as assessed by flow cytometry. Increased functional activation was revealed by upregulated expression of iNOS and decreased antigen uptake. Conclusions: Our findings indicate that PD-L1 antibodies induce strong activation of macrophages in vitro. These findings suggest that some of the observed immunological activities of PD-L1 therapeutic antibodies may be mediated by macrophage activation. Citation Format: Genevieve Hartley, William Wheat, Jonathan Coy, Steven Dow. PD-L1 antibodies induce macrophage phenotypic and functional activation [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A137.