Loss of Gag-specific IL-2⁺ central memory and IFNγ⁺ effector memory CD4⁺ T cells during progression to AIDS. Cytokine⁺ CD4⁺ T cells were assessed for surface expression of CD27 and CD45RO in 6 LTAs and 7 progressors both early and late in infection. Within the lymphocyte gate, CD3 was plotted against CD4. Next, the CD4⁺CD3⁺ T cells were gated. Within the CD4 gate, CD27 was plotted against CD45RO. Then the Cm population (CD27⁺CD45RO⁺) and the Em population (CD27^-CD45RO⁺) were selected and within each gate the specific IFNγ⁺ or IL-2⁺CD4⁺ T cells were determined. Gag-specific IFNγ⁺ Tem cells (A) and Gag-specific IL-2⁺ Tcm CD4⁺ T cells (C) are shown, as well as the percentage of CMV-specific IFNγ⁺ Tem cells (B) and IL-2⁺ Tcm cells (D). Naive cells and the terminally differentiated cells were excluded from the analyses because only very low levels of cytokine production were observed in the naive population, and the population of Td cells was too small to be reliably phenotyped. Results are depicted as the median fraction together with the 25th to 75th percentile. ▪ indicates LTAs; □, progressors.