Effects of capsid-specific CD8⁺ T cells on hF.IX expression from an AAV8 vector. In vitro expanded capsid-specific, L^d-restricted CD8⁺ T cells (cap-CD8) isolated from BALB/c mice were adoptively transferred by tail vein injection into Rag-1 ^−/− BALB/c mice after administration of AAV8-ApoE/hAAT-hF.IX vector (1 × 10¹¹ vg per mouse; n = 4 per experimental group). Cells were given 1 day (A-B) or 1 day, 7 days, or 14 days (C-D) after vector administration. (A,C) Systemic hF.IX expression. (B) Percent hF.IX⁺ hepatocytes 4 weeks after gene transfer. Statistically significant differences to the control group: *P < .05; **P < .01; ***P < .001. (D) Percent hF.IX⁺ hepatocytes 6 weeks after gene transfer. (E) Immunostains for hF.IX and CD8⁺ T cells 1 and 6 weeks after cap-CD8 T-cell administration to mice that had received AAV8 vector 7 days prior. Analyses were performed as for Figure 1.