Frequency of regulatory T cells in spleen and lymph nodes. (A-B) Male C57BL/6 mice (n = 5) injected with 1 × 10⁹ vg of exo- or standard AAV8-hF.IX and euthanized 2 weeks later. (A) Representative flow cytometry plot showing the frequency of CD25⁺FoxP3⁺ Tregs gated on CD3⁺CD4⁺ T cells. (B) Frequency of Tregs in spleens and inguinal lymph nodes. (C-D) Analysis of frequency of Tregs in male C57BL/6 mice (n = 5 per group) treated with 1 × 10⁹ vg of exo- or standard AAV5-hF.IX and euthanized 28 days later. Data are shown as mean ± SEM. *P < .05, **P < .01; Mann-Whitney U test.