• LY294002;
  • rapamycin;
  • cyclin D2;
  • phosphatidylinositol-3 kinase (PI3K);
  • immunosuppression;
  • T-cell proliferation;
  • interleukin-2 (IL-2)
  • 1
    T-cell proliferation is critical for mounting an effective adaptive immune response. It is regulated by signals through the T-cell receptor, through co-stimulation and through cytokines such as interleukin-2 (IL-2). Phosphatidylinositol 3-kinase (PI3K) lies downstream of each of these pathways and has been directly implicated in the regulation of lymphocyte proliferation.
  • 2
    In this study, we have shown that PI3K regulates cyclin D2 and cyclin D3, the first cell cycle proteins induced in T-cell proliferation, transcriptionally and post-transcriptionally. In T-lymphoblasts, LY294002, a PI3K inhibitor, prevents the induction of both D-type cyclin mRNA and protein, while rapamycin inhibits the induction of protein. Rapamycin inhibits mammalian target of rapamycin (mTOR), which lies downstream of PI3K.
  • 3
    Furthermore, our data show that the combination of LY294002 and rapamycin results in a co-operative inhibition of T-cell proliferation. This co-operation occurs in Kit225 cells stimulated with IL-2, and also in resting peripheral blood lymphocytes stimulated with antibodies to the T-cell receptor in the presence and absence of antibodies to CD28.
  • 4
    These data indicate that PI3K regulates T-cell proliferation in response to diverse stimuli, and suggest that combinations of inhibitors, perhaps isoform-selective, may be useful as alternative immunosuppressive therapies.

British Journal of Pharmacology (2005) 144, 791–800. doi:10.1038/sj.bjp.0706061