Removal of serine proteases by treatment with finely divided silicon dioxide

A method for preparing an Immunoglobulin G (IgG) composition having a reduced amount of a serine protease or a serine protease zymogen, the method comprising the steps of:

• (a) precipitating a cryo-poor plasma fraction, in a first precipitation step, with from about 6% to about 10% alcohol at a pH of from about 7.0 to 7.5 to obtain a first precipitate and a first supernatant;
• (b) precipitating IgG from the first supernatant, in a second precipitation step, with from about 23% to about 27% alcohol at a pH of from about 6.7 to about 7.3 to form a second precipitate;
• (c) suspending the second precipitate to form a first suspension;
• (d) contacting the first suspension with from about 0.02 grams fumed silica per gram precipitate formed in step (b) to about 0.06 grams fumed silica per gram precipitate formed in step (b) under a solution condition suitable to bind a serine protease or serine protease zymogen;
• and
• (e) separating the fumed silica from the first suspension to form a clarified suspension by:
• (i) filtering the suspension through a filter press to form a clarified suspension;
• (ii) washing the filter press with at least 3 filter press dead volumes of a wash buffer, thereby forming a wash solution;
• and
• (iii) combining the clarified suspension formed in sub-step (i) with the wash solution formed in sub-step (ii), thereby forming an enriched IgG composition.