Inhibition of Phosphatidylserine Recognition Heightens the Immunogenicity of Irradiated Lymphoma Cells In Vivo

Abstract

Strategies to enhance the immunogenicity of tumors are urgently needed. Although vaccination with irradiated dying lymphoma cells recruits a tumor-specific immune response, its efficiency as immunogen is poor. Annexin V (AxV) binds with high affinity to phosphatidylserine on the surface of apoptotic and necrotic cells and thereby impairs their uptake by macrophages. Here, we report that AxV preferentially targets irradiated lymphoma cells to CD8+ dendritic cells for in vivo clearance, elicits the release of proinflammatory cytokines and dramatically enhances the protection elicited against the tumor. The response was endowed with both memory, because protected animals rejected living lymphoma cells after 72 d, and specificity, because vaccinated animals failed to reject unrelated neoplasms. Finally, AxV–coupled irradiated cells induced the regression of growing tumors. These data indicate that endogenous adjuvants that bind to dying tumor cells can be exploited to target tumors for immune rejection.

Phosphatidylserine-Targeting Antibody Induces M1 Macrophage Polarization and Promotes Myeloid-Derived Suppressor Cell Differentiation

“…Binding to macrophage phosphatidylserine receptors triggers IL-10-and TGF-b-dependent immunosuppressive signals that stimulate them to engulf the phosphatidylserine-expressing cells without secreting inflammatory cytokines (19)(20)(21). Moreover, while intratumoral dendritic cells bind and ingest phosphatidylserine-expressing cells, they maintain an immature phenotype, lacking the costimulatory molecules required for APC activity (35,36). These data emphasize that exposed phosphatidylserine is a major factor in maintaining the immunosuppressed state in tumors, and further suggest that chemotherapy, radiotherapy, and androgen-deprivation therapy are undermined by the phosphatidylserine in the tumor microenvironment (37).…”

From regulation of dying cell engulfment to development of anti-cancer therapy

“…84 Because 3G4 substantially increases the engulfment of PS-expressing cells by bone marrow-derived mouse macrophages in vitro in an Fc-dependent fashion, it is likely that the mechanism of 3G4 cytotoxicity in vivo is mediated by macrophages and involves an Fc receptormediated inflammatory response and respiratory burst. 85 Another approach to restore immunogenicity of tumor cells is to block phagocytic clearance of apoptotic tumor cells using the PS-binding protein annexin-V. Injection of annexin-Vcoupled tumor cells in combination with experimental radiotherapy resulted in a strong anti-tumor effect, 3 with 90% of the mice rejecting the tumor after challenge compared to 25% of control animals. Moreover, in vivo clearance of annexin-Vcoupled tumor cells by thioglycollate-elicited macrophages was decreased.…”

“…We also discuss repelling signals that protect living cells from being engulfed. We will briefly consider how exposure of certain molecules on the surface of dying cells, such as phosphatidylserine (PS) and calreticulin, can be used for raising immunogenicity of tumor cells, 3,4 and how these findings could be applied for designing novel experimental anti-cancer treatments.…”

The liaison between apoptotic cells and macrophages – the end programs the beginning

“…These cells failed to promote TGF-b1 secretion, while TGF-b release was observed with PS-exposing apoptotic Jurkat cells (Huynh et al, 2002). Moreover, masking PS on irradiated tumor cells by annexin V averted TGF-b production in macrophages (Bondanza et al, 2004). A recently reported PS receptor, Stabilin-2, mediated AC engulfment and anti-Stabilin-2 antibodies induced TGF-b, supporting the indirect notion that PS receptor activation mediates TGF-b release .…”