Leukemic stem cells shall be searched in the bone marrow before "tyrosine kinase inhibitor-discontinuation" in chronic myeloid leukemia

Immunophenotypic features of early haematopoietic and leukaemia stem cells

Many tumours are organised in a hierarchical structure with at its apex a cell that can maintain, establish, and repopulate the tumour-the cancer stem cell. The haematopoietic stem cell (HSC) is the founder cell for all functional blood cells. Like HSCs, the leukaemia stem cells (LSC) are hypothesised to be the leukaemia-initiating cells, which have features of stemness such as self-renewal, quiescence, and resistance to cytotoxic drugs. Immunophenotypically, CD34+CD38- defines HSCs by adding lineage negativity and CD90+CD45RA-. At which stage of maturation the further differentiation is blocked, determines the type of leukaemia, and determines the immunophenotype of the LSC specific to the leukaemia type. No apparent LSC phenotype has been described in lymphoid leukaemia, and it is debated if a specific acute lymphocytic leukaemia-initiating cell is present, as all cells are capable of engraftment in a secondary mouse model. In chronic lymphocytic leukaemia, a B-cell clone is responsible for uncontrolled proliferation, not a specific LSC. In chronic and acute myeloid leukaemia, LSC is described as CD34+CD38- with the expression of a marker that is aberrantly expressed (LSC marker), such as CD45RA, CD123 or in the case of chronic myeloid leukaemia CD26. In acute myeloid leukaemia, the LSC load had prognostic relevance and might be a biomarker that can be used for monitoring and as an addition to measurable residual disease. However, challenges such as the CD34-negative immunophenotype need to be explored.

Peripheral Blood CD26 Positive Leukemic Stem Cells as a Possible Diagnostic and Prognostic Marker in Chronic Myeloid Leukemia

Background

CD26 is expressed in all chronic myeloid leukemia (CML) patients. This study investigated the role of CD26⁺ LSCs in diagnosis and follow up of CML patients.

Method

Flow cytometry was performed to evaluate CD26⁺ LSC in peripheral blood (PB) in CML patients. BCR-ABL1 transcript level measurement was performed using standard qRT-PCR technique.

Results

CD26⁺ LSCs were significantly correlated with BCR-ABL1 transcript level at diagnosis and after three months of treatment. CD26+ LSCs also were significantly associated with the risk score after 12 months of treatment.

Conclusion

CD26+ LSCs can be a useful marker in diagnosis and follow up of patients with CML.

CD26/DPP-4 in Chronic Myeloid Leukemia

CD26 expression is altered in many solid tumors and hematological malignancies. Recently, it has been demonstrated that it is a specific marker expressed on LSCs of CML, both in BM and PB samples, and absent on CD34+/CD38− stem cells in normal subjects or on LSCs of other myeloid neoplasms. CD26+ LSCs have been detected by flow-cytometry assays in all PB samples of Chronic-Phase CML patients evaluated at diagnosis. Additionally, it has been demonstrated that most CML patients undergoing Tyrosine Kinase Inhibitors (TKIs) treatment still harbored circulating measurable residual CD26+ LSCs, even when displaying a consistent deep molecular response without any significant association among the amounts of BCR-ABL transcript and CD26+ LSCs. Preliminary data of our Italian prospective multicenter study showed that CML patients with a poorer response presented with a higher number of CD26+ LSCs at diagnosis. These data confirmed that CD26 is a specific marker of CML and suggest that it could be considered for the monitoring of therapeutic responses.

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.

Targeting AraC-Resistant Acute Myeloid Leukemia by Dual Inhibition of CDK9 and Bcl-2: A Systematic Review and Meta-Analysis

PURPOSE

This study aims to determine the influence of targeting araC-resistant acute myeloid leukemia by dual inhibition cyclin-dependent protein kinase (CDK9) and B-cell lymphoma-2 （Bcl-2).

METHOD

The c-Myc inhibitor 10058-F4 and the CDK9 inhibitor AZD4573 were used to determine the cell cycle arrest and apoptosis.

RESULTS

10058-F4 reduces c-Myc protein levels and suppresses HepG2 cell proliferation, possibly by upregulating cyclin-dependent kinase (CDK) inhibitors, p21WAF1, and reducing intracellular alpha-fetal protein (AFP) levels.

CONCLUSION

The combination of AZD4573 and 10058-F4 has a synergistic anti-araC-resistant AML activity, providing a solid database for the aforementioned scientific hypothesis.

Emerging concepts for assessing and predicting treatment-free remission in chronic myeloid leukemia patients

INTRODUCTION

In chronic myeloid leukemia (CML) patients who have reached a deep and sustained reduction of residual disease can attempt a discontinuation. The 'treatment-free remission' (TFR) has become a real long-term endpoint for 30-40% of chronic phase patients.

AREAS COVERED

In this review, we focus our attention on possible prognostic features who can predict the success of tyrosine kinase inhibitors discontinuation and how we can assess the minimal residual disease (MRD) during the TFR phase. Broad research was made on Medline, Embase and archives from EHA and ASH congresses.

EXPERT OPINION

Median duration of TKI therapy and of deep molecular response are the main prognostic factors identified in most trials and real-life experiences on discontinuation. Immunological pathways have been proposed as possible control on successful TFR as also early molecular response dynamics. Appropriate molecular monitoring by RQ-PCR in the TFR phase has been proposed by several international recommendations and digital droplet PCR (ddPCR) seems to have a possible role in the future for a better identification of candidate to this possible therapeutic strategy.

TKI discontinuation in CML: how do we make more patients eligible? How do we increase the chances of a successful treatment-free remission?

Treatment-free remission (TFR) is a new and significant goal of chronic myeloid leukemia management. TFR should be considered for patients in stable deep molecular response (DMR) after careful discussion in the shared decision-making process. Second-generation tyrosine kinase inhibitors (TKIs) improve the speed of response and the incidence of DMR. Treatment may be changed to a more active TKI to improve the depth of response in selected patients who have not reached DMR. Stem cell persistence is associated with active immune surveillance and activation of BCR-ABL1-independent pathways, eg, STAT3, JAK1/2, and BCL2. Ongoing studies aim to prove the efficacy of maintenance therapies targeting these pathways after TKI discontinuation.