Development, characterization, and in vivo validation of a humanized C6 monoclonal antibody that Inhibits the membrane attack complex

Damage and disease of nerves activates the complement system. We demonstrated that activation of the terminal pathway of the complement system leads to the formation of the membrane attack complex (MAC) and delays regeneration in the peripheral nervous system. Animals deficient in the complement component C6 showed improved recovery after neuronal trauma. Thus, inhibitors of the MAC might be of therapeutic use in neurological disease. Here, we describe the development, structure, mode of action, and properties of a novel therapeutic monoclonal antibody, CP010, against C6 that prevents formation of the MAC in vivo. The monoclonal antibody is humanized and specific for C6 and binds to an epitope in the FIM1-2 domain of human and primate C6 with sub-nanomolar affinity. Using biophysical and structural studies, we show that the anti-C6 antibody prevents the interaction between C6 and C5/C5b by blocking the C6 FIM1-2:C5 C345c axis. Systemic administration of the anti-C6 mAb caused complete depletion of free C6 in circulation in transgenic rats expressing human C6 and thereby inhibited MAC formation. The antibody prevented disease in experimental autoimmune myasthenia gravis and ameliorated relapse in chronic relapsing experimental autoimmune encephalomyelitis in human C6 transgenic rats. CP010 is a promising complement C6 inhibitor that prevents MAC formation. Systemic administration of this C6 monoclonal antibody has therapeutic potential in the treatment of neuronal disease

Functional and Structural Characterization of a Potent C1q Inhibitor Targeting the Classical Pathway of the Complement System

The classical pathway of complement is important for protection against pathogens and in maintaining tissue homeostasis, but excessive or aberrant activation is directly linked to numerous pathologies. We describe the development and in vitro characterization of C1qNb75, a single domain antibody (nanobody) specific for C1q, the pattern recognition molecule of the classical pathway. C1qNb75 binds to the globular head modules of human C1q with sub-nanomolar affinity and impedes classical pathway mediated hemolysis by IgG and IgM. Crystal structure analysis revealed that C1qNb75 recognizes an epitope primarily located in the C1q B-chain that overlaps with the binding sites of IgG and IgM. Thus, C1qNb75 competitively prevents C1q from binding to IgG and IgM causing blockade of complement activation by the classical pathway. Overall, C1qNb75 represents a high-affinity nanobody-based inhibitor of IgG- and IgM-mediated activation of the classical pathway and may serve as a valuable reagent in mechanistic and functional studies of complement, and as an efficient inhibitor of complement under conditions of excessive CP activation

Structural basis for RNA-genome recognition during bacteriophage Q replication

Upon infection of Escherichia coli by bacteriophage Q, the virus-encoded -subunit recruits host trans-lation elongation factors EF-Tu and EF-Ts and riboso-mal protein S1 to form the Q replicase holoenzyme complex, which is responsible for amplifying the Q (+)-RNA genome. Here, we use X-ray crystallogra-phy, NMR spectroscopy, as well as sequence con-servation, surface electrostatic potential and muta-tional analyses to decipher the roles of the -subunit and the first two oligonucleotide-oligosaccharide-binding domains of S1 (OB1–2) in the recognition of Q (+)-RNA by the Q replicase complex. We show how three basic residues of the subunit form a patch located adjacent to the OB2 domain, and use NMR spectroscopy to demonstrate for the first time that OB2 is able to interact with RNA. Neutralization of the basic residues by mutagenesis results in a loss of both the phage infectivity in vivo and the ability of Q replicase to amplify the genomic RNA in vitro. In contrast, replication of smaller replicable RNAs is not affected. Taken together, our data suggest that the -subunit and protein S1 cooperatively bind the (+)-stranded Q genome during replication initiation and provide a foundation for understanding template discrimination during replication initiation

Nanobody‐mediated complement activation to kill HIV‐infected cells

Abstract The complement system which is part of the innate immune response against invading pathogens represents a powerful mechanism for killing of infected cells. Utilizing direct complement recruitment for complement‐mediated elimination of HIV‐1‐infected cells is underexplored. We developed a novel therapeutic modality to direct complement activity to the surface of HIV‐1‐infected cells. This bispecific complement engager (BiCE) is comprised of a nanobody recruiting the complement‐initiating protein C1q, and single‐chain variable fragments of broadly neutralizing antibodies (bNAbs) targeting the HIV‐1 envelope (Env) protein. Here, we show that two anti‐HIV BiCEs targeting the V3 loop and the CD4 binding site, respectively, increase C3 deposition and mediate complement‐dependent cytotoxicity (CDC) of HIV‐1 Env‐expressing Raji cells. Furthermore, anti‐HIV BiCEs trigger complement activation on primary CD4 T cells infected with laboratory‐adapted HIV‐1 strain and facilitates elimination of HIV‐1‐infected cells over time. In summary, we present a novel approach to direct complement deposition to the surface of HIV‐1‐infected cells leading to complement‐mediated killing of these cells

An Ultrahigh-Affinity Complement C4b-Specific Nanobody Inhibits In Vivo Assembly of the Classical Pathway Proconvertase

The classical and lectin pathways of the complement system are important for the elimination of pathogens and apoptotic cells and stimulation of the adaptive immune system. Upon activation of these pathways, complement component C4 is proteolytically cleaved, and the major product C4b is deposited on the activator, enabling assembly of a C3 convertase and downstream alternative pathway amplification. Although excessive activation of the lectin and classical pathways contributes to multiple autoimmune and inflammatory diseases and overexpression of a C4 isoform has recently been linked to schizophrenia, a C4 inhibitor and structural characterization of the convertase formed by C4b is lacking. In this study, we present the nanobody hC4Nb8 that binds with picomolar affinity to human C4b and potently inhibits in vitro complement C3 deposition through the classical and lectin pathways in human serum and in mouse serum. The crystal structure of the C4b:hC4Nb8 complex and a three-dimensional reconstruction of the C4bC2 proconvertase obtained by electron microscopy together rationalize how hC4Nb8 prevents proconvertase assembly through recognition of a neoepitope exposed in C4b and reveals a unique C2 conformation compared with the alternative pathway proconvertase. On human induced pluripotent stem cell–derived neurons, the nanobody prevents C3 deposition through the classical pathway. Furthermore, hC4Nb8 inhibits the classical pathway-mediated immune complex delivery to follicular dendritic cells in vivo. The hC4Nb8 represents a novel ultrahigh-affinity inhibitor of the classical and lectin pathways of the complement cascade under both in vitro and in vivo conditions