Selective precipitation-assisted recovery of immunoglobulins from bovine serum using controlled-fouling crossflow membrane microfiltration.

Efficient and economic recovery of immunoglobulins (Igs) from complex biological fluids such as serum, cell culture supernatant or fermentation cell lysate or supernatant, represents a substantial challenge in biotechnology. Methods such as protein A affinity chromatography and anion exchange chromatography are limited by cost and selectivity, respectively, while membrane chromatography is limited by low adsorptive area, flow distribution problems and scale-up difficulties. By combining the traditional salt-assisted precipitation process for selective removal of Igs from serum followed by constant-permeate flux membrane microfiltration for low fouling, we demonstrate an exciting new, efficient and economic hybrid method. The high selectivity of an ammonium sulfate-induced precipitation step was used to precipitate the Igs leaving the major undesirable impurity, the bovine serum albumin (BSA), in solution. Crossflow membrane microfiltration in diafiltration mode was then employed to retain the precipitate, while using axial flow rates to optimize removal of residual soluble BSA to the permeate. The selectivity between immunoglobulin G (IgG) and BSA obtained from the precipitation step was approximately 36, with 97% removal of the BSA with diafiltration in 5 diavolumes with resulting purity of the IgG of approximately 93% after the membrane microfiltration step. Complete resolubilization of the IgG was obtained without any aggregation at the concentrations of ammonium sulfate employed in this work. Further, membrane pore size and axial Reynolds number (recirculation rate) were shown to be important for minimizing fouling and loss of protein precipitate.