Identification of CD25 as STAT5-Dependent Growth Regulator of Leukemic Stem Cells in Ph+ CML

Area of Science:

• Hematology
• Cancer Biology
• Stem Cell Research

Background:

• Leukemic stem cells (LSCs) are a critical therapeutic target in chronic myelogenous leukemia (CML).
• Identifying novel markers and targets expressed by CML LSCs is essential for developing effective therapies.
• Current understanding of CML LSC-specific markers remains limited.

Purpose of the Study:

• To identify novel and relevant markers specifically expressed by CML LSCs.
• To investigate the role of these markers in LSC biology and potential therapeutic targeting.

Main Methods:

• CML LSCs were analyzed using flow cytometry, quantitative polymerase chain reaction (qPCR), and various bioassays.
• The multipotent CD25-positive (CD25(+)) CML cell line KU812 was examined.
• STAT5 signaling pathways and the effects of BCR/ABL1 inhibitors (nilotinib, ponatinib) and PI3K/mTOR blockers (BEZ235) were investigated.

Main Results:

• CD34-positive/CD38-negative (CD34(+)/CD38(-)) CML LSCs uniquely express the IL-2 receptor alpha chain (IL-2RA), also known as CD25, unlike normal hematopoietic stem cells.
• STAT5 signaling was found to induce CD25 expression in stem cells, and its depletion reduced CD25 levels in CML cells.
• BCR/ABL1 inhibitors decreased STAT5 activity and CD25 expression in CML LSCs, while a PI3K/mTOR blocker promoted STAT5 and CD25 expression.
• CD25-targeting shRNA enhanced CML cell proliferation and in vivo engraftment.
• BEZ235 demonstrated synergistic antineoplastic effects with nilotinib or ponatinib in CML cells.

Conclusions:

• CD25 is identified as a novel STAT5-dependent marker of CML LSCs.
• CD25 may serve as a valuable tool for LSC detection and isolation in clinical and research settings.
• CD25's role as a growth regulator in CML LSCs has significant biologic and clinical implications, potentially leading to new LSC-eradicating treatment strategies for CML.