Real time analysis of antibody-antigen reaction kinetics.

Surface plasmon resonance, i.e. detection of changes in refractive index on a surface, was used in a biosensor to evaluate the dissociation/association rate and affinity constants of human monoclonal IgG and IgM antibodies and Fab fragments. The results showed that an observed difference in affinity constants between intact and fragmented IgG anti-tetanus antibody was related to approximately 10-fold differences in dissociation rate constants, since the association rate constants were in the same range, i.e. 2-3 x 10(5) (M-1 s-1). Affinity constants, as determined by conventional solid phase enzyme immunoassay, were substantially higher than the constants produced by the biosensor. Human monoclonal IgM anti-Tn alpha antibodies showed, furthermore, one order of magnitude higher association rate constants, as compared with the IgG antibodies, but since the dissociation rate constants were more than ten times higher, the resulting affinity constants of the anti-carbohydrate IgM antibodies were still somewhat lower than those of the IgG antibodies.

Kinetic analysis of recombinant antibody-antigen interactions: relation between structural domains and antigen binding.

The relation between domain structures of recombinant monoclonal antibody fragments and their reaction kinetics was studied for the first time using a novel biosensor based on surface plasmon resonance technology. The association and dissociation rate constants of Fab, Fv and single domain (VH fragment) anti-lysozyme antibodies were determined and compared to the intact monoclonal antibody. Fab and Fv fragments showed similar reaction kinetics and had affinity constants of 6 x 10(9) M-1 and 25 x 10(9) M-1, respectively. The single domain antibody had significantly different reaction kinetics compared to the fragments consisting of paired heavy and light chain domains. The VH domain had both a higher dissociation and a lower association rate constant, which resulted in an affinity constant approximately 250 times lower than the Fab fragment. This rapid evaluation of antibody reaction kinetics should prove to be an important selection parameter when comparing antibody fragments for their utility in therapeutic or other applications.

Kinetic analysis of monoclonal antibody-antigen interactions with a new biosensor based analytical system.

An automated biosensor system for measuring molecular interactions has been used to study the kinetics of monoclonal antibody-antigen reactions. The system combines a microfluidic unit in contact with a sensor surface for surface plasmon resonance detection. The specificity of the surface is determined by the operator. Antibody or antigen is immobilised in a dextran matrix attached to the sensor surface. The interaction of matrix bound antibody or antigen with the corresponding partner in solution is monitored in real time. None of the interacting molecules needs to be labelled and it is not necessary to determine the concentration of the the matrix bound component in advance. Two systems were studied: matrix bound monoclonal antibodies (MAbs) interacting with HIV-1 core protein p24 and immobilised aminotheophylline reacting with MAbs. Control of the amount of immobilised ligand and reusable sensor surfaces permits the comparison of different MAbs reacting with antigen under almost identical conditions. Differences in affinity and reaction rates are immediately apparent. The calculated association rate constants for p24 MAbs ranged from 3 x 10(4) - 7.4 x 10(5) M-1 s-1 and for theophylline MAbs association rate constants as high as 1 x 10(6) M-1 s-1 were encountered. The calculated dissociation rate constants were in the region 2 x 10(-4) s-1 to 2 x 10(-2) s-1.