Abstract A56: Characterization of the tumor microenvironment of a humanized mouse model of ovarian cancer after treatment with anti-B7-H4 recombinant antibodies

Abstract

Abstract Ovarian cancer is the deadliest gynecological malignancy. Disease recurrence occurs in 70% of patients diagnosed with stage III or IV epithelial ovarian cancer, in part due to immune evasion and suppression in the tumor microenvironment. Tumor infiltration with tumor-associated macrophages (TAMs) has been associated with poor patient survival and TAMs express B7-H4, an orphan ligand that modulates T cell responses. Common features observed in tumor microenvironments include hypoxic stress and other environmental cues that prompt the expression of immunomodulators such as CTLA4 and PD1, leading to increased tumor cell ability to escape immune recognition. We showed that B7-H4 is also expressed on ovarian cancer cells in vivo, suggesting that tumor cells may also hamper cell-mediated anti-tumor immune responses via inhibition of T cell co-receptors. We thus sought to determine whether targeting functional cell subsets expressing B7-H4 could restore an anti-tumor immune response and/or promote tumor cell death. We isolated novel recombinant anti-B7-H4 antibodies by differential cell screening of a yeast-display single-chain fragments variable (scFv) library that was derived from B cells of ovarian cancer patients. We demonstrated that B7-H4 scFv-mediated inhibition could rescue activation of tumor antigen-TCR-specific T cells in vitro, and we also showed that anti-B7-H4 scFv administration could delay tumor growth in a novel humanized NSG mouse model of ovarian cancer (Dangaj, D. et al., Novel recombinant human B7-H4 antibodies overcome tumoral immune escape to potentiate T cell anti-tumor responses, Cancer Research, 2013). We hypothesize that use of anti-B7-H4 scFv in vivo targeted functionally diverse tumor mass components (TAMs and tumor cells) leading to the reprogramming of the tumor microenvironment towards tumor rejection. Here we present a preliminary ex vivo analysis of the human tumors infiltrated with human leukocytes harvested from the B7-H4-treated humanized NSG mice. Tumors from mice treated with two anti-B7-H4 scFv or with a control scFv were sectioned and labeled by immunofluorescence to characterize tumor cells and immune cells. Tumor cells were co-stained with EpCAM and Ki-67, and leukocytes with CD45 and Ki-67. Preliminary studies suggested that in vivo delivery of anti-B7-H4 scFv decreased tumor cell proliferation as evidenced by a reduction of cells co-stained by EpCAM and Ki-67 compared with the staining of tumor cells from mice treated with the control antibody. Concurrently, tumors from mice receiving anti-B7-H4 scFv presented an increase in cells that stained positive for both CD45 and Ki-67 compared with tumors from mice receiving a control scFv. These results suggest that anti-B7-H4 scFv enhances leukocyte proliferation. Additional work will be performed to statistically analyze these results over all experimental groups, to functionally phenotype the tumor-infiltrating leukocytes, and to assess the impact of B7-H4 scFv administration on tumor hypoxia, apoptosis and angiogenesis. We tentatively conclude that B7-H4 is another immune checkpoint and its inhibition by antibody targeting may open novel immunotherapeutic avenues for ovarian cancer. Citation Format: Bhairavi (Vivi) Tolani, Denarda Dangaj, Daniel J. Powell, Jr., Nathalie Scholler. Characterization of the tumor microenvironment of a humanized mouse model of ovarian cancer after treatment with anti-B7-H4 recombinant antibodies. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr A56. doi:10.1158/1538-7445.CHTME14-A56