Cutting Edge: p27 Kip1 Deficiency Reduces the Requirement for CD28-Mediated Costimulation in Naive CD8+ but Not CD4+ T Lymphocytes

Abstract

Cell cycle re-entry of quiescent T cells is dependent upon cyclin-dependent kinase 2. Inhibition of cyclin-dependent kinase 2 by p27Kip1 is believed to be the principal constraint on S-phase entry in T cells. We report that deficiency for p27Kip1 has a more pronounced effect on the expansion of murine naive CD8+ T cells and that this disparity is due to a reduced requirement for CD28-mediated costimulation in CD8+ but not CD4+ T cells lacking p27Kip1. These data highlight a previously unappreciated difference in the way CD28 signaling is coupled to the core cell cycle machinery in these two T cell subsets.