Phosphoinositide-dependent kinase l (PDK1) haplo-insufficiency inhibits production of alpha/beta (alpha/beta) but not gamma delta (gamma/delta) T lymphocytes

In the present study, we have explored the impact of deleting a single allele of PDK1 in T cell progenitors on alpha/beta and gamma/delta T cell development. The data show that deleting a single allele of PDK1 allows differentiation of alpha/beta T cells but prevents their proliferative expansion in the thymus. Accordingly, mice with T cells that are haplo-insufficient for PDK1 have reduced numbers of thymocytes and alpha/beta peripheral T cells. T cell progenitors also give rise to gamma/delta T cells but in contrast to the loss of alpha/beta T cells in T-PDK1 null and haplo-insufficient mice, there were increased numbers of gamma/delta T cells. The production of alpha/beta T cells is dependent on the proliferative expansion of thymocytes and is determined by a balance between the frequency with which cells enter the proliferative phase of the cell cycle and rates of cell death. Herein, we show that PDK1 haplo-insufficient thymocytes have no defects in their ability to enter the cell cycle but show increased apoptosis. PDK1 thus plays a determining role in the development of alpha/beta T lymphocytes but does not limit gamma/delta T cell development.