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Recovery of Immunoglobulins from Bovine Serum through a Combination of Selective Precipitation and Crossflow Microfiltration

Georges Belfort and Adith Venkiteshwaran. Chemical and Biological Engineering, Rensselaer Polytechnic Institute (RPI), 110 8th St., Troy, NY 12180

A large proportion of protein therapeutics in the product pipelines of biotechnology firms are monoclonal antibodies (IgG). The high binding specificity of protein A affinity ligands for monoclonal antibodies is usually exploited in their downstream recovery. However, high costs associated with these ligands, along with requirements such as high pH for cleaning and problems involved with leaching of the ligand from the column, have prompted the development of alternative strategies for selective monoclonal antibody separation. Exploiting physicochemical properties with synthetic membrane processes to recover IgG from bovine serum has not proved very successful. As a result we have developed a novel method to selectively recover IgG from bovine serum. The key steps involve the selective precipitation of IgG, by addition of an optimum amount of ammonium sulfate, combined with crossflow membrane microfiltration to retain the precipitate and remove the undesirable soluble bovine serum albumin (BSA). High transmission of the soluble BSA was obtained with minimal fouling of the 0.1 micron hydrophilized poly(vinylidene flouride) (PVDF) membrane with retention of all the IgG. A subsequent diafiltration step resulted in the removal of about 97% of the BSA, and a yield and purity of 88% and 87%, respectively, for the IgG. The effects of wall-shear rate and membrane pore-size on the filtration of the above precipitate-containing feed were also investigated in total recycle mode to obtain a further understanding of the behavior of the system. The higher membrane pore-size resulted in higher concentration polarization and fouling due to the loss of precipitate particles within the membrane pores.