261 A functional genetic screen uncovers regulators of intratumoral macrophage function and reveals CD24 as a novel target for cancer immunotherapy by macrophages

Background Cancer cells are capable of evading clearance by macrophages through the overexpression anti-phagocytic, innate immune checkpoint molecules called ‘don’t eat me’ signals, including CD47, 1 PD-L1, 2 and MHC class I. 3 Monoclonal antibodies that antagonize interaction signals with their macrophage-expressed receptors have demonstrated therapeutic potential in several cancers. However, variability magnitude durability responses to these agents has suggested presence additional, as yet unknown checkpoints. Here, we present a functional screening platform which identifies tumor-specific regulators intratumoral macrophage function. We show CD24 is dominant many solid tumors, ovarian cancer breast cancer. 4 Methods By applying our method, uncovered novel molecule, CD24. To characterize role checkpoint, leveraged MCF-7 human xenograft tumor model ID8 syngeneic model. evaluated anti-tumor effect antagonism genetic ablation experiments addition monoclonal antibody (mAb) blockade. also utilized primary specimens assess blockade either alone or combination additional tumor-targeting antibodies. Results demonstrate promotes evasion its inhibitory receptor Siglec-10. Genetic Siglec-10, well CD24–Siglec-10 using antibodies, robustly augmented phagocytosis all CD24-expressing tumors tested. Therapeutic resulted macrophage-dependent reduction growth vivo an increase survival time. The efficacy anti-CD24 mAbs was enhanced when combined second antibody. In particular, dual treatment HER2-positive cancers mAb trastuzumab, relative alone, even among inherent trastuzumab resistance (figure 1). Abstract 261 Figure Macrophage checkpoints targets. (A) There four defined signaling axes exist between cells, rely on ITIM ITSM cytoplasmic side macrophage. (B) Phagocytosis BT-474 (n = 8 donors) mAb, anti-HER2 treatment, compared IgG control. Conclusions These data reveal highly expressed, anti-phagocytic signal cancers, for immunotherapy, existing anticancer treatments. Collectively, this work suggests new paradigm redundant employed tissue-specific manner, makes clear need measure collective expression order optimize patient both adaptive immunotherapies. References Majeti R, et al . CD47 adverse prognostic factor target acute myeloid leukemia stem cells. Cell 2009; 138 : 286–299. Gordon SR, PD-1 tumour-associated inhibits tumour immunity. Nature 2017; 545 :495–499. Barkal AA, Engagement I LILRB1 suppresses immunotherapy. Nat Immunol 2018; 19 :76–84. Brewer RE, Markovic M, Kowarsky MA, SA, Zaro BW, Krishnan V, Hatakeyama J, Dorigo O, LJ, Weissman IL. siglec-10 2019; 572 :392–396. Ethics Approval Human Immune Monitoring Center Biobank Stanford Tissue Bank received IRB approval from University Administrative Panels Subjects Research complied ethical guidelines subjects research obtain samples patients cancer, informed consent patients.