The present study characterized two different internalization mechanisms used by macrophages to engulf apoptotic and necrotic cells. Our in vitro phagocytosis assay used a mouse macrophage cell line, and murine L929sAhFas cells that are induced to die in a necrotic way by TNFR1 and heat shock or in an apoptotic way by Fas stimulation. Scanning electron microscopy (SEM) revealed that apoptotic bodies were taken up by macrophages with formation of tight fitting phagosomes, similar to the 'zipper'-like mechanism of phagocytosis, whereas necrotic cells were internalized by a macropinocytotic mechanism involving formation of multiple ruffles directed towards necrotic debris. Two macropinocytosis markers (Lucifer Yellow (LY) and horseradish peroxidase (HRP)) were excluded from the phagosomes containing apoptotic bodies, but they were present inside the macropinosomes containing necrotic material. Wortmannin (phosphatidylinositol 3 0 -kinase (PI3K) inhibitor) reduced the uptake of apoptotic cells, but the engulfment of necrotic cells remained unaffected. Our data demonstrate that apoptotic and necrotic cells are internalized differently by macrophages.

Overexpression of CD70 has been documented in a variety of solid and hematological tumors, where it is thought to play a role in tumor proliferation and evasion of immune surveillance. Here, we describe ARGX-110, a defucosylated IgG1 monoclonal antibody (mAb) that selectively targets and neutralizes CD70, the ligand of CD27.   ARGX-110 was generated by immunization of outbred llamas. The antibody was germlined to 95% human identity, and its anti-tumor efficacy was tested in several in vitro assays. ARGX-110 binds CD70 with picomolar affinity. In depletion studies, ARGX-110 lyses tumor cells with greater efficacy than its fucosylated version. In addition, ARGX-110 demonstrates strong complement-dependent cytotoxicity and antibody-dependent cellular phagocytosis activity. ARGX-110 inhibits signaling of CD27, which results in blocking of the activation and proliferation of Tregs. In a Raji xenograft model, administration of the fucosylated version of ARGX-110 resulted in a prolonged survival at doses of 0.1 mg/kg and above. The pharmacokinetics of ARGX-110 was tested in cynomolgus monkeys; the calculated half-life is 12 days. In conclusion, ARGX-110 is a potent blocking mAb with a dual mode of action against both CD70-bearing tumor cells and CD70-dependent Tregs. This antibody is now in a Phase 1 study in patients with advanced malignancies expressing CD70 (NCT01813539).

Background Activation of the classical and lectin pathway of complement may contribute to tissue damage and organ dysfunction of antibody-mediated diseases and ischemia-reperfusion conditions. Complement factors are being considered as targets for therapeutic intervention Objective We here characterize ARGX-117, a humanized inhibitory monoclonal antibody against complement C2. Methods The mode-of-action and binding characteristics of ARGX-117 were investigated in detail. Furthermore, its efficacy was analyzed in in vitro complement cytotoxicity assays. Finally, a PK/PD study was conducted in cynomolgus monkeys. Results Through binding to the Sushi-2 domain of C2, ARGX-117 prevents the formation of the C3 proconvertase, and inhibits classical and lectin pathway activation upstream of C3 activation. As ARGX-117 does not inhibit the alternative pathway it is expected not to affect the antimicrobial activity of this complement pathway. ARGX-117 prevents complement-mediated cytotoxicity in in vitro models for autoimmune hemolytic anemia and antibody-mediated rejection of organ transplants. ARGX-117 exhibits pH- and calcium-dependent target binding and is Fc-engineered to increase affinity at acidic pH to FcRn, and to reduce effector functions. In cynomolgus monkeys, ARGX-117 dose-dependently reduces free C2 levels and classical pathway activity. A two-dose regimen of 80 and 20 mg/kg separated by a week, resulted in profound reduction of classical pathway activity lasting for at least 7 weeks. Conclusion ARGX-117 is a promising new complement inhibitor that is uniquely positioned to target both the classical and lectin pathway while leaving the alternative pathway intact.

Duchenne muscular dystrophy is characterized by structural degeneration of muscle, which is exacerbated by localized functional ischemia due to loss of nitric oxide synthase-induced vasodilation. Treatment strategies aimed at increasing vascular perfusion have been proposed. Toward this end, we have developed monoclonal antibodies (mAbs) that bind to the vascular endothelial growth factor (VEGF) receptor VEGFR-1 (Flt-1) and its soluble splice variant isoform (sFlt-1) leading to increased levels of free VEGF and proangiogenic signaling. The lead chimeric mAb, 21B3, had high affinity and specificity for both human and mouse sFlt-1 and inhibited VEGF binding to sFlt-1 in a competitive manner. Proof-of-concept studies in the mdx mouse model of Duchenne muscular dystrophy showed that intravenous administration of 21B3 led to elevated VEGF levels, increased vascularization and blood flow to muscles, and decreased fibrosis after 6–12 weeks of treatment. Greater muscle strength was also observed after 4 weeks of treatment. A humanized form of the mAb, 27H6, was engineered and demonstrated a comparable pharmacologic effect. Overall, administration of anti-Flt-1 mAbs in mdx mice inhibited the VEGF:Flt-1 interaction, promoted angiogenesis, and improved muscle function. These studies suggest a potential therapeutic benefit of Flt-1 inhibition for patients with Duchenne muscular dystrophy.

The expression of CD70 is normally restricted to activated B- and T- cells, as well as mature dendritic cells. Overexpression has been documented in a variety of solid and hematological tumors, where it is thought to play a role in evasion of immune surveillance. ARGX-110 is a defucosylated, humanized IgG1 monoclonal antibody that selectively targets and neutralizes CD70, a ligand of CD27. A detailed biological and functional characterization of ARGX-110 was carried out to support its clinical development for the treatment of cancers dependent on signaling through the CD70/CD27 axis. In competitive equilibrium binding experiments, ARGX-110 bound to human and cynomolgus monkey CD70 with affinities of approximately 0.4 nmol/L and 0.6 nmol/L, respectively. ARGX-110 inhibited in a dose-dependent fashion CD70/CD27-induced IL-8 release in Raji cells with IC50 values of 0.1 nmol/L. CD70 is minimally internalized (<40%) by most hematological cell lines, thus providing a plausible rationale to develop a therapeutic mAb designed to enhance ADCC. In cell depletion studies, ARGX-110 was associated with comparable to better cell lysis compared to Rituximab. Cell lysis by ARGX-110 was not dependent on the internalization rate of the ARGX-110/CD70 complex in hematological cell lines. Independence from CD70 copy numbers at the cell surface was also demonstrated. In a Burkitt lymphoma (CD70+ Raji cells) SCID mouse model, ARGX-110 administered intraperitoneally twice weekly at doses ranging from 0.001 to 10 mg/kg starting one day after inoculation resulted in a dose-response effect on animal survival. In cynomolgus monkeys, ARGX-110 did not demonstrate any toxicity upon repeated administration of high doses of 30 mg/kg. B, T and NK cell numbers remained unaltered. ARGX-110 is currently in phase I clinical trial for patients with CD70+ malignancies. Citation Format: Karen Silence, Hans De Haard, Torston Dreier, Peter Ulrichts, Mahan Moshir, Sofie Gabriels, Alain Thibault. Pre-clinical characterization of ARGX-110: A neutralizing, humanized monoclonal antibody to the human CD70 antigen with enhanced ADCC properties. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5470. doi:10.1158/1538-7445.AM2013-5470 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.