title: Effects of IL-12 on the generation of cytotoxic activity in human CD8+ T lymphocytes.
abstract: We have studied the effects of human rIL-12 on the proliferation and generation of cytotoxic activity in human CTL precursors. Purified human 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-12 resulted in a marked (10- to 20-fold), dose-dependent, augmentation of cytotoxicity per cell with a smaller (2-fold) increase in cell number. IL-12 augmentation of proliferation and cytotoxicity of CD8+ T cells was not inhibited by a mAb to the p55 subunit of the IL-2 receptor (alpha-Tac) at a concentration sufficient to block the activity of exogenously added IL-2, indicating that the activity of IL-12 did not require IL-2. Addition of IL-12 at the time of alpha-CD3 activation or 1 day later was highly effective at augmenting cytotoxicity, whereas delayed addition of IL-12 (day 2 or 3) resulted in a smaller increase in CTL activity with no increase in cell number. IL-12 at all doses tested synergized with low dose IL-2 in inducing the proliferation and differentiation of CD8+ T cells. The synergistic effect was not blocked by adding neutralizing serum to IFN-gamma. In contrast to this synergistic effect, IL-12 significantly inhibited the proliferation 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 observed when IL-12 was added to CD8+ T lymphocytes 3 days subsequent to activation 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 important immunoregulatory role on CTL development in vivo and may be a useful tool for manipulating this process in vivo for investigational and immunotherapeutic purposes.
authors.affiliation: Laboratory of Cellular Immunology, Food and Drug Administration, Bethesda, MD 20892.
authors.forename: P T
authors.initials: PT
authors.lastname: Mehrotra
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: J A
authors.initials: JA
authors.lastname: Crim
authors.forename: H S
authors.initials: HS
authors.lastname: Mostowski
authors.forename: J P
authors.initials: JP
authors.lastname: Siegel
mesh_terms: D016827:CD8 Antigens / Q000032:analysis*; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D004357:Drug Synergism; D006801:Humans; D018664:Interleukin-12; D007376:Interleukin-2 / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology; D007378:Interleukins / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects; D011994:Recombinant Proteins / Q000494:pharmacology; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology*
chemical_list: D016827:CD8 Antigens; D007376:Interleukin-2; D007378:Interleukins; D011994:Recombinant Proteins; D018664:Interleukin-12; D015847:Interleukin-4