Figure 1. The preimmunization repertoire of Env-specific memory CD4⁺ T cells.

Preimmunization repertoires of 20 donors were screened for Env reactivity using the T cell library method with 2 pools of overlapping peptides collectively spanning the entire consensus sequence protein (ConS). Positive control wells included phytohemagglutinin (PHA) and IL-2. Proliferative responses are shown for memory CD4⁺ T cells isolated from all 20 volunteers before vaccination (V2). Data are shown after background subtraction (mean ± SD). Positive responses were defined as greater than 3,000 cpm, with a stimulation index greater than 5 (dotted line).