Proliferative ability of immunization induced CD8⁺ T cells. PBMCs from 3 patients with melanoma underwent in vitro sensitization (IVS) with 1 μM 209-2M followed by a 7-day culture in IL-2 (300 IU/mL). The top panel shows the proportional expansion of tHLA⁺ T cells during IVS. The numbers in the histograms, as gated by the horizontal bars, represent the Tc-pf as percent of tHLA⁺ over CD8⁺CD3⁺ T cells. The rows depict the proliferative capacity of the same samples under usual IVS conditions (IL-2 + 209-2M), or when only antigen recall (209-2M), IL-2, or neither (no stimulation) was applied. Proliferation is presented as decreases in CFSE fluorescence proportional to number of cell divisions.