AnnexinA5 renders dead tumor cells immunogenic—implications for multimodal cancer therapies

Abstract

Multimodal tumor therapies should aim not only to kill the tumor cells, but also to stimulate a specific immune response to keep residual tumor (stem) cells and metastases under control. Apoptotic cells are mostly noninflammatory or even anti-inflammatory while necrotic cells stimulate the immune system. Whether the immunogenicity of apoptotic tumor cells can be increased by interfering with their swift and phosphatidylserine (PS)-dependent clearance by macrophages was examined. AnnexinA5 (AnxA5) is a naturally occurring highly specific ligand for PS. Proteins of the annexin family are characterized by a selective affinity for phospholipids in the presence of Ca2+ ions. The phagocytosis by macrophages of irradiated, apoptotic tumor cells (ITC) was partially inhibited when the ITC were preincubated with AnxA5. Activated macrophages secreted higher amounts of TNFalpha and IL-1beta after contact with ITC plus AnxA5 in comparison with ITC alone, while the amount of TGF-beta was decreased. Macrophages of AnxA5-deficient mice showed an increased phagocytosis of dead cells. Wild-type mice, where endogenous AnxA5 is present, displayed a significantly faster decline in size of allogeneic tumors in comparison with AnxA5-deficient animals. The addition of AnxA5 to ITC vaccines increased the percentage of tumor-free mice in syngeneic tumor protection and tumor cure assays. AnxA5 alone led to a retard of syngeneic tumor growth that was, however, less pronounced in comparison to treatment of the tumor with ionizing irradiation. In conclusion, AnxA5 disturbs the PS-dependent clearance by macrophages of dying tumor cells, leading to the accumulation of the latter, to the occurrence of secondary necrotic cells, and to an increased uptake of the dead cells by dendritic cells. Tumor cure appendages with dead tumor cells should be performed with AnxA5 as an immune stimulator and could be combined with irradiation, chemotherapy, and hyperthermia to induce immunogenic cell death forms in vivo or ex vivo.

Induction of Abscopal Anti-Tumor Immunity and Immunogenic Tumor Cell Death by Ionizing Irradiation - Implications for Cancer Therapies

“…2). Furthermore, we found that the blockade of macrophage clearance results in the generation of secondary necrotic cells and an accumulation of apoptotic cells that are then accessible for phagocytosis by DCs [117]. The observation that AnxA5 did not block the uptake of the tumor cells by DCs indicates that macrophages and DCs, in part at least, utilize different clearance mechanisms.…”

“…In vitro experiments revealed that AnxA5 shifts the cytokine release by activated macrophages that are phagocytosing irradiated tumor cells from an anti-inflammatory phenotype to an inflammatory phenotype (increased TNF-alpha and IL-1 beta and decreased TGF-beta levels). Combining RT with AnxA5 results in the most effective inhibition of tumor growth , as compared to treatment with RT or AnxA5 alone [117]. Recent work has identified additional Annexins (AnxA3, AnxA4, AnxA13 but not AnxA8) that can bind to PS which is exposed on dying (tumor) cells [120].…”

“…We have previously demonstrated that the growth of syngeneic tumors is retarded by a single injection of AnnexinA5 (AnxA5) around the tumor [117]. AnxA5 binds to the PS which is exposed by dying tumor cells with high affinity and thereby inhibits the uptake of apoptotic tumor cells by macrophages (Fig.…”

Clearance of Fetuin-A–Containing Calciprotein Particles Is Mediated by Scavenger Receptor-A

“…In addition, we tested the involvement of macrophage receptors, which might be involved in CPP uptake in BMMs derived from the respective knock-out mice. We included Fc␥-receptor, involved in the clearance of immunoglobulins, as well as the opsonic serum proteins C-reactive protein and serum amyloid P. 35,36 We studied annexin 5 and 6, which have been reported to mediate endocytosis of fetuin-A, 37,38 apoptotic cells, 39 and enhanced lipoprotein particle endocytosis, 40 respectively. The role of TLR-mediated signaling was further studied in TRIFdeficient mice.…”

Phagocytosis of dying tumor cells by human peritoneal mesothelial cells

“…The current notion is that dying cells in the abdominal cavity are eliminated by professional phagocytes: the peritoneal macrophages (Park et al, 2009;Frey et al, 2009;Gregory and Devitt, 2004). However, aside from macrophages, as the prototype of professional phagocytes, numerous examples of semi-professional, so-called 'amateur' phagocytes exist, including fibroblasts, endothelial, epithelial and mesenchymal cells (Gregory and Devitt, 2004;Dini et al, 1995;Cao et al, 2004;Dogusan et al, 2004).…”