Ammonium sulphate precipitation of recombinant adenovirus from culture medium: an easy method to increase the fetal virus yield

In the majority of the methods for purifying and concentrating recombinant adenoviruses (rAds) the virus that is associated with the helper cells is h arvested, while the virus that is present in the cell-culture medium is dis carded. During routine propagation of adenovirus type-5 vectors at optimise d conditions we noted that, on average, 47% of the fetal amount of virus is present in the culture medium. To recover and concentrate these rAds from the medium, we devised a method which is based on ammonium sulphate ((NH,), SO,) precipitation. At 40% (NH4)(2)SO4 saturation, 95 +/- 6% of the availab le virus precipitates from the medium, while the majority of the protein (8 5%) remains in solution. In contrast to adenovirus precipitation with polye thylene glycol, the (NH4)(2)SO4 precipitation technique allows collection o f precipitated rAds by filtration. We demonstrate here that (NH4)(2)SO4 pre cipitation of rAds from cell-culture medium is a simple and fast technique that can be used in combination with standard virus isolation methods to in crease the yields of rAds.