A potential new procedure for removing anti-factor VIII antibodies from hemophilic plasma

Affinity of human anti-factor VIII antibodies for functional polystyrene supports

Human anti-factor VIII antibodies (anti-FVIII) neutralize Factor VIII (FVIII) procoagulant activity. These antibodies appear in about 5-15 per cent of severely affected patients with haemophilia A treated with FVIII concentrates (Mannucci, 1993). In order to obtain non-thrombogenic materials able to interact specifically with anti-FVIII, amino acids residues that mimic part of the FVIII molecule recognized by anti-FVIII have been grafted. Several cross-linked polystyrenes were functionalized with sulphonate and tyrosine sulphamide groups or tyrosine derivatives sulphamide groups such as methyl ester tyrosine, or the peptides aspartic acid methyl amide tyrosine, tyrosine aspatic acid methyl amide or aspartic acid aspatic acid methyl amide tyrosine. The in vitro removal of anti-FVIII from haemophilic A plasma was performed on different supports. These polymers exhibit strong and selective affinity for the anti-FVIII. The amount of adsorbed anti-FVIII varies with the composition of the polymer and a maximum is achieved for 15-35 per cent of amino acid sulphamide groups. The influence of different chemical groups on the surface of the polymeric solid supports on the adsorption of anti-FVIII was also studied.

Regenerated cellulose-based hemodialyzers with immobilized proteins as potential devices for extracorporeal immunoadsorption procedures: an assessment of protein coupling capacity and in vitro dialysis performances

The development of immunoadsorbents usable with whole blood should offer the potential for making significant improvements in extracorporeal immunoadsorption procedures. In contrast to traditional chromatographic media, these hemocompatible matrices could be used without requiring the previous step of the separation of blood cells and plasma. Conventional hemodialyzers seem to be particularly appropriate for such a purpose. This paper describes a feasibility study of the preparation of immunoaffinity supports, from regenerated cellulose (Cuprophan)-based dialyzers by cyanogen bromide activation and coupling of bovine serum albumin or human immunoglobin G, used as models for immunochemical ligands. Several parameters of the activation and coupling steps were studied in order to define the optimum preparation conditions. In addition, the preservation of the transport properties (clearance and ultrafiltration) of the modified hemodialyzers was evaluated in vitro to ensure that the device potentially could be used in future human therapeutic applications with no risk of massive removal of solutes and fluid from the blood. Results indicate that 150-300 mg of immunoglobulins can be immobilized per square meter of Cuprophan. Modified hemodialyzers show a slight decrease of their clearance values and a slight increase of their ultrafiltration coefficients, and thus they can be proposed as reliable carrier material for extracorporeal cleansing systems.

Synthetic sorbents for removal of factor VIII inhibitors from haemophilic A plasma

Human factor VIII (FVIII) is a protein of the blood coagulation system that is absent or defective in patients with haemophilia A. A most serious complication following replacement therapy in 10-15% of patients treated with available FVIII concentrate is the development of inhibitors of FVIII (anti-FVIII). Some polymers functionalized with suitable chemical substituents which mimic part of the epitope of FVIII recognized by the inhibitors might be used in extracorporeal circulation to reduce the concentration of antibodies to FVIII. For this purpose, insoluble polystyrene bearing sulfonate and L-tyrosine methyl ester sulfamide groups have been synthesized. The in vitro removal of anti-FVIII inhibitors from plasmas of patients with haemophilia A was performed. Different chromatographic parameters were studied and optimized.

Immunoadsorption procedure as a potential method for the specific beta 2-microglobulin removal from plasma of patients with chronic renal failure

beta 2-Microglobulin (beta 2-M), which accumulates in the plasma of patients undergoing long-term dialysis, has been identified as the principal precursor protein of amyloid fibrils in dialysis-related amyloidosis. As no specific treatment for this affection has been yet established, an extracorporeal immunoadsorption procedure appears to be an attractive therapeutic approach to remove beta 2-M. Several murine monoclonal antibodies to human beta 2-M were developed and compared as affinity ligands. One of them was selected on the basis of its specificity and adsorption capacity. In order to achieve maximum efficiency in protein removal, different parameters of the procedure were studied and optimized: effect of antibody coupling density, determination of maximum adsorption capacity of the immunoadsorbents and influence of antigen concentration and of flow-rate on antigen capture efficiency. The conditions of regeneration of immunoaffinity sorbents were also investigated to allow their multiple use without loss of adsorption capacity. The results show the validity of the proposed technique in removing beta-M from plasma of patients with chronic renal failure.

Tyrosyl sulfamide derivatives as ligands for affinity adsorption of anti FVIII antibodies

Human anti factor VIII (anti FVIII) antibodies neutralize factor VIII procoagulant activity. These antibodies appear in about 5-10% of severely affected haemophiliac A patients treated with FVIII concentrates. In order to obtain non-thrombogenic materials able to interact specifically with anti FVIII, we have grafted amino acid residues which mimic part of the epitope of the FVIII molecule recognized by the anti FVIII. For this purpose, crosslinked polystyrenes functionalized with sulfonate and tyrosyl or methyl ester tyrosyl sulfamide groups have been synthesized and characterized. The in vitro removal of anti FVIII from haemophiliac patient plasma with antibodies, was performed on these different active supports. These polymers exhibit strong and selective affinity for the anti FVIII. The adsorption of the antibodies vary with the percentage of units bearing methyl ester tyrosyl sulfamide groups and present a maximum at 25% grafting rate. For the more efficient resin, the affinity constant, determined for the adsorption isotherm for the anti FVIII is about 10(9) M-1, whereas the affinity constant for the IgG in the same experimental conditions, is low (10(5) M-1). The influence of different chemical groups on the polymeric phase, on their affinity for the inhibitors was also studied. The most active resins can be selected and used in an extracorporeal circulation to reduce the concentration of anti FVIII in a blood epuration process.

Characterization of a monoclonal anti-idiotype antibody to human anti-factor VIII antibodies

Approximately 15% of individuals with hemophilia A develop antibodies (inhibitors) to therapeutically infused factor VIII that interfere with F.VIII coagulant activity. By using isoelectric focusing and immunospecific detection of anti-factor VIII antibodies, inhibitor plasma showed varied patterns of reactivity characteristic of a polyclonal response. Inhibitor plasma from patient Bt was observed to have an isolated banding pattern, or spectrotype, at pI 8.4 (SP8.4) distinct from his remaining anti-factor VIII antibodies. SP8.4 antibodies from this patient were partially purified and used to prepare monoclonal anti-idiotype antibodies. Monoclonal antibody Mab20-2H was found to detect a spectrotype in isoelectric-focused Bt plasma identical to SP8.4 and to bind anti-factor VIII antibodies. Furthermore, Mab20-2H binding could inhibit the binding of these anti-factor VIII antibodies to antigen, indicating that Mab20-2H recognizes an idiotope associated with antigen binding. Mab20-2H was also found to recognize antibodies from another inhibitor patient. This and other anti-idiotype reagents will be useful for defining genetic factors involved in the human immune response to factor VIII and in designing approaches to prevent or ameliorate this response.

Factor VIII-bypassing activity of bovine tissue factor using the canine hemophilic model

The bleeding disorder of hemophilia A currently treated by replacement therapy of the missing coagulation factor, factor VIII, is frequently complicated by the development of neutralizing antibodies. The therapeutic potential of attenuated forms of the lipid-associated glycoprotein tissue factor, a known initiator of coagulation, was investigated as a factor VIII-by-passing activity. The protein moiety of tissue factor (Apo-TF) was partially purified and exhibited minimal procoagulant activity before relipidation in vitro. In pilot studies, Apo-TF injection into rabbits previously anticoagulated with an antibody to factor VIII was found to have a procoagulant effect. The efficacy of the material was further demonstrated when injection of Apo-TF in hemophilic dogs resulted in a normalization of the cuticle bleeding time. Little or no change in the blood parameters associated with disseminated intravascular coagulation was observed at lower doses, although mild to moderate effects were seen at higher doses. These data suggest a novel role for Apo-TF preparations as a potential therapeutic agent for hemophiliacs with antibodies to factor VIII once the potential thrombogenicity of such materials is evaluated.