Métayer Lucy E, Vilalta Anna, Burke G A Amos, Brown Guy C
Department of Biochemistry, University of Cambridge, Cambridge, UK.
Department of Pediatrics, University of Cambridge, Cambridge, UK.
Oncotarget. 2017 Jun 15;8(37):60892-60903. doi: 10.18632/oncotarget.18492. eCollection 2017 Sep 22.
When expressed on the surface of cells, CD47 inhibits phagocytosis of these cells by phagocytes. Most human cancers overexpress CD47, and antibodies to CD47 have shown a remarkable ability to clear a range of cancers in animal models. However, the mechanism by which these antibodies cause cancer cell death is unclear. We find that CD47 is expressed on the surface of three B-cell lines from human malignancies: 697 (pre-B-ALL lymphoblasts), Ramos and DG-75 (both mature B-cells, Burkitt's lymphoma), and anti-CD47 antibodies greatly increase the phagocytosis of all three cell line by macrophages. In the presence of macrophages, the antibodies cause clearance of the lymphoblasts within hours, but in the absence of macrophages, the antibodies have no effect on lymphoblast viability. Macrophages engulf viable lymphoblasts containing mitochondria with a normal membrane potential, but following engulfment the mitochondrial membrane potential is lost indicating a loss of viability. Inhibition of phagocytosis protects lymphoblasts from death indicating that phagocytosis is required for anti-CD47 mediated cell death. Blocking either the antibody Fc domain or Fc receptors inhibits antibody-induced phagocytosis. Antibodies against cell surface markers CD10 or CD19 also induced Fc-domain-dependent phagocytosis, but at a lower level commensurate with expression. Thus, phagoptosis may contribute to the efficacy of a number of therapeutic antibodies used in cancer therapy, as well as potentially endogenous antibodies. We conclude that anti-CD47 antibodies induce phagocytosis by binding CD47 on lymphoblast and Fc receptors on macrophages, resulting in cell death by phagocytosis, i.e. phagoptosis.
当在细胞表面表达时，CD47可抑制吞噬细胞对这些细胞的吞噬作用。大多数人类癌症过度表达CD47，并且针对CD47的抗体在动物模型中显示出清除多种癌症的显著能力。然而，这些抗体导致癌细胞死亡的机制尚不清楚。我们发现CD47在源自人类恶性肿瘤的三种B细胞系表面表达：697（前B-ALL淋巴细胞）、Ramos和DG-75（均为成熟B细胞，伯基特淋巴瘤），抗CD47抗体极大地增加了巨噬细胞对所有这三种细胞系的吞噬作用。在有巨噬细胞存在的情况下，抗体在数小时内导致淋巴细胞的清除，但在没有巨噬细胞的情况下，抗体对淋巴细胞活力没有影响。巨噬细胞吞噬含有具有正常膜电位的线粒体的活淋巴细胞，但吞噬后线粒体膜电位丧失，表明活力丧失。吞噬作用的抑制可保护淋巴细胞免于死亡，这表明吞噬作用是抗CD47介导的细胞死亡所必需的。阻断抗体的Fc结构域或Fc受体可抑制抗体诱导的吞噬作用。针对细胞表面标志物CD10或CD19的抗体也诱导Fc结构域依赖性吞噬作用，但水平较低，与表达水平相当。因此，吞噬凋亡可能有助于多种用于癌症治疗的治疗性抗体以及潜在的内源性抗体的疗效。我们得出结论，抗CD47抗体通过结合淋巴细胞上的CD47和巨噬细胞上的Fc受体诱导吞噬作用，导致通过吞噬作用即吞噬凋亡的细胞死亡。
