Adoptive cell therapy, a subset of cancer immunotherapy, is collection of therapeutic approaches which aim to redirect the immune system by reprogramming patient T-cells to target antigenic molecules differentially and specifically expressed in certain cancers. One promising immunotherapy technique is CAR T-cell therapy, where cancer cells are targeted through the expression a chimeric antigen receptor (CAR), a synthetic trans- membrane receptor that functionally compensates for the T-cell receptor (TCR) but targets a tumor associated antigen on the cancer cell surface. While CAR T-cell therapy is promising with two clinically approved second-generation CARs (Kymriah and Yescarta), few studies have investigated the mechanism of signal propagation in T-cells and no studies have investigated the potential signaling response in the target cells. To gain further insight to CAR-based signaling, we stimulated third generation CD19 CAR-expressing Jurkat T-cells by co-culture with SILAC labeled CD19HI Raji B-cells and used two phosphoenrichment strategies coupled with liquid chromatography-tandem mass spec- trometry (LC-MS/MS) to detect and analyze global phosphorylation changes in both cell populations. Analysis of the phosphopeptides originating from the CD19-CAR T cells revealed an increase in many phosphorylation events necessary for canonical TCR signaling. We also observed for the first time a significant decrease in B-cell receptor- related phosphopeptide abundance in CD19HI Raji B-cells after co-culture with CD19-targetted CAR T-cells.