Phenotypic and genotypic characterization of monoclonal anti-digoxin antibodies

Immunological characteristics associated with the protective efficacy of antibodies to ricin

A/B toxins, produced by bacteria and plants, are among the deadliest molecules known. The B chain binds the cell, whereas the A chain exerts the toxic effect. Both anti-A chain and anti-B chain Abs can neutralize toxins in vivo and in vitro. B chain Abs block binding of the toxin to the cell. It is not known how anti-A chain Abs function. Working with ricin toxin, we demonstrate that immunization with A chain induces greater protection than immunization with B chain. A panel of mAbs, binding to A chain, B chain, or both chains, has been produced and characterized. Immunologic characteristics evaluated include isotype, relative avidity, and epitope specificity. The ability to inhibit ricin enzymatic or cell binding activity was studied, as was the ability to block ricin-mediated cellular cytotoxicity on human and murine cell lines. Finally, the in vivo protective efficacy of the Abs in mice was studied. The Ab providing the greatest in vivo protective efficacy was directed against the A chain. It had the greatest relative avidity and the greatest ability to block enzymatic function and neutralize cytotoxicity. Interestingly, we also obtained an anti-A chain Ab that bound with high avidity, blocked enzymatic activity, did not neutralize cytotoxicity, and actually enhanced the in vivo toxicity of ricin. Anti-A chain Abs with moderate avidity had no in vivo effect, nor did any anti-B chain Abs.

Preparation and characterization of monoclonal antibody against digoxin

Mouse-mouse hybridoma cell lines producing stable, highly specific and with good affinity monoclonal antibody (MAb) against the cardiac glycoside digoxin were established. Balb/c mice were immunized via injection of digoxin-3'-bovine serum albumin (BSA). The spleens of which were fused with myeloma cells of SP2/0 origin. Three clones designated as BBA, MBE, and BMG producing good antibodies displayed different patterns of fine specificity for digoxin and low cross-reaction with several digoxin analogues as elucidated by inhibition enzyme-linked immunosorbant assay (ELISA). All three MAbs were of the same class and subclass (IgG(1)). Affinity purification was performed for the selected clone BBA displaying the highest affinity and nearly no cross-reactivity with any of the structurally related molecules. Ultrafiltered concentrated hybrid cell supernatant was also purified by polyethylene glycol (PEG) 6000 precipitation for large-scale preparation and coated onto the wells of microtiter plates. The standard curve was constructed with a sensitivity of 10 pg/well covering up to 10 ng/well.

Association constants of monoclonal antibodies for hapten: heterogeneity of frequency distribution and possible relationship with hapten molecular weight

Using published data, we have investigated the relationship of the association constant (Ka) of 265 MAbs for haptens with molecular weights ranging from 111 to 1202 Da. The study indicates that: (1) differences of a factor 10(3)-10(5) are frequently found between the lowest and the highest value of Ka for the same hapten; (2) the relationship between log Ka and the hapten molecular weight of either the native drug or the molecular entity used for the Ka determination is described by a hyperbolic function; (3) beyond a critical molecular weight of approximately 300-325 Da, the log Ka reaches a plateau at a maximal value near 10(-12) M-1.

Monoclonal antibodies in hapten immunoassays

This review deals with the potency of monoclonal antibodies (MAbs) to haptens in immunoassays. Specificity and affinity of MAbs to haptens are the major determinants to be considered. Specificity of MAbs depends on the selection of the hapten coupling site to the carrier protein and the antigen used for the screening of MAbs. Nevertheless, cross-reactivity can occur with compounds related to the hapten. This polyspecificity may be circumvented with the use of many MAbs, as has been demonstrated for MAbs to cyclosporine. Affinity of MAbs to haptens is often lower than that of corresponding polyclonal antibodies (PAbs), thereby limiting assay sensitivity. Low affinity is more frequently observed with low molecular weight (100-300) haptens than with larger haptens, such as digoxin or cyclosporine. Affinity enhancement by increasing resemblance to the immunogen can be effective in resolving the lack of sensitivity. With suitable selection strategies. MAbs exhibit real advantages over classical PAbs to haptens because large amounts of worldwide standardized reagents can be prepared.

Generation of monoclonal anti-digoxin antibodies

Anti-digoxin monoclonal antibodies are a useful model for basic immunochemical studies, for investigation of endogenous digoxin-like substances and in immunoassay for cardiac glycosides. The complete phenotypic characterization is a requisite for the selection of antibodies with desired binding parameters for different purposes. Twenty-two high-affinity monoclonal antibodies specific for digoxin were obtained in two fusion experiments. Treatment of antigen-antibody complex with potassium thiocyanate (KSCN) and absorption ELISA were used for the selection of high-affinity antibodies at the earliest stages of hybridoma growth. The true affinity constants of selected antibodies were determined in ELISA. They had proven to vary between 10(-7) and 10(-10) M. The fine specificity of 21 anti-digoxin monoclonal antibodies was determined by cross-reactivity experiments with 25 structurally related compounds. Cardiac glycosides, digoxin metabolites, endogenous steroids and spironolactone were used in the elucidation of the antigenic recognition pattern of antibodies. The elucidation of the binding characteristics of anti-digoxin monoclonal antibodies makes possible the selection of antibodies possessing binding characteristics appropriate for a wide range of designations.

Removal of digoxin from the circulation using immobilized monoclonal antibodies

High-affinity (Ka = 3.0 X 10(8) M-1) monoclonal antidigoxin antibodies were covalently coupled to Sepharose CL-6B, Bio Gel A5m, Affi-gel 15, and agarose:polyacrolein microsphere (APAM) beads. Antibody immobilized to these supports was characterized in its ability to remove digoxin in vitro from biological fluids. Equilibrium binding studies of digoxin in plasma revealed that antibody coupled to Sepharose, Bio Gel, and Affi-gel 15 retained 38-42% of theoretical binding capacity, whereas antibody coupled to APAM beads retained only 13%. Increasing flow rates from 0.5 to 5.0 mL/min across antibody immobilized to APAM beads decreased the removal of digoxin from plasma from 90 to 55%. In comparison, no decreases were observed in the amount of digoxin removed from plasma as the flow rates were increased across antibody immobilized to the other agarose supports. Antibody coupled to Affi-gel 15 was used for in vivo extracorporeal hemoperfusion studies. These studies indicated that although 5-20% of the total dose was removed from three guinea pigs, plasma digoxin levels were not lowered when compared with preperfusion concentrations. In addition, antibody columns which were reused following regeneration with glycine:HCl, pH 2.5 revealed that 80% of the original antibody activity was lost after two hemoperfusions. Hematological parameters were unchanged with the exception that platelets were significantly decreased following the 3-h perfusion study. These data indicate that immobilized antidigoxin antibodies were able to remove digoxin from the circulation, and immunoaffinity hemoperfusion may be a viable means of removing substances from blood.

Immunological approach to poisoning

The use of antibodies in the diagnosis and treatment of drug poisoning is becoming an important aspect of emergency medicine. Digoxin-specific antibodies selectively inhibit the pharmacologic and toxic effects of the digitalis glycosides. Digoxin-specific Fab fragments rapidly reverse digitalis toxicity in animals and man. Furthermore, these Fab fragments are eliminated in the urine and are less immunogenic than whole antibodies. Anti-digoxin Fab fragments have been approved by the Food and Drug Administration for the treatment of digitalis intoxication. Alternative ways of using antidrug antibodies in the treatment of poisoning are being explored. Studies that demonstrate that antidrug antibodies immobilized on solid matrices remain functional have been conducted. Such immobilized antidrug antibodies are being evaluated for their ability to remove drugs from the circulation by extracorporeal perfusion. These areas of research promise to provide significant advances in the treatment of poisoning.