Chimeric antigen receptors (CARs) are synthetic proteins that redirect T cell specificity by linking an extracellular ligand binding domain to intracellular T cell signaling domains. CAR-expressing T (CAR-T) cells have demonstrated significant efficacy for the treatment of refractory B cell malignancies and are being evaluated as immunotherapeutic reagents for many other cancers. CAR designs are based on the fundamental principles of TCR recognition and most CARs employ the T cell-activating CD3z endodomain alongside a costimulatory domain from CD28 or 4-1BB. However, emerging data suggest that CD28/CD3z and 4-1BB/CD3z signaling modules promote divergent metabolic pathways, gene expression programs, and cell fates. To determine how CAR phosphoprotein signaling drives these disparate cell fates, we analyzed CAR ligation-induced signaling networks in primary human T cells using shotgun mass spectrometry. We isolated CD8+CD62L+ T cells from healthy donors and introduced a CD28/CD3z or 4-1BB/CD3z CAR by lentiviral transduction. Transduced T cells were purified by FACS and expanded once in vitro. When the cells returned to a resting state, CD28/CD3z or 4-1BB/CD3z CAR-T cells were stimulated for 10 or 45 minutes with magnetic microbeads coated with a monoclonal antibody specific for a 9 amino acid tag in the CAR extracellular sequence. CAR-T cells were also left unstimulated for 10 or 45 minutes to serve as controls. Altogether, 8 unique conditions were tested in an experiment and three independent experiments were performed.