Acid precipitation of mammalian cell fermentation broth.

The broth harvested from the "fermentation" of mammalian cells contains many contaminants produced by the cells, including nucleic acids, proteins, and complex polysaccharides, in addition to the product. These contaminants can foul filtration membranes, precipitate during storage or processing steps, and interfere with the performance of chromatographic separations. Acidification of hybridoma cell fermentation broth at the time of harvest from the fermenter has been investigated as a method of selectively precipitating the major contaminants from the soluble antibody product. Between pH values of 6.0 and 4.5, precipitation of the major contaminants is rapid and independent of the temperature (4-37 degrees C), with less than 10% of the antibody coprecipitating in 4 of 5 cases. Antibody activity and physical characteristics were found to be unaltered above a pH of 3.8. Recovery of antibody at the stage of concentrated (50 x), diafiltered bulk was improved from 63% to 84% by using the acid precipitation step. An additional benefit is that retrovirus is effectively inactivated by incubation at a pH below 4.2.