Immune responses to vaccinia virus after pretreatment with denileukin diftitox and vaccination with rV-Inf(A)NP34/TRICOM (+ rF-GM-CSF) in a foreign antigen system. C57BL/6 mice were subcutaneously vaccinated on day 0 with 5 × 10⁷ pfu rV-Inf(A)NP34/TRICOM (admixed with 10⁷ pfu rF-GM-CSF) and boosted on day 14 with 5 × 10⁷ pfu rF-Inf(A)NP34/TRICOM (admixed with 10⁷ pfu rF-GM-CSF) (vaccine alone). One group additionally received an intraperitoneal injection of 0.75 μg denileukin diftitox 1 day before the vaccine prime (vaccine + denileukin diftitox, day −1). Immune assays were performed on day 35, 3 weeks after the boost. Background-subtracted values are shown. (A) Mean CD4⁺ T-cell proliferation to the indicated concentrations of inactivated vaccinia virus (± SD) was assessed by ³H-thymidine uptake of triplicate wells. (B) Mean serum levels of antivaccinia IgG (± SD) were measured by ELISA.