Macrophage as an important surveillance system is escaped by human cancer cells expressing CD47. To reinstate macrophage functionality in clearing tumor cells targeting CD47 and thereby blocking phagocytosis inhibitory CD47-SIRPalpha interaction has been an important strategy in immune-oncology therapy. We profiled a large panel of tumor cell lines, Crown's proprietary PDX models and clinical lung cancer tumors for CD47 expression. Although it has been reported as a ubiquitously expressed immune-escape marker in cancer cells, the expression levels of CD47 vary among different tumor cell lines and models when the cells were examined by flow cytometry. It is of interest that a portion of tumor cells in fact do not present CD47. To tackle the cause for the loss of CD47 expression, whole-exome sequencing was performed to examine the intactness of the gene in the CD47 loss models. The results will be presented. We next established a robust and reproducible in vitro assay platform to support anti-CD47 drug research. We applied a macrophage differentiation system using isolated CD14+ monocytes as starting material, and were able to achieve >80% of M1 and M2 populations, respectively, through the 6-day differentiation. Differentiated macrophage was co-cultured with target tumor cells labeled for flow cytometry analysis. In the presence of blocking anti-CD47 antibody BRICK126, steady and specific phagocytosis effect was observed when target tumor cells express high level of CD47 markers. BRIC126 antibody blocks the CD47-SIRPalpha interaction. In contrast, aCD274 antibody did not yield more than background phagocytosis effect in the same assay. To prove the CD47-specific effect, we constructed isogenic cell models from a couple of parental cell models in that CD47 gene is knocked out in one sub-cell line and overexpressed in another sub-cell line. The isogenic systems were then subject to the CD47 biology assay and more profound changes in phagocytosis responses were observed. Furthermore, the in vitro findings were validated in in vivo setting.
Citation Format: Huajun Yang, Zhongliang Li, Phillip Wang, Beibei Tang, Qinyun Ma, Frank Xing, Qian Shi. Phagocytosis response of macrophage to CD47 expression of tumor cells in anti-CD47 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4556.