Inhibition of cell cycle progression by rapamycin induces T cell clonal anergy even in the presence of costimulation

Costimulation (signal 2) has been proposed to inhibit the induction of T ce ll clonal anergy by either directly antagonizing negative signals arising f rom TCR engagement (signal 1) or by synergizing with signal 1 to produce IL -2, which in turn leads to proliferation and dilution of negative regulator y factors. To better define the cellular events that lead to the induction of anergy, we used the immunosuppressive agent rapamycin, which blocks T ce ll proliferation in late G1 phase but does not affect costimulation-depende nt IL-2 production. Our data demonstrate that full T cell activation (signa l 1 plus 2) in the presence of rapamycin results in profound T cell anergy, despite the fact that these cells produce copious amounts of IL-2, Similar to conventional anergy (induction by signal 1 alone), the rapamycin-induce d anergic cells show a decrease in mitogen-activated protein kinase activat ion, and these cells can be rescued by culture in IL-2, Interestingly, the rapamycin-induced anergic cells display a more profound block in IL-3 and I FN-gamma production upon rechallenge. Finally, in contrast to rapamycin, fu ll T cell activation in the presence of hydroxyurea (which inhibits the cel l cycle in early S phase) did not result in anergy, These data suggest that it is neither the direct effect of costimulation nor the subsequent T cell proliferation that prevents anergy induction, but rather the biochemical e vents that occur upon progression through the cell cycle from G1 into S pha se.