AAV6 and AAV8 pseudotypes escape neutralization more efficiently than AAV2 via portal vein delivery. Mean AAV2 neutralizing titers generated by IVIG in SCID mice (n = 5 per group) are as indicated for each group. At 24 hours after IVIG administration, 1 × 10¹¹ vg/mouse of AAV-hFIX with specified pseudotypes were delivered via the portal vein. hFIX expression was measured at 4 weeks. (A) Mean FIX levels (ng/mL) from each group. (B) Percent of mean FIX levels in IVIG-treated group compared with that in non–IVIG-treated controls. P values from Bonferroni post test in one-way ANOVA are listed above the columns. Error bars indicate SD in each group.