Annexin-V promotes anti-tumor immunity and inhibits neuroblastoma growth in vivo

Abstract

The goal of the current study is to determine the effects of blocking phosphatidylserine (PS) on the growth of neuroblastoma in mice. PS, an anionic phospholipid restricted to the cytoplasmic surface of plasma membranes in most cells, is externalized to the surface of apoptotic cells. PS has been shown to induce immune tolerance to self-antigens. PS can also be found on the surface of live cells and in particular tumor cells. Annexin-V (AnV) is a protein that specifically binds and blocks PS. To determine the effects of blocking PS with AnV on tumor growth and immunogenicity, mice were inoculated with AGN2a, a poorly immunogenic murine neuroblastoma that expresses high level of PS on the cell surface. Survival and anti-tumor T cell response were determined. AGN2a were engineered to secrete AnV. Secreted protein effectively blocked tumor PS. 40 % of mice inoculated with AnV-expressing AGN2a cells survived free of tumor, whereas none of the mice inoculated with control cells survived (p = 0.0062). The benefits of AnV were lost when mice were depleted of T cells. The findings suggest that AnV could protect mice from tumor challenge through an immune mediated mechanism. Mice were then immunized with irradiated AnV-secreting or control cells, and challenged with wild-type AGN2a cells. AnV-secreting cell vaccine protected 80 % of mice from AGN2a challenge, while control cell vaccine prevented tumor growth in only 30 % of animals (p = 0.012). ELISPOT analysis demonstrated that AnV-secreting cell vaccine induced a greater frequency of interferon-gamma producing splenic T cells. T cells isolated from mice immunized with AnV-secreting but not control vaccine lysed AGN2a. In summary, AnV blocked PS, enhanced T cell mediated tumor immunity, and inhibited tumor growth.

Phosphatidylserine-targeting antibodies augment the anti-tumorigenic activity of anti-PD-1 therapy by enhancing immune activation and downregulating pro-oncogenic factors induced by T-cell checkpoint inhibition in murine triple-negative breast cancers

“…TNBC represents one of the most malignant subtypes of BC. Current treatment strategies for patients diagnosed with TNBC rely on systemic cytotoxic chemotherapeutics, causing exposure of PS in the tumor microenvironment, which in turn promotes an immunosuppressive condition [ 14 , 52 ]. Previous work has demonstrated that PS-driven immune suppression can be blocked or reversed by PS-targeting antibodies [ 14 , 22 ].…”

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

“…Recent evidence indicates that exposure of phosphatidylserine in the tumor microenvironment contributes to the immunosuppressed state of tumors (36,43,44). This suggests that the benefit of chemotherapy, radiotherapy, and other treatments that trigger tumor cell apoptosis is undermined by the increase in local tumor immunosuppression caused by phosphatidylserine exposed on dying tumor cells and their microvesicles (25,43,45).…”

Antibody-Mediated Phosphatidylserine Blockade Enhances the Antitumor Responses to CTLA-4 and PD-1 Antibodies in Melanoma

“…An underlying challenge to virtually all cytotoxic cancer therapies is therapy-induced exposure of PS that exacerbates immunosuppression in the tumor microenvironment (38,49,50). We have found that PS-driven immune suppression can be inhibited by antibody-mediated PS blockade (38,51).…”