Dynamic feedback control of oncogenic tyrosine kinase signaling in acute leukemia.

CD25 is a subunit of the interleukin-2 (IL-2) receptor on T cells and natural killer (NK) cells. Acute leukemias with oncogenic tyrosine kinases often include CD25+ leukemia subpopulations, which portend poor clinical outcomes for patients; however, acute leukemia cells do not respond to IL-2. Here, we identified CD25 and its phosphorylation by protein kinase Cδ (PKCδ) as central elements of a feedback loop that stabilized fluctuations in oncogenic tyrosine kinase signaling in acute lymphoblastic and myeloid leukemia. Genetic ablation of CD25 in murine and patient-derived xenograft (PDX) models of acute leukemias reduced clonal fitness, colony formation, and leukemia-initiation capacity in serial transplant recipients. Oncogenic tyrosine kinase signaling in leukemia cells stimulated NF-κB-mediated CD25 expression, whereas PKCδ-mediated phosphorylation of CD25 suppressed oncogenic tyrosine kinase signaling through inhibitory phosphatases, such as PTPN6. Interactome analyses and mass spectrometry-based global phosphoproteomic analyses showed that CD25 deletion abolished the phosphatase activity of PTPN6, resulting in enhanced activation of tyrosine kinases and NF-κB. Four injections of a CD25 antibody-drug conjugate induced complete remission in mice transplanted with PDX refractory leukemia. These findings highlight the dependency of tyrosine kinase-driven leukemias on robust feedback control and the role of PKCδ and CD25 in assembling its components.