Low-speed centrifugation of retroviral vectors absorbed to a particulate substrate: a highly effective means of enhancing retroviral titre

For many gene therapy applications the effective titre of retroviral vector s is a limiting factor both in vitro and in vivo. Purification and concentr ation of retrovirus from packaging cell supernatant can overcome this probl em. To this end we have investigated a novel procedure which involves compl exing retrovirus to a dense and particulate substrate followed by a short l ow-speed centrifugation. The study reported here uses heat-killed formaldeh yde fixed Staphylococcus aureus (Pansorbin) absorbed to PG13 derived retrov irus. This complex was then used to harvest retrovirus from packaging cell supernatant: centrifugation and washing of this complex allows the retrovir us to be both purified and concentrated This procedure increases the effect ive titre of retrovirus by up to 7500-fold after an only 200-fold reduction in volume. The affinity of Pansorbin for retrovirus allows concentration r egardless of its encoded genes and makes this protocol applicable to other popular packaging cells and envelope proteins. Possible explanations for th e marked increase in titre of concentrated virus and the mechanism governin g the complexing of retrovirus to Pansorbin are discussed.