Modulation of cord blood CD8+ T-cell effector differentiation by TGF-beta1 and 4-1BB costimulation.

Transforming growth factor-beta1 (TGF-beta1), an immunosuppressive cytokine, inhibits cytotoxic T cell (CTL) immune responses. In contrast, 4-1BB (CD137), a costimulatory molecule in the tumor necrosis factor (TNF) receptor family, amplifies CTL-mediated antitumor immune responses. We investigated whether TGF-beta1 responses could be reversed by 4-1BB costimulation during in vitro differentiation of naive CD8+ T cells into effector CTL cells. TGF-beta1 potently suppressed CTL differentiation of human cord blood naive CD8+ T cells as determined by reduced induction of characteristic phenotypes of effector cells and cytotoxic activity. TGF-beta1-mediated suppression of CTL differentiation was abrogated by 4-1BB costimulation but not by CD28 or another member in the TNF receptor family, CD30. 4-1BB costimulation suppressed Smad2 phosphorylation induced by TGF-beta1, suggesting that 4-1BB effects were at the level of TGF-beta1 signaling. 4-1BB effects on the TGF-beta1-mediated suppression were enhanced by interleukin 12 (IL-12) but counteracted by IL-4; 4-1BB expression was up- or down-regulated, respectively, by IL-12 and IL-4. IL-4 was more dominant than IL-12 when both cytokines were present during 4-1BB costimulation in the presence of TGF-beta1. This indicates critical roles for IL-4 and IL-12 in regulating 4-1BB effects on TGF-beta1-mediated suppression.