Effect of 4-1BB costimulation on the generation of a cytotoxic effector cell population derived from CB CD8⁺ T cells.

Costimulation by 4-1BB results in the generation of a highly cytotoxic effector-cell population derived from CB CD8⁺ T cells. CB CD8⁺ T cells were cultured with IL-15 and IL-12 for 5 days. The cells were then stimulated for 3 days in plates precoated with anti-CD28 (or control IgG) and anti–4-1BB plus anti-CD3 and analyzed for cell surface levels of CD28 and CD8 by FACS. Cells were divided into 3 subsets—I, II, and III—on the basis of the intensity of staining for CD28 and CD8 (A). The percentages shown in the dot plots represent the proportion of the cells in subset III. These results are representative of 6 experiments. Cells from subsets I, II, and III were separated by cell sorting and used as effectors in a standard⁵¹Cr release assay with EBV-transformed B cells as target cells at the indicated effector-to-target cell ratios (B). The reaction mixtures included anti-CD3 at 1 μg/mL for redirected antibody-dependent T-cell–mediated cytotoxicity. The data are displayed as the percentage of specific lysis. These results are representative of 3 experiments.