Triple-fusion protein (TriFu): A potent, targeted, enzyme-like inhibitor of all three complement activation pathways

The introduction of a therapeutic anti-C5 antibody into clinical practice in 2007 inspired a surge into the development of complement-targeted therapies. This has led to the recent approval of a C3 inhibitory peptide, an antibody directed against C1s and a full pipeline of several complement inhibitors in preclinical and clinical development. However, no inhibitor is available that efficiently inhibits all three complement initiation pathways and targets host cell surface markers as well as complement opsonins. To overcome this, we engineered a novel fusion protein combining selected domains of the three natural complement regulatory proteins decay accelerating factor, factor H and complement receptor 1. Such a triple fusion complement inhibitor (TriFu) was recombinantly expressed and purified alongside multiple variants and its building blocks. We analyzed these proteins for ligand binding affinity and decay acceleration activity by surface plasmon resonance. Additionally, we tested complement inhibition in several in vitro/ex vivo assays using standard classical and alternative pathway restricted hemolysis assays next to hemolysis assays with paroxysmal nocturnal hemoglobinuria erythrocytes. A novel in vitro model of the alternative pathway disease C3 glomerulopathy was established to evaluate the potential of the inhibitors to stop C3 deposition on endothelial cells. Next to the novel engineered triple fusion variants which inactivate complement convertases in an enzyme-like fashion, stoichiometric complement inhibitors targeting C3, C5, factor B, and factor D were tested as comparators. The triple fusion approach yielded a potent complement inhibitor that efficiently inhibits all three complement initiation pathways while targeting to surface markers.

Mitigating placental injuries through up-regulating DAF in experimental APS mice: new mechanism of progesterone

Anti-phospholipid syndrome (APS) is characterized by recurrent pathological pregnancy, arterial or venous thrombosis in the presence of anti-phospholipid antibody (aPL). Complement activation is recognized as an intermediate link leading to placental thrombosis and placental inflammation in APS model mice. Decay accelerating factor (DAF, CD55), MAC-inhibitory protein (MAC-IP, CD59) and membrane co-factor protein (MCP, CD46) are important complement inhibitory proteins (CIPs) highly expressed in normal placenta to curb excessive complement activation and its mediated injuries. Anti-β2 glycoprotein I (anti-β2GPI) antibody is an important aPL. We found that placental DAF and CD46 decreased in β2GPI passively immunized APS model mice, accompanied by C3 deposition, neutrophil infiltration and increased proinflammatory cytokine levels detected in its placenta. Progesterone supplement can up-regulate DAF but not CD46 expression, curb C3 activation and decrease proinflammatory cytokines levels to reduce fetal loss frequency. Progesterone receptor antagonist (mifepristone) or knock-down DAF with specific siRNA, above the protective effects of progesterone, were significantly weakened. Another sex hormone, oestrogen, has no significant effect on placental DAF and C3 contents and fetal loss frequency in the APS mice model. This may be an important mechanism by which progesterone induces maternal-fetal immune tolerance. At the same time, it may provide evidence for the use of progesterone in APS abortion patients.

Bee Venom Alleviates Atopic Dermatitis Symptoms through the Upregulation of Decay-Accelerating Factor (DAF/CD55)

Bee venom (BV)—a complex mixture of peptides and toxic proteins including phospholipase A2 and melittin—promotes blood clotting. In this study, we investigated the anti-atopic properties of BV and the mechanism associated with its regulation of the complement system. BV treatment upregulated the mRNA and protein levels of CD55 in THP-1 cells. Further experiments revealed that the phosphorylation of ERK was associated with upregulation of CD55. A complement-dependent cytotoxicity assay and a bacteria-killing assay showed that BV inactivated the complement system through the induction of CD55. The serum levels of C3 convertase (C3C) and Membrane attack complex (MAC) increased, while CD55 decreased in mice with AD-like lesions from DNCB treatment. However, the levels were inverted when the AD-like mice were treated with BV using subcutaneous injection, and we observed that the AD symptoms were alleviated. BV is often used to treat AD but its mechanism has not been elucidated. Here, we suggest that BV alleviates AD through the inactivation of the complement system, especially by the induction of CD55.

Coupling complement regulators to immunoglobulin domains generates effective anti-complement reagents with extended half-life in vivo

Complement activation and subsequent generation of inflammatory molecules and membrane attack complex contributes to the pathology of a number of inflammatory and degenerative diseases, including arthritis, glomerulonephritis and demyelination. Agents that specifically inhibit complement activation might prove beneficial in the treatment of these diseases. Soluble recombinant forms of the naturally occurring membrane complement regulatory proteins (CRP) have been exploited for this purpose. We have undertaken to design better therapeutics based on CRP. Here we describe the generation of soluble, recombinant CRP comprising rat decay accelerating factor (DAF) or rat CD59 expressed as Fc fusion proteins, antibody-like molecules comprising two CRP moieties in place of the antibody Fab arms (CRP-Ig). Reagents bearing DAF on each arm (DAF-Ig), CD59 on each arm (CD59-Ig) and a hybrid reagent containing both DAF and CD59 were generated. All three reagents inhibited C activation in vitro. Compared with soluble CRP lacking Fc domains, activity was reduced, but was fully restored by enzymatic release of the regulator from the Ig moiety, implicating steric constraints in reducing functional activity. In vivo studies showed that DAF-Ig, when compared to soluble DAF, had a much extended half-life in the circulation in rats and concomitantly caused a sustained reduction in plasma complement activity. When given intra-articularly to rats in a model of arthritis, DAF-Ig significantly reduced severity of disease. The data demonstrate the potential of CRP-Ig as reagents for sustained therapy of inflammatory disorders, including arthritis, but emphasize the need for careful design of fusion proteins to retain function.