Traditional antibody-mediated neutralization of HIV-1 infection is thought to result from the binding of antibodies to virions, thus preventing virus entry. However, antibodies that broadly neutralize HIV-1 are rare and are not induced by current vaccines. We report that four human anti-phospholipid monoclonal antibodies (mAbs) (PGN632, P1, IS4, and CL1) inhibit HIV-1 CCR5-tropic (R5) primary isolate infection of peripheral blood mononuclear cells (PBMCs) with 80% inhibitory concentrations of <0.02 to ∼10 µg/ml. Anti-phospholipid mAbs inhibited PBMC HIV-1 infection in vitro by mechanisms involving binding to monocytes and triggering the release of MIP-1α and MIP-1β. The release of these β-chemokines explains both the specificity for R5 HIV-1 and the activity of these mAbs in PBMC cultures containing both primary lymphocytes and monocytes.

Phosphatidylserine (PS) and phosphatidylethanolamine (PE) are segregated to the inner leaflet of the plasma membrane of resting mammalian cells. We have previously shown that PS is exposed on the outer surface of virus‐infected cells and on enveloped viruses that bud out of these virus‐infected cells. The internal positioning of PS is maintained by aminophospholipid translocase, suggesting that this transporter is inhibited during viral infection. Because aminophospholipid translocase tranports both PS and PE from the outer to the inner leaflets of the plasma membrane, we hypothesized that PE would also be exposed on the outer surface of virus‐infected cells and on enveloped viruses. If so, the external PE could serve as a target for anti‐viral therapy. To target PE, we modified the 19‐amino‐acid PE‐binding tetracyclic peptide duramycin by conjugating it to biotin (DLB). The modification reduces the hemolytic activity and toxicity of the peptide but retains its PE binding abilities. DLB neutralizes multiple viruses in vitro. DLB also shows therapeutic efficacy in a lethal murine model for human cytomegalovirus. Our study demonstrates the promise of using PE as a target for broad‐spectrum anti‐viral drugs.

Androgen deprivation therapy (ADT) is initially effective against prostate cancer, but many patients eventually relapse and die from the outgrowth of castration-resistant disease. Here, we tested the hypothesis that tumor immunity against castration-resistant prostate cancer can be elicited by combining ADT with treatment with a monoclonal antibody that binds exposed phosphatidylserine (PS). The rationale was that PS is an immunosuppressive lipid that becomes exposed on tumor blood vessels and malignant cells in prostate tumors responding to ADT, and inhibits immune responses to prostate tumor antigens. To validate this hypothesis, we castrated TRAMP mice after they had developed prostatic adenocarcinomas and treated them with the PS-targeting antibody, mch1N11. We first demonstrated that PS exposure was induced on tumor vascular endothelium and tumor cells by castration. PS exposure on vessels coincided with regions of hypoxia generated in the tumor microenvironment. Next, we demonstrated that castration combined with treatment with mch1N11 inhibited tumor growth and progression. About half of the treated TRAMP mice did not develop castration-resistant tumors, and eventually died of old age. Immunohistochemical studies revealed that the mch1N11 treatment combined with castration generated T-cell immune responses against TRAMP tumor antigens that kept the tumor in check. Extensive disruption of tumor vasculature and abundant infiltration of immune cells, including CD8 positive T lymphocytes, Natural killer (NK) cells and dendritic cells were observed. Splenocytes from mice treated with mch1N11 plus castration were able to kill TRAMP-C2 specifically in vitro, whereas splenocytes from mice in the other groups could not. These results demonstrate that PS, which becomes exposed on prostate cancer cells and tumor vasculature after ADT, inhibits immunity to TRAMP tumor antigens. Treatment with the PS-targeting antibody mch1N11 reactivates tumor immunity, which can permanently hold new tumor development in check. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4395. doi:1538-7445.AM2012-4395

The anionic phospholipid phosphatidylserine (PS) is found exclusively in the inner leaflet of the plasma membrane of resting mammalian cells. We hypothesized that certain events that occur during virus replication (eg cell activation or membrane rearrangement) would trigger the exposure of anionic phospholipids on the outer surface of virus- infected cells and subsequently on the enveloped viruses that bud out of these virus- infected cells. We further hypothesized that these exposed anionic phospholipids would serve as targets for anti-viral therapy. We demonstrate here that anionic phospholipids become exposed on the enveloped Pichinde Virus (a model virus for Lassa Fever virus, a potential bioterrorism agent) and on Pichinde virus-infected cells. To detect anionic phospholipids, we used a chimeric monoclonal antibody, bavituximab, that binds anionic phospholipids in a B2-glycoprotein I dependent manner. We show that bavituximab treatment is able to cure overt disease in guinea pigs lethally infected with Pichinde virus. Bavituximab treatment reduced the amounts of virus in multiple tissues and caused direct clearance of virus from the blood. Direct clearance of free virus and antibody-dependent cellular cytotoxicity of virus-infected cells appear to be the major mechanisms that contribute to the anti-viral effect of bavituximab. Bavituximab-treated survivors were immune to reinfection. Furthermore, the murine version of bavituximab, 3G4, shows therapeutic efficacy in a lethal murine model for human cytomegalovirus. Our study demonstrates the promise of anionic phospholipids as targets for new broad-spectrum anti-viral drugs.