Identification of peripheral blood CD26+ leukemic stem cells has a potential role in the rapid diagnosis of chronic myeloid leukemia

Background: Chronic myeloid leukemia (CML) is a hematopoietic stem cell (SC) neoplasm diagnosed by the demonstration of t(9;22)(BCR-ABL1) fusion gene. We performed a flow cytometric assay to identify CD26+ CML leukemic stem cells (LSCs) for its value as a standalone diagnostic investigation for CML and its utility for detection of residual disease in CML patients on therapy.

Methods: Patients with clinical suspicion of CML/CML on follow-up were included, and peripheral (PB) and/or bone marrow (BM) samples were utilized for flow cytometric analysis. PB and/or BM of patients with diseases other than CML were used as controls. A pre-titrated antibody cocktail containing CD45, CD34, CD38, and CD26 MoABs was used.

Results: A total of 104 samples (63 PB and 41 BM) from 64 patients [suspected CML (n = 30), CML on follow-up (n = 15), and non-CML (n = 19)] were tested. CD26+ LSCs were identified in all patients with a confirmed diagnosis of CML (median = 0.07 (range 0.002%-26.79%)). None of the patients in the control group (non-CML) and follow-up patients with negative reverse transcriptase-polymerase chain reaction (RT-PCR) results showed the presence of CD26+ LSCs. Also, there was a strong correlation between CD26+ CML LSCs in the PB and BM (r = .917).

Conclusion: Flow cytometric identification of CD26+ LSCs in the peripheral blood can be a cheap, rapid, robust, and potential diagnostic tool for the diagnosis of CML compared to available testing methods. It is irrespective of BCR-ABL1 transcript type, and its role in residual disease monitoring needs thorough investigation.