Characterisation of a monoclonal antibody to von Willebrand factor as a potent inhibitor of ristocetin-mediated platelet interaction and platelet adhesion

We studied a murine monoclonal antibody (211 A6) to von Willebrand factor (vWF) with a view to investigating structure-relationship of plasma vWF. The specificity of this antibody has been substantiated by ELISA tests and indirect immunofluorescence. It reacts with purified vWF, normal plasma but not with plasma or platelets from a severe von Willebrand's disease patient. Monoclonal antibody 211 A6 is a potent inhibitor of ristocetin-induced platelet aggregation. The 125I-FVIII/vWF binding to platelets in presence of ristocetin is totally inhibited by low 211 A6 concentrations. Thrombin-induced binding of vWF to platelets is not affected by 211 A6. The ability of this antibody to inhibit platelet adhesion to subendothelium and to collagen was investigated with a perfusion model. The complete inhibition of platelet adhesion by 211 A6 questions the similarity or the interrelationship in vWF domains involved in ristocetin-induced platelet functions and platelet adhesion.     

French mirror site of the NPAC Visible Human Viewer: first year evaluation

The NPAC visible human viewer (NPAC VHV), graphical interface written in JAVA, freely accessible by the Web, allows the display of anatomic cross-sections of the Visible Human Project developed by the National Library of Medicine. In April 1997, the Medical Media Library of Lyons undertook the construction of a French-language mirror site of the NPAC VHV. The aim of this work is to evaluate first year utilisation of this site. From May 1st, 1997 to April 30th, 1998, the mirror site was consulted 34,752 times. In 45.14% of cases, the request came from France, in 4.42% of cases from Belgium, in 3.98% from Canada and in 2.12% from Switzerland. Other connections came either from a country responsible for fewer than 1% of connections or from unidentified computers. Data analysis showed a peak of connections between 15:00 and 17:00, and an increased number of connections from September to March 1998. The NPAC VHV is housed in 5 sites in the world. It is a software very simple to use. As the figures have no legends, it is more appropriate for group teaching than for self-teaching.     

In vitro and in vivo Evaluation of a Factor VIII Concentrate Heat-Treated to Inactivate HTLV-III/LAV Viruses

We report here the results of our evaluation of the effects of a dry heat treatment (96 h at 68 degrees C) to eliminate LAV/HTLV-III virus on factor VIII (FVIII) and von Willebrand factor (vWf) present in an intermediate-purity concentrate. This thermal inactivation appears to have little effect on FVIII. There is an acceptable loss (12.3 +/- 3.6%; n = 25) in FVIII coagulant activity (FVIII: C) and a good in vivo performance in haemophilia A patients. A precise analysis of vWf indicates that whereas the vWf antigen and its ristocetin cofactor activity decrease during heating, there is an increase in potentially functional forms of vWf. Heat treatment induces an increase in high molecular weight forms of vWf and an enhancement in platelet adhesion to collagen. These changes probably explain the correcting effect on the bleeding time of the heated FVIII concentrate in patients with von Willebrand's disease. Thus, this heat-treated concentrate appears to be equivalent to the untreated product in haemophilia A, with the additional benefit of being efficient for the treatment of von Willebrand's disease.     

Case report: relevance of metabolite identification to detect new synthetic opioid intoxications illustrated by U-47700

International Journal of Legal Medicine - Today, new psychoactive substances (NPS) producers increasingly appear to be targeting new synthetic opioids (NSOs), and the recent emergence of NSOs is...     

Leu 697-->Val mutation in mature von Willebrand factor is responsible for type IIB von Willebrand disease

Type IIB von Willebrand disease is characterized by the selective loss of high molecular weight von Willebrand factor (vWF) multimers from plasma and enhanced platelet agglutination of platelet-rich-plasma in the presence of low concentrations of ristocetin. We identified, in two related patients, a C-->G transversion resulting in the substitution of Valine for Leucine at position 697 of the mature subunit of vWF. We reproduced this mutation in vWF cDNA and expressed the recombinant protein in Cos-7 cells. The subunit composition and multimeric structure of mutated protein (rvWFLeu697Val) were similar to the wild- type recombinant (WTrvWF). Ristocetin-induced binding of rvWFLeu697Val to platelets was markedly increased in the presence of low doses of ristocetin and slightly increased with botrocetin as compared with that for WTrvWF, whereas collagen binding was not affected by the mutation. These data show that the Leu 697-->Val substitution is not a rare polymorphism but is responsible for the subtype IIB characteristic abnormalities identified in the two affected patients; however, it is not located in the area of vWF (amino acid 540 to amino acid 578) where most of the other type IIB mutations have already been reported.     

A human anti-D monoclonal antibody selected for enhanced FcgammaRIII engagement clears RhD+ autologous red cells in human volunteers as efficiently as polyclonal anti-D antibodies

A human anti-RhD immunoglobulin G1 monoclonal antibody (mAb), R297, was tested in a phase I study to assess its ability to induce the clearance of antibody-coated autologous RhD⁺ red blood cells (RBCs) in healthy male volunteers. The clearance potency of R297 was compared with that of a marketed human polyclonal anti-D product (Rhophylac^®). This mAb has been selected for its ability to strongly engage Fc-gamma receptor IIIA and to mediate a potent antibody-dependent cell cytotoxicity (ADCC) against RhD⁺ RBCs. Autologous RhD⁺ RBCs were sensitized with either Rhophylac^® or R297 at three different coating percentages (25, 12·5 and 6·25%), before re-infusion. This phase I study showed that the human R297 mAb promoted rapid and complete clearance of RBCs, and showed activity that was at least as potent as the human polyclonal anti-D antibody preparation. Clearance of RBCs could still be observed when the percentage of R297 used to coat the RBCs was reduced to 6·25%. Finally, none of the adverse events was severe or considered to be related to R297. Thus, R297 is a promising candidate for the prevention of allo-immunization and represents a new generation of Fc-modified monoclonal antibodies with increased FcγRIII binding and increased ADCC.     

Effect of zinc on human IgG1 and its FcγR interactions

In the present study, we show that histidines 310 and 435 at the CH2-CH3 interface of the Fc portion of human IgG1 can coordinate a Zn2+ and participate in the control of the CH2-CH2 interdomain opening. Structures obtained in the absence of Zn2+ have a reduced interdomain gap that likely hamper FcγR binding. This closed conformation of the Fc is stabilized by inter-CH2 domain sugar contacts. Zinc appears to counteract the sugar mediated constriction, suggesting that zinc could be an important control factor in IgG1/FcγR interactions. The results of binding studies performed in the presence of EDTA on FcγR expressing cells supports this hypothesis. When a mutated Fc fragment, in which histidines 310 and 435 have been substituted by lysines (Fc H/K), was compared with the wild-type Fc in crystallographic studies, we found that the mutations leave the interface unaltered but have a long-range effect on the CH2 interdomain separation. Moreover, these substitutions have a differential effect on the binding of IgG1 to Fcγ receptors and their functions. Interaction with the inhibitory FcγRIIB is strongly perturbed by the mutations and mutant IgG1 H/K only weakly engages this receptor. By contrast, higher affinity FcγR are mostly unaffected.     

Chronic lymphocytic leukaemia cells are efficiently killed by an anti-CD20 monoclonal antibody selected for improved engagement of FcgammaRIIIA/CD16

Patients with chronic lymphocytic leukaemia (CLL) treated with a combination of fludarabine, cyclophosphamide and rituximab show a high response rate. However, only a poor response is observed following rituximab monotherapy. The use of chemo-immunotherapy is often associated with haematological and infectious complications. Thus, an antibody with an enhanced ability to kill CLL cells could lead to better clinical responses to antibody monotherapy and the possibility of lowering drug doses during chemo-immunotherapy. We generated a chimeric anti-CD20 monoclonal antibody (mAb), EMAB-6, which has a low fucose content. Apoptosis and complement activities for EMAB-6 were similar to those seen for rituximab. By contrast, EMAB-6 mAb showed improved Fcγ receptor IIIA (FcγRIIIA)/CD16 binding and FcγRIIIA-dependent effector functions. It induced a higher in vitro antibody-dependent cellular cytotoxicity against CLL cells and a higher FcγRIIIA-mediated interleukin-2 production by FcγRIIIA⁺ Jurkat cells in the presence of CLL cells at both low and maximally saturating concentrations. Comparative studies between CLL and lymphoma cells coated with EMAB-6 or rituximab indicated that the difference of efficacy was more pronounced at low doses and when target cells expressed fewer CD20 molecules. Thus, EMAB-6 mAb represents a promising drug candidate for the treatment of CLL by inducing a strong cytotoxicity against tumour cells that express low CD20 levels.     

Selection of a human anti-RhD monoclonal antibody for therapeutic use: impact of IgG glycosylation on activating and inhibitory Fc gamma R functions

The substitution of plasmatic anti-RhD polyclonal antibodies by a monoclonal antibody (mAb) for preventing the hemolytic disease of the newborn (HDN) is an important issue due to supply and safety concerns. Since it has been suggested that FcgammaR are involved in the prevention of HDN, the in vitro functional properties of two anti-RhD mAbs differing through their glycosylation profiles were compared using FcgammaR-based assays to select a candidate mAb. T125(YB2/0), a low fucosylated antibody, bound strongly to both activating FcgammaRIII and inhibitory FcgammaRII, as opposed to its highly fucosylated counterpart. It also exerted a strong ADCC against RhD+ RBCs and a potent FcgammaRIIB-mediated inhibition of cytokine release. Moreover, an in vivo RhD+ red blood cells (RBCs) clearance assay showed that this antibody exhibits a RhD+ RBCs clearance as potent as polyclonal anti-RhD antibodies in NOD-SCID mice. Thus, T125(YB2/O) has been selected to be tested for the prevention of anti-RhD allo-immunization.     

A resolution of reported discrepancies in the characteristics of platelet glycoproteins IV (GPIV) and IIIb (GPIIIb).

The terms glycoprotein IV (GPIV) and glycoprotein IIIb (GPIIIb) have been used interchangeably and reports in the literature have indicated this glycoprotein as having a molecular weight variously described as either 88,000 or 97,000, a fast anodal mobility on crossed electrophoresis and either 13 or less than 1 methionine residues on amino acid analysis of the purified glycoprotein. To resolve these discrepancies, we have evaluated the characteristics of GPIV both in whole platelets and after isolation. These studies have shown that the term GPIV defines a protease-resistant platelet surface glycoprotein with Mr 88,330 +/- 2,240 which is immunologically identical with the CD36 differentiation antigen, which migrates with a relatively slow anodal mobility on crossed immunoelectrophoresis and which contains approximately 13 methionine residues per mole.