Column-purified AAV2-hFIX escapes neutralization more efficiently than CsCl-purified vector. SCID mice without or with IVIG treatment received injections via the portal vein of 1 × 10¹¹ vg/mouse column- or CsCl-purified AAV2-hFIX. The column-purified vector has a ratio of total particles to genome-containing particles of 12:1, whereas the CsCl vector preparation contains only full vectors. FIX levels were measured 4 weeks after vector injection. P value from unpaired 2-tailed t test is shown above the bar.