IL-12 and IL-15 induction of cytotoxic activity and CD28⁻ CB CD8⁺ T cells.

CD8⁺ T cells freshly isolated from PB and CB were compared for cytotoxic activity against an EBV-transformed B-cell line by a standard ⁵¹Cr release assay (A). The reaction mixtures included anti-CD3 at 1 μg/mL for redirected antibody-dependent T cell–mediated cytotoxicity. Data are expressed as the percentage of specific lysis at the indicated effector-to-target cell ratios. Cytotoxic activity was driven largely by anti-CD3 because the percentage of specific lysis without anti-CD3 remains lower than 15% of that obtained with anti-CD3. Also, CD8⁺ T cells isolated from PB and CB were incubated with IL-12 (2 ng/mL) and IL-15 (10 ng/mL) for 5 days and used as effectors against the same targets (B). The CD8⁺ T cells cultured without (C) or with (D) IL-15 and IL-12 were then analyzed for surface expression of CD28 and 4-1BB by 2-color staining with anti-CD28–FITC and anti–4-1BB–PE. The numbers in the upper right corners of the plots represent the percentage of the cells in each quadrant. These results are representative of 3 experiments.