Antigen-specific T-cell memory. (A-B) CD4 memory responses to VZV (middle) or TT (right) antigens or in control conditions (left) for a representative healthy donor (A) or patient with ALL (B). Gates represent proliferating/activated CD4 cells and percentages in gates are indicated on the dot plots. HLA-DR indicates human leukocyte antigen-DR. (C-D) CD4 response (percentage of CD4⁺ T cells proliferating) in patients with ALL (n = 10) or healthy children (n = 10) to VZV antigen (C) or TT (D). Error bars represent standard error of the mean.