CD4⁺CD28^– T cells are class II–restricted cytotoxic CMV-specific T cells. (A) Dot plots gated on either CD4⁺ T cells (left column) or CD8⁺ T cells (right column) show intracellular cytokine staining for IFNγ in unstimulated cells (medium), cells stimulated with CMV Ag (for CD4⁺ T cells), or CMV peptide (for CD8⁺ T cells), with a control autologous LCL, or with an autologous LCL transduced with a pp65 construct. SEB is the positive control. Numbers indicate the percentage of CD69⁺ IFNγ⁺ cells within total CD4⁺ or CD8⁺ T cells, respectively. (B) Dot plots gated on either total CD4⁺ lymphocytes, CD4⁺CD28^– cells, or CD4⁺CD28⁺ cells (from left to right) show intracellular cytokine staining for IFNγ in unstimulated cells (medium), cells stimulated with autologous LCLs loaded with CMV Ag, LCLs loaded with a CMV HLA-DR4–restricted peptide, or with SEB as a positive control. Numbers indicate the percentage of CD69⁺ IFNγ⁺ cells within the population shown. (C) Graph shows the percentage of specific lysis measured in a ⁵¹Cr-release assay of total PBMCs using either CMV Ag or CMV HLA-DR4–restricted peptide–loaded autologous LCLs as target cells. The second bar shows the percentage of lysis of CMV Ag–loaded autologous LCLs in the presence of a class II–blocking antibody.