The phosphorylation levels of ten signaling proteins that are frequently altered in T-ALL (namely Akt, MAPK Erk1/2, c-Jun NH2-terminal protein kinase (JNK), lymphocyte-specific protein tyrosine kinase (Lck), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65, p38, STAT3, STAT5, zeta-chain-associated protein kinase 70 (ZAP70), and retinoblastoma protein (Rb)) were analyzed at the single-cell level in the T-ALL cell lines CEM, MOLT4, and Jurkat, using phospho-specific flow cytometry (Figure 1). Here, LCK is linked to acute lymphoblastic leukemia.