Human telomerase reverse transcriptase expression in a CD34‐positive hematopoietic progenitor of myelodysplastic syndrome and acute myelogenous leukemia

Myelodysplastic syndrome (MDS) represents a heterogeneous group of clonal disorders of hematopoietic stem cells. It is characterized by ineffective hematopoiesis and increased risk of leukemic transformation. Although gene mutations contributing to MDS pathogenesis and progression have been discovered, the mechanisms driving MDS toward acute myelogenous leukemia (AML) have not been fully elucidated yet. In most normal somatic cells, telomere shortening occurs during cell division, and cells lose their proliferative potential when telomeres reach a critical degree of shortening. In contrast, immortalized cells show stable telomeres maintained by the activation of telomerase and unlimited proliferative potential. Elevated telomerase activity (TA) has been found in the advanced stage of most common cancers, including advanced MDS and acute leukemia. However, conventional TA measurement by telomeric repeat amplification protocol (TRAP) assay or quantitative polymerase chain reaction (PCR) for TERT mRNA in bulk bone marrow (BM) cells cannot determine the site of TA upregulation during disease progression. We previously developed a method to detect nuclear TERT protein in a subpopulation of hematopoietic cells, using concurrent staining cell surface antigen and multicolor flowcytometry. Determination of TERT expression in CD34+ hematopoietic progenitor cells and very small CD34+/CD38− stem cells in MDS has not been reported and should help elucidate the role of TA in MDS progression. After informed consent is obtained, heparinized BM samples were collected from 69 MDS and 29 AML patients. Fifty six of the MDS patients were diagnosed with low‐risk MDS, including MDS single‐ lineage dysplasia, MDS multilineage dysplasia, and unclassified MDS. Thirteen were diagnosed with high‐risk MDS (EB‐1 or EB‐2), based on the World Health Organization (WHO) 2016 classification. Six low‐blast‐count AML cases, in which blast percentage was 20% to 29.8%, were categorized as AML‐LBC. This study was approved by the Institutional Review Board of Gunma University Hospital in accordance with the Helsinki Declaration. Eleven low‐risk MDS, four high‐risk MDS, four AML‐LBC, and seven de novo AML patients were subjected toTRAP assays. We used a three‐color flowcytometry method for measuring TERT expression. Optimal staining was achieved as described previously. Data were analyzed with the Kruskal‐Wallis test, Mann‐Whitney U test, or