EFFECTS OF IL-12 ON THE GENERATION OF CYTOTOXIC ACTIVITY IN HUMAN CD8-LYMPHOCYTES( T)

We have studied the effects of human rIL-12 on the proliferation and g eneration of cytotoxic activity in human CTL precursors. Purified huma n blood CD8+ T lymphocytes were stimulated overnight with immobilized alpha-CD3 and cultured 3 to 4 additional days under various conditions . The addition of IL-1 2 resulted in a marked (10- to 20-fold), dose-d ependent, augmentation of cytotoxicity per cell with a smaller (2-fold ) increase in cell number. IL-12 augmentation of proliferation and cyt otoxicity of CD8+ T cells was not inhibited by a mAb to the p55 subuni t of the IL-2 receptor (alpha-Tac) at a concentration sufficient to bl ock the activity of exogenously added IL-2, indicating that the activi ty of IL-12 did not require IL-2. Addition of IL-12 at the time of alp ha-CD3 activation or 1 day later was highly effective at augmenting cy totoxicity, whereas delayed addition of IL-12 (day 2 or 3) resulted in a smaller increase in CTL activity with no increase in cell number. I L-12 at all doses tested synergized with low dose IL-2 in inducing the proliferation and differentiation of CD8+ T cells. The synergistic ef fect was not blocked by adding neutralizing serum to IFN-gamma. In con trast to this synergistic effect, IL-1 2 significantly inhibited the p roliferation observed in the presence of higher concentrations of IL-2 (4,500 and 13,500 pg/ml). An inhibitory effect of IL-12 was also obse rved when IL-12 was added to CD8+ T lymphocytes 3 days subsequent to a ctivation with alpha-CD3 and IL-2. This broad set of potent effects of IL-12 on CD8+ T cell responses suggests that IL-12 may play an import ant immunoregulatory role on CTL development in vivo and may be a usef ul tool for manipulating this process in vivo for investigational and immunotherapeutic purposes.