STI-571–treated APCs restore the responsiveness of tolerant CD4⁺ T cells from tumor-bearing mice. PEMs (1 × 10⁵/well) or BM-derived DCs (1 × 10⁴/well) from BALB/c mice were treated as in Figure 1 and then cultured with 5 × 10⁴ T cells isolated from the spleen of A20HA-bearing mice, in the presence or not of 12.5 μg HA peptide_110-120. After 48 hours, supernatants were collected, and IL-2 and IFN-gamma production by clonotype-positive T cells in response to HA-peptide presented by either PEMs (A-B) or BM-derived DCs (C-D) was determined by ELISA. Data represent mean ± SE of triplicate cultures and are expressed as the amount of cytokines produced per 100 clonotype⁺ T cells/well. Shown is a representative experiment of 4 independent experiments with similar results (*P statistically significant for the difference in cytokine production between treatment with LPS + STI-571 and LPS alone).