Intracellular cytokine staining assay. CD4⁺ T-cell responses to Gag Consensus (Con) B peptides. The percentage of CD4⁺ T cells expressing interleukin (IL)-2 or interferon (IFN)-γ (A) or expressing CD40 ligand (CD154) (B), in response to Gag Con B peptide pools. Human immunodeficiency virus-1-specific CD4⁺ and CD8⁺ T-cell responses were measured using a validated Intracellular cytokine staining assay. Results shown are from samples obtained 2 weeks after the prime (d14) and 2 weeks after boost vaccination (d70) for each treatment group. Responders are shown as red dots, and nonresponders are shown as blue triangles. Box plots show the distribution of the magnitude of response in positive responders only. The box indicates the median and interquartile range (IQR); whiskers extend to the furthest point within 1.5 times the IQR from the upper or lower quartile. Numbers at the top of each panel show the number and percentage of responders from each group. One Group 4 participant had a CD8⁺ T-cell response to Gag Con B at day 14 (data not shown). Abbreviations: T1, 4.6 × 10³ PFU; T2, 4.6 × 10⁴ PFU; T3, 4.8 × 10⁵ PFU; T4, 4.2 × 10⁶ PFU; and T5, 3.4 × 10⁷ PFU. d, day; PFU, particle-forming units.