Patient cells were subjected to maximum mitogen stimulation or exposed to 2 µmol/l MRK 1, 40 µmol/l VPA, 2 µmol/l MRK 10 and 10 µmol/l MRK 11 for 24 h. Cells were washed and co-cultured with CD8-depleted PBMC as detailed in methods. Frequency of virus outgrowth from cells treated with HDACi was compared to the frequency of outgrowth from maximally stimulated cells (PHA). Each icon represents independent studies of patient cell samples; patient samples were simultaneously tested with mitogen or HDACi on the same day. Dashed lines indicate the limit of detection of the assay. HDAC, histone deacetylase; PBMC, peripheral blood mononuclear cell; VPA, valproic acid.