In vitro human CD4+ and CD8+ T cell clones, or mouse CD4+ T cells that produce both interferon-γ (IFN-γ) and IL-10, can be differentiated by T cell receptor (TCR)-stimulation in the presence of IL-12 (Chang et al., 2007; Gerosa et al., 1996; Jeannin et al., 1996; Meyaard et al., 1996; Windhagen et al., 1996).