Experimental kinetic aspects of hollow fiber membrane-based pseudobioaffinity filtration: Process for IgG separation from human plasma

The pseudobiospecific affinity ligand L-histidine was immobilized through an ether linkage onto poly(ethylene vinyl alcohol) hollow fiber cartridge to obtain an affinity support for IgG purification or IgG removal from human plasma with a view to clinical apheresis for the treatment of immune disorders, alloimmunization and cancer. The kinetics and mass transfer aspects were studied in order to determine the optimum loading flow rate for IgG adsorption. Experiments were run at various filtrate flow rates (various residence times) in cross flow mode with recirculation of both the retentate and the permeate in the reservoir. The results showed that this affinity membrane had the potential of fractionating plasma proteins at fast flow rates (residence times below 10 s). However, protein trapping into the membrane was enhanced by residence times below 5 s. Comparison of equilibrium and dynamic maximum capacities determined using Langmuir isotherms showed that dynamic capacity (190 mu g/cm(2)) was somewhat higher than the equilibrium capacity (148 mu g/cm(2)). The dissociation constants for IgG were determined using the Langmuir isotherm equation to be 3.7 X 10(-6) M (dynamic mode) and 9.8 X 10(-6) M (equilibrium binding analysis), indicating medium affinity, which was typical for pseudobiospecific affinity ligands. The cartridge was loaded with human serum or human plasma to test its ability to fractionate these protein solutions. The affinity membrane showed high selectivity for IgG from two fold diluted human plasma or serum. IgM was also adsorbed to a certain extent. When the serum or plasma was not diluted with equilibration buffer before loading the cartridge, the amount of adsorbed proteins was significantly (50%) smaller than with the 2 or 10 fold dilutions, but the specificity remained.