Memory cells can be reactivated by tumor cells in vitro but do not eradicate tumors in C5–hosts without DC reactivation. (A) IL-2 secretion by memory CD4 A18 T cells after stimulation with untransfected (▪), C5-transfected (•), or C5 peptide-pulsed (▴) LK35 tumor cells. The figure shows T-cell activation as assessed by proliferation of triplicate cultures of IL-2—dependent CTLL cells using an alamar blue—based assay. (B) Percentage of tumor-free mice following inoculation with C5-transfected LK35 tumor cells (5 × 105) for groups of mice lacking T cells (•), with DC-reactivated effector CD4 T cells (•), or with memory CD4 T cells (▴). Symbols represent individual data for groups of 5 mice. All memory or effector T cells were derived from mice that had been injected with naive A18 TCR transgenic T cells and syngeneic DCs.
