Separation of immunoglobulin G precipitate from contaminating proteins using microfiltration

A small-scale stirred-cell device was used to separate an antivenom antibody precipitate from a suspension containing contaminating soluble proteins. The device has a total volume of 200 ml and is equipped with a filter membrane with a cut-off size of 3 (mu)m. About 90% of the antibody-precipitate particles in the feed were 29 (mu)m or smaller, and the concentration of solids was 12% (w/w). The microfiltration cell was operated in a constant-volume (continuous/diafiltration) mode, and its performance was compared with an industrial disc-stack centrifuge currently used in the manufacture of antibody precipitate. In terms of product purity, the separation performance of the microfiltration operation was found to be comparable with the disc-stack centrifuge, whereas the overall yield was 10% better than that obtained from the centrifuge. This was attributed to the ability of microfiltration to reduce material losses by integrating a number of operations in a single piece of equipment. These included separation, concentration and buffer exchange, as well as dissolution and final recovery of the antibody in an appropriate buffer. The results obtained from the stirred cell are potentially scaleable, and dynamic microfiltration is shown to be an attractive process option.