The invention provides new methods for purifying and concentrating viruses. The
inventors have discovered that high molecular weight proteoglycans present in retroviral
stocks are co-concentrated with the retroviruses, and can inhibit retroviral transduction.
The new purification and concentration methods feature treatment of virus stock
with an anionic polyelectrolyte and a cationic polyelectrolyte, followed by centrifugation.
The new methods minimize the amount of proteoglycan co-precipitated with the infectious virus.
