A profound deficiency in thymic progenitor cells in mice lacking Jak3

Humans and mice with genetic deficiencies that lead to loss of signaling th rough common gamma-chain (gamma c)-containing cytokine receptors have sever e defects in B and T lymphocytes. In humans, these deficiencies lead to a c omplete absence of T cells, whereas in mice, small thymuses give rise to no rmal numbers of peripheral T cells. We have examined the first wave of deve loping T cells in Jak3(-/-), IL-7(-/-), mad IL-7R alpha(-/-) fetal mice, an d have found a near absence of thymic progenitor cells. This deficiency is highlighted by the complete inability of Jak3(-/-) progenitor cells to reco nstitute T cell development in the presence of competing wild-type cells. T hese data clearly demonstrate a strong common basis for the T cell deficien cies in mice and humans lacking gamma c/Jak3 signaling pathways.