Lentivirus coated with VSV-G may be concentrated using multiple rounds of centrifugation. A. Titration of shRNA lentivirus following concentration by one round versus four rounds of centrifugation. Flow cytometry dot plots show the transduction rates following transduction with 5 μL of concentrated lentiviral stock, 50 μL of unconcentrated viral supernatant or 100 μL of supernatant that was decanted following a round of centrifugation. B. The increase in viral titres (bars) following successive rounds of centrifugation is additive as shown by the fold change relative to one round of centrifugation (diamonds). C. Lentiviral particles that are concentrated using multiple rounds of centrifugation are able to transduce primary mouse bone marrow cells.