Fetal recipients of AAV8.GFP or AAV6.2.GFP underwent postnatal IM challenge with AAV1.GFP. Serum anti-GFP antibodies prior to challenge and weekly for 4 weeks post challenge were assessed by ELISA. Control animals received the postnatal challenge without IUGT. The control animal generated a robust humoral (IgG) immune response to GFP (I). In contrast, recipients of IUGT with AAV8.GFP (A) or AAV6.2.GFP (E) did not generate anti-GFP antibodies. Results from 3 weeks post challenge are shown. Similar results were seen on analysis at 1, 2 and 4 weeks (data not shown). At 6 months of age, GFP expression was assessed at the site of postnatal challenge in the hindlimb muscle; AAV8 (B,C,D), AAV6.2 (F,G,H) and control (J,K,L). All animals demonstrated GFP expression which was associated with a significant inflammatory cell influx in the control but not the recipients of IUGT. IHC, immunohistochemistry; H&E, hematoxylin and eosin.