Interleukin (IL)-7 is a cytokine that plays a central role in the development, survival, and proliferation of T and B cell lymphocytes. Overexpression of IL-7 in mice (transgenic (Tg) IL-7) leads to both increased proliferation of early T and B cell progenitors and T and B cell lymphomas. Genetic evidence indicates that known IL-7 receptor (IL-7R)-dependent proteins, including prosurvival protein BCL-2, may not be solely responsible for the effects of IL-7. Other studies indicate that known IL-7-induced signaling proteins dock to a specific tyrosine (Tyr(449)) residue on the alpha-subunit of the IL-7R. We have previously shown in an IL-7Ralpha(449F) knock-in model that IL-7-induced lymphomas require Tyr(449) phosphorylation and that loss of this phosphorylation confers protection from disease. However, the mechanism by which this lymphoma protection occurs remains unclear. Using this genetic model, we aimed to identify novel prosurvival factors important for IL-7-mediated lymphocyte development and lymphomagenesis. An iTRAQ (isobaric tags for relative and absolute quantitation) proteomics analysis was performed comparing CD4(-)CD8(-) double negative T cell progenitors from mice overexpressing IL-7 (Tg IL-7) (lymphoma-prone) with Tg IL-7 mice with a mutated IL-7 receptor (Tg IL-7/IL-7Ralpha(449F)) (lymphoma-protected). Several proteins involved in survival, proliferation, and apoptosis were found to be differentially expressed between the two samples, and three proteins of particular interest, GIMAP4, BIT1, and FKBP51, were validated by immunoblot analysis.