Adoptive transfer of splenocytes from hemophilia B C3H/HeJ mice, which had received intranasal administration of peptide 2A-54 and hepatic AAV-hF.IX gene transfer (□). Recipients were naive wild-type C3H/HeJ mice, and controls (▴) received splenocytes from other naive wild-type C3H/HeJ mice. All recipients were immunized with hF.IX in cFA 36 hours after adoptive transfer. Shown are average anti-hF.IX IgG titers ± SD for cohorts of mice that had received CD4^–, CD4⁺, CD4⁺CD25⁺, or CD4⁺CD25^– cells (2.5 weeks after immunization, n = 4-5 per experimental cohort).P values are indicated.