Use of phage display for the generation of human antibodies that neutralize factor IXa function

The use of libraries of phage-displayed human single-chain antibody fragments (scFv) has become a new, powerful tool in rapidly obtaining therapeutically useful antibodies. Here, we describe the generation of human scFv and F(ab')2 directed against the gamma-carboxyglutamic acid (Gla) domain of coagulation factor IX. A large library of human scFv, displayed either on M13 phage or expressed as soluble proteins, was screened for binding to human Gla-domain peptide (Tyr1-Lys43). Among a panel of scFv that bound to the factor IX-Gla domain, six scFv clones recognized full-length factor IX and exhibited strong inhibitory activity of factor IX in vitro. After reformatting as F(ab')2, the affinity for factor IX of three selected clones was determined: 10C12 Kd = 1.6 nmol/l, 13D1 Kd = 2.9 nmol/l, and 13H6 Kd = 0.46 nmol/l. The antibodies specifically bound to factor IX and not to other coagulation factors, as assessed by enzyme-linked immunosorbent-type and human plasma clotting assays. The complementarity determining region amino acid sequences of clones 10C12 and 13D1 only differed at a single residue, whereas 13H6 showed little homology, suggesting that 13H6 binds to a different epitope within the factor IX-Gla domain. Despite the slightly lower affinity of 10C12 F(ab')2 versus 13H6 F(ab')2, 10C12 was consistently more potent than 13H6 in prolonging the activated partial thromboplastin time (APTT), in inhibiting platelet-mediated plasma clotting, and in inhibiting factor X activation by the intrinsic Xase complex. Finally, 10C12 F(ab')2 also recognized and neutralized factor IX/factor IXa of different species, as demonstrated by the specific APTT prolongation of dog, mouse, baboon and rabbit plasma. In summary, the results validate the usefulness of scFv phage-displayed libraries to rapidly generate fully human antibodies as potential new therapeutics for thrombotic disorders.

A human antibody that binds to the gamma-carboxyglutamic acid domain of factor IX is a potent antithrombotic in vivo

10C12, a human antibody F(ab')2, which specifically binds to the Gla domain of factor IX, interfered with all known coagulation processes that involve factor IX/IXa. These include the function of the intrinsic Xase complex and the activation of zymogen factor IX by factor XIa and by the tissue factor:factor VIla complex. Furthermore, 10C12 potently inhibited activated partial thromboplastin clotting times (APTT) in plasma of guinea pig and rat, thus enabling in-vivo evaluation. In guinea pigs, a bolus administration of 10C12 (10 microg/kg) prevented cyclic flow variations in damaged carotid arteries without affecting coagulation or bleeding parameters. At a 100-fold higher dose, 10C12 had no effect on normal hemostasis as assessed by the cuticle bleeding time. At this dose, 10C12 was also efficacious in a rat arterial thrombosis model, substantially reducing clot weight and duration of vessel occlusion while prolonging ex-vivo APTT only 1.2-fold. The dose of heparin required to produce comparable antithrombotic effects prolonged the APTT by 12-fold and increased the tail bleeding time (TBT) by 8-fold. In contrast, 10C12 had no effect on TBT. However, rat tails showed a tendency for rebleeding which 10C12 exacerbated. In conclusion, the antithrombotic potency of the 10C12 antibody in two species provides evidence for an important role of F.IX, and its Gla domain in particular, during thrombogenesis under arterial flow conditions. The relative safety at effective doses of this fully human antibody suggests that it may have therapeutic value for treatment of thrombotic disorders.

Cell activation and apoptosis by bacterial lipoproteins through toll-like receptor-2

Apoptosis is implicated in the generation and resolution of inflammation in response to bacterial pathogens. All bacterial pathogens produce lipoproteins (BLPs), which trigger the innate immune response. BLPs were found to induce apoptosis in THP-1 monocytic cells through human Toll-like receptor-2 (hTLR2). BLPs also initiated apoptosis in an epithelial cell line transfected with hTLR2. In addition, BLPs stimulated nuclear factor-kappaB, a transcriptional activator of multiple host defense genes, and activated the respiratory burst through hTLR2. Thus, hTLR2 is a molecular link between microbial products, apoptosis, and host defense mechanisms.