Frequency of IFNγ-secreting CD8 and CD4 T cells in mice and macaques. Frequency of CD8 and CD4 T cells secreting IFNγ in response to stimulation with a gag peptide pool was assessed using Intracellular Staining (ICS) and FACS analysis in mice (A and B, CD8 and CD4, respectively) and macaques (C and D, CD8 and CD4, respectively). Each symbol corresponds to IFNγ+ CD8 or CD4 frequency in individual animals, expressed as the percentage of total CD8 or CD4. Horizontal line represents geometric mean.