Interleukin 7 (IL-7) is a member of the Type I cytokine family that is critical for T and B cell development and survival. It is produced by non-hematopoietic cells in the thymus, lymphoid organs, and by bone marrow stromal cells (Lundström et al.). IL-7 binds to a receptor (IL-7R) composed of common gamma chain and IL-7Ra (CD127) and signals through the JAK/STAT and PI3K pathways. IL-7 regulates the survival of naïve and memory CD4+ and CD8+ T cells, γδ T cells, NK T cells, innate lymphoid cells, and T regulatory cells (Carrette and Surh). Although a deficiency in IL-7R still permits the generation of normal numbers of peripheral B cells in humans, stimulation of human B cell precursors with IL-7 could promote STAT-5-dependent proliferation and survival in vitro (Clark et al.; Corfe and Paige).